Organometallics 1986, 5 , 12-16
12
parameter p was adjusted to give minimum variation in average w(lFol - lFc1)2as a function of lFol and (sin O)/kfinal p = 0.0001. Neutral atom scattering factors with anomalous dispersion corrections were used throughout.12 Computer programs were run on a VAX 111750 machine.l'J3 A thermal ellipsoid diagram14 of the molecule showing the atomic labeling scheme is given in Figure 1. Final coordinates of the non-H atoms are given in Table I11 and selected interatomic distances and angles in Table IV. Thermal motion corrections (Table IV) were derived by two methods: various rigid-body models15 for distances involving M O ~ ( C ~ H , C H ~ ) ~ ( S C Cand ~ Hriding ~ S ) motion16 for the carbonyls. The rigid-body models involving only the atoms of the central core of the molecule fitted the experimental parameters well, but, as expected, agreement was less satisfactory for models involving (12) "InternationalTables for X-ray Crystallography";Kynoch Press: Birmingham, England, 1974; Vol. 4, pp 99, 149. (13) Watkin, D. J.; Carruthers, J. R. 'CRYSTAL User Guide",Chemical Crystallography Laboratory, University of Oxford, 1981. (14) Davis, E. K. "CHEMGRAFUser Guide",Chemical Crystallography Laboratory, University of Oxford, 1983. (15) (a) Cruickshank, D. W. J . Acta Crystallogr. 1956, 9, 754. (b) Schomaker, V.; Trueblood, K. N . Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem.-1968, B24,63. (16) Busing, W. R.; Levy, H. A. Acta Crystallogr. 1964, 17, 142.
more peripheral atoms. Nevertheless they do give an estimate of the correction that should be applied to these outer bond lengths. Corrections to angles have not been listed. In the main they are 3a(F,). T h e two R h atoms are bridged both by the two P P h z ligands and t h e alkyne, with the latter bonded in a cis-dimetalated olefin mode. The alkyne C-C bond is parallel to the Rh-Rh single bond (Rh-Rh = 2.687 (1) A). Each R h is further coordinated by one COD ligand in an approximately trigonal-bipyramidal coordination geometry. T h e low-temperature synthesis of the unstable complex Rh2(pPPhz)2(norbornadiene)2is also described. T h e binuclear phosphide-bridged Rhz and Ir2 complexes 1 a n d 2 prepared by M e e k a n d co-workersla appear to be
8
Pph2
I \ Ir-Ir/ \ , I I/ 1
\/
'I
2
ideal molecules with which t o explore bimetallic reactivity since (1)they contain active group 8 metals, (2) they have (1) (a) Kreter, P. E.; Meek, D. W. Znorg. Chem. 1983, 22, 319. (b) Meek, D. W.; Kreter, P. E.; Chriistoph, G. G., J. Organomet. Chem. 1982, 231, C53. (c) Fultz, W. C.; Rheingold, A. L.; Kreter, P. E.; Meek, D. W. Inorg. Chem. 1983,22, 860.
0276-7333/86/2305-0012$01.50/0
bridging p-PPh, ligands t o help maintain molecular integrity under reaction conditions, a n d (3) they a r e coordinately unsaturated and possess 1,bcyclooctadiene (COD) ligands which should be easily removable by hydrogenation. However, relatively few reactions of these molecules have been reported. Meek and co-workers examined their phosphine substitution chemistry and found t h a t bidentate phosphines will displace b o t h COD ligands whereas monodentate phosphines only replace one COD.la* I n related work, we have shown that both COD's can be replaced by PEt, ligands when t h e reaction is carried o u t under Hz which apparently removes t h e COD's by hydrogenation2 I n t h i s regard, Meek a n d Kreter also demonstrated t h a t (2) Burkhardt, E. W.; Mercer, W. C.; Geoffroy, G. L. Inorg. Chem. 1984,23, 1779.
