Diiron-Hydride Complexes: Synthesis, Structure, and Reactivity of

Organometallics 1995,14, 2325-2341

2325

Diiron-Hydride Complexes: Synthesis, Structure, and Reactivity of trans-[Fe2(CO).&-H)(cc-CO)(cc-PCy2)(cc-Ph2PCH2PPh2)I Graeme Hogarth," Mark H. Lavender, and Khalid Shukri Chemistry Department, University College London, 20 Gordon Street, London WClH OAJ, U.K. Received February 2, 1995@ The diphosphine-stabilized diiron complex [Fez(Co)s@-Co)@-dppm)] (dppm = PhZPCHzPPh2)reacts readily with dicyclohexylphosphineupon W irradiation t o give the phosphido-hydrido complex [Fez(C0)4@-H)@-CO)@-PCy2)01-appm)](1)shown to contain a trans arrangement of phosphorus-containing ligands, which is maintained throughout reactions. Two general types of reactivity are noted for 1,namely, insertion of unsaturated compounds into the diiron-hydride moiety with concomitant loss of carbon monoxide and hydride elimination reactions, which may or may not occur with carbonyl loss. Insertion of ethyne affords [F~~(CO)~@-HC=CHZ)@-PC~~)@-~~~~)I(~). With propyne, an inseparable mixture of isomers [Fe~(C0)4@-MeC=CHz)@-PCyz)@-dppm)l(3a)and [Fez(C0)4@-HC=CHMe)@-PCyz)@-dppm)I(3b) is formed in a 2.5:l ratio, while with phenylethyne, regioselective insertion yields only the 8-alkenylcomplex [Fe2(CO)&HC=CHPh)@-PCyz)@-dppm)1(4). The "windshield-wiper"0-JCalkenyl fluxionality of these complexes has been monitored by both 'H and 31P NMR spectroscopy, the former revealing that the fluxional process does not interconvert the ,&hydrogen atoms. The free energies of activation vary considerably between a-and 8-substituted alkenyl complexes, an effect which is believed to be steric in origin. Unactivated disubstituted alkynes do not react with 1;however, the activated alkyne dimethyl acetylenedicarboxylate(DMAD) readily inserts to afford the metallacyclic complex [Fe4(C0)4{~2-C(C0~Me)=CH-C(oMe)=o)@-PCy~)@-dppm)](5)as a result of cis-trans vinyl isomerization and ester carbonyl coordination. Addition of allene to 1 affords 3a via selective proton transfer to the external carbons. Carbon dioxide is unreactive toward 1, but carbon disulfide readily inserts to yield the dithioformato complex [Fez(C0)4@-SzCH)@-PCy~)@-dppm)l(6). Organic isothiocyanates (RNCS)also insert into 1,giving N-thioformamido [Fez(CO)r@-RNCHS)@-PCyz)@-dppm)l(7a-c;R = allyl, Et, Ph) and formimidoyl [Fez(C0)4@-RN=CH@-PCy~)(p-dppm)l(8a,b)complexes. Both result from selective hydride transfer to carbon, which occurs with sulfur loss in the case of the latter. Heating a toluene solution of 7b leads to the formation of 8b as a result of sulfur loss. Another formimidoyl complex [ F ~ z ( C O ) ~ @ - ~ B ~ N = C H ) @ - P C ~ ~ ) @-dppm)](8d) has been prepared as the only product from the reaction of 1 with tert-butyl isocyanide, while in contrast 1 is unreactive toward nitriles. Both N-thioformamido 7 and formimidoyl8 complexes contain an sp2-hybridizednitrogen and partial carbon-nitrogen double-bond character. Chromatography of 1 on alumina in the presence of dichloromethaneaffords [Fe~(C0)4@-OH)@-PCyz)@-dppm)l(9) together with chloro-bridged[Fez(C0)4@-Cl)@-PCy~)@-dppm)] (10).The latter is more easily prepared upon reaction of 1 with hydrochloric acid. Addition of iodine to 1 yields the analogous iodo-bridgedcomplex [Fez(C0)4(11)in moderate yield. Thermolysis of 1 in the presence of diphenylphosphine @-I)@-PCyz)@-dppm)] affords mixtures of [Fe2(C0)4@-PPhz)@-PCy~)@-dppm)I(12)and [Fez(C0)4@-PPhz)~@-dppm)l(13). In a separate experiment, thermolysis of 12 with diphenylphosphine did not afford 13, indicating that phosphido-bridge exchange occurs prior to the formation of the electron-precise bis(phosphid0)-bridged species. Thermolysis of 1 alone results in benzene elimination to yield [Fez(CO)s@-,PCyz)@-PhPCHzPPhz)I (14). Complexes 1,2,4,7a,8a,and 11 were characterized by single-crystal X-ray diffraction analyses. Crystal data: for 1,space group Pi, a = 10.2577(34)A, b = 13.0315(81)A, c = 15.8986(71)A, a = 81.902(43)", 8 = 84.672(31)", y = 72.272(38)", 2 = 2, 4136 reflections, R = 0.068; for 2,space group P i , a = 11.7987(15)A, b = 12.8813(16)A, c = 17.0025(9)A, a = 73.670(8)",j3 = 77.770(8)", y = 64.870(8)",2 = 2, 6506 reflections,R = 0.046; for 4,space group P i , a = 12.5326(15)A, b = 12.5939(16)8,c = 18.4748(25) A, a = 105.240(10)",j3 = 91.975(10)", y = 118.025(10)",2 = 2, 7416 reflections, R = 0.051; for 7a,space group P i , a = 11.9777(39)A, b = 13.5843(36)A, c = 13.7530(51)A, a = 88.912(26)",8 = 89.293(28)", y = 78.931(25)", 2 = 2,4235 reflections,R = 0.061; for 8a,space group P21lc, a = 11.8267(32)A, b = 15.5264(29) A, c = 27.1868(71) A, a = go", 8 = 91.366(22)", y = go", 2 = 4, 3252 reflections, R = 0.088; for 11, space group Pi,a = 11.8975(20)A, b = 12.9829(16)A, c = 16.6072(25) A, a = 72.937(12)", j3 = 76.891(13)", y = 64.089(11)",2 = 2, 5957 reflections, R = 0.069.

Introduction

As the simplest possible ligand system, the hydride moiety is of fundamental interest, while its involvement * E-mail: [email protected].

Abstract published in Advance ACS Abstracts, May 1, 1995.

in a variety of important stoichiometric and catalytic processes has led to its extensive commercial exploitation. Not surprisingly then, transition metal hydride complexes have received considerable attention, with the synthesis, properties, and reactivity of the ligand bound to both mono- and polynuclear metal centers

0276-733319512314-2325$09.00/0 0 1995 American Chemical Society

Hogarth et al.

2326 Organometallics, Vol. 14,No. 5, 1995

being extensively deve1oped.l Among the most notable examples of this latter class of compounds are the formally unsaturated dihydride complexes [OS~(CO)~O@-H)2I2and [Mn~(CO)sCu-dppm)@-H)2],~ which display an extensive chemistry that is centered around the insertion of unsaturated organics into one or both of the hydride moieties. Recently we have been concerned with the development of the chemistry of the hydride ligand when bound to low-valent diiron center^,^-^ primarily since such complexes should be easy to prepare from relatively cheap and abundant starting materials and are anticipated to display high reactivity. Diiron complexes containing a metal-metal double bond are, however, extremely rare,g and t o our knowledge no such hydridecontaining species are known. In view of this, we have developed the synthesis of diiron-hydride complexes, which, while formally being electronically saturated, readily lose carbon monoxide and thus can be considered as “masked”iron-iron doubly bonded One such example of a complex of this type is [Fez(C0)4@-H)@-CO)@-PPh~)@-dppm)Il-Ph, which we have previously shown t o readily lose a carbonyl and insert alkynes to afford a-n alkenyl complexes with high regio-6 and stereoselectivity.8 The phosphorus-containing ligands in the latter serve a dual purpose. Firstly, they hold the two metal atoms in close proximity, thus preventing fragmentation into mononuclear species (a reaction prevalant in low-valent diiron carbonyls), while allowing a large range of internuclear separations which can vary by up to 1 A in order to accommodate the electronic and steric requirements of other metal-bound ligands. Their second role is one of practical importance; namely, they act as excellent NMR probes, allowing simple monitoring of reactions, often providing mechanistic insight and allowing simple structure elucidation on the basis of phosphorus-phosphorus coupling constants and signal structure. For example, reaction of ethyne with 1-Ph affords the p-ethenyl (2complex [Fez(CO)4(pu-HC=CH2)(p-PPh2)(p-dppm)1 Ph),shown to contain a trans configuration of phosphorus-containing ligands on the basis of the relatively large phosphorus-phosphorus coupling constants,6and a static vinyl moiety by the observation of two diphosphine signals at room t e m p e r a t ~ r e .Complexities ~ arise (l)Hlatky, G. G.; Crabtree, R. H. Coord. Chem. Rev. 1985,65 1. Moore, D. S.; Robinson, S. D. Chem. SOC.Rev. 1983,415. (2)Knox, S.A. R.; Koepke, J . W.; Andrews, M. A,; Kaesz, H. D. J. Am. Chem. SOC.1976,97, 3942. Deeming, A. J. Adu. Organomet. Chem. 1986,26,1. (3)Riera, V.: Ruiz, M. A.: Tiriuicchio. A.: Tiriuicchio-Camellini, M. J . Chem. SOC.,Chem’. Commun.-l986, 1505. Ckrefio, R.; Riera,’V.; Ruiz, M. A.; Bois, C.; Jeannin, Y. Organometallics 1993,12,1946 and

references given therein. (4)Boothman, J.; Hogarth, G. J. Organomet. Chem. 1992,437,201. (5)Hogarth, G.J. Organomet. Chem. 1991,407,91. (6)Hogarth, G.;Lavender, M. H. J.Chem. Soc., Dalton Trans. 1992,

2759. (7)Hogarth, G.;Lavender, M. H. J.Chem. Soc., Dalton Trans. 1993, 143. (8) Hogarth, G.;Lavender, M. H. J.Chem. Soc., Dalton Trans. 1994, 3389. (9)Walther, B.; Hartung, H.; Reinhold, J.; Jones, P. G.; Mealli, C.; Bottcher, H.-C.; Baumeister, U.;Krug, A.; Mockel, A.Organometallics 1992, 11, 1542. Walther, B.; Hartung, H.; Bambirra, S.; Krug, A.; Bottcher, H.-C. Organometallics 1994,13,172. Adams, M. R.; Galluci, J.; Wojcicki, A. Inorg. Chem. 1991,31, 2. Nicholas, K;Bray, L. S.; Davis, R. E.; Pettit, R. J. Chem. Soc., Chem. Commun. 1971, 608. Schmitt, H.J.; Ziegler, M. L. 2.Naturforsch. 1973,28B,508. Cotton, F. A.;Jamerson, J. D.; Stults, B. R. J.Am. Chem. SOC.1976,98,1774. Calderon, J. L.;Fontana, S.; Frauendorfer, E.; Day, V. W.; Iske, S. D. A. J. Organomet. Chem. 1974,64,C16. Seyferth, D.; Breuer, K. S.; Wood, T. G.; Cowie, M.; Hilts, R. W. Organometallics 1992,11,2570.

in this system, however, upon insertion of primary alkynes, since, while the process occurs with high regioselectivity associated with Markovnikov addition, mixtures of isomers arise differing in the relative orientation of the phosphorus-containing ligands, namely, cis and trans.6 This appears t o be a result of the preferred cis arrangement of these ligands in [Fe2(C0)4@-H)@-CO)@-PPh2)(p-dppm)l(l-Ph), while upon insertion the formation of the alkenyl moiety favors a trans configuration. In order to carry out a full investigation of the reactivity of these hydride complexes, we sought t o simplify possible products by developing the synthesis of a starting hydride complex in which the phosphoruscontaining ligands adopt a relative trans disposition, anticipating that this would be retained in consequent products. In order to achieve this while minimizing changes to the electronic properties of the diiron center, we sought to replace the diphenylphosphido ligand by the bulkier dicyclohexylphosphido moiety, expecting that this would lead to a preferred trans orientation with respect to the diphosphine. Herein we describe the synthesis of [Fe2(C0)4(~-H)@-CO)@-PCya)@-dppm)l(l), shown by X-ray crystallography to adopt the trans configuration, and extensive reactivity studies during which the trans configuration is always maintained. No aspects of this work have been previously communicated. Results and Discussion 1. Synthesis and Structure of [ F ~ P ( C O ) & - H ) ~ CO)@-PCydj~-dppm)l (1). The synthesis of a variety of binuclear phosphido-hydrido complexes has previously been achieved via the oxidative addition of secondary phosphines t o bimetallic centers.1° Addition of dicyclohexylphosphine to [Fe2(Co)6@-Co)@-dppm)l in the absence of W irradiation does not lead to any appreciable reaction, which is in keeping with the general reactivity of the latter.11-13 Upon photolysis however, a slow reaction takes place over approximately 16 h, which can be accelerated somewhat by the introduction of a slow nitrogen purge of the solution, to generate the phosphido-hydrido complex [Fez(CO)r(pH)@-CO)(~-PCy2)(p-dppm)l (1) in 60% yield (eq 1). Characterization initially appeared to be straightforward on the basis of a comparison of spectroscopic properties with the analogous diphenylphosphidobridged complex6 which contains a cis arrangement of phosphorus-containing ligands. In the 31PNMR spectrum, a triplet at 192.2 and a doublet at 75.2 ppm in the ratio 1:2 were assigned to the phosphido bridge and equivalent phosphorus atoms of the diphosphine, respectively, the coupling constant of 41 Hz appearing to indicate a cis arrangement of phosphines, while in the lH NMR spectrum the hydride appeared as a doublet of triplets at 6 -10.14 (J = 24.1, 45.3 Hz). Full spectroscopic data for 1 together with data for all new complexes described herein is given in Table 1. (10)C a m , A. J.; Mays, M. J.; Raithby, P. R. J . Chem. SOC.,Dalton Trans. 1991,2329 and references given therein. (11)Hogarth, G.; Kayser, F.; f i o x , S. A. R.; Morton, D. A. V.; Orpen, A. G.; Turner, M. L. J. Chem. SOC.,Chem. Commun. 1988,358. (12)Doherty, N. M.; Hogarth, G.; Knox, S. A. R.; Macpherson, K A.; Melchior, F.; Morton, D. A. V.; Orpen, A. G. Znorg. Chim. Acta 1992, 198-200,257. (13)Knox, S.A. R.; Morton, D. A. V.; Orpen, A. G.; Turner, M. L. Inorg. Chem. Acta 1994,220,201.

