Organometallics 1983, 2, 60-63
60
Crystal and Molecular Structure of Binuclear C O ~ ( ~ - P P ~ ~ ) ~ ( C O ) ~a( Phosphido-Bridged PE~~P~)~, Compound with a Formal Cobalt-Cobalt Double Bond A. Dale Harley, Robert R. Whittle, and Gregory L. Geoffroy" Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 Received September 9, 1982
The new phosphido-bridged cobalt carbonyl complex C O ~ ( ~ - P P ~ ~ ) ~ ( C O )1, ~ has (PE been ~ ~charP~)~, acterized by a complete single-cr stal X-ray diffraction study. It crystallizes in the space group PT with a = 11.565 (3) A, b = 12.356 (5) c = 8.993 (5) A, a = 108.30 (3)O, 0 = 108.50 (3)O, y = 64.79 (3)O, V = 1078 (1)A3, and 2 = 1. The structure was refined by using the 2927 reflections with I 2 2 4 0 to give final residuals of R = 0.051 and R, = 0.078. Each Co in 1 is coordinated by one CO, one PEhPh, two bridging p-PPh, ligands, and the other Co. The three phosphorus ligands and the carbonyl are in a psuedotetrahedral arrangement about each cobalt. The C O ~ ( ~core - P )is~rigorously planar as imposed by a crystallographic inversion center in the middle of the dimer. The Co-Co bond length of 2.343 (2) A implies a formal metal-metal double bond as required by the effective atomic number rule. The structure is discussed in its relationship to other known and hypothetical compounds of similar structure.
1,
Although numerous compounds with single, triple, and quadruple metal-metal bonds have been prepared and characterized, compounds with metal-metal double bonds are still relatively rarq.' This is unfortunate since such compounds have proven extremely useful for the directed synthesis of polynuclear organometallic clusters via addition of mononuclear metal fragments across the metalmetal double bond^,^^^ e.g., eq 13band 2.3e Such coordinatively unsaturated binuclear and polynuclear compounds also react with olefins, alkynes, and other organic substrates to give interesting organometallic derivative^.^
Table I. Crystal and Intensity Data for the X-ray Diffraction Study of Co,(p-PPh,),(CO),(PEt,Ph), , 1 Crystal Parameters cryst system: triclinic V = 1078.3 (1) A3 space group Pi z=1 a = 11.565(5)A P(ca1cd) = 1.350 g cm3 b = 12.356 (5)A abs coeff 9.850, not corrected c=8.993(3)A T = 25°C cu = 108.30 (3)" P = 108.50 (3)" 7 = 64.79 ( 3 ) "
CO14
os
A
(CO)~OS=OS(CO)~ 'H/
0 C / \ Cp-Co=Co-Cp 'C/ 0
t Pt(PPh3I&C2H4)
t
Fe2(CO)9
hr
-
O S Z P ~ H ~ ( C O ) , ~ ( P(1) P~~I~
C O ~ F ~ ( C P ' ) ~ ( CfO I ~
Fe(CO15
(2)
