Organometallics 1983,2,679-681
679
Communications Photochemical Preparatlon of a New Complex Contalnlng a Monodentate Dlthlocarbamate Llgand: Trlcarbonyl( q5-cyclopentadlenyl)(q'-dlmethylcarbamodHhloato)tungden(I I )
0.7
0.6
Harmon B. Abrahamson' and Michael L. Freeman Department of Chemistry, University of Oklahoma Norman, Oklahoma 730 19 Received September 14, 1982
0.5 C 0
n
6 0.1 vl
n
Summary: The photolysis of [(q5-C5H5)(C0),W] in the presence of tetramethylthiuram disulfide, using either visible or ultraviolet irradiation, produces the title complex (q5-C5H5)(CO),WSC(S)N(CH3)2,I, in good yield. This can be transformed to the known bidentate complex (a5C5H5XCO)2WS2CN(CH3)2, I I, either thermally or photochemically. Photolysis of the tungsten dimer in the presence of other organic disulfides, RSSR, produces in a similar fashion the simple coupling products (q5C5H5)(CO),WSR, and preliminary evidence for some of these is included. Dithiocarbamates are widely used as ligands in transition-metal comp1exes.l Most syntheses result in the dithiocarbamate ligand being bonded to the metal in a symmetrical q2 fashion, coordinating through both sulfur atoms to form a four-membered chelate ring, A. Very few complexes containing monodentate dithiocarbamate ligands B are known2 We would like to report the synthesis
A
B
of the title complex I, that is to our knowledge the first example of a monodentate dialkyldithiocarbamatecomplex of a group 6 metal. Previous attempts3to prepare cyclopentadienyl group 6 carbonyl dithiocarbamate complexes via thermal reactions have led to complexes containing a chelating dithiocarbamate ligand. We have discovered a room-temperature photochemical route to I, which appears to be the prototype for a general reaction of metal-metal single bonds and organic disulfides. Both metal-metal bonded transition-metal carbonyl dimers7v8 and dithiocarbamate complexesg react via ap(1) For example, see: Steggerda, J. J.; Cras, J. A.; Willemse, J. Recl. Trau. Chim. Pays-Bas 1981,100,41-48. ( 2 ) (a) Nagao, G.; Tanaka, K.; Tanaka, T. Inorg. Chim. Acta 1980,42, 43-48. (b) Robertson, D. R.; Stephenson, T. A. J. Chem. Soc., Dalton Trans, 1978,486-495. (c) Alison, J. M. C.; Stephenson, T. A. Ibid. 1973, 254-263. (d) Dubrawski, J. V.; Feltham, R. D.Inorg. Chem. 1980,19, 355-363. (e) de Croon, M. H. J. M.; van Gaal, H. L. M.; van der Ent, A. Inorg. Nucl. Chem. Lett. 1974,10,1081-1086. (f) Busetto, L.;Palazzi, A.; Foliadis, V. Inorg. Chim. Acta 1980, 40, 147-152. (3) This is true whether the reaction is metal carbonyl dimer plus tetraalkylthiuram disulfide' or metal carbonyl halide plue the sodium salt6 or a tin complex6 of the dialkyldithiocarbamate. (4) Cotton, F. A.; McCleverty, J. A. Inorg. Chem. 1964,3,139&1402. (5) Glass, W. K.;Shiels, A. J. Organomet. Chem. 1974,67,401-405. (6) Abel, E. W.;Dunster, M. 0. J. Chem. Soc., Dalton Trans. 1973, 98-102. (7) Gftoffroy, G. L.; Wrighton, M. S. "OrganometallicPhotochemistry"; Academic Press: New York, 1979.
0276-7333/83/2302-0679$01.50/0
a 0.3 0.2 0.1
2100
2000
1900
1800
Wavenumber cm-'
Figure 1. Infrared spectral changes (recorded in linear absorbance mode) resulting from visible light irradiation of a toluene solution M, in a 0.10-mm of CpzWz(CO)6and Me4TDS,each at 7 x sealed solution cell under a nitrogen atmosphere. Cumulative irradiation timea are 0,15,30, and 75 s for traces a 4 respectively. The base-line absorption by toluene is denoted by bl. The small amount of reaction found at zero irradiation is caused by the visible component of the infrared beam.
