3628
Journal of the American Chemical Society
/
1OO:l I
/ M a y 24, I978
Novel Binuclear Cationic Complexes of Rhodium(1) and Iridium(1) Sir: There is intense interest in the preparation and characterization of polynuclear metal complexes and in their use for the study of multicentered catalysts.' W e wish to report the preparation of a series of cationic binuclear complexes of rhodium(1) and iridium(1) one of which appears to be the first example wherein a metal-metal bond is simultaneously bridged by chloride and carbonyl ligands. These compounds significantly extend the known "A-frame" type complexes, of which the recently reported [ R ~ ~ ( C O ) ~ ( F - S ) ( D P (DPM M)~]~ = bis(dipheny1phosphino)methane) is the first structurally characterized example. Successive treatment of an ethanolic solution of [Rh(CO)2C12]- (ref. 3) with equimolar quantities of DPM in chloroform and NaB(C6H5)4 in ethanol under a CO atmosphere produced a yellow solid. Recrystallization from chloroform-ethanol under C O yielded yellow crystals of R~~(CO)~(F-CI)(~-CO)(DPM)~] B(C6H5)4 (1). Complex 1 is obtained analytically pure and exhibits UC-0at 1992 (s), 1977 (vs). and 1863(s) cm-I (Nujol mull). In CH2C12 solution UC=O occurs at 2008 (sh), 1991 (vs), and 1873 (m) cm-l. Complete characterization of 1 was achieved via a singlecrystal x-ray diffraction study. Complex 1 crystallizes in the space group P 1 with a = 14.451 (2), b = 17.661 (2), c = 13.726(1)A;a= 102.06(1),~=95.59(l),y=75.56(1)0; V=3313.8A3(Z=2,Pcalcd= 1.416,~obsd=1.40(2)g/Cm3). Intensity data were collected on an automated Picker, fourcircle diffractometer using two crystals and Cu K a radiation (20 < 128"; scan range, 1.9" in 20 plus correction for al-a2 separation). Of the 9390 unique intensities, 8523 had Fo2 2 3u(FO2)and were used in the solution and refinement of the structure. Conventional Patterson methods provided the location of the heavy atoms. Location of the remaining atoms and refinement of the model was accomplished by the successive application of the usual Fourier and least-squares techniques. At the present stage of refinement (decomposition correction, isotropic thermal parameters, phenyls treated as rigid groups with C-C = 1.392 A); R = 0.116 and R , = 0.17 1 .4 As shown in Figure 1, each rhodium atom is coordinated by five donor atoms in a significantly distorted trigonal-bipyramidal arrangement (CI-Rhl-C2, 113.4 ( 5 ) ; C I Rhl-CI, 144.2 (4); C*-Rhl-CI, 102.4 (3); Cz-Rhz-Cj, 118.8 ( 5 ) ; Cj-Rh2-C1, 137.7 (4); C2-Rh*-CI, 103.5 (3)"). The Rhl-Rhz distance of 2.841 ( I ) 8, is somewhat longer than those considered to involve normal two-electron Rh-Rh bonds (2.617 (3) to 2.796 (8)A);5 however, several features of the structure strongly indicate that a metal-metal bond is present. ( I ) The acute angles at chlorine (Rhl-CI-Rh2, 66.39 (7)") and a t Cz (Rhl-C2-Rh2, 87.7 (4)") together with the C2- - -Cl distance of 3.441 A are indicative of considerable compression of this four-membered ring along the Rh-Rh axis. (2) The intraligand P- - - P distances of 3.364 ( P I - - -Pz) and 3.429 A (P3- - -P4) are both significantly longer than the Rhl-Rh2 distance again indicating a compression along the metal-metal axis (Figure (3) Conventional electron counting yields a 17-electron configuration for each metal so that a metal-metal interaction is necessary to account for the observed diamagnetism. In addition I I J R ~ .= ~127.8 ~ ~ Hz (vide infra) which indicates significant Rh-Rh interaction. Even at the present stage of refinement, the bridging chlorine and carbonyl ligands are unsymmetrically placed (Rhl--C>, 2.09 ( I ) ; Rh2---C2, 2.01 (1); Rhl--CI, 2.578 (3); Rh2-CI, 2.610 (3) A). This is consistent with the facile CO exchange (vide infra) and the ready formation of [Rhz( C 0 ) 2 ( p L - C O ) ( ~ - C DPM)*]Cl l)( from [ Rhz( C0)2C12(DPM)2]X and CO in polar solventa. Complex 1 is thus an
0002-7863/78/ 1.500-3628$01.OO/O
Figure 1. A perspective view of the inner coordination sphere of [Rh,(CO),CI(DPM),]+. Only the first carbon atom of each phenyl ring is shown.