Organometallics, Vol. 14, No. 5, 1995 2327

Diiron-Hydride Complexes

Table 1. Spectroscopic Data for New Complexes

IR (YCO) (cm-')a 1993.6 (m), 1970.1 (SI, 1931.1 (s), 1710.0 (m) 1971.5(m),1943.5 (m), 1909.5 (m), 1892.0 (sh)

no. 1 2

3a

1966.4 (m), 1938.9 (s), 1906.5 (m), 1888.0 (sh)

3b

1966.4 (m), 1938.9 (91, 1906.5 (m), 1888.0 (sh)

4

1970.8 (m), 1941.1 (s), 1909.1 (m), 1890.0 (sh)

6

2002.5 (m), 1938.0 (81, 1891.7 (m), 1887.5 (m)

6

1980.2 (m), 1950.1 (s), 1920.8 (m), 1902.5 (sh)

?a

1971.9 (m), 1939.2 (s), 1908.1 (m), 1887.4 (sh)

7b

1971.3 (m), 1938.8 (81, 1907.5 (m), 1886.8 (sh)

7c

1973.5 (m), 1940.0 (s), 1910.7 (m), 1889.8 (sh)

8a

1968.1 (m), 1937.0 (s), 1901.0 (m)

8b

1966.5 (m), 1934.8 (s), 1898.8 (m), 1885.2 (sh)

&1

1964.2 (m), 1932.9 (s), 1894.8 (m), 1883.9 (sh)

9

1970.0 (m), 1940.0 (s), 1900.0 (m)

10

11 14 a

1980.5 (m),1950.5 (s), 1915.7 (m) 1979.0 (m), 1949.5 (s), 1915.7 (m), 1898.1 (sh) 3013.0 (s), 1962.0 (81, 1939.0 (s), 1907.0 (sh)

IH (a), J (Hdb 7.8-7.2 (20H, m, Ph), 2.60 (2H, br, CHz), 2.4-0.9 (22H, m, Cy), -10.14 (lH, dt, J = 24.1,45.3,p-H) 8.2-6.7 (20H, m, Ph), 6.50 (1H, m, Ha), 3.74 (1H, 242.8 (t,J = 84, 79), 87.7 (dd, q, J = 10.6, CH3), 2.60 (lH, dd, J = 5.8,2.5 Hjcid, J = 67, 78), 77.4 (dd, J = 67,84) 2.64 (IH, dt, J = 9.1, 7.8, Hptrans), 2.76 (1H, dt, J = 8.8, 14.3, CHz), 2.7-1.1 (22H, m, cy) 7.7-7.0 (20H, m, Ph), 3.80 (lH, dt, J = 15.2,9.3, 247.1 (dd, J = 74, 85), 79.3 (dd, CHz), 3.48 (lH, q, J = 9.3, CHz), 3.44 (lH, q, J = 74, 1171, 78.0 (dd, J = 117,85) J = 9.3), 2.61 (lH, d, J = 12.7, Hptrans), 2.2-1.1 (22H, m, Cy), 0.83 (3H, d, J, Me) 8.2-7.0 (20, m, Ph), 6.05 (lH, ddt, J = 28.8, 12.0, 242.8 (t, J = 79),82.8 (t,J = W, 6.5, Ha), 3.91 (lH, M, Hp), 2.64 (lH, dt, J = 14.5, 79.4 (t, J = 74P 9.4, CHz), 2.32 (lH, q, J = 11.0, CHd, 2.2-0.8 (22H, m, Cy), 0.45 (3H, d, J = 5.9, Me) 7.7-6.5 (25H, m, Ph), 6.79 (lH, m, Ha), 3.93 (lH, 242.0 (t,J = 78), 81.1 (t, J = 751, m, CHz), 2.63 (lH, dt, J = 9.4, 13.1), 2.40 (lH, 77.6 (t, J = SOP br, Hp), 2.8-1.2 (22H, m, CyP 7.8-7.0 (20H, m, Ph), 5.98 (lH, s, CHI, 4.43 (lH, 227.0 (dd, J = 87, 29),64.0 (dd, m, CHz), 3.98 (lH, m, CHz), 3.79 (3H, s, COfie), J = 83, 2% 56.5 (t,J = 85) 3.47 (3H, s, CO&fe), 2.4-0.9 (22H, m, Cy) 10.66 (lH, J = 4.0, CH), 7.7-7.0 (20H, m, Ph), 4.40 236.5 (t, J = 721, 58.0 (d) (1H, q, J = 11.8, CHz), 3.31 (1H, q, J = 11.5, CHd, 2.3-0.9 (22H, m, Cy) 8.21 (lH, q, J = 3.3, CHI, 8.0-6.9 (20H, m, Ph), 5.24 242.8 (t, J = 81),59.5 (dd, J = 82, (lH, dt, J = 10.0, 7.2, HA, 4.92 (1H, d, J = 10.0, Hb), 134), 57.9 (dd, J = 80, 134) 4.74(1H, d, J = 16.9, Ha),4.34(2H,t,J= 10.9, CHd, 3.16(1H,q,J=7.2,Hd),2.81(1H,q,J=6.9,Hd), 2.4-1.0 (22H, m, Cy) 8.22 (lH, q, J = 3.4, CH), 7.9-6.9 (20H, m, Ph), 4.34 242.0 (t, J = 81),59.0 (dd, J = 82, (2H, dt, J = 11.0, 4.5, t, CHd, 2.31 (2H, m, CHZ,Et), 134), 57.5 (dd, J = 80, 134) 0.80 (3H, t, J = 7.0, Me) 2.4-0.8 (22H, m, Cy) 8.28 (lH, q, J = 3.2, CH), 8.0-6.1 (25H, m, Ph), 4.53 240.0 (t,J = 811, 57.6 (dd, J = 79, (lH, q, J = 11.4, CHz), 4.35 (lH, q, J = 12.8, CHz), 130), 55.0 (dd, J = 82, 130) 2.5-0.8 (m, 22H, Cy) 9.71 (lH, s, CH), 7.9-7.0 (20H, m, Ph), 5.30 (lH, q, 263.2 (dd, J = 104, 72), 55.8 (dd, J = 10.0, Hc),4.93(1H, d , J = 9 . 8 , Hb),4.71 (lH, d, J = 72, 58), 52.6 (dd, J = 104, 58) J = 17.0,Ha),3.88(1H,q,J=1l.9,CH2),3.37(1H, m,Hd), 3.10(1H,dt,J = 9 . 8 , 13.5, CHz),2.98(1H, m, Hd), 2.3-0.8 (22H, m, cy) 9.73 (lH, t, J = 4.0, CH), 7.9-7.0 (20H, m, Ph), 3.89 262.7 (dd, J = 72, 104), 55.9 (dd, (lH, m, CHz), 2.99 (dt, J = 9.6, 13.8, CHz), 2.79 (lH, J = 59, 72), 53.2 (dd, J = 59, 104) m, CHz, Et), 2.42 (lH, m, CHz, Et), 2.30 (1H, t, J = 4.1, CH), 2.2-0.8 (22H, m, Cy), 0.61 (2H, t, J = 7.2, CH3) 259.7 (dd, J = 70, 107),54.3 (dd, 8.04(1H, t , J = 8 . 0 , CH), 7.7-6.9(20H,m,Ph),4.11 (lH, q, J = 12.6 CHz), 3.20 (lH, dt, J = 9.3, 13.2, J = 70,61), 50.8 (dd, J = 61, 107) CHz), 2.4-0.8 (22H, m, Cy), 0.62 (9H, s, tBu) 7.5-7.2 (20H, m, Ph), 3.46 (lH, q, J = 10.0, CHd, 195.5 (t,J = 107),59.9(d) 2.95 (lH, q, J = 10.4, CHz), 2.3-0.8 (22H, m, Cy), -2.33 (lH, m, p-OH) 7.8-7.3 (20H, m, Ph), 3.51 (lH, q, J = 11.4, CHd, 217.0 (t,J = 99), 60.7 (d)d 3.00 (lH, q, J = 10.4, CHz), 2.3-1.1 (20H, m, Cy) 7.8-7.2 (20H, m, Ph), 4.06 (lH, dt, J = 14.8, 9.9, 195.4 (t,J = 108),60.2(d)d CHz), 3.69 (lH, d t , J = 14.7, 10.1, CHz), 2.2-1.1 (22H, m, Cy) 7.8-6.7 (15H, m, Ph), 4.38 (2H, dt, J = 3.0, 12.2, 192.3 (dd, J = 135,49),96.5 (dd, CHd, 1.8-1.3 (22H, m, Cy) J = 135, 103), 22.9 (dd, J = 49, 103) 31P(61, J (HzIb 192.2 (t, J = 411, 75.2 (d)

In CHzClz. In CdC13 (293 K). In CDCldCHzClz (203 K). In CsD6 (293 K).e In CDzClz (293 K). 0 C

0 C

selected bond lengths and angles. As expected, the molecule consists of two iron atoms in close contact with one another [Fe(l)-Fe(2), 2.579(2) AI being bridged approximately symmetrically by dicyclohexyl hosphido [Fe(l)-P(3), 2.241(3) Fe(2)-P(3), 2.259(3) ! i 1, diphosphine [Fe(l)-P(l), 2.234 A;Fe(2)-P(2), 2.257(3) AI, and carbonyl [Fe(l)-C(l), 1.984(8)A; Fe(2)-C(l), 1.967(7) A] moieties. Each iron atom also carries two terminal carbonyls which are bent slightly out of the plane bisecting the two phosphorus ligands, lying closer to the dicyclohexylphosphido moiety. The most notable feature of the molecule in light of the spectroscopic data is the trans arrangement of the diphosphine and dicyclohexylphosphido ligands [P(l)-Fe(l)-P(3), 152.7(1)"; P(2)-Fe(2)-P(3), 152.6(1)"1. The hydride was not located, however, inspection of the molecule strongly

A;

cv,

'

0

1

P h z P w PPh, 1

In order to fully elucidate the structure of 1 an X-ray crystallographic study was carried out, the results of which are summarized in Figure 1,while Table 2 gives

2328 Organometallics, Vol. 14,No. 5, 1995

Hogarth et al.

C1441

Figure 1. Molecular structure of 1. Table 2. Selected Bond Lengths (den) for 1 Fe(l)-Fe(2) Fe(l)-P(l) Fe(2)-P(2) Fe(l)-P(3) Fe(2)-P(3) Fe(1)-C( 1) P(l)-Fe(l)-P(3) P(2)-Fe(2)-P(3) Fe(l)-P(3)-Fe(2) P(3)-Fe(l)-C(l) P(3)-Fe(2)-C(l) Fe(l)-C(l)-O(l)

2.579(2) 2.234(3) 2.257(3) 2.241(3) 2.259(3) 1.984(8) 152.7(1) 152.6(1) 69.9(1) 76.7(2) 76.6(3) 140.0(6)

(A) and Angles

Fe(2)-C( 1) Fe(l)-C(2) Fe(l)-C(3) Fe(2)-C(4) Fe(2)-C(5) C(1)-0(1) Fe(2)-C(l)-O(l) Fe(2)-Fe(l)-C(2) Fe(2)-Fe( 1)-C(3) Fe(l)-Fe(2)-C(4) Fe(l)-Fe(2)-C(5)

