REACTIONS OF CO2RH2(CO)12 WITH ISOCYANIDES AND 1-ALKYNES - CHARACTERIZATION OF NEW ISOCYANIDE AND 1-ALKYNE COMPLEXES OF CO-RH MIXED-METAL SYSTEMS AND THE STRUCTURES OF [RH(CN-C6H3ME2-2,6)4][CO(CO)4] AND CO2RH2(CO)7(MU-CO)2(MU-4,ETA-2-HCCBUN)(PPH3)

Reactions of Co2Rh2(CO)12 with isocyanides and 1-alkynes are studied. With isocyanides, fragmentation of the tetranuclear framework into dinuclear units occurs to give a series of new mixed-metal dinuclear complexes, CoRh(CO)7-n(CN-Bu(t))n (n = 1, 2) and [Rh(CN-R)4][Co(CO)4] (R = Bu(t) cyclohexyl, 2,6-Me2C6H3). In all cases, isocyanide ligands are exclusively bonded to the rhodium atom. The structure of [Rh(C = N-C6H3Me2-2,6)4][Co(CO)4] is confirmed by X-ray crystallography, which crystallizes in monoclinic unit cell with space group P2(1)/c (a = 10.820 (2) angstrom, b = 16.3206 (9) angstrom, c = 21.646 (4) angstrom; beta = 90.700 (7)-degrees; Z = 4). Least-squares refinement led to a value for R of 0.032 (R(w) = 0.039) and a goodness of fit of 1.52 for 3892 reflections with I > 3-sigma(I). The rhodium moiety is square planar and the cobalt moiety is tetrahedral with slight distortion in both moieties. The Rh-Co distance is 3.3785 (9) angstrom, and one of the Co-CO bonds is eclipsed with one of the Rh-C = N-R bonds. 1-Alkynes insert into the Co-Co bond of the tetranuclear cluster to give butterfly clusters, Co2Rh2(CO)10(HC = CR) (R = Bu(n), Ph, SiMe3). Triphenylphosphine complexes of the new 1-alkyne-bridged butterfly clusters, Co2Rh2(CO)10-n(HC = CBu(n))(PPh3)n (n = 1, 2), Co2Rh2(CO)8(HC = CPh)(PPh3)2, and Co2Rh2(CO)9(HC = CSiMe3)(PPh3), are also synthesized. IR, H-1 NMR, and C-13 NMR spectroscopic data and elemental analyses support the formulation of these complexes as butterfly structures and the X-ray crystal structure of Co2Rh2(CO)9(HC = CBu(n))(PPh3) is determined: triclinic, space group P1BAR (a = 10.389 (5) angstrom, b = 17.40 (2) angstrom, c = 10.03 (2) angstrom; alpha = 105.9 (1)-degrees, beta = 103.7 (1)-degrees, tau = 82.59 (6)-degrees; Z = 2; R = 0.051 (R(w) = 0.063); a goodness of fit = 1.73 for 4832 reflections with I > 3-sigma(I).