parently radical pathways. In the course of attempting to induce a new metal-metal interaction, we observed'" that a tricarbonyl complex was the primary photoproduct when cp2w2(co)6 and Fe(Me4tc):l were irradiated in the same solution. We hypothesized this complex to be compound I, since it could be converted easily to the known dicarbonyl chelate 11. This assignment has been confirmed by the synthesis of I from cp2w2(co)6 and the dimer of Me2dtc-tetramethylthiuram disulfide, Me4TDS,12a preliminary account of which is reported herein. When oxygen-free toluene solutions containing cp2w2(co)6 and tetramethylthiuram disulfide (Me,TDS) are irradiated with visible light,13the color of the solution changes from red to orange with a shift in the visible absorption maximum from 492 to 460 nm with an isosbestic point at 477 nm. At the same time, the carbonyl stretching bands of the metal dimer in the infrared spectrum decrease in intensity and new bands grow in with maintenance of isosbestic points (Figure 1). The product isolated from photolyzed ~olutionsis the tricarbonyl complex I, formed [(q5-C5H5)W(C0)3]2 + Me4TDS
hu
~(V~-C~H~)(CO)~WSC(=S)NM~~ (1) I (8)Chiaolm, M. H.; Rothwell, I. P. h o g . Inorg. Chem. 1982,29,1-72. (9) (a) Schwendiman, D.P.; Zink, J. I. J. Am. Chem. SOC.1976, 98, 124&1252,4439-4443. (b) Miessler, G. L.; Zoebisch, E.; Pignolet, L. H. Inorg. Chem. 1978,17,3636-3644. (10) Abrahamson, H.B.unpublished observations; thia is true for both visible and ultraviolet irradiations. (11) Abbreviations used in this paper: R2dtc- = dialkyldithiocarbamate (dialkylcarbamodithioate)S,CN&-; Cp = $-cyclopentadienyl. (12) MelTDS = bis(dimethylthiocarbamy1) disulfide, [SC(S)N(CHdz12. (13) Visible irradiation source was a GE 40W high intensity desk lamp.
0 1983 American Chemical Society
680 Organometallics, Vol. 2, No. 5, 1983 Table I.
Communications
Carbonyl Region Infrared Data for CDW(CO),SR~,~
SR SC(=S)N(CH,), SC,H,NC SCH, SCH, SCd-4 SC,H,CH,
v C ~ c ,m -~'
2040, 2036, 2028, 2030, 2033, 2033,
Scheme I ccPw(co),l,
ref
1 9 6 2 , 1933 1958, 1935 1942
this w o r k this w o r k this w o r k
1943d
e
1947 194Sd
this w o r k
CpW(CO),*
t RSSR
e
Prepared in this w o r k b y the visible light photolysis o f nitrogen-purged solutions of RSSR a n d Cp,W,(CO), in In t o l u e n e soluan amalgam-sealed 0 . 1 0 - m m NaCl cell. t i o n unless otherwise n o t e d . 2-pyridyl sulfide. CCl, solution. e Watkins, D. D.; George, T. A. J. Organomet. Chem. 1975, 102, 71-77. Crystalline c o m p o u n d s f o r SR = S,CNMe, and SC,H, have been isolated a n d give satisfactory elemental analyses.
in the expected ratio of 2:l (producktungsten dimer consumed)14from the formal cross-couplingof the two dimers. Monochromatic 546-nm irradiation also effects this transformation. Since only the metal dimer and not the disulfide absorbs in this region, the primary photoprocess must involve an excited state of the metal dimer.16 If traces of oxygen are present during photolysis, only uncharacterized decomposition products are found, as expected for a reaction proceeding through a reactive metal species. Radical species produced by homolysis of the metal-metal bond7,*must be viewed as the most likely intermediates, rather than unsaturated species resulting from loss of carbon monoxide,l' since the dicarbonyl chelate I1 is not a prompt photoproduct. The quantum yield for the production of I from the tungsten dimer is 0.36, and the quantum yield for disappearance of the dimer is 0.18.18 These values are only marginally higher than those reported for the production of CpW(CO),Cl from the 550-nm irradiation of the same tungsten dimer in carbon tetrachloride.20a The ratio of (14) Pure I can be separated from residual starting material by column chromatography and recrystallization from hexane. A recrystallized sample of I had a satisfactory elemental analysis (Schwarzkopf). Anal. Calcd for C1lHIINOBSzWC, 29.15; H, 2.45; N, 3.09; S, 14.15; W, 40.57; 0 (by difference), 10.59. Found: C, 29.15; H, 2.60; N, 3.35; S, 14.62; W, 40.03; 0 (by difference), 10.25. An infrared spectrum of I has peaks at 2046 (6.1),1972 (10.0),and 1943 (10.0) cm-' (hexane) and 2040 (8.7),1962 (10.0), and 1933 (8.7) cm-I (toluene). The electronic spectrum of I has a band at 460 nm (c 1270 mol-' L cm-') (toluene). The 60-MHz 'H NMR spectrum (in CDClJ consists of two singlets, one at 6 3.59 (6 H, methyl) and another at 6 5.78 (5 H, cyclopentadien 1). The monodentate nature of the dithiocarbamate ligand is confirmed%by the presence of a doublet (1005 (m),970 (s) cm-') for v(CS) and a relatively low v(C=N) (1487 (m) cm-') in a