1.967(7) 1.820(9) 1.779(8) 1.787(9) 1.773(9) 1.163(9) 138.4(6) 118.0(3) 139.5(3) 137.2(3) 117.6(3)

suggests that it resides between the two iron atoms, lying in the vacant coordination site trans to C(3) and C(4), since the site on the opposite side of the molecule is occupied by the bridging carbonyl that lies trans to C(2) and C(5) [C(l)-Fe(l)-C(2), 166.9(3)";C(l)-Fe(2)C(5), 167.0(4)"1. We were initially concerned that the apparent contradiction between the relatively small phosphorusphosphorus coupling constant (41 Hz) and the trans arrangement of phosphines may be a consequence of cis-trans isomerization of the latter during the recrystallization process; however, NMR spectra of the recrystallized material were identical t o those from crude samples. A further explanation, namely, that bulk samples of 1 contained the cis phosphine configuration while the crystal chosen for diffraction contained a trans arrangement, was easily ruled out on the basis that the crystal chosen was from a homogeneous sample and, more importantly, the observation that all complexes derived from 1 contain the trans phosphine configuration. The latter is in marked contrast to the diphenylphosphido analogue [Fez(C0)4@-H,@-CO)@-PPhz)@dppmll (1-Ph),which is shown to give mixtures of o-n alkenyl complexes with cis and trans phosphine configurations upon addition of alkynes.6 Thus we believe that, while in 1,the phosphines adopt a trans configuration, in 1-Ph they are cis. The reason for this major

structural difference is unlikely to be due to the differing electronic properties of the diphenyl- and dicyclohexylphosphido moieties and is almost certainly a consequence of the greater steric bulk of the latter. Thus, in adopting the trans phosphine configuration, adverse steric interactions between these relatively bulky ligands are minimized. A recent report details the preparation of the unsubstituted phosphido-hydrido complexes [HFez(C0)7@PR2)1,14 although none have been characterized by crystallography. The unsubstituted heptacarbonyl complexes almost certainly have a core geometry similar to that found in 1 since they have similar spectroscopic properties. For example, [HFe2(C0)&PtBu2)1 shows a bridging carbonyl in the IR spectrum (1804 cm-l), while the hydride appears a t 6 -10.7 (d, J = 51.0 Hz) in the lH NMR spectrum.14 A related diruthenium phosphido-hydrido complex, namely, [Ru2(C0)5(PtBu2H)@-H)@-CO)@-PtBu2)l,has recently been prepared,15 but is only stable under an atmosphere of carbon monoxide. In solution, in the absence of CO and presence of tBuzPH, rapid formation of the unsaturated @ - ~ Bwhich U~)I complex [ R u ~ ( C O ) ~ ( ~ B U ~ P H ) ~ @ - H )occurs contains a bridging carbonyl in the solid state. 2. Hydrodimetalation of Primary Alkynes and (T-ZAlkenyl 'Windshield-Wiper"Fluxionality. The insertion of alkynes into metal-hydrogen bonds (hydrometalation) to afford alkenyl complexes is a wellknown process. At binuclear centers this process is termed "hydrodimetalation", and Carty and co-workers have recently shown that the parent phosphido-hydrido complex [HFez(C0)7(pdppm)l readily inserts both alkynes and diynes to afford u--~t alkenyl and o-n alkenyl-enyl complexes, respectively.16 Indeed we have also recently shown that the insertion of primary alkynes into diiron-hydrido complexes is a facile proc~ss.~,~ Addition of ethyne to a toluene solution of 1 results in the exclusive formation of [Fez(C0)4(~-HC=CH2)(~PCyz)@-dppm)1(2) in 69% yield (eq 2). Characterization

cv9 HC,H, - CO

H \

H

c /c. ,

H

C

C

O

I

2

0

was easily made on the basis of spectroscopic data (Table 11.- At room temperature the-ethenyl L o u p is static as shown by the inequivalent ends of the diphosphine which appear as doublets of doublets at 87.7 (J = 78,67 Hz) and 77.4 (J= 84,671 ppm in the 31PNMR (14)Walther, B.; Hartung, H.; Bottcher, H.-C.; Baumeister, U.; Bohland, U.; Reinhold, J.; Sider, J.; Ladriere, J.; Schiebel, H.-M. Polyhedron 1991, 10, 2423. (15) Bottcher, H.-C.; Rheinwald, G.; Stoeckli-Evans,H.; Suss-Fink, G.; Walther, B. J.Organomet. Chem. 1994,469, 163. (16)McLaughlin, S. A.; Doherty, S.; Taylor, N. J.; Carty, A. J. Organometallics 1992, 11, 4315.

Diiron-Hydride Complexes

Organometallics, Vol. 14,No. 5, 1995 2329

b

C B I'

w

I

"I,&,

CI32l A

Figure 2. Molecular structure of 2. Table 3. Selected Bond Lengths (A)and Angles (deg) for 2CHzC12 Fe(1)-Fe(2) Fe(1)-P( 1) Fe(2)-P(2) Fe(l)-P(3) Fe(2)-P(3) Fe(1)-C( 1) Fe(l)-C(2) P(l)-Fe(l)-P(3) P(2)-Fe(2)-P(3) Fe(l)-P(3)-Fe(2) P(3)-Fe(l)-C(5) P(3)-Fe(2)-C(5) P(3)-Fe(2)-C(6)

2.577(1) 2.225(1) 2.221(1) 2.224(1) 2.249(1) 1.744(5) 1.774(4) 152.0(1) 151.0(1) 70.4(1) 85.8(1) 81.8(8) 83.8(8)

Fe(2)-C(3) Fe(2)-C(4) Fe(l)-C(5) Fe(2)-C(5) Fe(2)-C(6) C(5)-C(6) Fe(l)-C(5)-Fe(2) Fe(a)-Fe(l)-C(l) Fe(2)-Fe(l)-C(2) Fe(l)-Fe(2)-C(3) Fe(l)-Fe(2)-C(4)

1.762(4) 1.757(4) 1.953(3) 2.099(4) 2.168(4) 1.390(5) 78.9(1) 108.6(1) 145.7(1) 91.4(1) 156.8(2)

spectrum. That the trans arrangement of the phosphorus-containing ligands is maintained throughout the insertion process is readily ascertained from the magnitude of the coupling constants to the phosphido-bridge signal at 242.8 ( J = 84, 78 Hz)ppm. The lH NMR spectrum was most informative, revealing, in addition to the phenyl, cyclohexyl, and inequivalent methylene protons of the diphosphine, signals a t 6 6.50, 3.60, and 2.64, which were assigned on the basis of chemical shiRs and coupling constants to Ha, Hgcis, and Hgtrans,respectively. On the basis of the spectroscopic data, however, we were not able to assign the position of the vinyl group with respect to the phosphido moiety, that is, exo or endo. Thus an X-ray crystallographic study was carried out, the results of which are summarized in Figure 2, while Table 3 gives selected bond lengths and angles. The molecule shows the main structural features as expected, namely, a short iron-iron vector [Fe(l)Fe(2),2.577(1)AI bridged approximately symmetrically by diphos hine [Fe(l)-P(l), 2.225(1) A; Fe(2)-P(2), 2.22 1(1) and dicyclohexylphosphido [Fe(l)-P(3),

1

A;

2.224(1) Fe(2)-P(3), 2.249(1)A]moieties. Each iron atom also carries two carbonyls, one approximately trans t o the metal-metal vector, while the second lies cis to it and trans to the ethenyl ligand. The latter also bridges the diiron center, being 0-bound t o Fe(1) [Fe(l)-C(5), 1.953(3) AI and n-bound t o Fe(2) [Fe(2)C(5),2.099(6)A;Fe(2)-C(6), 2.168(4) AI. As expected, the carbon-carbon bond of the ethenyl is elongated [C(5)-C(6), 1.390(5)AI as a result of metal coordination. It adopts an endo position with respect t o the dicyclohexylphosphido moiety, that is, the /3-carbon lies above the C(l)-Fe(l)-Fe(2)-C(3) plane and toward the dicyclohexylphosphido moiety, while Ca lies below this plane. While a number of structures have been elucidated in which the dimetal center is spanned by the ethenyl ligand,16J7it is most useful to compare the structure of 2 in the solid state with that of the closely related diiron hexacarbonylcomplex [ F ~ z ( C O ) ~ ~ - H C = C H Z ) ~ - P P ~ ~ In the latter the ethenyl moiety also adopts an endo configuration with the phosphido bridge suggesting that the adoption of this arrangement in 2 is not a consequence of the relative steric bulk of the phosphoruscontaining ligands, but rather is an electronic effect. Other major structural features of the two molecules are also similar. Thus no significant changes in the metal-metal, metal-phosphido, or metal-ethenyl bond lengths occur upon diphosphine coordination, and, while there is a slight increase in the Ca-CB bond length [1.379(5)vs. 1.390(5)AI, it is not significant. The main structural change which occurs upon coordination of the (17)See for example: Huang, Y.-H.; Stang, P. J.; Arif, A. M. J.Am. Chem. SOC.1990,112, 5648. Iggo, J. A.; Mays, M. J.; Raithby, P. R.; Hendrick, K. J. J. Chem. SOC.,Dalton Trans. 1983,205. Orpen, A. G.;Pippard, D.; Sheldrick,G. M.; Rouse, K. D. Acta Crystullogr., Sect. B 1978,34,2466.

Hogarth et al.

2330 Organometallics, Vol. 14, No. 5, 1995 diphosphine is concerned with the relative orientations of the carbonyls on adjacent metal centers. Hence in 2, the carbonyls that lie cis to the metal-metal bond, namely, CO(2)and C0(4),lie approximately in a plane with the metal-metal vector which lies perpendicular to the phosphido bridge, while in [Fez(C0)6@-Hc=CH& @-PPhz)lthe appropriate carbonyls are staggered, with one lying above and the second lying below the plane. Thus coordination of the diphosphine has had the effect of twisting the two tricarbonyl fragments with respect to one another. This is also manifested in the coordination geometries about the metal atoms in both complexes which, ignoring the metal-metal bond, are approximately trigonal bipyramidal. The axial ligands at Fe(1) in 2 are best considered to be CO(2) and C(5) of the vinyl ligand, and the C(2)-Fe(l)-C(5) angle of 158.0(2)' varies by 8" from the corresponding angle in [Fe2(CO)s@-HC=CH2)(iu-PPhz)I[166.1(1)"1. An even greater variation occurs a t Fe(21, where P(3) and P(2) are best considered the axial ligands (taking the midpoint of the Ca-CB vector as an equatorial site), the P(2)-Fe(2)-P(3) angle being 151.0(1)" as compared to 168.3(1)"in the unsubstituted complex. From this it is apparent that, while both trigonal centers are twisted upon diphosphine coordination, it is the z-bound center Fe(2) which is most affected. The hydrodimetalation of other primary alkynes also proceeded smoothly upon reaction with 1. Insertion of propyne affords an inseparable mixture of a- and /?-substitutedcomplexes [Fez(C0)4@-MeC=CHz)@-PCy2)@-dppmll 3a with [Fez(CO)4Cu-HC=CHMe)(iu-PCy2)(iudppm)] 3b in an approximate 2.5:l ratio, while with phenylethyne the P-substituted isomer [Fe2(CO)&HC=CHPh)(p-PCyz)@-dppm)l 4 is formed exclusively (eq 3). Characterization of isomers proved relatively c,Y2

O

3a

0

C 0

C 0 3b R = Me, 4 R = Ph

straightforward by lH NMR spectroscopy, with P-substituted complexes 3b and 4 showing a relatively high field signal associated with Ha, while for the a-substituted complex 3a, the alkenyl protons appeared between 6 3.5 and 2.5. That all complexes adopted the expected trans disposition of phosphorus-containing ligands was easily shown by the relatively large phosphorusphosphorus coupling constants of between 90 and 70 Hz to the high-field phosphido-bridge resonance [213 K: 3a, 247.1 (dd, J = 85, 74); 3b, 242.8 (t, J = 79) ppml. In order to confirm the assignment of 4 as the 6-substituted isomer, an X-ray crystallographic study was carried out, the results of which are summarized in Figure 3, while Table 4 gives selected bond lengths and angles.

Table 4. Selected Bond Lengths (A)and Angles (deg) for 4CHzC12 Fe( 1)-Fe(2) Fe(l)-P(l) Fe(2)-P(2)

Fe(l)-P(3) Fe(2)-P(3) Fe( 1)- C(1) Fe(l)-C(2) P(l)-Fe(l)-P(3) P(2)-Fe(2)-P(3) Fe(l)-P(3)-Fe(2) P(3)-Fe(l)-C(5) P(3)-Fe(2)-C(5) P(3)-Fe(2)-C(6)

2.564(1) 2.229(1) 2.234(1) 2.222(1) 2.256(1) 1.768(4) 1.738(5) 151.9(1) 151.2(1) 69.8(1) 85.7(1) 81.7(1) 82.1(1)

Fe(2)-C(3) Fe(2)-C(4) Fe(l)-C(5) Fe(2)-C(5) Fe(2)-C(6) C(5)-C(6) Fe(l)-C(5)-Fe(2) Fe(2)-Fe(l)-C(l) Fe(2)-Fe(l)-C(2) Fe(l)-Fe(2)-C(3) Fe(l)-Fe(2)-C(4)

1.745(4) 1.761(5) 1.971(4) 2.104(5) 2.261(4) 1.395(5) 77.9(2) 109.5(2) 145.2(1) 88.0(2) 157.1(1)

As expected, the main structural features are very similar to those found in 2, the short iron-iron vector [Fe(l)-Fe(2), 2.564(1) AI being bridged symmetrically by the phosphorus-containing ligands which adopt the relative trans disposition. The unsubstituted a-carbon of the alkenyl li and bridges the diiron vector [Fe(l)C(5), 1.971(4) Fe(2)-C(5), 2.104(5) fil while the P-carbon is bound only t o a single iron center [Fe(2)C(6), 2.261(4) AI, and again the alkenyl moiety adopts an endo position with respect to the dicyclohexylphosphido moiety. The most interesting feature of 4 is the orientation of the phenyl substituent, which is endo to the diphosphine ligand and lies over one of the phenyl rings of the latter. Thus, the distance between the ring centroid of this ring [C(7O)-C(75)1 and the phenyl substituent [C(3O)-C(35)1 of 3.683 A is indicative of a weak n-stacking interaction. Indeed, while the orientation of the phenyl substituents on the diphosphine varies little for three of the rings between 2 and 4, this latter has undergone a significant twist in order to accommodate the phenyl substituent. The selectivity for a-substituted complexes during hydrometalation reactions constitutes a Markovnikov type addition process and is generally observed, for example, at d i i r ~ nand ~ , ~other binuclear metal centers.l* In the case of 1, the regioselectivity of the insertion process is strongly dependent upon the nature of the alkyne. Close inspection of the solid-state structure of 4 sheds light onto this. Substitution by a phenyl group at the a-carbon would lead to unfavorable steric interactions between it and the substituents on the phosphorus-containing ligands in either the endo or exo conformation. Hence it appears that the high regioselectivity for anti-Markovnikov addition in the case of the insertion of phenylethyne into 1 is sterically controlled. In contrast, the major product of the insertion of propyne is the a-substituted isomer 3a. Here the methyl group is less sterically demanding and can be tolerated in either site. In terms of reducing unfavorable steric interactions, it is still the P-site that is favored since this removes the substituent away from the sterically congested diiron center. Thus it is tempting to suggest that Markovnikov addition which affords the a-substituted products is electronically favored, while the anti-Markovnikov hydrodimetalation which affords P-substituted isomers is sterically preferable. We,5 Carty,16 and SeyferthlShave noted that phosphido-bridged diiron alkenyl complexes show an unusu-

1;

(18)Xue, Z.; Sieber, W. J.;Knobler, C. B.; Kaesz, H. D. J.Am. Chem. SOC. 1990,112,1825. Breckenridge, S.M.; McLaughlin, S. A.; Taylor, N. J.; Carty, A. J. J . Chem. SOC.,Chem. Commun. 1991,1718. (19) Seyferth, D.; Hoke, J. B.; Womack, G. B. Organometallics 1990, 9, 2662. Seyferth, D.; Archer, C. M.; Ruschke, D. P.; Cowie, M.; Hilts, R. W. Organometallics 1991,10,3363.