1986 American Chemical Society
Organometallics, Vol. 5, No. 1, 1986 13
Dirhodium and Diiridium 1,5-Cyclooctadiene Complexes 1 is an active olefin hydrogenation catalyst or catalyst precursor.la The molecular structures of complexes 1and 2 have not been determined, although spectroscopic data are consistent with the structures drawn above. The 31PNMR chemical shifts of the p-PPh2 ligands imply that complex 1 has no Rh-Rh bond (6 - 71.7) whereas complex 2 does (6 l 6 6 ) . l @ y 4 Complex 2 is further assumed to have a double bond in order to give a satisfactory electron count, and it is similar to other diphosphido-bridged Ir2 complexes for which double-bond formulations have been given5 Alkynes are interesting substrates with which to investigate the chemistry of complexes 1 and 2 since these ligands can react in a variety of ways.6 Alkynes can coordinate as two- or four-electron donors to one metal center or can bridge the two metals with the alkyne C-C bond parallel or perpendicular to the metal-metal vector. Since complexes 1 and 2 are coordinately unsaturated, alkynes could add without displacing the COD ligands or could substitute for one or both COD'S. Insertion of alkyne into the M-PPh, bonds to give modified phosphine ligands is also a possible reaction.' We have studied the chemistry of 1 and 2 with alkynes and find that binuclear oxidative addition of alkyne occurs across the bimetallic framework to give complexes with cis-dimetalated olefin formulations. These are the first examples of such a binuclear oxidative-addition reaction of phosphido-bridged compounds, although this type of reaction has considerable precedent in the chemistry of A-frame complexes&l0and Ir2(p-SR)2complexes." These reactions are described herein as well as the synthesis and properties of the previously unreported complex Rh2(pPPh2)2(NBD)(NBD= norbornadiene) .
Mz(p-PPhz)z(COD)z
+
CH30zCC~CC0,CH3
1. M=Rh 2, M = I r
I
P2\
3, M=Rh 4. M = I r
(3)Typically p-PPh, ligands bridging metal-metal bonds show downfield chemical shifts (6 50 d 200)whereas upfield shifts (6 50 d - 200) are found when metal-metal bonds are absent. See: (a)Petersen, J. L.; Stewart, R. P., Jr. Inorg. Chem. 1980,19,186. (b) Carty, A. J.; MacLaughlin, S. A.; Taylor, N. J. J. Organomet. Chem. 1981,204,C27. (c) Carty, A. J. Adu. Chem. Ser. 1982,No. 196,163. (d) Garrou, P. Chem. Rev. 1981,81,229.(e) Johannsen, G.; Steltzer, 0. Ibid. 1977,110,3438. (4)Exceptions to this correlation have recently appeared, and thus it must be used with caution. See: (a) Jones, R. A.; Wright, T. C.; Atwood, J. L.; Hunter, W. E. Organometallics 1983,2,470.(b) Rosen, R. P.; Hoke, J. B.; Whittle, R. R.; Geoffroy,G. L.; Hutchinson, J. P.; Zubieta, J. A. Ibid. 1984,3,346. (c) Targos, T. S.; Rosen, R.; Whittle, R. R.; Geoffroy, G. L. Inorg. Chem. 1985,24,1375. (5)(a) Mason, R.; Sotofte, I.; Robinson, S. D.; Uttley, M. F. J. Organomet. Chem. 1972,46,C61. (b) Bellon, P. L.; Benedicenti, C.; Caglio, G.; Manessero, M. J. Chem. SOC.,Chem. Commun. 1973,946. (6)Sappa, E.; Tiripicchio, A,; Braunstein, P. Chem. Rev. 1983,83,203. (7)(a) Regragui, R.; Dixneuf, P. H.; Taylor, N. J.; Carty, A. J. Organometallics 1984,3,814.(b) Smith, W.F.; Taylor, N. J.; Carty, A. J.
sponding diiridium complex 2 reacts in an analogous fashion to yield a similar complex 4. Excess alkyne must be used to drive these reactions to completion (by 31P NMR), but the excess alkyne complicates the workup and purification of the products as it does not separate well from 3 and 4 upon chromatography. Furthermore, chromatography induces slow decomposition of 3 and rapid decomposition of 4. Thus neither complex was isolated in analytically pure form, but the X-ray structural analysis for 3 (see below) and the spectroscopic data for both confirm that the formulations given in eq 1 are correct. Both complexes show parent ions in their mass spectra 'HI corresponding to the indicated formulations. The 31P( NMR spectrum of 3 shows a triplet at 6 176 assigned to the two equivalent p-PPh2 ligands with JP-Rh = 100 Hz. The downfield chemical shift implies that the p-PPh2 ligands bridge two Rh centers joined by a Rh-Rh bond>4 consistent with the determined structure (Rh-Rh = 2.687 (1)A). Likewise, the 31P(1H)NMR spectrum of 4 shows a downfield singlet at 6 111 implying two equivalent FPPh2 ligands bridging two Ir atoms jointed by an Ir-Ir bond. The reaction of the Ir, complex 2 with CH302CC=CO2CH3 is the first reported reaction of this complex with any substrate. Earlier, Meek and Kreterla had shown that 2 does not react with CO nor with bidentate phosphines under any conditions examined. The structural data, see below, imply that the alkyne ligand in complex 3 is best formulated as a cis-dimetalated olefin, similar to a number of other binuclear alkyne complexes.&" A similar formulation is implied for the Ir2 complex 4. In forming complexes 3 and 4 the alkyne has oxidatively added across the two metal centers in 1 and 2. Such a one-electron oxidative addition to each Rh center in 1 creates two 17e metals which then form a metal-metal bond to achieve a satisfactory electron count. Alkyne addition to 2 to give 4 represents a one-electron oxidative addition to each metal across the metal-metal double bond. Accordingly, the metal-metal bond order is reduced to one in the final product. The observation that only alkynes with electron-withdrawing substituents capable of accepting electron density from the metals react with 1 and 2 is consistent with the view of this reaction as an oxidative-addition process. I t is also interesting to note that Rh2(p-PPh2)2(COD)2 is air-sensitive but coordination of the alkyne gives complex 3 which is air-stable.