spectrum of the complex in a KBr pellet. (15) For discussions of infrared evidence for mono- vs. bidentate coordination see: Bonati, F.; Ugo, R. J. Orgonomet. Chem. 1967, 10, 257-268. Nakamoto, K. "Infrared and Raman Spectra of Inorganic and Coordination Compounds", 3rd ed.; Wiley-Interscience: New York, 1978; p 339. (16) Visible light cleaves the tungsten dimer with reasonable efficiency by exciting a da-a* transition, see ref 20. (17) (a) Tyler, D. R.; Schmidt, M. A.; Gray, H. B. J . Am. Chem. SOC. 1979, 102,2753-2755. (b) Caspar, J. V.; Meyer, T. J. Ibid. 1980, 202, 7794-7795. (c) Fox, A,; Poe, A. Zbid. 1980,102, 2497-2499. (18) Quantum yields were measured on 3 mL of nitrogen-purged toluene solution containing CpzW2(CO)6and Me,TDS at the same concenM) in a 1-cm quartz cuvette capped with a rubber tration (4 X septum. The sample was irradiated with a 546-nm source (filtered medium-pressure Hg lamp), the strength of which was determined by Reineckate a~tinometry.'~The concentrations of tungsten dimer and product I as a function of time were calculated from changes in absorbance at 492 and 460 nm. Quantum yields were determined for each irradiation time and extrapolated back to zero time over the fwst 20% of irradiation to obtain limiting quantum yield. (Some decrease in quantum yield at longer irradiation times was noted due to product absorption at the irradiation wavelength.) (19) Wegner, E. E.; Adamson, A. W. J. A n . Chem. SOC.1966, 88, 394-404. (20) (a) Wrighton, M. S.; Ginley, D. S. J . Am. Chem. SOC.1975, 97, 4246-4251. (b) Laine, R. M.; Ford, P. C. h r g . Chem. 1977,16,388-391.
RS*
+
-
LL-
CpCCO),W-S*
-
[CpW(CO),l,
+
RS*
RS* f
RS*
CpW(CO),*
(a)
2cpW(co)3*
R
-
I /S--R
(b)
CpW(CO),SR CpW(CO),SR
-
+
CpW(CO),SR RSSR
+
CpW(CO),*
RS*
(c)
(d) (e)
our two quantum yields is 2.0, in good accord with the overall stoichiometry of reaction 1. The fact that this reaction can be driven nearly to completion, even with only a 1:l ratio of metal dimer and disulfide, demonstrates that both halves of the organic disulfide are used to produce product. No other bands are observed in the carbonyl stretching region of the infrared spectrum, and isosbestic points are maintained in both the infrared and electronic spectra to large conversions. Ultraviolet irradiation is also effective in inducing reaction 1, but the product tricarbonyl I is photosensitive and with irradiation loses one carbon monoxide ligand to
I). the known dicarbonyl chelate II.21 Visible light is much less efficient in promoting this transformation, and under visible photolysis nearly all of the tungsten dimer can be converted to product I before transformation of I to I1 begins. Unlike reaction 1, reaction 2 proceeds even in the presence of air with no appreciable decomposition for short irradiation times. Reaction 2 can also be driven by heat as well as light; in fact, attempts to record the melting point of I resulted in decomposition of I to I1 in the melting point capillary at 106-108 0C.22 That the process represented in reaction 1is a general one can be seen from the results of irradiation of other disulfides with cp,w2(c0)6 (Table I). In every case, the primary photoproduct is the tricarbonyl thiolate complex CpW(CO),SR and is formed with the maintenance of isosbestic points in the infrared spectrum. The detailed mechanism for reaction 1probably involves attack of the photoproduced metal radical on the organic disulfide to produce an unstable intermediate that would quickly lose RS. to form product I (see Scheme Ib). The fate of the RS. radical so formed is less clear. One possibility is that it may attack a molecule of metal dimer to produce metal radical and product I (Scheme IC). Since the quantum yields for formation of I are not very different from those for other photoreactions of the tungsten dimer,2O we feel that a radical chain mechanism such as this is not likely. Another possibility is that the RS. radical is unreactive enough so that it exists in solution until it encounters another radical (metal or sulfur) with which (21) The dicarbonyl can be recrystallized from CHzClz/hexaneand displays an infrared spectrum identical with that previously reported: 1943 (10) and 1846 (8.5) cm-' (CH,Clz) and 1943 (10) and 1853 (7.2) cm-' (toluene, this work); 1952 (IO) and 1867 (7.3) cm-' (cyclohexane)6and 1943 and 1854 cm-' (carbon disulfide).6 (22) A sample of I was heated in a Hoover melting point apparatus, and decomposition was noted. The capillary was crushed, and the compound was dissolved in dichloromethane; an infrared spectrum of the resulting solution showed bands for both I and 11.