Measurement of Intensity Data diffractometer : Enraf-Nonius CAD4 radiation: M o Kcu ( A 0.710 73 A ) monochromator: graphite crystal scan type: 8-28 scan speed: variablea takeoff angle: 28" std reflctns: 3 std reflctns measd every 3 h ; n o significant variation data limits: 3" < 28 < 60" reflctns measd: + h , i k , r i unique data: 6428 nonzero data: 2927 (I > 2u(I)) R = 0.051; R, = 0.077
See ref 7. During the course of our investigations into the chemistry of a series of phosphido-bridged cobalt carbonyl or [ C O ( ~ - P P ~ ~ ) ( Cwith O ) ~PEhPh. ], The complex is most complexes,5we isolated and spectroscopically characterized conveniently prepared in high yield via the direct reaction the new complex C O ~ ( ~ - P P ~ ~ ) ~ ( C O ~1, ) by ( Pthe E ~ ~ P ~ ) ~ ,in eq 3.5 This new complex is particularly interreaction of either C O ~ ( ~ - P P ~ , ) ~ (C CO O ~) ~( ~, - P P ~ , ) ~ ( C Oshown )~,
C02(C0)8 + 2PEtzPh (1) (a) Cotton, F. A.; Walton, R. A. "Multiple Bonds Between Metal Atoms"; Wiley: New York, 1982. (b) Chisholm, M. H., Ed. "Reactivity of Metal-Metal Bonds", American Chemical Society: Washington, D.C., 1981; ACS Symp. Ser. No. 155. (2) Roberts, D. A.; Geoffroy, G. L. In "ComprehensiveOrganometallic Chemistry"; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds., Pergamon Press: Oxford, 1982; Chapter 40. (3) (a) Curtis, M. D.; Klingler, R. J. J.Organomet. Chem. 1978,161, 23. (b) Farrugia, L. J.; Howard, J. A. K.; Mitrprachachon, P.; Spencer, J. L.; Stone,F. G. A.; Woodword, P. J. Chem. SOC.,Chem. Commun. 1978, 260. (c) Burkhardt, E.; Geoffroy, G. L. J. Organomet. Chem. 1980,198, 179. (d) Byers, L. R.; Uchtman, V. A.; Dahl, L. F. J. Am. Chem. SOC. 1981,103, 1942. (e) Cirjak, L. M.; Huang, J.-S.; Zhu, Z.-H.; Dahl, L. F. Ibid. 1980,102,6623. (4) (a) Tachikawa, M.; Shapley, J. R.; Pierpont, C. G. J. Am. Chem. SOC.1976,97,7172. (b) Deeming, A. J.; Hasso, S.; Underhill, M. J . Chem. Soc., Dalton Trans. 1975,1614. (c) Dawoodi, Z.; Henrick, K.; Mays, M. J. J. Chem. Soc., Chem. Commun. 1982, 696. ( 5 ) Harley, A. D.; Guskey, G. J.; Geoffroy, G. L. Organometallics, submitted for publication.
0276-7333/83/2302-0060$01.50/0
+ 2PPh2H
+ + 110 "C,4 h
toluene
CO~(~-PP~,)~(CO)Z(PE~~P~)~ 6CO H2 (3) 1(70%)
esting since it should possess a formal cobalt-cobalt double bond in order to satisfy the effective atomic number rule. A single-crystal X-ray diffraction study was thus undertaken in order to fully characterize this new species, and those results are described herein. Experimental Section X-ray Structure Determination of C O ~ ( ~ - P P ~ ~ ) ~ ( C O ) ~ (PEt2Ph),, 1. Black crystals of 1, prepared as described in ref 4 (eq 3), were grown by slow evaporation of solvent from a saturated CHzClzsolution of the complex under Nz.An irregularly shaped crystal of approximately 0.25 mm per side was sealed in a glass capillary under N2, fixed into an aluminum pin, and