J . Chem. Soc., Chem. Commun. 1976,896. (8) (a) Mague, J. T.; Klein, C. L.; Majeste, R. J.; Stevens, E. D. Organometallics 1984,3, 1860. (b) Mague, J. T.; DeVries, S. H. Inorg. Chem. 1982,21,1632. (c) Mague, J. T. Inorg. Chem. 1983,22, 1158. (9)(a) Cowie, M.; Dickson, R. S. Inorg. Chem. 1981, 20, 2682. (b) Cowie, M.; Dickson, R. S.; Hames, B. W. Organometallics 1984,3,1879. (c) Sutherland, B. R.; Cowie, M. Organometallics 1984,3, 1869. (d) Cowie, M.; Southern, T. G. Inorg. Chem. 1982,21,246. (e) Cowie, M.; Southern, T. G. J. Organomet. Chem. 1980,193,C46. (10)Balch, A. L.; Lee, C.-L.; Lindsay, C. H.; Olmstead, M. M. J. Organomet. Chem. 1979,177,C22. (11)(a) Devillers, J.; Bonnet, J.-J.; de Montauzon, D.; Goly, 3.; Poilblanc, R. Znorg. Chem. 1980,19,154. (b) Giulmet, E.;Maisomot, A.; Poilblanc, R. Organometallics 1983,2,1123.
(12)Jarvis, A. C.; Kemmitt, R. D.; Russell, D. R.; Tucker, D. J. Organomet. Chem. 1978,159,341. (13)Dickson, R. S.;Johnson, S. H.; Kirsch, H. P.; Lloyd, D. J. Acta Crystallogr.,Sect. B Struct. Crystallogr. Cryst. Chem. 1977,B33,2057. (14)Dickson, R. S.;Mok, C.; Pain, G. J.Organomet. Chem. 1979,166, 385. (15)Davidson, J. L.;Harrison, W.; Sharp, D. W. A.; Sim, G. A. J . Organomet. Chem. 1972,46,C47. (16)Koie, Y.;Shinoda, S.; Saito, Y.; Fitzgerald, B. J.; Pierpont, C. G. Inorg. Chem. 1980,19,110. (17)Smart, L.E.;Browning, J.; Green, M.; Laguna, A.; Spencer, J. L.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1977,1777.
,
Results and Discussion Reaction of M2(p-PPh2),(COD), (M = Rh, Ir) with CH302CC=CC02CH3. The binuclear complex Rh2(pPPh2)2(COD)2(1) does not react with electron-rich alkynes such as PhC=CCH3 and PhCECPh. However, reaction does occur with the electron-withdrawing alkyne CH3O2CC=CC02CH3 to give complex 3 (eq 1). The corre-
-
-
14 Organometallics, Vol. 5, No. 1, 1986 Table I. Crystallographic Data for
Rh2(fi-PPhz)z(p-CH302CCwCOzCH3)(COD)p (3) Crystal Data mol formula C40H5002P2Rh2 cryst system monoclinic 0.08 X 0.28 X 0.35 cryst dimensions, mm space group mlc a, A 17.718 (4) b, A 12.345 (2) c, A 20.047 (5) 6, deg 113.34 (2) v,A 4026 ( 2 ) Z 4 p(calcd), g cmm3 1.54 p(abs coeff), cm-l 9.11 T , "C 21 Measurement of Intensity Data diffractometer Nicolet R3 Mo K a ( A = 0.71073 A) radiation monochromator graphite crystal scan type w/28 scan speed variable 4-20' min-' scan range f0.9O std reflctns 3 per 197 (no decay) data limits 4.0 < 28 < 48.0 rflctns collected kh,k,l unique data 6301 4737 (F, > 30(F0)) obsvd data weighting factor," g 0.0008 RFb 0.063 RWF' 0.071 GOFd 1.48
Synthesis and Reactivity of Rhz(p-PPh2),(NBD), (5). A complex analogous to 1 with the COD ligands replaced by NBD (norbornadiene) ligands has not been previously reported. Such a compound should be interesting since the NBD ligands should be more easily displaced than the COD ligands of 1. We have found that such a complex can be prepared at -78 "C by the reaction of LiPPh2 with Rh,(p-Cl),(NBD), (eq 2). However, this
,.