Diiron-Hydride Complexes

Organometallics, Vol. 14, No. 5, 1995 2331

Cl14) (3131

c14

Ct43l

5J

ct421

c1341w Ct33l

Figure 3. Molecular structure of 4.

Figure 4. u-n Alkenyl fluxionality.

ally high barrier t o exchange via the "windshield-wiper" process.20 The four p-alkenyl complexes described above are of two different types with respect to the size of the energy barrier to this exchange process, 2 and 3a having relatively high energy barriers while for the #?-substituted complexes 3b and 4,the energy barrier is lowered considerably. This is readily apparent from their room temperature 31PNMR spectra, the former displaying inequivalent ends of the diphosphine indicative of a slow exchange regime, while for the latter the spectrum is simplified significantly such that the diphosphine appears as a single doublet in accord with fast alkenyl exchange (Figure 4). In order to investigate this further, variable temperature 31PNMR studies were performed. Warming a tolueneds solution of 2 resulted in a gradual broadening of the diphosphine resonances; however, even at 100 "C coalescence was not observed. In an analogous experiment, warming a toluene-da solution Of 3a also resulted in a broadening of the diphosphine signals at 70 "C. At temperatures above this, however, the spectrum changed radically, with a number of new species growing in at the expense Of 3a. Indeed, upon warming to 80 "C and cooling back to room temperature all traces of 3a had disappeared. The precise details of these irreversible thermal transformations are currently under investigation. In related experiments, cooling CH&12/CDC13 solutions of 3b and 4 led to changes in the spectra in

accord with the freezing out of the "windshield-wiper" fluxionality such that a t 213 K three well-resolved signals were observed for each complex. From the separation of the inequivalent ends of the diphosphine when frozen out (2,1652;3a,233;3b, 556;4,573 Hz) and the coalescence temperature (2,>378; 3a, >353; 3b,253;4,233 K),approximate free energies of activation for the process are calculated as 268f2 (21, 268f2 (3a),47f2 (3b),and 34f2 (4)k J mol-l. The nature of this pronounced difference in the free energies of activation between those complexes substituted in the #?-position,3b and 4,with respect to those not substituted in this position, 2 and 3a,is open for debate. In view of the large difference between isomers 3a and 3b of 221 k J mol-l and the relative similarity of 3b and 4 which have electron-releasing and electronwithdrawing substituents on the ,!?-carbon,respectively, it is difficult to imagine that electronic effects alone can account for these observations. For example, one might imagine a development of charge in the transition state being stabilized either by a phenyl or a methyl group on the #?-carbon,but not both. Instead we favor an explanation based primarily on steric factors. This necessitates that for the #?-substitutedcomplexes relief of unfavorable steric interactions must occur in the transition state, thus lowering the activation barrier for the fluxional process. This is easy to image for 4, since in the ground state the phenyl substituent lies direct over one of the phenyl groups of the diphosphine while in the transition state it will lie between the two ends of the diphosphine since there is a plane of symmetry bisecting the iron-iron vector (Figure 4). For 3b, a similar release of unfavorable steric interactions is envisaged; however, since the methyl group is smaller, then these will be smaller in the ground state, and thus

Hogarth et al.

2332 Organometallics, Vol. 14, No. 5, 1995

the effect will not be so pronounced. For 2 and 3a, the steric nature of the alkenyl moiety will not vary significantly between the ground and transition state since the a-carbon (and hence its substituent) are fixed during the fluxional process. Hence we suggest that the high energy barriers noted for the exchange process in these and related phosphido-bridged diiron complexes596J6J9 are electronic in origin. As detailed above, 31P NMR spectroscopy is a particularly convenient method for observing the u-n alkenyl fluxionality since in the slow-exchange region inequivalent diphosphine resonances are observed which are made equivalent in the fast-exchange regime. Conventionally this process has been studied by 13C NMR spectroscopy, monitoring changes in the carbonyl signals. The latter approach is handicapped by a number of factors including the low natural abundance of carbon-13, long relaxation times of metal-bound carbonyls, and the occurrence of other carbonyl exchange mechanisms (e.g., trigonal rotation, bridgeterminal exchange) with similar energies to the “windshield-wiper” fluxionality. The 31P NMR spectra, however, give no insight into the mechanistic details of the transformation, namely, whether the two P-protons interconvert during the fluxional process. Generally this is not found to be the case;20however, in a few instances, proton exchange has been found to be concomitant with the alkenyl fluxionality,21 and we had reason to suspect that this may be the case for 2-4.8 Thus, the a--n alkenyl fluxionality in 2 was also monitored by lH NMR spectroscopy. At room temperature in toluene-& signals assigned to the vinylic protons are broadened slightly, while those due to the cyclohexyl and phenylic hydrogens are sharp. Warming to 100 “C results in a gradual broadening of the latter, while in contrast, the vinylic protons sharpen and remain distinct. Hence we conclude that under these conditions, the “windshield-wiper”fluxionality does not occur with exchange of the P-hydrogens, indicating that rotation about the C,-Cp vector cannot occur in the transition state and suggesting that the latter is not significantly zwitterionic in nature.8 3. Hydrodimetalation of the Activated Alkyne Dimethyl Acetylenedicarboxylate. While 1 does not react appreciably with unactivated disubstituted alkynes, addition of an excess of the activated alkyne, dimethyl acetylenedicarboxylate (DMAD), resulted in a rapid reaction a t 50 “C. The compound isolated was not, however, the expected hydrodimetalation product, namely, cis-[Fez(CO)4@-C(CO&le)=CH(CO&le]@-PCy~)@-dppm)],but rather the metallacyclic complex [Fez( C0 1.4 { r2-C ( C OzMe)=CH-C ( OMe)=O ]( p -PCyd(pdppm)] ( 5 ) formed in 71% yield (eq 4). Characterization was straightforward based on a comparison of spectroscopic data with that of the analogous diphenylphosphido complex which we have crystallographically characterized.8 The most notable feature that distinguishes 5 from a simple hydrodimetalation product is the carbonyl region of the IR spectrum, which differs significantly from those containing two iron dicarbonyl units, indicating Fe(C0)3 and Fe(C0) (20)Shapley, J. R.; Richter, S. I.; Tachikawa, M.; Keister, J. B. J . Organomet. Chem. 1976,94,C43. Farrugia, L.J.; Chi, Y.; Tu, W.-C. Organometallics 1993,12,1616 and references given therein. (21)Beck, J. A.;Knox, S. A. R.; Riding, G. H.; Taylor, G. E.; Winter, M. J. J . Organomet. Chem. 1980,202,C49. Liu, J.;Deeming, A. J.; Donovan-Mtunzi, S. J. Chem. Soc., Chem. Commun. 1984,1182.

CY

2

1

moieties. The most noteworthy features of 5 are the trans orientation of the vinyl substituents and the metal coordination of one of the carbonyl groups of the ester. A number of mononuclear complexes containing a metallacycle of this type have been reported previously.22 In the analogous diphenylphosphido chemistry, we were able to isolate and crystallographically characterize the cis hydrodimetalation product; however, monitoring the reaction between 1 and DMAD by IR and 31P NMR spectroscopy did not reveal the formation of any species other than 5. The reason for this difference becomes apparent when one considers the relative arrangements of the phosphorus-containing ligands in 1 and 1-Ph, being trans and cis, respectively. Thus, insertion of DMAD into 1-Phaffords cis,cis-[Fez(C0)4@(MeC02)C=CH(COzMe)]@-PPhz)@-dppm)lwhich contains a cis arrangement of phosphorus ligands and a cis alkenyl moiety, and it is only upon thermolysis in toluene that both cis-trans alkenyl and cis-trans phosphine rearrangements occur.* In contrast, since 1 already contains a trans arrangement of phosphines, then rearrangement of the initially formed insertion product trans ,cis-[Fez(C0)4@-MeCO~)C=CH(CO~Me)]@-PCyz)@-dppm)lto 5 must be extremely facile under the reaction conditions employed, and thus we conclude that it is the cis-trans rearrangement of the phosphoruscontaining ligands which is the high-energy process in the formation of 5-Ph. 4. Hydrodimetalation of Cumulenes and Heterocumulenes. A wide range of compounds with cumulated double bonds have been shown to insert into metal-hydrogen bonds at mononuclear centers,23while in contrast, hydrodimetalation reactions of cumulenes have been studied t o a far lesser extent.24 Hydrodimetalation of allene can occur to give either u--?t alkenyl or allyl complexes, resulting from the addition of the proton to the external and internal carbon centers, respectively. A number of reports have detailed such reactivity, and the selectivity of the transfer process appears to be highly dependent upon the nature of the dimetallic hydride complex itself. Thus selectivity toward the formation of u--n etheny16sz5and allylz6 (22)Vessey, J. D.; Mawby, R. J. J . Chem. Soc., Dalton Trans. 1993, 51. Vander Zeijden, A.A. H.; Bosch, H. W.; Berke, H. Organometallics 1992,11,563. Alt, H. G.;Engelhardt, H. E.; Thewalt, U.; Riede, J. J . Organomet. Chem. 1986,288,165. Werner, H.; Weinand, R.; Otto, H. J . Organomet. Chem. 1986,307,49. (23)Jia, G.;Meek, D. W. Znorg. Chem. 1991,30,1953and references

given therein. (24)Garcia Alonso, F.J.; Garcia-Sanz, M.; Riera, V. J. J . Organomet.

Chem. 1991,421,C12. (25)Horton, A.D.; Mays, M. J.;J . Chem. SOC.,Dalton Trans. 1990, 155.

Diiron-Hydride Complexes

Organometallics, Vol. 14, No. 5, 1995 2333

complexes has been reported, while in other examples, mixtures of products result from competitive hydrogen transfer reactions. Addition of allene to a toluene solution of 1 results in the exclusive formation of [FezCC0)4@-MeC=CHz)@-PCyz)@-dppm)]3a in 55% yield, in a n analogous fashion to that previously reported for the diphenylphosphido complex6 and resulting from selective proton transfer to an external carbon of the allene. In contrast, hydrodimetalation of carbon disulfide by 1 resulted in the exclusive formation of the dithioformato complex [Fe~(CO)4@-SzCH)@-PCyz)gl-dppm)l (6) in 83% yield (eq 5). That transfer of the proton had

a541 n

asl

.

a41 c141

1

Cl451

u341

Figure 5. Molecular structure of 7a.

c

c 0

0

6

occurred exclusively at the central carbon atom was easily verified by the 31PNMR spectrum, which showed a triplet a t 236.5 and doublet at 58.0 ppm ( J = 72 Hz) assigned to phosphido and diphosphine moieties respectively, indicating that the molecule contained a plane of symmetry bisecting the metal-metal vector. Other spectroscopic data also support this formulation; for example, there was an absence of any C=S and S-H absorptions in the IR spectrum. The dithioformato proton could not be assigned since it lay under the phenylic region in the lH NMR spectrum. In contrast to the facile insertion of carbon disulfide, carbon dioxide did not react with 1 even over prolonged periods. We have, however, synthesized the anticipated product of the latter, namely, [Fez(C0)4@-OzCH)@-PCyz)Cu-dppm)l via an alternative route.27 Thus, it appears that coordination of the heterocumulene to the binuclear center may be a necessary prerequisite for the insertion reaction. The insertion of carbon disulfide into mononuclear metal hydrides is again a well-established process, and proton transfer is generally selective t o carbon.28 While the hydrodimetalation of carbon disulfide appears to be quite rare, this is shown to occur with similar selectivity. Hydrometalation of isocyanates and isothiocyanates can in theory result in the formation of three products via proton transfer to carbon, nitrogen, or the heteroatom. While organic isocyanates do not react with 1, isothiocyanates readily insert with loss of carbon monoxide. The major insertion products in all cases were N-thioformamido complexes [Fez(CO)&-RNCHS)@(26) Hay, C. M.; Horton, A. D.; Mays, M. J.; Raithby, P. R.

Polyhedron 1988, 7 , 987.