0 1983 American Chemical Society
Structure of C o z ( P - P P ~ z ) z ( C 0 ) z ( P E ~ ~ h ) 2
Organometallics, Vol. 2, No. 1, 1983 61
Table 11. Atomic Positional and Thermal Parameters for Co,(P-P-PPh,),(CO),(PEt,Ph),, 1" ~
atom __
co
P1 P2 01
c1 c2 c3
c4 c5 C6 c7 C8 c9 c10
c11 c12 C13 C14 C15 C16 C17 C18 c19 c20 c21
x
0.6172 (1) 0.0476 (4) 0.4886 (2) 0.0482 (8) 0.6512 (2) 0.0494 ( 9 ) 0.9514 ( 7 ) 0.171 ( 5 ) 0.8189 (9) 0.082 ( 4 ) 0.5753 ( 9 ) 0.049 (3) 0.4750 (10) 0.061 (41 0.5344 i i i i 0.067 i4i ~.~~~~ o.ci925 (iij 0 5 7 7 (ij 0.7903 (10) 0.117 (6) 0.7332(10) 0.095 (5) 0.3914 (9) 0.053 (3) 0.2445 (10) 0.054 ( 4 ) 0.1738 (11) 0.071 i 4 j 0 . 2 4 6 5 ( i z j 0.060 ( 4 j 0.3924 1121 0.050 (41 ~.~~~ 0.4625 ( i o ) 0.054 ( 4 j 0.8328(8) 0.057 (3) 0.8900 (10) 0.065 ( 4 ) 1.0229 (10) 0.084 ( 4 ) 1.1010 (11) 0.104 ( 6 ) 1.0455 ( i z j 0.089 ( 5 j 0.9117 (101 0.062(41 0.4996 ( 9 ) 0.064 ( 4 j 0.3352(12) 0.111 (6) 0.6577 (12) 0.047 ( 4 ) 0.7893 (14) 0.093 (7) ~~
~~
U(2A
U(3.3)
u(i,z)
0.0287 (3) 0.0303 (6) 0.0339 (7) 0.104 (3) 0.049 (3) 0.033 (2) 0.037 (31 0.035 i3i 0.053 ( 3 j 0.081 (4) 0.054 (3) 0.031 ( 2 ) 0.067 (4) 0.109(6) 0.073 ( 5 j 0.048 141 01045 (3j 0.032 (2) 0.053 (3) 0.066 ( 4 ) 0.065 ( 4 ) o.o60(4j 0.049 (31
0.0347 ( 4 ) 0.0416(8) 0.0441 (9) 0.041 (3) 0.048 (4) 0.056 ( 4 ) 0.069 (41 0.095 i5i 0.092 0.060 0.052 0.054 0.063 ( 4 ) 0.075 ( 5 ) 0.104 (sj 0.114 ( 6 ) 01079 ( 4 j 0.046(3) 0.056 ( 4 ) 0.057 ( 5 ) 0.054 ( 5 ) 0.074 ( 5 j 0.063 (41 0.057 ( 4 j 0.067 (5) 0.095 (6) 0,100 (7)
-0.0162 (3) -0.0154 ( 5 ) -0.0179 (6) -0.078 (3) -0.033 (3) -0.014 ( 2 ) -0.017 12)
U(L1)
z
Y
0.06861 ( 9 ) 0.03205 ( 7 ) 0.1170(2) -0.1576 (1) 0.2228 (3) 0.1010 (2) 0.1031 ( 7 ) 0.0400(6) 0.0903 (8) 0.0383 (6) 0.1308 ( 7 ) -0.2800(5) 0.1367 (7) -0.3928 ( 6 ) 0.1466 i s i -0.4871 i 6 i o.1500 (sj -0.4709 ( 6 j 0.1428 (10) -0.3614 (7) 0.1334 ( 9 ) -0.2651 (7) 0.2557 (7) -0.2405 (6) 0.2518 (9) -0.2234 (8) 0.3592 ( 9 ) -0.2840 ( 9 ) 0.4718 (sj -0.3629(9j 0.4792 (81 -0.3793 (7) 0.3728 ( 7 j -0.3204 (sj 0.2426 ( 7 ) 0.2189(5) 0.3560 ( 8 ) 0.2438 (7) 0.3679 (8) 0.3361 ( 7 ) 0.2692 ( 9 ) 0.4011 ( 8 ) o.i560(9j 0.3772(8j 0.1414 ( 8 ) 0.2872 (71 0.2122 ( s j 0.1777 ( 7 j 0.2142 (10) 0.1025(9) 0.3863 (8) -0.0155 ( 7 ) 0.4314 (11) -0.0847 (9)
~~~I
~~~~I ~~~~~
~~~~~
010si (3j 0,102 (6) 0.038 (3) 0.059(5)
a T h e form of the anisotropic thermal parameter is exp[-2n2(U,,h'o*' 2U,,hlo*c* + 2U,,klb*c*)].