(NBD)Rh
\CI/
Rh(NBD) -I- 2LiPPh,
-78
-c
Ph2 5
complex is unstable, decomposing upon warming above -10 "C, and we were unable to isolate it. The -60 "C 31P{1H) NMR spectrum of 5 shows a triplet at 6 -72 (C&h = 80 Hz)which is close to the upfield triplet observed for the COD complex 1 at 6 -71.7 (Jp-Rh = 100 Hz).'" The upfield position of this resonance also implies the absence of a Rh-Rh bond in 5 as in l . 3 3 4 The instability of 5 has precluded an evaluation of its chemistry although it was observed to react with PhC=CCH, and CH3=CCH3 at low temperatures to give low yields of products whose spectroscopic data (see Experimental Section) imply formulations similar to 3. X-ray Diffraction Study of Rh,(p-PPh,),(pCH302CC=CC02CH3)(COD)2 (3). An ORTEP drawing of complex 3 is shown in Figure 1. Crystallographic details, atomic positional parameters, and relevant bond length and bond angle data are respectively given in Tables 1-111.
Targos et al. Table 11. Atom Coordinates (XlO') and Temperature Factors (A3 X lo3) atom X 2 U Y 3403 (1) 3162 (1) 29 (1)" Rh(1) 2310 (1) 4541 (1) 29 (1)" 3881 (1) Rh(2) 3268 (1) 31 (1)" 4070 (2) 4195 (1) P(1) 2132 (1) 2140 (2) 3511 (1) 34 (1)" P(2) 3412 (1) 53 (3)" 359 (5) 3040 (4) O(1) 1327 (4) 62 (3)" 1722 (5) 2559 (4) O(2) 462 (4) 48 (3)" 1046 (5) 4410 (3) O(3) 1230 (4) 415 (5) 5047 (3) 55 (3)" O(4) 2503 (4) 2549 (6) 72 (5)" -379 (8) C(1) 765 (6) 1423 (6) 2976 (4) 31 (3)" C(2) 1119 (5) 3469 (4) 31 (3)" 2071 (6) C(3) 1821 (5) 26 (3)" 1862 (6) 4161 (4) C(4) 2256 (4) 35 (3)" 1007 (6) 4593 (4) C(5) 2050 (5) 57 (4)" 311 (8) 4785 ( 5 ) (36) 897 (6) 3753 (7) 2159 (4) 41 (2) C(l1) 1221 (5) 4933 (7) 1927 (5) -50 (2) C(l2) 1133 (6) 5705 (8) 2458 (5) 56 (3) C(13) 1717 (6) 5236 (7) 2958 (5) 43 (2) C(14) 2529 (5) 4617 (7) 2713 (5) 46 (2) C(15) 3009 (6) 4379 (7) 1926 (5) 52 (3) C(16) 2812 (6) 3348 (7) 1646 (5) 47 (2) C(17) 2304 (6) 3036 (7) 2020 (4) 41 (2) C(l8) 1739 (5) 4272 (7) 5056 (4) 37 (2) C(21) 4193 (5) 3560 (7) 4780 (4) 39 (2) C(22) 4570 (5) 2731 (7) 5209 (5) 51 (2) (23) 5184 (6) 2044 (8) 5731 (5) 58 (3) C(24) 4939 (6) 1918 (7) 5498 (5) 44 (2) C(25) 4017 (5) 2643 (7) 5686 (4) 40 (2) C(26) 3523 (5) 3684 (8) 6123 (5) 57 (3) C(27) 3834 (6) 4362 (7) 5866 (5) 50 (2) C(28) 4396 (6) 3304 (5) 3896 (2) 44 (2) C(41) 520 (4) 3078 (5) 4081 (2) 65 (3) C(42) -144 (4) 3238 (5) 4792 (2) 72 (3) C(43) -74 (4) 3624 (5) 5318 (2) 66 (3) C(44) 660 (4) 3851 (5) 5134 (2) 57 (3) C(45) 1325 (4) 3691 (5) 4423 (2) 37 (2) C(46) 1255 (4) 6067 (5) 3965 (3) 52 (2) C(51) 1359 (3) 7175 (5) 4057 (3) 68 (3) C(52) 1278 (3) 7749 (5) 4577 (3) 76 (3) C(53) 1922 (3) 7215 (5) 5005 (3) 75 (3) C(54) 2646 (3) 6107 (5) 4913 (3) 55 (3) C(55) 2727 (3) 5533 (5) 4393 (3) 38 (2) C(56) 2084 (3) 482 (4) 2490 (3) 56 (3) C(61) 2905 (4) -588 (4) 2253 (3) 76 (3) C(62) 2737 (4) -1409 (4) 2749 (3) 76 (3) C(63) 2794 (4) -1160 (4) 3481 (3) 66 (3) C(64) 3019 (4) -90 (4) 3718 (3) 49 (2) C(65) 3187 (4) 731 (4) 3222 (3) 39 (2) C(66) 3131 (4) 2906 (4) 2970 (3) 53 (2) C(71) 4609 (4) 2810 (4) 2869 (3) 63 (3) C(72) 5341 (4) 1917 (4) 3150 (3) 72 (3) C(73) 5851 (4) 1121 (4) 3532 (3) 80 (3) C(74) 5629 (4) 1217 (4) 3632 (3) 68 (3) C(75) 4897 (4) 2109 (4) 3351 (3) 40 (2) C(76) 4387 (4) Equivalent isotropic u defined as one-third of trace of the orthogonalized U tensor.