Organometallics 1983,2,681-682 it would combine to form either I or the starting disulfide (Scheme Id,e).23 We have found few previous reports of photolytic reactions of metal dimers with disulfides. Irradiation of M = Fe24and R u together ~ ~ (CH3S), and [CPM(CO)~]~, produces the corresponding CpM(CO),(SR) complexes in fair yield; no speculation as to mechanism was advanced, although disulfide cleavage was implied in one case.25 In other work, metal-metal bonded carbonyl complexes including [CPM(CO)~]~, M = Mo and W, were reacted with (CF3S)22sunder ultraviolet photolysis. The coupling products formed are analogous to those found here (mononuclear MSR complexes) but were postulated to result from the cleavage of the disulfide as the primary photoprocess. Our results demonstrate that this type of reaction arises instead from an initial photoinduced homolytic cleavage of the metal-metal bond of the metal carbonyl dimer. Work is presently underway to ascertain the detailed mechanism of this new mode of metal carbonyl radical reactivity.
681
(py)]PF6/CH2C12(cod = 1,5-cyclooctadiene; c-Hx = cyclohexyl; py = pyridine) binds ROH strongly, we wondered whether the presence of an OH group on one face of a suitable substrate might steer H2 addition to that face. Only rarely have such steering effects been observed in homogeneous hydrogenation. In the best known case: an alkoxide, formed from the substrate, was bound to Wilkinson's catalyst. Under relatively severe conditions (50 "C (7 atm)), H2 addition took place from the face of the molecule containing the OH group. In order to be generally useful, first, the catalyst should be able to reduce tri- and tetrasubstituted C=C groups, so that any directing effect would be widely applicable to organic synthesis; the effect can only give distinct stereoisomeric products for tetra-, tri-, and 1,l-disubstituted olefins. Second, a substantial directing effect should be obtained with a common unmodified group such as OH. The catalyst system [Ir(cod)P-c-Hx,(py)]PF,, when dissolved in a noncoordinating solvent, e.g., CH2C12,fulfills these conditions. We find that terpinen-4-o14 1, is reduced by Pd/C in EtOH to give a 20230 ratio of 2a and 2b in which H2 has been preferentially added from the less hindered side of the molecule5 (eq 1). In cyclohexane, a 53:47 ratio was
Acknowledgment. We wish to thank M. C. Palazzotto for a sample of Me4TDS. Some initial experiments related to this work were performed at the Massachusetts Institute of Technology while H.B.A. was a Predoctoral Fellow of the National Science Foundation. Fb&try NO.I, 84693-743;II,39531-00-5;[(TJ~-C&~)(CO)~W]~, 12091-65-5;CPW(CO)~SC~H~N, 84680-94-4;CpW(C0)3SCH3, 12108-26-8; CpW(CO)3SC~H6,12110-93-9; (CH3),N(S)CSSC(S)N(CH3)2, 137-26-8;C5HINSSCSH4N, 2127-03-9;CH,SSCH3, 624-92-0; CBH5SSCBH6, 882-33-7.
2a
1
(23)Cross-coupling of photogenerated thiyl radicals has been observed: Gupta, D.; Knight, A. R. Can. J. Chem. 1980,58, 1350-1354. (24)King, R.B.; Bisnette, M. B. Znorg. Chem 1965,4,482-485. (25)Killops, S.D.; Knox, S. A. R. J. Chem. SOC.,Dalton Trans. 1978, 1260-1269. (C,&S)z and (C6H6CHzS)zwere also used in this case. (26)(a) Davidson, J. L.; Sharp, D. W. A. J. Chem. SOC.,Dalton Trans. 1972,107-109.(b) Davidson, J. L.; Sharp,D. W. A. Zbid. 1973,1957-1960. ( C B F ~ Swas ) ~ also used in this case.