Co-Co' Co-P1 Co-P1'
2.343 ( 2 ) 2.176(2) 2.172 ( 2 )
Co-P2 CO-C1 C1-01
2.187 (2) 1.731 ( 7 ) 1.148 (8)
mounted onto an eucentric goniometer. Diffraction data were collected on an Enraf-Nonius four-circle CAD4 automated diffractometer controlled by a PDP8a computer coupled to a PDP11/34 computer. The Enraf-Nonius program SEARCH was used to obtain 25 accurately centered reflections which were then used in the program INDEXto obtain an orientation matrix for data collection and to provide cell dimensions! Pertinent crystal and intensity data are listed in Table I. Details of the data collection and reduction procedures have been previously described? Of the two poasihle triclinic space groups PI and PI,the latter was indicated for 2 = 1and subsequently verified aa correct by the successful solution of the structure. The coordinates of the Co and P atoms and several of the phenyl carbon atoms were located by the use of the direct methods program MULTAN! The heavyatom positions were subsequently verified in a three-dimensional Patterson map. The coordinates of the remaining 17 non-hydrogen atoms were located by successive least-squares refinements and difference Fourier maps. After three cycles of least squares with anisotropic temperature factors, the phenyl and methylene hydrogen atoms were fixed at their calculated witions with C-H = 0.97A and given fixed isotropictemperature factms (B) of 5.0 A2. Refmement was continued for two additional least-squares cycles, and a difference Fourier map at this point located the methyl hydrogens H21A and H23A. The positions of the remaining four methyl hydrogens were calculated from these positions, and all six methyl hydrogenn were then fixed with C-H = 0.97 1\ and an isotropic temperature factor of 5.0 A2. In the (6) Programs uaed in thie study are either part of the Enraf-Nonius Structure Determination Package (SDP),Em&-Nonius, Delft, Holland, 1915, or B l d version of X-Ray 67,Stewart, J. M.,University of Ma-
ryland. Crystallographic Computer Systems. (7) Steinhardt. P. C.: Gladfelter. W. L.: Harlev. .. A. D.:. Fax.. J. R.: Cwffroy. G. L. Inorg. Chem. 1980.'19.332: 181 Main, P. -ML'LTAN 78. A System ofCompuwr hograms for the Automatic Solutions of Crystal Strueturd. Depsnment of Physics. University of Vurk. York, England, 1978.
~~~~~
t U,h'b*'
P1-Co-P1' P1-Co-P2 P1-Co-P2' P1-Co-C1 Pl'-Co-Cl P2-Co-C1 P1-Co-Co' Pl'-Co-Co' P2-Co-Co' C1-Co-Co'
-0.022
izi
-0.030 (3j -0.054 (3) -0.039 (3) -0.021 ( 2 ) -0.020 (3) -0.032 ( 4 ) -o.o18(3j -0.005 (3) -0.014 (3j -0.018(2) -0.029 (3) -0.049 (3) -0.048 (3) -0.031 ( 4 j -0.025 (31 -0.026 (3j -0.053 ( 4 ) -0.014 (3) -0.018(5)
~(1~3) 0.0058 (3) 0.0086 (7) 0.0066 (7) 0.0053 (6) 0.012 (2) 0.016(3) 0.011 (3) 0.004 (3) 0.015 ( 2 ) 0.009(3) 0.008 (3) 0.022 13) 0.020 i 4 i 0.015 (3) 0.038 (31 0.002 ( 4 j 0.032 (3j 0.004 ( 4 ) 0.018 (3) 0.003 ( 4 ) 0.002 ( 2 ) 0.013 (3) 0.015 (3) 0.013 (3) 0.036 (3) 0.018 ( 4 ) 0.042 ( 4 j 0.009 ( 4 ) 0.028 ( 4 ) 0.025 ( 4 j 0.019 ( 3 j 0.022 (3) 0.009 ( z j 0.008(3) 0.007 (3) 0.013 (3) 0.000 (3) 0.010 (4) 0.017 ( 4 ) -0.009 (4) 0.033 (4) -0.009 ( 4 ) 0.014 (3) 0.004 ( 3 j 0.017 ( 3 j 0.017 (3) 0.015 ( 4 ) 0.019(5) 0.008 ( 4 ) -0.000 ( 4 ) 0.024 ( 5 ) -0.028(6)
+ U,,l'c*' + 2U,,hha*b*
114.77 ( 5 ) 112.14 ( 7 ) 108.99 (6) 109.2 ( 2 ) 115.2 (3) 95.0 ( 2 ) 57.30 ( 5 ) 57.48 (5) 130.66 (7) 134.4 ( 2 )
Co-P1-Co'
t
65.23 (5)
CZ-Pl-C8 Co-Pl-CZ Co'-Pl-C2 Co'-Pl-C8 Co-Pl-CB
98.5 (3) 122.6 ( 2 ) 123.4 ( 2 ) 123.7 ( 2 ) 123.6 (2)
CO-C1-01
178.1 ( 7 )
Figure 1. An ORTEP drawing of Co2G-PPh2)2(C0)2(PE~Ph)z, 1, showing the atom numbering scheme. Thermal ellipsoids are drawn at the 25% probability level. final leastsquares refinement, 244 parameters were varied including the overall scale factor and positional and anisotropic thermal parameters for all non-hydrogen atoms. Convergence was achieved with R = 0.051 and R, = 0.078. The residuals are defined as R = X(IIFJ - IV'JI)/XIFoI and R, = [Zw(lF.I ~~l~2/Z~lFolz11~z. In the last cycle of refinement the maximum shift per error was 0.346,and the average shift per error was 0.024. A final difference Fourier map showed the largest peak to he less than 0.11 times the height of a carbon atom. The final error of an ohservation of unit weight was 1.71. Atomic positional and anisotropic temperature parameters are listed in Table 11. Selected bond lengths and angles are given in Tables I11 and IV, respectively. The derived pasitions of the hydrogen atoms (Table A) and the structure factors (Table B) are given in the supplementary material.
