Reactions of Co₂Rh₂(CO)₁₂ with Isocyanides and 1-Alkynes. Characterization of New Isocyanide and 1- Alky ne Complexes of Co-Rh Mixed-Metal Systems and the Structures of [Rh(C≡N-C₆H₃Me₂-2, 6)₄][Co(CO)₄] and Co₂Rh₂(CO)₇(μ-CO)₂(μ₄, η²-HC=CBuⁿ)(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 P2₁/c (a = 10.820 (2) Å, b = 16.3206 (9) Å, c = 21.646 (4) Å; β = 90.700 (7)°; 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 > 3σ(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) Å, 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 = Buⁿ, Ph, SiMe₃). Triphenylphosphine complexes of the new 1-alkyne-bridged butterfly clusters, Co₂Rh₂(CO)_10-n(HC≡CBuⁿ)(PPh₃)_n (n = 1, 2), Co₂Rh₂(CO)₈(HC≡CPh)(PPh₃)₂, and Co₂Rh₂(CO)₉(HC≡CSiMe₃)(PPh₃), are also synthesized. IR, ¹H NMR, and ¹³C 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=CBuⁿ)(PPh₃) is determined: Triclinic, space group P1 (a = 10.389 (5) Å, b = 17.40 (2) Å, c = 10.03 (2) Å; α = 105.9 (1)°, β = 103.7 (1)°, τ = 82.59 (6)°; Z = 2; R = 0.051 (R_w = 0.063); a goodness of fit = 1.73 for 4832 reflections with I > 3σ(I).