(27) Corby, D.;Hogarth, G.; Lavender, M. H. Manuscript . in preparation. (28) (a) Robinson, S. D.; Sahajpal, A.Znorg. Chem. 1977,16, 2718. (b)Adams, R. D.; Golembeski, N. M.; Selegue, J. P. J.Am. Chem. SOC. 1981,103, 546. ~~

PCyz)@-dppm)l(7a-c), formed in yields of 27-47% as a result of proton transfer to the central carbon atom (eq 6). These were identified on the basis of spectroCY,

'

0

Ph,PvPPh2

1

1

,H

C

C

C

C

0

0

0

0

7 a-c

8 a-b

scopic data; notably all showed a resonance in the lH NMR spectrum around 6 8.2 assigned to the unique proton bound to the central carbon atom, while IR spectra did not contain absorptions assignable to nitrogen-hydrogen or sulfur-hydrogen moieties. In order to confirm this assignment, and elucidate structural features of the bridging N-thioamidate ligand, an X-ray crystallographic study was carried out on 7a, the results of which are summarized in Figure 5, while Table 5 gives selected bond lengths and angles. The structure of 7a confirms the spectroscopic assignment, and major features are as expected. The diiron vector [Fe(l)-Fe(2), 2.741(2) AI is significantly elongated with respect to those found in other complexes reported herein [Fe(l)-Fe(2), 2.577-2.580 AI. The major structural change due to this elongation is as expected an opening up of the angle at the bridging phosphido ligand, Fe( l)-P(3)-Fe(2), 75.4( as compared to the range of 69.9-71.0' for the other complexes. The remaining coordination sites on the diiron center l)O,

2334 Organometallics, Vol. 14, No. 5, 1995 H I

I4

Hogarth et al. Cl64)

H

R \ N 4 \ s

1Fe-

-!F

I-

i

Fe Fe

A

Fe

Ct631

B

Figure 6. Canonical representations of 7. Table 5. Selected Bond Lengths (A) and Angles (deg) for 7a Fe(lkFe(2) Fe(l)-P(l) Fe(2)-P(2) Fe(l)-P(3) Fe(2)-P(3) Fe(l)-C( 1) Fe(1)-C(2) P(1)-Fe( 1)-P(3) P(2)-Fe(2)-P(3) Fe(l)-P(3)-Fe(2) P(3)-Fe(l)-N(l) P(3)-Fe(2)-S(2) Fe(2)-Fe(l)-C(l) Fe(2)-Fe(l)-C(2)

2.741(2) 2.277(2) 2.245(2) 2.247(2) 2.234(2) 1.775(8) 1.738(7) 146.6(1) 144.9(1) 75.4(1) 90.8(2) 92.0(1) 161.8(3) 86.4(2)

Fe(2)-C(3) Fe(2)-C(4') Fe(l)-N(l) Fe(2)-S(1) N(l)-C(6) S(l)-C(6) Fe(1)-Fe(2)-C( 3) Fe(l)-Fe(2)-C(4) Fe(l)-N(l)-C(G) Fe(2)-S(l)-C(6) N(l)-C(6)-S(l) Fe(l)-N(l)-C(7) C(6)-N(l)-C(7)

1.767(8) 1.727(8) 2.031(6) 2.324(2) 1.274(10) 1.695(7) 161.9(2) 101.7(3) 124.8(5) 109.2(3) 127.6(6) 120.8(5) 114.4(6) W

C(151 are occupied by the N-thioamidate ligand which is bound to Fe( 1)through nitrogen [Fe(l)-N( l ) , 2.031(6) Figure 7. Molecular structure of 8a. A], while Fe(2) is sulfur-bound [Fe(2)-S(l), 2.324(2) A]. The solid-state structure also reveals that the allyl substituent adopts a position endo to the phosphido bridge and exo to the diphosphine. A number of possible resonance forms can be drawn for the diiron N-thioamidate core (Figure 6). In A, the C D nitrogen is pyramidal and there is a carbon-sulfur Figure 8. Canonical representations of 8. double bond, while in B it is planar and it is the carbonnitrogen interaction that contains n-character. Scrutiny identified as [F~~(CO)~(,LQ-RN=CH)(,M-PC~~)(~-~ of the bond lengths and angles within the dimetalacyclic (8a,b)and resulting from proton addition to carbon and unit clearly shows that it is form B that is the predomiloss of sulfur (eq 6). Spectroscopic data for 8 were very nant valence-bond representation. Thus, the central similar to that for 7; for example, IR spectra are nitrogen-carbon bond N(l)-C(6) at 1.274(10) is a virtually identical in the carbonyl region indicating that shortened considerably with respect to the external both new ligands have similar electron-donating abiliinteraction to the allyl moiety [N(l)-C(7), 1.493(9)AI, ties. Microanalytical results showed, however, that which is a simple a-interaction and within the range sulfur had been lost, while the unique proton is shifted found for carbon-nitrogen single bonds. More impordownfield with respect to 7, appearing as a triplet at tantly, the geometry about nitrogen is planar as eviabout 6 9.7 in the lH NMR spectrum. In order to denced by the sum of the bond angles about N( l)being confirm this assignment and to gain more insight into 360" [Fe(1)-N( l)-C(6), 124.8(6)"; Fe(1)-N( l)-C(7), the bonding within the dimetallacyclic ring, and X-ray 120.8(5)";C(6)-N(l)-C(7), 114.4(6)"]. In further supcrystallographic study was undertaken of 8a, the results port of the imine formulation, C(7) lies approximately of which are summarized in Figure 7 and Table 6. in the plane of the metallacycle as expected for an sp3The structure of 8a is very similar to that of 7a, the hybridized carbon. The carbon-sulfur bond [Fe(2)diiron vector [Fe(1)-Fe(2), 2.680(3)A] being bridged by S(1), 1.695(7)A] is, however, also slightly shorter than the new formimidoyl ligand which is linked to Fe(1) would be expected for a simple a-interaction, suggesting through the carbon [Fe(l)-C(6), 1.975(16) A] and to that A might play a small role; however, the bond angle Fe(2) through nitrogen [Fe(2)-N(l), 2.015(13) A]. While a t sulfur [Fe(2)-S(l)-C(6), 109.2(3)"1is clearly repretwo resonance forms (C and D) can be drawn for the sentative of sp3 hybridization, being similar to that formimidoyl ligand (Figure 8), representation C, in found in thioethers. Only a handful of related Nthe there is a carbon-nitrogen double bond, thioformamido complexes have been ~ h a r a c t e r i z e d , ~ ~ ,which ~~ predominates as shown by the relatively short carbonand 7a appears to be the first such binuclear complex nitrogen contact [C(6)-N(l), 1.210(23)& and the planar crystallographically characterized. Most similar is the triosmium complex [Os3(CO)g(PhPMe2)@-H)@-q2-Ph- nature of the latter. Thus as in 7a, the angles about nitrogen sum to 360", while the methylene carbon of the NCHS)],30 which shows similar carbon-nitrogen allyl ligand, C(7), lies in the metallacyclic plane. Indeed, [1.32(1)A] and carbon-sulfur [1.69(1)A] bond lengths. in a number of other crystallographically characterized With both allyl and ethyl isothiocyanate, a second formimidoyl complexes, similar short carbon-nitrogen product was obtained from the hydrodimetalation of 1, distances are found31 for example, in [Os3(CO)g(p-H)@ ~ - H C = N C G H ~ - ~ - F )the ( ~ ~carbon-nitrogen -S)] bond is (29) Robinson, S. D.; Sahajpal, A. Inorg. Chem. 1977,16,2722. 1.213(14) A further point of note in relation to a (30)Adams, R. D.; Dawoodi, Z.; Foust, D. F.; Segmuller, B. E. Organometallics 1983,2,315. comparison of the two structures is the exo nature of

Organometallics, Vol. 14, No. 5, 1995 2335

Diiron-Hydride Complexes Table 6. Selected Bond Lengths (deg) for 8a.C&2 Fe(l)-Fe(2) Fe(l)-P(l) Fe(2)-P(2) Fe(l)-P(3) Fe(2)-P(3) Fe(l)-C(l) P(l)-Fe(l)-P(3) P(2)-Fe(2)-P(3) Fe(l)-P(3)-Fe(2) P(3)-Fe(2)-N(l) P(3)-Fe(l)-C(6) Fe(a)-Fe(l)-C(l)

2.680(3) 2.207(4) 2.257(5) 2.193(4) 2.224(4) 1.752(19) 152.6(2) 138.1(2) 74.7(1) 83.3(4) 84.2(4) 152.6(5)

(A)and Angles

Fe(l)-C(2) Fe(2)-C(3) Fe(2)-C(4) Fe(2)-N( 1) Fe(l)-C(G) N(l)-C(6) Fe(l)-Fe(2)-C(3) Fe(l)-Fe(2)-C(4) Fe(2)-N(l)-C(6) Fe(l)-C(G)-N(l) Fe(2)-N(l)-C(7) C(6)-N(l)-C(7)

1.783(17) 1.779(20) 1.771(17) 2.015( 13) 1.975(16) 1.210(23) 155.8(6) 108.8(5) 110.1(11) 113.2(12) 130.6(12) 119.3(15)

the allyl moiety with respect to the phosphido bridge. This is presumably a result of steric effects; in the smaller ring, positioning of the allyl group endo to the dicyclohexylphosphido ligand would result in considerable steric interactions with a cyclohexyl group, while in the larger ring it is moved further away, thus minimizing the latter. The insertion of organic isothiocyanates into metalhydrogen bonds has been reported in only a few instances previously and generally yields N-thioformamido c o m p l e ~ e showever, ; ~ ~ ~ ~ amido-substituted ~ thioacyl complexes have also been noted.32 Most relevant to this work is that of Adams and co-workers who have described the insertion of both aryl and alkyl isothiocyanates into [ O S ~ ( C O ) ~ ~ @ H Thus ) ~ Iat . ~25 ~ "C, insertion occurs to afford ql-thioformamido complexes [oS3(CO)~DC~-H)C~~-T~-SCH=NR)I which rearrange with loss of CO when irradiated to give q2-complexes [os3(co)g(,u-H)(p3-q2-SCHNR)].Interestingly, when octane solutions of the latter are refluxed, rapid carbon-sulfur bond cleavage occurs to afford sulfido-formimidoyl complexes [ O S ~ ( C O ) ~ C ~ - H ) C ~ - H C = ~ )In @light ~ - S )of~ . these results, we considered that N-thioformamido complexes 7 may be precursors to formimidoyl complexes 8. Indeed, thermolysis of a toluene solution of 7b for 9 h afforded 8b in 57%yield. We have previously found that carbon-sulfur bond cleavage in isothiocyanates a t organometallic metal centers can be a very facile process.33 Robinson and co-workers in a series of papers have shown that the insertions of carbon disulfide,28aisothiocyanates,29and ~ a r b o d i i m i d e at s ~late ~ transition metal mononuclear centers are directly comparable, the latter being a useful synthetic route toward the synthesis of N,"-formamidinato complexes via selective proton transfer to carbon. Thus as a comparison, the hydrodimetalation of dicyclohexylcarbodiimide(CyN=C=NCy) by 1 was attempted. Warming a toluene solution to 60 "C, however, resulted in only a very slow reaction from which a number of low-yield products were observed, none of which displayed spectroscopic data consistent with the anticipated N,"-formamidinato complex. 5. Other Insertion Reactions. In a recent publication, the unsubstituted phosphido-hydrido complex

[HFez(CO)sCu-CO)Cu-PPh2)]has been shown to react with oxygen to afford the corresponding hydroxide complex [Fez(C0)601-OH)Cu-PPh2)3,formally resulting from the insertion of an oxygen atom into the hydride;14 indeed this type of oxygen insertion reaction has been known for some time.35 We have also shown that a similar insertion process occurs for the diphosphinesubstituted derivative 1-Ph,albeit only very slowly and giving the corresponding hydroxide [F~~(CO)~@-OH)QAPPhz)$-dppm)] in low yield.' Bubbling dry air through a toluene solution of 1 for 48 h did not, however, result in the formation of the corresponding hydroxide complex [Fez(C0)4@-OH)@-PCy2)@-dppm)l(9); rather, slow decomposition of l was noted. In a similar attempt t o synthesize a thiolate-bridged complex, toluene solutions of 1 were reacted with both elemental sulfur and propene sulfide, the latter being an excellent source of a sulfur atom. Both of these reactions, however, failed to yield the desired product; indeed 1 was recovered unchanged in both instances. In view of the formation of formimidoyl complexes via sulfur loss from an isothiocyanate, the synthesis of one such complex was attempted via the hydrodimetalation of tBuNC by 1. Warming a toluene solution of 1 with a slight excess of tBu'NC at 60 "C resulted in the selective formation of [Fe2(C0)4(u-HC=NtBu)+-PCy2)@-dppm)l (8d) in 83% yield (eq 7). Characterization proved straightforward, spectroscopic data being in accord with the other formimidoyl derivatives. CY2

' 0 PhzP-PPh,

1

1

H

Bu', N-C'

C

c

0

0

8C

(31) Adams, R. D.; Golembeski,N. M. J.A m . Chem. SOC.1979,101, 2579. Mays, M. J.; Prest, D. W.; Raithby, P. R. J . Chem. SOC.,Chem. Commun. 1980, 171. Aspinall, H. C.; Deeming, A. J. J. Chem. SOC., Chem. Commun. 1983,838. Beringhelli, T.; D'Alfonson, G.; Freni, M.; Giani, G.; Moret, M.; Sironi, A. J . Organomet. Chem. 1990,339, 291. Garcia Alonso, F. J.; Garcia Sanz, M.; Riera, V.; Abril, A. A.; Tiripicchio, A,; Ugozzoli, F. Organometallics 1992,11, 801. (32)Seyferth, D.; Womack, G. B.; Archer, C. M.; Fackler, J. P., Jr.; Marler, D. 0. Organometallics 1989, 8, 443. (33)Hogarth, G.; Skordalakis, E. J . Organomet. Chem. 1993,458,

In light of the successful insertion of an isocyanide into 1,insertion of nitriles was also attempted. Complex 1 proved to be sparingly soluble in acetonitrile a t room temperature, but even upon warming to 60 "C, while the solubility increased, no spectroscopic changes resulted, indicating that insertion had not occurred. In an additional experiment, an excess of acrylonitrile was added to a toluene solution of 1; however, again, no detectable reaction occurred. 6. Hydride Elimination Reactions. In a number of reactions of 1, rather than insertion into the diironhydride moiety, elimination of the hydride occurs. For example, chromatography of 1 on an alumina support, eluting with dichloromethane-petroleum ether mixtures, results in the slow formation of two new complexes, [Fe2(C0)4(~-OH)@-PCy2)@-dppm)l(9) and EFe2(C0)4(~-Cl)~-PCy2)OL-dppm)] (lo),the yields of which vary with exposure time on the column (eq 8). Hence, 1 can be eluted virtually unchanged on very short columns

CA. - -. (34)Brown, L.D.; Robinson, S. D.; Sahajpal, A.; Ibers, J. A. Znorg. Chem. 1977,16, 2728.