The two Rh atoms of complex 3 are bridged by two p-PPh, ligands and the alkyne ligand. Each Rh is further coordinated by a COD ligand. The Rh2P2core of the molecule is essentially planar with a [P(l)-Rh(l)-P(2)]-[P(l)-Rh(2)-P(2)]dihedral angle of 3.2". The alkyne lies above this plane with the C-C bond parallel to the Rh-Rh axis. The coordination geometry of each Rh is approximately trigonal bipyramidal with the two phosphorus atoms and one olefinic bond of the COD ligand defining the trigonal plane. The molecule possesses approximate C2 symmetry with the rotation axis defined by a line joining the midpoints of the Rh(1)-Rh(2) and C(3)-C(4) vectors. The Rh-Rh distance of 2.687 (1)8, in 3 is consistent with a single Rh-Rh bond as required by the 18-electron rule. This distance agrees well with other structurally characterized molecules in which a Rh-Rh single bond has been invoked (e.g., Rh2-
Dirhodium and Diiridium 1,5-Cyclooctadiene Complexes
Organometallics, Vol. 5, No. 1, 1986 15
respectively, consistent with the cis-dimetalated olefin coordination mode with sp2 hybridization of the alkyne carbon atoms.
Experimental Section
C24
Figure 1. An
ORTEP drawing of Rh2(p-PPh2)(p-CH302CC= CC02CH3)(COD), (3). Thermal ellipsoids are drawn at the 40% probability level, and the PPh2 phenyl rings have been omitted for clarity.
Table 111. Selected Bond Distances and Angles for Rh2(p-PPh2)2(p-CHSO2CC&C02CHS)(COD)2 (3) Rh(l)-Rh(2) Rh(l)-P(l) Rh(l)-P(2) Rh(2)-P(l) Rh(2)-P(2) Rh(l)-C(3) Rh(2)-C(4) Rh(l)-C(11) Rh(l)-C(14) Rh(l)-C(15) Rh(l)-C(18) Rh(2)-C(21) Rh(2)-C(22) Rh(2)-C(25) Rh(2)-C(26) C(3)-C(4) C(2)-C(3) Rh(l)-P(l)-Rh(B) Rh(l)-P(2-)Rh(2) P(l)-Rh(l)-P(2) P(l)-Rh(2)-P(2) Rh(l)-Rh(2)-C(4) Rh(2)-Rh(l)-C(3) Rh(l)-C(3)-C(4) Rh(2)-C(4)-C(3) Rh(l)-C(3)-C(2) Rh(2)-C(4)-C(5) C(4)-C(3)-C(2) C(3)-C(4)-C(5)
Bond Distances (A) 2.687 (1) C(4)-C(5) 2.363 (3) C(ll)-C(12) 2.377 (2) C(12)-C(13) 2.363 (2) C(13)-C(14) 2.363 (3) C(14)-C(15) 2.062 (8) C(15)-C(16) 2.072 (7) C(16)-C(17) 2.208 (7) C(17)-C(18) 2.360 (9) C(21)-C(22) 2.341 (11) C(22)-C(23) 2.153 (8) C(23)-C(24) 2.316 (8) C(24)-C(25) 2.319 (9) C(25)-C(26) 2.199 (8) C(26)-C(27) 2.177 (9) C(27)-C(28) 1.318 (10) C(28)-C(21) 1.480 (IO)
1.499 (12) 1.519 (12) 1.497 (12) 1.506 (12) 1.371 (15) 1.502 (13) 1.532 (13) 1.520 (16) 1.349 (14) 1.493 (11) 1.537 (16) 1.520 (14) 1.402 (14) 1.530 (12) 1.537 (16) 1.522 (13)
Bond Angles (deg) 69.3 (1) C(4)-Rh(2)-C(26) 69.1 (1) C(4)-Rh(2)-C(25) 110.5 (1) C(4)-Rh(2)-C(21) 111.0 (1) C(4)-Rh(2)-C(22) 70.4 (2) C(3)-Rh(l)-C(ll) 70.8 (2) C(3)-Rh(l)-C(18) 109.3 (5) C(3)-Rh(l)-C(14) 109.2 (6) C(3)-Rh(l)-C(15) 124.9 (5) C(22)-Rh(2)-C(25) 126.0 (5) C(21)-Rh(2)-C(26) 125.7 (8) C(15)-Rh(l)-C(18) 124.8 (7) C(l4)-Rh(l)-C(ll)
95.4 (3) 97.4 (3) 166.1 (3) 160.1 (3) 96.3 (3) 94.2 (3) 159.0 (4) 167.0 (4) 79.0 (3) 79.3 (3) 79.8 (3) 78.4 (3)