Occurrence and Orlgln of a Pronounced Dlrecting Effect of a Hydroxyl Group in Hydrqenatlon wlth [ I r ( c0d)P-c-Hx,(py)]PF, Robert H. Crabtree' and Mark W. Davis Sterling Chemistry Laboratory, Department of Chemistry Yale University, New Haven, Connecticut 065 11 Received October 15, 1982
Summary: [ Ir(cod)P-c-Hx3(py)]PF, has been shown to catalyze hydrogenation of an unsaturated alcohol, terpinen-4-01, with a ca. 1OOO:l preference for hydrogen addition to the face of the substrate bearing the OH group. This effect is due to chelation of the alcohol to the catalyst, as evidenced by the detection ('H NMR, 0 "C)of a catalyst-substrate complex related to the proposed intermediate cis, trans [ IrH2(endo-5-norbornen-2-01)-
-
(PPh3),IBF,.
The control of stereochemistry in transformations of organic compounds is an important area in which organometallic chemistry has been able to make useful c0ntributions.l Since our catalyst2 [Ir(cod)P-c-Hx3(1) Sharpless, K. B.; Yezhoeven, T. R. Aldrichimica Acta 1979,12,63. Kishi Y.Zbzd. 1980,13, 23.
2b
W/C
20
80
lrlcod IPC3 Ipyl'
99.9
0.1
found. In contrast, the iridium catalyst gives at least a 1OOO:l ratio,5dthe predominant isomer being the one (2a) in which H2has been added from the more hindered side of the molecule. (Conditions: 0 "C; CH2C12,15 mL; H2, 1atm; catalyst, 10 mM; substrate, 0.43 M; reaction time, 90 min.) This degree of selectivity is exceptionally high and is attained neither with heterogeneous catalysts, in which binding to the OH is not as strong, nor among other homogeneous catalysts,6where not only is binding usually (2)(a). Crabtree, R.H.; Felkin, H.; Morris, G. E. J. Organomet. Chem. 1977,141,205.(b) Crabtree, R. H.; Demou, P. C. Eden, D.; Mihelcic, J. M.; Parnell, C. A.; Quirk, J. M.; Morris, G. E. J. Am. Chem. SOC.1982, 104,6994. (3)Thompson, H. W.;McPherson, E. J. Am. Chem. SOC.1974,96, 6232. (4)Our sample was obtained from Aldrich Chemical Co. and contained no 2. Minor impurities (-5%) were present in 1, but these did not interfere with our product analyses. (5)(a) 2a: mp 51.0-51.5 "C (lit.5b51-52 "C); 'H NMR (500 MHz, Brucker instrument, CDCl,) 6 0.908 (d, J = 6.8 Hz, Me), 0.918 (d, J = 6.7 Hz,i-Pr); IR u(OH) 3618 cm-l. Anal. Calcd for CloH 0: C, 76.86;H, 12.90. Found C, 76.93;H, 12.81. 2b: n"5~ 1.459 (lit$ n 2 O ~1.461);'H NMR 6 0.919 (d, J = 6.8 Hz, Me and i-Pr) (the overlapping doublets were resolved with Eu(fod)J; IR v(OH) 3619 cm-'. The stereochemistryof this series of terpenes was first established by Pascual and Cokk it is still accepted.5b(b) Bowman, R. M.; Chambers, A.; Jackson, W. R. J . Chem. SOC.C 1966,612. Schenk, G . 0.; Gollnick, K.; Buchwald, G.; Schroeter, S.; Ohloff, G. Justus Liebig's Ann. Chem. 1964,674,93,98.(c) Pascual, J.; Coll, C. An. Quim. 1953,49,547,553. (d) Essentially only 2a was formed with the Ir catalyst (GC, Perkin-Elmer Model 900,flame ionization detector, 1/8 in. X 13 ft 5% FFAP on Chromoaorb P/AW; integration was performed with a Hewlett-Packard 3390A Digital Integrator). Essentially no 2b was formed with the Ir catalyst. Our 1ooO:lratio arises from a consideration of the probably experimental error and reapresents an upper limit for 2b.
0276-7333/83/2302-0681$01.50/00 1983 American Chemical Society