analogue of [ R ~ z ( C O ) ~ ( F - S ) ( D P Mwith ) ~ ] a molecule situated in the postulated active site.2 Complex 1 is also novel in that it is the second example of a system wherein reversible binding of carbon monoxide to a bridging site O C C U ~ S Thus .~ on flushing a dichloromethane or acetone solution of 1 with argon or dinitrogen the lowest energy C O band disappears and an orange complex (2) can be isolated which analyzes for [Rh2(CO)2Cl(DPM)2]B(C6H~)4 and shows UC-0at 1997 (s) and 1978 (vs) cm-l (Nujol mull) and 2006 (s), 1992 (vs) cm-' (CH2C12 solution). Regeneration of 1 occurs readily by briefly passing C O through a dichloromethane solution of 2. This together with the observed 1 : l electrolyte behavior (A(10-3 M ) = 99 SZ-I cm2 equiv-I, acetone solution) suggests formulation of 2 as [ R h 2 ( C 0 ) 2 ( ~ CI)(DPM)2]B(CbH5)4, a cationic analogue of [Rhz(C0)2(F-S)(DPM)21. Exchange experiments with I3CO show that the terminal carbonyl ligands in borh 1 and 2 are also readily exchanged. Thus on flushing a dichloromethane solution of either complex with I3CO (1 -2 min a t 25 "C), the original C O bands essentially completely disappear and are replaced by bands at I964 (sh), 1945 (s), and 1832 (m) cm-I. Subsequent flushing with dinitrogen removes the lowest energy band to give the fully enriched analogue of 2. Further insight into the C O exchange process is obtained by treating a solution of 2 in dichloromethane with increasing amounts of I3CO a t -70 "C and examining aliquots of the resulting solution at room temperature. Initially one observes new bands at 195 1 and 1873 cm-' and a marked decrease in the intensity of only the 2006-cm-' band. As more I3CO is added, the first two bands continue to grow at the expense of the third and a new band appears at 1830 cm-l. Concurrent with the increase in the intensity of the 1830-cm-' band is a decrease i n the 1992-cm-' band which in the initial stages appears to remain at its original intensity. These observations imply that the 1 which is initially formed contains I2CO in the bridging position and is enriched in I3CO at only one terminal position. This in turn strongly suggests that the CO exchange and the interconversion of 1 9 2 occur via a bridge-terminal exchange (eq I ) . Analogues of 1 and 2 containing bis(dipheny1arsino)methane can be prepared similarly and show the same C O exchange behavior. Complex 2 reacts readily with SO2 to give red crystals analyzing as [Rh2(CO)2Cl(SO,)(DPM)*] B(C6H5)4 (3) with UC=O a t 2014 (vs) and I984 (s) cm-l and us0 at 1229 (m) and 1068 (m) cm-l. These latter values are similar to those found for [Rh2(CO)zCl2(S02)(DPPP)2] (DPPP = I ,3-bis(dipheny1phosphino)propane)I" and for [Fez(CO)x(p-S02)] I I which contain terminal and bridging SO? molecules, respectively; SO the determination of the mode of SO2coordination must await $2 1978 American Chemical Society
3629
Communications to the Editor
indicates that the metal-metal interaction in 2 should be similar to that proposed for this neutral dimer.1° Support for this comes from the electronic spectrum of 2 which shows an analogous “proximity shifted” band at 443 nm (CH2C12 SOlution) which is absent in the spectrum of 1. Complex 2 thus presents an interesting contrast to [Pd2C12(DPM)2I9 in that addition of the bridging carbonyl leads to the formation of a metal-metal bond.
Acknowledgments. The support of the Tulane University Chemistry Department, the University of Alberta, the National Research Council of Canada and the Alberta Research Council is gratefully acknowledged. We also thank Professors M. R. Churchill, D. J. Darensbourg, R. Eisenberg, and G . L. McPherson for helpful discussions. References and Notes
J
Z I I F ~ ~-
U ICC
E. L. Muetterties, Bull. SOC. Chim. BeIg., 84, 959 (1975), and references therein. C. P. Kubiak and R. Eisenberg, J. Am. Chem. Soc., 99, 6129 (1977). Prepared by passing CO through a refluxing solution of RhCIy3H20 in aqueous ethanol for 4 h. R= ~ F ~ ~ ~ / ZR,= \ F J[ z; w ( ( F , ( - I F , I ) ~ / Z W F ~ ~ ] ~ / ~ , 0. S. Mills and J. P. Nice, J. Organomet. Chem., 10,337 (1967); 0.S. Mills and E. F. Paulus, ibid,, IO, 331 (1967); E. F. Paulus, Acta Crystallogr., Sect. 5,25, 2206 (1969); C. H. Wei, Inorg. Chem., 8, 2384 (1969); R. S. Dickson, S.H. Johnson, H. P. Kirsch, and D. J. Lloyd, Acta CrystaIIogr., Sect. 6, 33, 2057 (1977); W. A. Herrmann, C. Kruger, R. Goddard, and I. Bernal, Angew. Chem., Int. Ed. Engl., 16,334 (1977). This is to be contrasted with the situation in the related complex [Rh2(C0)&12 (CGH~)~ASCH*AS(CBHS)~)~~’ where the Rh-Rh separation while the intraligand As- -As distance is 3.288 A. The is 3.396 (1) Rh-Rh interaction here is clearly repulsive. J. T. Mague, lnorg. Chem., 8, 1975 (1969). J. T. Mague and J. P. Mitchener, lnorg. Chem., 8, 119 (1969). M. M. Olmstead, H. Hope, L. S.Benner, and A. L. Balch, J. Am. Chem. Soc., 99, 5502 (1977). A. L. Balch and 6. Tulyathan, Inorg. Chem., 16,2840 (1977). E. Braye and W. Hubel, Angew. Chem., lnt. Ed. Engl., 2, 217 (1963). Confirmed by independent measurements on 1 under CO and 2 under
Hz
L’
Figure 2. The 3’P(’HJN M R spectrum of a mixture of [RhZ(C0)3CI(DPM)l]+ (left) and [Rhl(CO)2Cl(DPM)2]+ (right) in CD2C12 under N2 at selected temperatures.