Harley, Whittle, and Geoffroy
62 Organometallics, Vol. 2, No. 1, 1983
Ph-
Ph2
2
analogoh to that of 1 with a short Ir-Ir separation (2.551 (1)A,', 2.554 A13) consistent with a metal-metal double bond and a pseudotetrahedral ligand arrangement about each iridium. The Ir,(p-P), core of the latter is also rigorously planar with an inversion center in the middle of Figure 2. An oaTEP drawing of Coz(~-PPhz)z(C0)2(PEt2Ph)2, the molecule. The isoelectronic complex Ir,(p-PPh&1, showing the core of the molede. Thermal ellipsoids me drawn (COD = 1,5-cyclooctadiene) has not been at the 25% probability level. structured, but its electron count would predict an Ir-Ir double bond. The far downfield 31PNMR chemical shift Results of the bridging p-PPh, ligands at 6 166 imply a strong An ORTEP drawing showing the molecular structure and metal-metal interaction in the latter comp1ex."J5 atom numbering scheme for Co,(p-PPh,),(CO)z(PE~Ph),, A Rh analogue of 1 and 2 is not known, but there is no 1, is shown in Figure 1. Figure 2 shows a different view reason why it should not exist, providing the PR, ligands with the phosphorus organic substituents removed for are sufficiently small. Such a compound does not form clarity. Relevant bond distances and angles are listed in upon pyrolysis of HRh(CO)(PPh,),, analogous to the Tables 111and IV, respectively. With one molecule per preparation of 2 via reaction 4, presumably because of too unit cell in the space group PI, the complex has a cryssevere steric crowding induced by the PPh, and p-PPhz tallographically imposed inversion center in the middle of ligands in such a complex.'E We also find that a Co dethe molecule. The Co,(p-P), core is thus rigorously planar rivative analogous to l and 2 cannot he prepared by using and the virtual symmetry of the complex is C,. The two PPh, instead of PEhPh, for apparently similar steric p-PPh, ligands, the Co, and the PEt,Ph ligand are arreasons, although a P(n-Bu), derivative does form.5 The ranged in a pseudotetrahedral fashion about each cobalt. closest known Rh analogue to 1 and 2 is Rh,(p-PPh,)zThe P1-Co-Pl', Pl-Co-P2, and P1-Co-C1 bond angles (COD)(PEt,),, 3, which was recently structured by Meek of 114.77 (5)", 112.12 (7)O, and 109.2 (2)O closely approxand co-workers.'7 Although 3 is isoelectronic with 1 and imate the ideal tetrahedral angle of 109.5'. Only the P22, the 2.752 (2)-A Rh-Rh separation does not imply a Co-C1 angle of 95.0 (2)'' differs significantly from this Rh-Rh double bond. Rather this molecule appears best value. The latter angle is apparently suppressed because described as having a donoracceptor bond between Rh(1-) of steric crowding induced by the Substituents on the and Rh(l+) centers.17 phosphorus ligands. The angle between the P1-Co-P1' The first characterized complex with a structure analand Cl-Co-P2 planes is 86.6". close to the 90' angle ex3, a comogous to 1 and 2 is Ru2(p-PPh2),(NO),(PPh3)z, pected for pseudotetrahedral coordination. The Cc-Co bond length of 2.343 (2) 8, is quite short