12,2908.

(35) Treichel, P. M.; Dean, W. IC;Calabrese, J. C. Inorg. Chem. 1973,

2336 Organometallics, Vol. 14, No. 5, 1995

Hogarth et al. C1641

CY, ,p\

C1651 Cl631 Cl621 CIS31

1

9

C1661 c1551

10

and short exposure times, while after approximately 2 h on a long column, complete conversion occurs. We have previously found that the diphenylphosphido complex 1-Ph also reacts with an alumina support; however, in the case of the latter, the reaction occurs almost instantaneously upon alumina absorption, and the hydroxide complex [Fe2(C0)4(p-OH)(p-PCyz)(p-dppm)l is the only product. In an attempt to explore the role Figure 9. Molecular structure of 11. of the dichloromethane in the formation of 10, chromatography of 1 was carried out on a similar alumina Table 7. Selected Bond Lengths (A)a n d Angles support while eluting with diethyl ether-petroleum (deg) for 11CH2C12 ether mixtures. Under these conditions, 1 was eluted Fe(WFe(2) 2.580(2) Fe(l)-C(2) 1.714(11) from the column unchanged, indicating that the presFe(l)-P( 1) 2.235(3) Fe(2)-C(3) 1.760(12) ence of the chlorinated solvent is critical to both the Fe(2)-P(2) 2.245(3) Fe(2)-C(4) 1.740(10) Fe(1)-P(3) 2.219(3) Fe(1)-I( 1) 2.604(2) formation of chloro- and hydroxide-bridged species. In Fe(2)-P(3) 2.224(2) Fe(2)-1(2) 2.606(1) separate experiments both of the latter were eluted Fe(WC(1) 1.783(10) unchanged from an alumina support by dichloroP(l)-Fe(l)-P(3) 151.1(1) Fe(a)-Fe(l)-C(l) 153.96) methane-petroleum ether mixtures, indicating that P(2)-Fe(2)-P(3) 150.4(1) Fe(2)-Fe(l)-C(2) 98.3(3) they are formed via different degradation routes but Fe(l)-P(3)-Fe(2) 71.0(1) Fe(l)-Fe(2)-C(3) 153.1(3) probably via a common intermediate. While the nature P(3)-Fe(l)-I(l) 82.4(1) Fe(l)-Fe(2)-C(4) 101.0(4) of such an intermediate remains unknown, it is temptP(3)-Fe(2)-1(1) 82.3(1) Fe(l)-I(l)-Fe(2) 59.4(1) ing t o speculate that it may result from a supportmediated carbonyl loss from 1 and undergoes competinometallic diiron complexes are relatively rare,36 a crystallographic study was carried out, the results of tive attack of chloride (from the solvent) and hydroxide which are shown in Figure 9 and Table 7. (from the support). In 11, the short iron-iron vector [Fe(l)-Fe(2), Chloro-bridged 10 is more easily prepared via addition 2.580(2) AI is bridged approximately symmetrically by of HC1 to 1, either in gaseous or aqueous form. This the iodide [Fe(l)-I(l), 2.604(2) A; Fe(2)-1(1), 2.606(1) reaction presumably results from hydride elimination AI, the bond angle at the latter [Fe(l)-I(l)-Fe(2), with concomitant formation of hydrogen. Hydride 59.4(1)"1being relatively acute, and the metal-carbonyl elimination also occurs upon reaction of 1with iodine, interactions traFs to the iodide are shortened [Fe(1)which affords the iodo-bridged complex [Fez(CO)&-I)(321, 1.714(11)A, Fe(2)-C(4), 1.740(10)AI with respect b-PCyz)(p-dppm)l(ll)in 60% yield (eq 9). Characterto those trans to the metal-metal bond [Fe(l)-C(l), 1.783(10) A; Fe(2)-C(3), 1.760(12) AI) indicating that $Y 2 the relative o-inductive effects of the iodide and metalmetal bond are quite different. We have previously shown that thermolysis of [Fez(C0)4(pCL-H)(p-CO)(p-PPhz)Cu-dppm)l (1-Ph)in the presence of dicyclohexylphosphineresults in loss of hydrogen to afford the mixed phosphido-bridged complex [FezI (C0)4(p-PCy2)@-PPh2)(p-dppm)l (l!2)? In an analogous cv, experiment, heating a toluene solution of 1 in the presence of a slight excess of diphenylphosphine gave the expected mixed phosphido-bridged complex 12 in 60% yield, while also affording the bis(dipheny1)phosphido complex [Fez(CO)&-PPh2)2(-dppm)I(13) in 30% yield (eq 10). The formation of 13 was unexpected and 11

ization was easily made on the basis of analytical and spectroscopic results; however, since iodo-bridged orga-

(36) See for example: Mott, G. N.; Carty, A. J.Znorg. Chem. 1979, 18,2926. Kilner, M.; Midcalf, C. J.Chem. Soc., Chem. Commun. 1971, 944. Koerner von Gustorf, E.; Grevels, F.-W.; Hogan, J. C. Angew. Chem., Int. Ed. Eng. 1969,8,899.

Organometallics, Vol. 14, No. 5, 1995 2337

Diiron-Hydride Complexes

Table 8. Crystallographic Data 1

color space group a,A

b, A

c, A

a,deg

A deg ,;

z

$!

F(OO0) dcaled, dcm3 p(Mo Ka),cm-l orientation reflns: no.; range (281, deg no. of data measd no. of unique data no. of unique data with I 2 3.Ootn no. of params R" RWb

largest shiWesd, final cycle largest peak, e/&

2CHzC12

7a

4CHzClz

8aCsHiz

11CHzClz

ocange P1 10.2577(34) 13.0315(81) 15.8986(71) 81.902(43) 84.672(31) 72.272(38) 2001.30 2 868 1.38 8.84 37; 11-27

ocange P1 11.7987(15) 12.8813(16) 17.0025(9) 73.670(8) 77.770(8) 64.870(8) 2228.62 2 952 1.37 9.16 39; 19-30

ocange P1 12.5326(15) 12.5939(16) 18.4748(25) 105.240(10) 91.975(10) 118.025(10) 2440.43 2 1032 1.35 8.42 30; 24-32

red P1 11.9777(39) 13.5848(36) 13.7530(51) 88.912(26) 89.293(28) 78.931(25) 2195.71 2 944 1.37 8.54 25; 13-26

orange P21Ic 11.8267(32) 15.5264(29) 27.1868(71) 90 91.366(22) 90 4990.80 2 1908 1.21 7.13 30; 11-24

orpge P1 11.8975(20) 12.9829(16) 16.6072(25) 72.937(12) 76.891(13) 64.089(11) 2191.23 2 1028 1.54 16.30 34; 19-30

7542 7333 4395

8325 8287 6870

9344 9017 7815

8211 7924 4459

9933 9047 3449

8439 8175 6287

469 0.068 0.076 0.005

484 0.046 0.053 0.003

535 0.051 0.064 0.06

505 0.061 0.052 0.001

497 0.093 0.02

472 0.069 0.074 0.02

1.16

1.00

1.61

0.44

0.58

1.76

formally results from the substitution of a dicyclohexylfor a diphenylphosphido moiety. In order to ascertain the point a t which the substitution occurred, (i.e., before

0.088

cleavage of the metal-metal bond to form an intermediin ate [Fez(CO)s(H)(Ph)@-PCyz)@z-q3-PhzPCHzPPh)1 which the new phenyl ligand is metal-bound, and this transforms rapidly via benzene loss into the observed

CY,

'

PhzP-

1

0

1 PPh2

I

12

13

or after hydrogen loss), a toluene solution of 12 was heated in the presence of an excess of diphenylphosphine; however, even after a prolonged period, the starting material was recovered unchanged. Thus, it appears that phosphido-bridgeexchange occurs prior to the formation of the electron-precise bis(phosphid0) complexes. Hydride elimination from 1 also occurs in the absence of external reagents. Thermolysis of a toluene solution of 1 for 2 h results in loss of benzene and the formation - P Cin ~ Z71% )] of [ F ~ Z ( C O ) & - ~ ~ - P ~ Z P C H Z P P ~ ) @(14) yield (eq 111, characterization being made by comparison of spectroscopic data with that of the crystallographically characterized diphenylphosphido derivat i ~ e The . ~ most interesting feature of the formation of 14 is that hydride elimination occurs without loss of carbon monoxide. This leads us t o suggest that the pathway by which these elimination reactions occur may not be via initial loss of a carbonyl, but rather via metal-metal bond cleavage and retainment of the carbonyl. Thus in the formation of 14,initial oxidative addition of the carbon-phosphorus bond may occur with

14

product. Addition of HC1 is likely to occur via initial protonation a t the metal-metal bond to give the dihydride [Fez(C0)5@-H)z@-PCyz)Ol-dppm)If, which leads to loss of Hz and a carbonyl upon complexationof chloride; however, the precise sequence of events cannot be ascertained. Experimental Section General Procedures. All reactions were carried out under a nitrogen atmosphere using predried solvents. NMR spectra were recorded on a Varian VXR 400 spectrometer, and IR spectra were recorded on a Nicolet 205 FT-IRspectrometer. Column chromatography was carried out on columns of deactivated alumina (6%w/w water). Elemental analysis was performed within the chemistry department of University College. Ultraviolet photolysis was carried out using a Hanovia medium-pressure lamp. Dicyclohexylphosphine and propyne were purchased from Fluorochem; diphenylphosphine, phenylethyne, and isothiocyanates were purchased from Aldrich and used as supplied. Unless otherwise stated, all complexes were recrystallized upon slow d i f i s i m of methanol into a dichloromethane solution.

2338 Organometallics, Vol. 14,No. 5, 1995 Table 9. Positional Parameters ( x lo4) and U,, (A2 x 103) for 1 X

3459(1) 3354(1) 3763(2) 3659(2) 3195(2) 830(6) 6014(7) 1723(8) 1342(8) 5767(8) 1964(8) 5058(9) 2383(8) 2117(9) 4812(10) 3423(8) 2624(8) 1265(8) 370(9) 808(11) 2142(12) 3042(11) 5459(8) 6395(9) 7700(11)) 8062(10) 7132(10) 5834(9) 5339(8) 5486(10) 6752(11) 7932(9) 7825(11) 6555(10) 2474(8) 2006(9) 1129(10) 724(10) 1176(11) 2040(10) 4643(9) 4554(11) 5859(12) 6118(11) 6169(11) 4849(10) 1621(11) 882(12) -407(15) -1166(13) -399(13) 825(16)

Y

z

2466(1) 1585(1) 4009(2) 2930(2) 817(2) 3249(5) 1748(6) 3312(6) 910(7) -178(6) 2729(6) 2029(7) 2974(7) 1173(7) 529(8) 4186(6) 5311(6) 5393(7) 6357(7) 7258(7) 7227(8) 6248(7) 4179(6) 4226(8) 4262(9) 4330(9) 4328(9) 4257(7) 2730(6) 3109(8) 2943(9) 2383(9) 2010(11) 2170(9) 3469(6) 2764(7) 3155(8) 4228(9) 4951(8) 4570(7) -385(6) - 1445(7) -2382(8) -2484(8) - 1447(8) -525(7) 491(9) 37(11) - 179(13) 395(16) 731(11) 1066(16)

1920(1) 3472(1) 2195(1) 4111(1) 2312(1) 2920(4) 856(5) 473(5) 4657(4) 4076(5) 2822(5) 1288(6) 1046(5) 4197(5) 3833(6) 3337(5) 1737(5) 1584(5) 1217(6) 1027(7) 1199(8) 1546(7) 1901(5) 2460(6) 2154(8) 1302(7) 746(7) 1023(6) 4536(5) 5301(6) 5609(7) 5150(7) 4409(8) 4113(7) 5000(4) 5602(5) 6283(6) 6376(6) 5776(6) 5106(6) 2051(5) 2569(6) 2377(7) 1450(7) 925(7) 1101(6) 2102(7) 2865(7) 2705(9) 2027(11) 1224(8) 1417(9)

Preparation of [Fez(CO)4(u-H)(IrCO)(Ir-PCy~)(Ir-dppm)l

Hogarth et al. Table 10. Positional Parameters ( x lo4) and U, (& x l o 3 ) for 2CHzC12 X

542(1) 2742(1) -320(1) 2329(1) 2193(1) -1579(3) 563(3) 5166(3) 3624(3) -741(4) 569(3) 4213(4) 3255(3) 986(3) 1870(4) 912(3) -1483(3) - 1886(3) -2778(4) -3214(4) -2828(4) -1971(4) -1220(3) -1108(3) - 1928(4) -2833(4) -2949(4) -2143(4) 2088(3) 975(5) 875(6) 1874(6) 3008(6) 3112(5) 3461(3) 3123(4) 3940(4) 5131(4) 5486(4) 4659(3) 2840(3) 2062(4) 2572(2) 3963(6) 4733(5) 4239(4) 2308(4) 3457(4) 3521(5) 2308(5) 1209(5) 1086(4) 1734 320 2738