( P - P P ~ ~ ) ~ ( P E ~ , ) ~ ( 2.752 C O D(1) ) , A;lb see also Table IV). The bridging alkyne ligand of 3 appears best described as a cis-dimetalated olefin analogous to the formulations given for other complexes with similar geometrie~.~"The C(3)-C(4) bond length of 1.32 (1) A in 3 falls within the 1.27-1.34 range observed for other complexes with a cis-dimetalated olefin formulation (Table IV) and is comparable to a normal C=C double bond length (1.337 (6) By comparison, the C-C triple bond lengths of free alkynes are ca. 1.20 A.18 The C(4)-C(3)-C(2) and C(3)C(4)-C(5) bond angles in 3 are 125.7 ( 8 ) O and 124.8 (7)O, (18) 'International Tables for X-ray Crystallography"; Kynoch Press: Birmingham, England, 1974; Vol. 111, Table 4.2.2.
All manipulations were carried out in standard Schlenk glassware under prepurified N2. Solvents were reagent grade or better, dried by stirring over Na/benzophenone (THF, benzene, toluene, hexane) or BaO (CH2C12),followed by distillation under N2. The compounds Rh2(p-PPh2)2(COD)2(1),la and Ir2(pPPh2)2(COD)2(2),la Rh,(p-C1)2(NBD)2,'g and LiPPh220 were prepared by literature procedures. PPh2H (Pressure Chemical Co.), n-BuLi, CH302CC=CC02CH3, CH3C=CC02Me, HC= CC02Me, P h M C H , , CH3C=CCH,, P h M P h , P h G S H , and NBD (Aldrich Chemical Corp.) were purchased and used as received. Instruments used in this research have been previously describede2' Elemental analyses were performed by Schwartzkopf Microanalytical Laboratory, Woodside, NY. P r e p a r a t i o n of Rh2(p-PPh2)2(p-CH302CC=CC02CH3)(COD)2 (3). An excess of CH302CC=CC02CH3 (0.108 mL, 0.76 mmol) was added via syringe to a 20 mL T H F solution of Rh2(N-PP~~)~(CO (0.15 D ) g, ~ 0.19 mmol) at 22 "C. The green solution was stirred for 1h during which time it became dark red-brown. The solvent was evaporated, and the product was extracted into -1 mL of CH2ClP. Chromatography was conducted on silica gel under N2 with CH2C12as eluant. An orange band containing Rh2(p-PPh2)z(p-CH302CC~CC02CH3)(COD)2 was the only one to elute from the column, and 0.138 g of material slightly contaminated with free alkyne was isolated by solvent evaporation. A dark brown band remained at the top of the column. Further attempted purification failed to remove all of the excess alkyne, and the best analysis obtained corresponded to a sample containing -67% of 3 and -33% of free alkyne. Anal. Calcd for (3): C, 59.11; H, 5.35. Found: C, 56.33; H, 4.95. C46H5002P2Rh2 3: 31P(1H} NMR (22 OC, C6D6)6 176 (t, Jp-Rh = 100 Hz); 'H NMR (22 "c,C&) 6 8.25-6.40 (Ph), 5.13 (br, s, olefinic CH), 2.71 (s, CO2CH3), 2.5-1.2 (br, m, CH,); MS (FD), m/z 934 (M+),792 (M+ - alkyne); IR (THF) vco 1680 cm-'. P r e p a r a t i o n of Ir2(p-PPh2)2(p-CH302CC=CC02CH3)(COD)2 (4). An excess of CH,O2CC=CCO2CH3 (0.060 mL, 0.42 mmol) was added via syringe to a suspension of 1 r , ( ~ - P P h ~ ) ~ (COD)2 (0.20 g, 0.22 mmol) in 25 mL of THF. The red suspension was allowed to stir for 3 days a t 22 "C during which time a yellow-orange solution formed. The solution was then filtered through Celite on a glass frit and the solvent evaporated to yield 0.227 g of impure Ir2(p-PPh2)2(p-CH302CC=CC02CH3)(COD)2 (4) contaminated with free alkyne. Extensive decomposition occurred upon continued purification attempts, and analytically pure material was not obtained. 