and implies a formal double bond between the Co atoms, as required to achieve 18 valence electrons about each metal. Ph2 This distance compares well with the Co-Co distance in two other molecules for which the effective atomic number 3 d e requires a C d o double bond. Cg(~s-C&¶e~,b-CO)2 pound prepared and structured by Eisenberg and cohas a Co-Co bond length of 2.338 ( 2 ) A,9 and in [CozH3workers18 in 1972. Thia complex also has a crystallo(l,l,l-tris((diphenylar~ino)methyl)ethane)~]BPh~, the graphically imposed planar Ru,(p-P), core with a pseuCOCOseparation is 2.377 (8)kO ' Notably, these distance dotetrahedral ligand arrangement about each metal. The are less than the C c d o separation of 2.506 A in Co metal." short Ru-Ru separation of 2.629 ( 2 ) A is consistent with The Co-P1-Co bond angle of 65.23 (5)' in Co,(pa Ru-Ru double bond, as required by the effectiveatomic PPh~)z(CO),(PEt,Ph),is the most acute M-P-M angle number rule. Interestingly, a satisfactory synthesis of 3 found in any compound with a bridging p-PR, ligand. has never been achieved, and the complex was only ohLikewise the metal-metal distance which this ligand bridges is the shortest observed in any known p-PR2 structure. (12) Belon, P. L.; Benedicenti,C.; Csplio. C.: Manassem. M. J . Chem. ~
Discussion It is interesting to consider the structure of Coz(pPPh2),(CO),(PEt2Ph),, 1, in its relationship to other metal-metal doubly bonded compounds. Co2(p-PPh,)r (CO)2(PEt2Ph),is isoelectronic with Irz(p-PPh~),(CO),(PPh3),, 2, which has been prepared by the pyrolysis reaction shown in eq 4 and structured by two independent research gro~ps.'~J~ The latter complex has a structure (9) Ginsberg, R E.;Cirjsk, L. M.; Dahl, L. F.J. Chem. Soc., Chem. Commun. 1979.468. (10) Dspporto, P.; Midollini, S.;Sacconi, L. Inorg. Chem. 1975,14, 1643. (11) ' I n t e m t i d Tables for X-Ray Crystallogrsphy";Kynccb Preas: Birmingham, England, 1962; Vol. 111, p 282.
~~~
Soc., Chem. Commun. 1973.946. (13) Mason. R.: Sotofte. I.: Robinson, S. D.: Ultley, M.R. J . Orgono. met. Chem. l972,46, C61. (14) (a) Kreter, P. E.; Meek, D. W., submitted for publication. (b) Kreter, P. E. Ph.D. Thesis, The Ohio State University,Columbus, Oho, 1980. (16) (a)The CPR, ligands in compounds with metal bonds generally show down-field (6 50-300) NMR resonances, whereas upfield (6 50 6 -200) resonances are observed for compounds in which the r P R , ligand bridges two metals not joined by a metal-metal band.'bf (b) Petersen,J. L.; Stewart, R.P., Jr. Inorg. Chem. 1980.19,186. (e) Carty, A. J.; MacLaughlin, 9. A.; Taylor, N. J. J . Orgonomet. Chem. 1981,204, C27. (d) Carty, A. J. Ad". Chem. Ser. 1982, 196, 163. (e) Garrou, P. Chem. Re". 198l,81, 299. (0J o h n s e n , G.;Stelzer, 0. Chem.Ber. 1977, 110, 3438. (g) Mott, G. N. Ph.D. Thesis, University of Watarloo, Waterloo, Ontario, Canada, 1981. (16) Private communication from Jack Jamerean, Union Carbide Corp., South Charleston. WV. (17) Meek, D. W.; Kreter, P. E.; Christoph,G. G. J. Ownomet. Chem. 1982,231, C53.