Y

2724(1) 2675(1) 4589(1) 4552(1) 1115(1) 2203(3) 1968(3) 1867(4) 2114(3) 2424(3) 2250(3) 2186(4) 2340(3) 3447(3) 2963(3) 5185(3) 5676(3) 5342(3) 6191(4) 7346(5) 7694(4) 6855(3) 4972(3) 5749(3) 6083(4) 5638(3) 4866(4) 4531(3) 5563(3) 6439(4) 7163(5) 7027(5) 6150(5) 5422(4) 4937(3) 6065(3) 6359(4) 5539(4) 4436(4) 4132(3) 26(3) -702(3) -1443(4) -2216(4) -1509(4) -775(3) 137(3) -92(4) -894(5) -506(5) -398(5) 45x4) 10731 11577 9900

z

7819(1) 7139(1) 7937(1) 7049(1) 7579(1) 7737(2) 9606(2) 6140(3) 8725(2) 7759(2) 8903(2) 6535(3) 8107(2) 6685(2) 6059(2) 7765(2) 7240(2) 6682(2) 6170(2) 6197(3) 6748(3) 7284(3) 8917(2) 9280(2) 9981(2) 10306(2) 9946(3) 9252(2) 6045(2) 5847(3) 5072(3) 4489(3) 4664(3) 5437(3) 7373(2) 7484(3) 7748(3) 7888(3) 7776(3) 7509(2) 8508(2) 8972(3) 9788(3) 9658(4) 9177(3) 8355(3) 6900(2) 6245(3) 5718(3) 5370(3) 6055(3) 6566(3) 1445 1828 2167

U.0

(1). U V irradiation of a toluene solution (150 cm3)of [Fe(CO)e(u-CO)(u-dppm)l(l.Og, 1.45 mmol) and dicyclohexylphosphine mmol) was saturated with propyne and stirred for 48 h. (0.30 g, 1.51 mmol) for 16 h while purging with a steady stream Removal of the solvent under reduced pressure and chromaof nitrogen resulted in a color change from deep red to orange. tography eluting with 40-60 "C petroleum ether-diethyl ether Removal of the solvent under reduced pressure and washing (9:l) afforded a n orange band which gave a mixture of 3a and with 40-60 "C petroleum ether afforded orange crystalline 1 3b~ (2.5:l (720 mg, 60%). Anal. Calcd for C ~ Z H ~ ~ O ~ P ~ F ~ ~ * C, O.SCH C ~ ~ :by 31PNMR spectroscopy) (0.22 g, 72%). Crystallization upon cooling a saturated hexane solution of the 58.18; H, 5.25. Found: C, 58.47; H, 5.23. Preparation of rFea(CO)4(Ir-HC=CH2)(Ir-PCy2)(Ir-dppm)l mixture afforded a n orange crystalline solid. Anal. Calcd for C~H4904P3Fez:C, 62.41; H, 5.79. Found: C, 61.77; H, 6.32. (2). Slow purging of ethyne through a toluene solution (20 Slow purging of allene through a toluene solution (20 cm3) cm3) of 1 (0.20 g, 0.24 mmol) for 10 min and stirring for a n of 1 (0.4 g, 0.48 mmol) for 10 min and stirring for an additional additional 4 h at 50 "C in a water bath resulted in a change 12 h at room temperature resulted in a change in the carbonyl in the carbonyl region of the IR spectrum. Removal of the region of the infrared spectrum. Removal of the solvent and solvent and chromatography gave upon elution with 40-60 chromatography gave upon elution with 40-60 "C petroleum "C petroleum ether-dichloromethane (4:l) a yellow-orange ether-dichloromethane (9:l) a n orange band which afforded band which afforded 2 as a bright yellow solid (0.14 g, 69%). 3a as a n orange solid (0.23 g, 55%). Anal. Calcd for C ~ ~ H ~ ~ O ~ P ~ F ~C,Z57.58; C H ~ H, C ~5.34. Z: Found: C, 57.69; H, 5.41. Preparation of [Fe&20)4@-HC=CHPh)@-PCy2)0IPreparation of [Fe2(C0)4(Ir-MeC=CH2)(Ir-PCy2)(Ir- dppm)] (4). A toluene solution (50 cm3) of 1 (0.50 g, 0.61 dppm)l (3a) and [Fez(C0)4(Ir-HC=CHMe)(Ir-PCyz)(Ir- mmol) and phenylethyne (0.12 g, 1.17 mmol) was stirred for dppm)] (3b). A toluene solution (50 cm3) of 1 (0.30 g, 0.36 48 h. Removal of the solvent and chromatography gave upon

Organometallics, Vol. 14,No. 5, 1995 2339

Diiron-Hydride Complexes Table 11. Positional Parameters ( x 104) and U, (A2 x 10s) for 4CHzC12 X U z UW 3413(1) 1977(1) 2241(1) 542(1) 3685(1) 2905(4) 5902(3) 624(3) 1242(3) 3109(4) 4900(4) 1176(3) 1532(4) 3151(3) 3372(3) 666(3) 1973(3) 829(4) 718(5) 1725(5) 2852(5) 2993(4) 2645(3) 3693(4) 3926(5) 3124(5) 2113(5) 1875(4) 428(3) 647(4) 517(5) 193(5) -20(5) lOO(4) -1076(3) -1994(4) -3196(4) -3534(4) -2653(5) -1423(4) 3469(4) 4566(4) 4225(6) 3813(6) 2759(6) 3088(5) 5051(4) 4712(5) 5829(5) 6801(6) 7183(5) 6086(4) 3160(3) 2885(4) 2754(5) 2920(5) 3210(5) 3327(4) 8060(13) 8188(4) 9249(7)

4053(1) 4808(1) 2002(1) 2947(1) 5988(1) 3452(3) 4467(4) 4056(3) 6640(3) 3699(4) 4290(4) 4345(3) 5904(4) 4289(3) 5376(3) 1653(3) 832(3) -227(4) - "3) -968(4) 8U5) 985(4) 1286(3) 2009(4) 1454(5) 205(5) -515(4) 18(4) 2602(3) 1701(4) 1497(5) 2183(5) 3096(5) 331l(4) 2438(4) 1201(4) 811(5) 1605(5) 2829(5) 3257(4) 6393(4) 6735(4) 6907(6) 7882(6) 7555(6) 7412(5) 7543(3) 8389(4) 9666(5) 9481(6) 8684(5) 7408(4) 5430(3) 6319(4) 6422(5) 5640(6) 4772(5) 4653(4) 6630(12) 7964(4) 6257(7)

2097(1) 2700(1) 1967(1) 2782(1) 2288(1) 441(2) 2229(3) 1184(2) 3451(2) 1096(2) 2186(3) 1781(2) 3174(2) 3161(2) 3738(2) 2102(2) 1049(2) 695(2) 18(2) -302(2) 36(3) 711(3) 2599(2) 3171(2) 3678(3) 3605(3) 3041(3) 2529(2) 3688(2) 3841(2) 4547(3) 5084(3) 4945(3) 4245(2) 2459(2) 2380(3) 2111(3) 1933(3) 2026(3) 2285(2) 1417(2) lOOl(3) 256(3) 367(3) 797(3) 1554(3) 2909(2) 3486(3) 3925(3) 4274(3) 3679(3) 3257(3) 4529(2) 4966(2) 5718(3) 6050(3) 5637(3) 4879(2) 1431(8) 1740(3) 1407(4)

Table 12. Positional Parameters ( x lo4) and U, (A2 x 10s) for 7a X

1922(1) 3088(1) 1385(2) 1110(2) 2565(2) 2984(2) 508(5) 1336(6) 3972(5) 4194(7) 5370(5) 1480(7) 3154(7) 3749(7) 4436(8) 1175(6) 406(6) -504(6) -428(9) -992(11) 1621(6) 2073(7) 2396(9) 2278(11) 1826(11) 1502(8) -420(6) -1240(7) -2353(7) -2674(9) -1895(9) -754(7) 2365(7) 3293(8) 3201(11) 2175(11) 1218(10) 1300(8) 3438(6) 4003(7) 4603(8) 4629(9) 4112(10) 3477(8) 2327(6) 2843(7) 2199(8) 2125(8) 1587(7) 2253(7) 4318(6) 5154(6) 6296(6) 6149(7) 5338(7) 4174(6)

Y

3740(1) 2069(1) 3614(2) 2365(1) 1571(1) 4556(1) 4323(4) 4819(5) 2923(4) 2986(5) 2308(5) 4432(6) 3216(5) 3045(4) 2616(6) 1667(5) 4230(5) 4946(5) 6023(7) 6767(8) 1433(5) 1717(6) 1036(7) 71(8) -234(7) 442(6) 2556(5) 2332(6) 2459(8) 2785(7) 3028(6) 2915(6) 1007(5) 709(7) 267(8) 157(8) 458(7) 890(6) 503(5) 657(6) -121(7) -1086(7) -1267(7) -476(5) 5717(5) 5771(5) 6680(6) 7649(6) 7582(5) 6706(5) 4799(5) 5122(6) 5155(6) 5842(7) 5535(6) 5485(6)

z

ue,

2977(1) 1315(1) 504(1) 3182(1) 1441(1) 2013(1) 2204(5) 4781(5) 4048(4) -588(5) 1979(5) 4041(6) 3598(5) 158(6) 1757(6) 2052(5) 1291(6) 2686(6) 2761(9) 2514(12) 4129(5) 4980(5) 5736(6) 5644(8) 4814(8) 4064(7) 3495(6) 2875(7) 3180(9) 4091(10) 4696(8) 4414(7) 274(5) -317(7) -1192(8) -1530(7) -966(7) -60(6) 2090(5) 2919(6) 3472(7) 3186(8) 2340(8) 1823(7) 1323(5) 293(5) -285(6) 247(6) 1248(6) 1843(6) 2566(5) 1812(5) 2286(6) 3156(6) 3887(6) 3452(5)

Preparation of [Fez(C0)4(lr-SzCH)Cu-PCy~)@-dppm)l

(6). Addition of carbon disulfide (0.10 g, 1.32 mmol) to a toluene solution (20 cm3) of 1 (0.40 g, 0.48 mmol) and subsequent stirring for 6 h at 50 "C in a water bath resulted in dissolution of 1 and formation of a n orange solution. The solvent was removed, and the resulting orange solid was elution with 40-60 "C petroleum ether-dichloromethane (4: adsorbed onto alumina and chromatographed. Elution with 1)an orange band which afforded 4 as a bright orange solid "C petroleum ether-dichloromethane (9:l) afforded an (0.18 g, 33%). Anal. Calcd for C ~ ~ H ~ I O ~ P ~ F ~ Z ' CC,H Z C ~40-60 Z: orange band which on removal of the solvent yield 6 as an 60.42; H, 5.34. Found: C, 59.72; H, 5.04. orange microcrystalline solid (0.35 g, 83%). Anal. Calcd for Preparation of [F~z(CO)~{~~-C(COZM~)=CH-C(OC ~ ~ H ~ ~ O ~ P ~ S ~ F ~ C, Z ~55.16; . ~ C HH,Z C 4.98; ~ Z S, : 6.92. Me)=O}@-PCyz)@-dppm)] (5). A toluene solution (20 cm3) Found: C, 55.16; H, 4.92; S, 6.87. of 1 (0.50 g, 0.60 mmol) and DMAD (0.20 cm3, 1.63 mmol) was Preparation of [Fez(CO)r@-RNCHS)@-PCyz)@-dppm)I stirred a t room temperature for 96 h, resulting in dissolution (7a-c) and [Fe~(C0)4@-RN~H)(lr-PCy~)@-dppm)I (8a,b). of 1 and formation of a bright orange solution. Removal of Addition of allyl isothiocyanate (0.20 g, 2.04 mmol) to a toluene the solvent under reduced pressure gave an orange solid, which solution (20 cm3) of 1 (0.40 g, 0.48 mmol) and subsequent was chromatographed on alumina. Elution with 40-60 "C stirring for 6 h a t 50 "C in a water bath resulted in dissolution petroleum ether-dichloromethane (4:l) gave an orange band of 1 and formation of an orange solution. The solvent was which afforded 5 (0.40 g, 71%). Anal. Calcd for C47H5108P3removed, and the resulting orange solid was adsorbed onto Fez: C, 59.49; H, 5.38. Found: C, 59.29; H, 5.81.

Hogarth et al.