4: 31P{1H} NMR (22 "C, THF-d,) 6 111 (5); 'H NMR (22 "C, THF-d8) 6 7.98-8.01 (Ph), 4.43 (br, s, olefinic CH), 2.56 (s, CO2CH3), 2.28-1.73 (br m, CH,); MS (EI), m / z 1114 (M'), 1006 (M+ - COD); IR (THF) uc0 1687 cm-'. Reaction of Rh2(p-PPh2)2(COD)zwith Nonactivated Alkynes. In separate experiments, 4 equiv of PhCECH, PhC=CPh, CH3C2CCH3, and PhC=CCH3 were added to 2 mL of 80:20 THF/benzene-d6 solutions of Rh2(p-PPh2),(COD), (0.050 g, 0.063 NMR mmol) in 10-mm NMR tubes. Analysis of the 31P(1H} spectra after the solutions were agitated for 24 h at 22 "C showed that no reaction had occurred. Preparation of Rh2(p-PPh2)2(NBD)2( 5 ) . One milliliter of a 75:25 THF/C6D6 suspension of LiPPh2 (0.075 g, 0.390 mmol) in a 10-mm NMR tube was cooled to -60 "C in the NMR probe. At this temperature, a 1-mL THFlbenzene-d, solution of Rh,(p-Cl),(NBD), (0.090 g, 0.195 mmol) was added. The resultant solution was allowed to spin for 20 min in the NMR probe, and then the 31P{1H}NMR spectrum was recorded: 6 -72.3 (t, JP-Rh = 80 Hz). Upon warming to 0 "C, loss of all resonances in the 31P(1H}NMR spectrum occurred, indicating decomposition. A 'H NMR spectrum of 5 was similarly recorded: 'H NMR (-60 (19) Abel, E. W.; Bennett, M. A.; Wilkinson, G. J . Chem. SOC.1959, 3178. (20) Issleib, K.; Tzschock, A. Chem. Ber. 1959,92, 118. (21) Breen, M.J.; Shulman,P. M.; Geoffroy, G. L.; Rheingold, A. L.; Fultz, W. C. Organometallics 1984,3,782.
16 Organometallics, Vol. 5,No. 1, 1986
Targos et al.
Table IV. Structural Data for Selected Bimetallic Complexes Containing a n Alkyne Ligand in a Cis-Dimetalated Olefin Coordination Mode" dhl-M,
x
dcd
calk'
A R~~(~-PP~~)~(~-CH~O~CCECC (3)O ~ C H ~2.687 ) ( C(1) OD)~
1.32 (1)
RhzClz(dppm)2(p-CF3C=CCF3)
2.7447 (9)
1.315 (1)
[Rh2(CN-t-Bu)4(dppm)2(p-CF3C~CCF3)]2C 2.9653 (6) RhzClz(p-CO)(dppm)(p-CH302CC~CC02CH3) 3.3542 (9) [RhzC1(CNMe)z(dppm)z(p-CF3C=CCF3)] 2.7091 (8)
1.318 (9) 1.32 (1) 1.32 (1)
R~~(CO)~CP,(~L-CF~CECCF~)
2.682 (1)
1.269 (14)
P~(CO)Z(PPhJ2(fi-CH~O&C~CCO&HJ [Ir,C1(CNMe)z(dppm)z(p-CF3C~CCF3)]+
2.6354 (8) 2.7793 (3)
1.341 (22) 1.344 (8)
complex
Cfd,-CfJ,-R, deg 124.8 (7) 125.7 (8) 127.4 (9) 128.3 (9) 126.2 (5) 123.8 (4) 129.3 (7) 124.9 (7) 127.8 (1.1) 129.2 (1.0) 122.5 (8) 125.4 (5) 119.5 (5)
ref this work 9 8 9 9
13 16 9
'dppm = PhzPCHzPPhz,Cp = q-C,H, "C, CDC13) 6 3.92 (s, bridgehead CH), 3.58 (s, olefinic CH), 1.17 goniometer. Lattice parameters were obtained from the least(s, apex CH,). squares fit of angular settings of 25 well-centered reflections, 25" Reaction of Rh2(pPPh2)2(NBD)zwith P h C 4 C H 3 . A < 20 C 30". Data collection and refinement procedures used were 20-mL THF solution of LiPPh, was cooled to -78 "C, and a 10-mL as previously reported.22 Pertinent details are provided in Table T H F solution of Rh,(p-Cl),(NBD), (0.300 g, 0.6 mmol) and I. Lorentz and polarization corrections were applied to the data, as was an empirical (+scan) absorption correction (Tm,JTmm= PhCzCCH, (0.175 mL, 0.162 g, 1.40 mmol) was added by 0.332/0.444). dropping funnel. The resultant deep purple solution was then The two Rh atoms were located by an automated Patterson stirred for 2 h a t -78 "C, warmed to -20 "C, and stirred for 12 h a t this temperature during which time the color changed to interpretation procedure, and the remaining non-hydrogen atoms yellow-brown. The solution was then warmed to 22 "C, and the were obtained from a difference map