d,
-
+
N2,
In 2 the separation of the major peaks ‘&h_pI) is 113.0 Hz while for [Rh&O)&I (DPM)2] the resonance is centered at 6 16.0 ppm with ’JRh-p ‘JRh-pI = 114.0 HZ.
I
Martin Cowie* Department of Chemistry, Unicersity of Alberta Edmonton, Alberta, Canada T6G 2C2
1
* -co + co
A+
I/,‘\I
Rh
Rh
(1)
Joel T. Mague* Department of Chemistry, Tulane University New Orleans, Louisiana 70018
2
the results of a crystal structure analysis of 3 now in progress. The arsine analogue of 3 is prepared similarly. [Rh2(CO)2(p-CI)(p-CO)(DPM)2]+can also be obtained as the [Rh(C0)2C121- salt (4) from a 50% excess of [Rh2(C0)4C12] or [ R ~ ~ C I ~ ( C - C ~under H I ~CO. ) ~ ]By this route, [Ir2(C0)2(p-CI)(p-CO)(DPM)2] [Ir(C0)2C12] (5) can be obtained from the analogous iridium(1) precursors. Complex 5 shows VC=O for the cation at 2000 (sh) 1993 (vs), and 1843 (m) cm-l. The anion shows vcC-oa t 2058 (m) and 1982 (s) cm-I. The conductivity of 84 Q-I cm2 equiv-l in acetone indicates it to be a 1:l electrolyte. Figure 2 shows the 31P{lH\N M R spectrum obtained from a solution of 1 in CD2Cl2 under Nz.The 233 K spectrum shows two complex, second-order patterns attributable to 1 (6 26.0 ppm vs. external H 3 P 0 4 ) and 2 (6 15.4 ppm), respectively.I2 The presence of 2 is consistent with the ready loss of CO from 1. On warming, rapid CO exchange between 1 and 2 appears to occur. The spectrum of 1 has been successfully analyzed as an AA’A”A”XX’system with I J R h - p = 118.3 Hz, 2 J ~ h - p= -24.1 H z and 1 ’ J R h - R h l = 127.8 Hz. The analysis of the spectrum of 2 is less satisfactory because of the near coincidence of many of the weaker lines. However the close resemblance to the 31P{1H1 spectrum of [Rh2(C0)2C12(DPM)2]’3 0002-1863118 J 1500-3629$01 .OO/O
+
Alan R. Sanger* Alberta Research Council Edmonton, Alberta, Canada T6G 2C2 Receiued January 3, I978
An Unusual Reaction of Tri-tert-butylphosphine with Rhodium(II1) and Iridium(II1) Chlorides Sir:
Recent studies’ demonstrate that tertiary phosphines containing bulky substituents on phosphorus often form unusual products with transition metals. For example, the hydrido c o m p l e ~ e s [~(, ~~ - B u ) ~ P ] ~ M Hwhere ~ C I , M = Rh or Ir are obtained from the reactions of tri-tert-butylphosphine with hydrated iridium(I1I) and rhodium(II1) chlorides. Recently, we found4 that tri-tert-butylphosphine undergoes a facile reaction with platinum(I1) and palladium(I1) chlorides to form the i n t e r n a l l y e t a l l a t e d complexes of the type [(t-Bu)?PC(CH3)2CH2]M[(t-Bu)3P]C1 (where M = Pt or Pd). The formation of internally metallated hydrido complex [ ( ~ - B U ) ~ P C ( C H ~ ) ~ C W ~ H C Iby ( Nthe C ~reaction H ~ ) ~of 0 1978 American Chemical Society