-
Structure of
CoZ(~-PPh2)2(C0)2(PEt~h)2
Organometallics, Vol. 2, No. 1, 1983 63
tained in exceedingly low ~ i e l d . ' ~ JAlthough ~ they have not been reported, Fe and Os analogues to 3 should also exist. The only other compound with a double metal-metal bond and with two p-PR, bridging ligands which has structured is V2(p-PMe2)2(C0)8, 4.,O This complex results from the direct reaction of V(COI6with Me2PH (eq 5) and
2V(CO),
t
-
2MezPH
Me2
P / \ (CO)4V=V(CO),
t HE t
CO
(5)
'P/
Me,
4
has a planar V,(p-P), core with a V-V separation of 2.733
A (average of four independent molecules). Nb and Ta
analogues of 4 have not been reported. Notable missing members of the expected series of bis(phosphid0)-bridged doubley bonded binuclear compounds are Mn,(pu-PPhz),L6 and Rez(p-PPhz),L6(L = CO, PR,), e.g., 5. L\ / L-MMn=
/
L
\
Ph2 / p\ (PE t2Ph)(CO)Co=Co(CO)(PEt2Ph)
t
CO(1 a t m )
25
'P/ Ph2
/L
Mn -L
C03(P-PPh2)3(C0)6
R2
5
The position of the 31PNMR resonances for bridging p-PPh, ligands has been correlated with the M-P-M bond angles and the metal-metal bond distances which these ligands bridge.15 In general, the resonances have been observed to progressively move to lower field as the bond angles and metal-metal distances decrease.'"Pf One would thus expect the 31PNMR resonance for the bridging pPPh2 ligands in 1 to be far downfield, since the Co-Pl-Co' bond angle is so acute and the Co-Co separation is very small. Indeed, the resonance is downfield at 6 173.4.5 This bond angle/di~tance-~lP NMR chemical shift correlation is not perfect, however, since the resonance of the p-PPh, ligands in C O , ( K - P P ~ ~ ) ~ is ( Cmuch O ) ~ further downfield (18)Eisenberg, R.; Gaughan, A. P., Jr.; Pierpont, C. G.; Reed, J.; Schultz, A. J. J. Am. Chem. SOC.1972,94, 6240. (19)Eisenberg, R., private communication. (20)Vahrenkamp, H. Chem. Ber. 1978,111, 3472. (21)(a) Hayter, R. G. J.Am. Chem. SOC.1964,86,823.(b) Green, M. L. H.; Moelwyn-Hughes, J. T. Z.Naturforsch., B 1962,17b,783. (22)(a) Abel, E. W.; Sabherwal, I. H. J. Organomet. Chem. 1967,10, 491. (b) Hieber, W.; Opasky, W. Chem. Ber. 1968,101,2966.
(6)
.95%
L'
\p'
'C, 1 h
1
RZ
P
at 6 244 even though the Co-P-Co angles (average 73.9 (1)O) and Co-Co distances (average 2.610 (3) A) in the latter complex are much greater than in l.,, Even so, the chemical shift position of the resonance of bridging p-PR, ligands is a useful qualitative indicator of the presence or absence of significant metal-metal bonding in compounds of unknown s t r ~ c t u r e . ' ~ , ~ ~ Even though C O ~ ( ~ - P P ~ ~ ) ~ ( C O )possesses , ( P E ~a~ P ~ ) ~ formal metal-metal double bond and would appear useful for the synthesis of polynuclear organometallic clusters in reactions similar to those of eq 1 and 2,,s3 such will probably not be the case since the dimer is easily disrupted. As detailed in ref 5, we find that exposure of solutions of 1 to CO results in rapid loss of PEbPh and rearrangement to form Co,(p-PPh,),(CO), in quantitative yield (eq 6).
This reaction presumably proceeds through initial addition of CO to coordinatively unsaturated 1, but the bridging p-PPh, ligands are simply not sufficient to hold the binuclear complex together and rearrangement occurs.
Acknowledgment. This research was supported by the National Science Foundation (Grant CHE8201160) and in part by grants from the Standard Oil Co. of Ohio, Celanese, Union Carbide, and Air Products, and Chemicals, Inc. G.L.C. gratefully acknowledges the Camille and Henry Dreyfus Foundation for a Teacher-Scholar Award (1978-1983) and the John Simon Guggenheim Memorial Foundation for a fellowship (1982-1983). Registry No. 1, 83462-95-7; Co, 7440-48-4. Supplementary Material Available: Listings of the derived positions of the hydrogen atoms (Table A) and the structure (14 pages). factors (Table B) for Coz(r-PPhz)z(CO)z(PEtzPh)z Ordering information is given on any current masthead page. (23)Huntaman, J. R. Ph.D. Thesis, University of Wisconsin, Madison, Wisc., 1973. (24)Breen, M. J.; Duttera, M. R.; Geoffroy, G. L.; Novotnak, G. L.; Roberts, D. A,; Shulman, P. M.; Steinmetz, G. R. Organometallics 1981, 1, 1008.