phased by the two Rh atoms. solvent was removed by evaporation. The brown oily product With the incorporation of hydrogen atoms in fixed, idealized was extracted into -50 mL of benzene and the solution was positions (d(C-H) = 0.96 A) and rigid-body constraints on the filtered through Celite on a glass frit followed by evaporation of four phenyl rings (d(C-C) = 1.395 A), the refinement process smoothly converged to the residuals reported in Table I. The solvent. Chromatography on SiOz under N, using neat CH2C12 as eluant gave one dark red brown band which slowly eluted from final difference map revealed no unusual or chemically relevant features (highest peak = 1.03 e/A3). the column. Only 0.025 g of dark red-brown Rh2(p-PPh,),During all calculations the analytical scattering factors for ( P ~ C Z C C H ~ ) ( N B D(7) ) ~was recovered ( 4 % yield). 7: 31P11HJ neutral atoms were corrected for both Af 'and i A f Rterms. Final NMR (22 "C, C&3) 6 188.2 (dd, J p q h = 110,107 Hz); MS (FD), positional parameters are collected in Table II; thermal parameters m / z 876 (M'), 760 (M' - PhC=CCH3). appear in the supplementary material which also contains the Reaction of R ~ & L - P P ~ , ) , ( N B w D i)t~h C H 3 C 4 C H 3 . A 10-mL T H F solution of Rh2(p-C1)2(NBD)2(0.20 g, 0.434 mmol) structure factors and full bond length and angle data. and CH3C=CCH3 (0.136 mL, 0.094 g, 1.73 mmole was added by Acknowledgment. This research was supported by the dropping funnel to a 10-mL THF solution of LiPPh, (0.167 g, 0.868 National Science Foundation (CHE82-01160). We gratemmole which had been cooled to -78 "C. After being stirred a t -78 "C for 1h, the dark purple solution was warmed to -30 "C fully acknowledge Johnson-Matthey, Inc., for a loan of and stirred for an additional 12 h. The solvent was then evapRhC13*3H,O. orated at 22 "C and the product extracted with -30 mL of toluene Registry No. 1, 82829-24-1; 2, 83681-88-3; 3, 99128-47-9; 4, which was then filtered through Celite on a glass frit. The toluene 99147-74-7; 5 , 99128-48-0; 7, 99128-49-1; Rhz(p-Cl),(NBD),, was removed by evaporation, the reaction product was dissolved 12257-42-0; R~~(@-PP~~)~(CH~CECCH~)(NBD)~, 99128-50-4; in 2 g of benzene-d6, and a 31P(1HJNMR spectrum was recorded: CH3O2CC=CCOZCH3,762-42-5; LiPPh2,4541-02-0; PhC=CCH3, 6 186 (t, JP..Rh = 110 Hz) plus several unresolved resonances in 673-32-5; C H ~ C E C C H ~503-17-3. , the 6 63-20 spectral region. Nothing would elute upon chromatography of this reaction mixture on SiO2even when using neat Supplementary Material Available: Tables of anisotropic CHzCl, as eluant. thermal parameters, complete bond lengths and angles, calculated X-ray Diffraction S t u d y of R h 2 ( ~ - P P h 2 ) z ( ~ - C H 3 0 2 C C ~ hydrogen atom positions, and structure factors for 3 (33 pages). CCOZCH3)(COD), (3). Crystals of 3 were obtained by slow Ordering information is given on any current masthead page. evaporation of a solution under reduced Nzpressure. A suitable crystal was mounted in an arbitrary orientation on a glass fiber (22) Rheingold, A. L.; Sullivan, P. J. Organometallics 1983,2, 327. which was then fixed onto an aluminum pin on a eucentric