2340 Organometallics, Vol. 14, No. 5, 1995 Table 13. Positional Parameters ( x lo4) and U,, (Azx lo3) for 8aGH12

2949(2) 4524(4) 4192(4) 2568(3) 3316(13) 5660(11) 1308(14) 4159(13) 197512) 3449(13) 4869(15) 1948(18) 3736(14) 4291(14) 2313(13) 937(16) 1106(22) 857(23) 6064(14) 6463(15) 7623(19) 8290(21) 7932(20) 6772(21) 4083(14) 3942(20) 3648(22) 3488(23) 3687(27) 3931(18) 3864(12) 3695(15) 3446(16) 3409(15) 3614(18) 3823(16) 5691(15) 6398(18) 7546(22) 7954(17) 7256(22) 6129(16) 1068(15) 256(14) -952(22) -1209(19) -535(18) 683(20) 3180(11) 3403(13) 4077(15) 3504(18) 3262(15) 2571(13) 9827 9864 10133 9437 9359

8417(1) 6627(2) 7503(2) 8933(2) 7538(9) 8859(7) 8992(10) 9989(8) 7428(8) 7602(10) 8445(11) 8737(12) 9358(11) 6462(8) 7156(9) 7039(12) 6580(25) 5831(21) 6522(9) 6828(10) 6736(12) 6305(18) 6042(24) 6083(15) 5589(9) 5514(11) 4726(13) 4030(12) 4081(13) 4864(11) 7163(11) 6330(11) 6117(14) 6743(16) 7578(15) 7803(12) 7786(10) 7279(12) 7441(16) 8150(16) 8662(14) 8507(12) 9019(14) 9383(10) 9390(26) 9180(24) 8780(15) 8738(31) 9971(8) lOOOl(9) 10774(10) 11581(11) 11564(10) 10807(9) 2352 2860 3713 3636 3803

1958(1) 1354(1) 2323(1) 1209(1) 45(5) 1013(5) 2570(6) 2223(5) 1724(6) 463(7) 1056(6) 2401(7) 2102(5) 2005(5) 1337(7) 1940(9) 2351(13) 2486(12) 1260(6) 851(6) 727(8) 1036(9) 1449(11) 1576(7) 1090(6) 595(7) 386(9) 662(9) 1143(10) 1360(8) 2949(6) 3094(6) 3578(6) 3914(7) 3789(7) 3305(7) 2404(5) 2686(7) 2737(7) 2507(9) 2253(8) 2190(7) 986(6) 1344(7) 1178(10) 750(12) 386(7) 587(12) 1003(5) 454(5) 323(6) 488(7) 1024(6) 1175(5) 1247 936 1039 692 298

Table 14. Positional Parameters ( x lo4) and Ueq (Azx 10s) for 11CHzC12 2234(1) 4478(1) 3902(1) 2663(2) 5344(2) 2792(2) -183(9) 1259(8) 6586(7) 4364(8) 768(10) 1659(9) 5782(9) 4393(9) 4110(8) 1567(9) 358(9) -441(10) -69(11) 1128(11) 1933(10) 2837(9) 3868(12) 3903(15) 2965(17) 1875(18) 1796(12) 6501(8) 6954(10) 7861(12) 8275(11) 7871(11) 6970(10) 6270(8) 6149(9) 6963(10) 7866(10) 7964(10) 7169(9) 2650(9) 1720(10) 1597(11) 2830(12) 3571(11) 3920(10) 2197(9) 822(10) 358(13) 1103(15) 2494(15) 2988(11) 7001(25) 5374(9) 7730(18)

2311(1) 2198(1) 1565(1) 417(2) 299(2) 3827(2) 3137(9) 2946(7) 2826(6) 2832(7) 2799(9) 2681(7) 2526(8) 2580(8) -254(8) 40(8) 833(9) 502(11) -610(11) -1407(9) -1104(8) -585(8) -1557(10) -2254(13) -2070(13) -1098(16) -330(12) -832(8) -1999(9) -2854(10) -2526(12) - 1406(12) -552(10) -30(7) -747(8) -1043(9) -612(9) 121(10) 407(8) 4779(8) 4724(9) 5571(10) 5347(11) 5441(10) 4593(9) 4911(7) 5735(9) 6535(11) 7235(11) 6458(11) 5625(9) 5762(23) 6604(8) 4838(16)

2844(1) 2261(1) 3888(1) 2975(1) 21940 ) 2419(1) 3877(7) 1253(5) 2125(5) 465(5) 3489(7) 1895(6) 2212(6) 1174(6) 2307(5) 2616(5) 2485(6) 2428(7) 2145(7) 2286(7) 2516(7) 4023(5) 4240(7) 5016(9) 5603(8) 5428(8) 4621(7) 2902(5) 2862(7) 3370(8) 3913(7) 3945(7) 3435(6) 1184(5) 766(6) 46(6) -261(6) 144(6) 859(6) 3127(6) 3912(6) 4438(7) 4662(7) 3885(7) 3338(7) 1457(6) 1585(7) 728(9) 307(9) 188(7) 1023(7) 1334(17) 1775(5) 2245(12)

8b (0.10 g, 24%). Further elution with 40-60 "C petroleum

ether-diethyl ether (4:l) gave a n orange band which on removal of the solvent afforded a n orange microcrystalline solid, 7b (0.20 g, 47%). Anal. Calcd for C ~ ~ H ~ O O ~ N I P ~ S I FeyCH2C12 (a): C, 55.21; H, 5.31; S, 3.27; N, 1.43. Found: C, 55.19; H, 5.40; S, 3.54; N, 1.49. Anal. Calcd for C45H50alumina and chromatographed. Elution with 40-60 "C peO ~ N I P ~ F ~ Z (8b): C ~ HC, I ~62.69; H, 6.48; N, 1.46. Found: C, troleumether-diethyl ether (9:l) afforded a yellow band which 62.46; H, 6.40; N, 1.22. on removal of the solvent yielded a yellow solid, 8a (0.10 g, Addition of phenyl isothiocyanate (0.30 g, 2.22 mmol) t o a 24%). Further elution with 40-60 "C petroleum ether-diethyl toluene solution (30 cm3) of 1 (0.30 g, 0.36 mmol) proceeded ether (4:l) gave a n orange band which on removal of the in an analogous manner. Chromatography eluting with 40solvent afforded a n orange microcrystalline solid, 7a (0.15 g, petroleum ether-dichloromethane (4:l) gave an orange 35%). Anal. Calcd for C ~ ~ H ~ O O ~ N ~ P & F ~ ~(7a): - O .C,~ C H ~60C"C ~Z band which yielded 7c as a n orange solid (0.09 g, 27%). Anal. 57.63; H, 5.38; S, 3.38; N, 1.48. Found: C, 57.09; H, 5.36; S, Calcd & 59.17; . ~ C HH, Z 5.19; C ~ ~S, : 3.34; N, 1.52. Anal. Calcd for C ~ ~ H ~ O O ~ N ~ P ~ @a): F~Z'C~H I Z for C ~ ~ H ~ O O ~ N ~ P ~ S I F ~ C, 3.25; N, 1.42. Found: C, 59.56; H, 4.29; S, 3.06; N, 1.29. C, 62.69; H, 6.48; N, 1.46. Found: C, 62.46; H, 6.40; N, 1.22. Addition of ethyl isothiocyanate (0.20 g, 2.30 mmol) to a Preparation of [Fez(C0)40-tBuN=CH)O-PCy2)01toluene solution (20 cm3) of 1 (0.40 g, 0.48 mmol) proceeded dppm)] (8d). Addition of tert-butyl isocyanide (0.10 g, 1.20 mmol) in a toluene solution (20 cm3) of 1 (0.40 g, 0.48 mmol) in a n analogous manner. Chromatography eluting with 40and subsequent stirring for 6 h at 50 "C resulted in the gradual 60 "C petroleum ether-diethyl ether (9:l) afforded a yellow fading of the orange coloration. Removal of the solvent and band which on removal of the solvent yielded a yellow solid,

Diiron-Hydride Complexes chromatography eluting with 40-60 "C petroleum etherdichloromethane (9:l) gave a yellow band which afforded 8d as a yellow powder (0.35 g, 83%). Anal. Calcd for C46H5404NlP3Fez: C, 62.09; H, 6.07; N, 1.57. Found C, 62.86; H, 6.19; N, 1.14.

Organometallics, Vol. 14, No. 5, 1995 2341 Thermolysis of [Fe~(C0)40(-EtNCS)(lr-PCyd(lr-dppm)l ('7b). Thermolysis of a toluene solution (20 cm3)of 7b (0.07 g, 0.08 mmol) for 9 h led to the isolation of 7 ' b (0.015 g) and 8b (0.03 g, 57%)(yield based on the amount of 7b consumed) after chromatography.

Preparation of [Fe~(C0)4(lr-OH)(lr-PCy~)(lr-dppm)l(S). Thermolysis of [Fez(CO)r(lr-PPhz)O(-PCyz)(lr-dppm)l (12) with Diphenylphosphine. Thermolysis of a toluene solution (20 cm3)of 12 (0.10 g, 0.10 mmol) with diphenylphos-

Complex 1 (1.00 g, 1.20 "01) was adsorbed onto alumina and chromatographed. Elution with 40-60 "C petroleum ether produced a n orange band. The solvent was subsequently removed t o yield 10 as a n orange solid (0.38 g, 38%). Further elution with 40-60 "C petroleum ether-dichloromethane (9: 1) produced an orange band which changed to pink as it moved down the column. Removal of the solvent afforded 9 (0.4 g, 41%)as an orange solid. NMR spectra revealed that samples of 9 were contaminated with 10 (up to lo%),which proved difficult to remove. Anal. Calcd for C41H4605P3Fez (9): C, 59.85; H, 5.47. Found: C, 59.63; H, 5.26.

phine (0.10 g, 0.54 mmol) for 24 h did not lead to a color change, and 12 was recovered quantitatively. Crystal Structure Determinations. Crystals of 1, 2, 4, 7a, and 11 were grown from the slow diffusion of methanol into dichloromethane solutions, while 8a was crystallized upon concentration of a 40-60 "C petroleum ether solution. Crystals were mounted on a glass fiber. All geometric and intensity data were taken from this sample using an automated fourcircle diffractometer (Nicolet R3mV) equipped with Mo Ka Preparation of [Fe~(C0)4(lr-Cl)(lr-PCy~)(lr-dppm)](lO). radiation (1= 0.710 73 A) at 1 9 f l "C. The lattice vectors were Addition of 40% concentrated hydrochloric acid (0.1 cm3)to a identified by application of the automatic indexing routine of toluene solution (20 cm3) of 1 (0.30 g, 0.36 mmol) and the diffractometer t o the positions of a number of reflections subsequent stirring for 12 h a t room temperature followed by taken from a rotation photograph and centered by the diffracan additional 2 h a t 50 "C in a water bath resulted in tometer. For 1,2,4,7a,and 11 the w-28 technique was used dissolution of 1 and formation of a n orange solution. A color to measure reflections in the range 5" 5 28 5 50", while for change to yellow-orangewas noted. The solvent was removed, 8a the w technique was used. For 2, 4, 7a, 8a, and 11 three and the resulting orange solid was adsorbed onto alumina and standard reflections (remeasured every 97 scans) showed no chromatographed. Elution with 40-60 "C petroleum ether significant loss in intensity during data collection; however, afforded a n orange band which on removal of the solvent for 1 a 10% loss of intensity was noted. The data were yielded an orange microcrystalline solid, 10 (0.20 g, 61%).Anal. corrected for Lorentz and polarization effects, and 1,2,4,7a, Calcd for C ~ ~ H M O ~ P ~ C ~ ~ F ~C, ~ C54.45; H Z C H, ~ Z :4.75. and 11 were corrected empirically for absorption. The unique Found: C, 54.08; H 5.34. data with I 2 3.0dl) were used t o solve and refine the Hydrogen chloride gas was bubbled through a toluene structures. solution (20 cm3) of 1 (0.30 g, 0.36 mmol) until a saturated The structures were solved by direct methods and developed solution was obtained (approximately 2 min), during which by using alternating cycles of least-squares refinement and time a n orange solution formed which rapidly faded to yellowdifference-Fourier synthesis. All non-hydrogen atoms were orange. The solution was left to stir for an additional 2 h, refined anisotropicallyexcept those of the solvate in 4,8a, and and the solvent was removed. Adsorption onto alumina and 11 and C(12) in 8a. All hydrogens were placed in idealized chromatography afforded 10 (0.19 g, 62%). positions (C-H, 0.96 A) and assigned a common isotropic Preparation of [Fez(C0)4(lr-I)(lr-PCyz)(lr-dppm)l (11). thermal parameter (U= 0.08 k).Structure solution used the Addition of a 2-fold excess of iodine (0.29 g, 0.79 mmol) to a SHELXTL PLUS program package on a microVax I1 comtoluene solution (20 cm3) of 1 (0.30 g, 0.36 mmol) afforded a pute~-.~'The final R and R , values together with residual red-orange solution with a white precipitate after 12 h of electron density levels and other important crystallographic stirring. Filtration and removal of the solvent afforded an parameters are given in Table 8. Positional parameters for orange solid. Chromatography eluting with 40-60 "C petro1,2,4,7a,8a, and 11 are listed in Tables 9-14, respectively. leum ether gave a pink band which afforded 11 (0.20 g, 60%) Note Added in Proof. The crystal structure of as an orange solid. Anal. Calcd for C41H~03311Fez:C, 52.79; [Fez(CO)6Oc-H)Oc-PButz)lhas recently been reported: H, 4.72; I, 13.63. Found: C, 52.55; H, 4.88; I, 13.50.

Preparation of [Fez(C0)4(lr-PPhz)(lr-PCyz)(lr-dppm)l Bottcher, H.-C.; Hartung, W.; Krug, A.; Walther, B. (12) and [Fe~(C0)4(lr-PPh~)~(lr-dppm)l (13). A toluene Polyhedron 1994, 13, 2893. solution (40 cm3) of 1 (1.00 g, 1.20 mmol) was refluxed with diphenylphosphine (0.30 g, 1.60 mmol) for 3 h. Removal of Acknowledgment. We thank University College the solvent and chromatography afforded upon elution with Access Fund for the award of a postgraduate scholarship 40-60 "C petroleum ether-dichloromethane ( 9 : l ) an orange (M.H.L.) and Dr. Glyn D. Forster and Mr. Simon P. band which afforded 13 (0.71 g, 60%)as an orange-yellowsolid. Redmond for help with aspects of the crystallography. Further elution with 40-60 "C petroleum ether-dichloromethane (4:l) gave a second orange band which afforded 12 (0.35 g, 30%)as an orange solid.

Preparation of [Fez;(CO)aGu-PCy~)(lr-PhPCHaePhz)l (14). A toluene solution (100 cm3) of 1 (1.00 g, 1.20 mmol) was refluxed for 2 h, and color changes from orange to an intermediate green and then t o orange-brown were noted. Removal of the solvent under reduced pressure gave a n orange solid, which was chromatographed on alumina. Elution with light petroleum ether gave a yellow band which afforded 14 (0.65 g, 71%). Anal. Calcd for C36H3906P3Fez'0.4CHzCl~: C, 55.29; H, 5.03. Found: C, 55.65; H, 4.09.

Supplementary Material Available: For 1,2,4,7a,8a, and 11, text giving additional details of the structure determination, figures giving additional views of the structure, and tables of positional and thermal parameters and bond distances and angles (58 pages). Ordering information is given on any current masthead page. OM9500883 _____

(37) Sheldnck, G. M. SHELXTL; University of Gottingen: Gottingen, Germany, 1985.