Mixed-metal cluster chemistry VI ¹: Phosphine substitution at CpMoIr₃(μ-CO) ₃(CO) ₈; X-ray crystal structure of CpMoIr₃(μ-CO) ₃(CO) ₇(PPh₃)

Reactions of CpMoIr₃(μ-CO)₃(CO)₈ (1) with stoichiometric amounts of phosphines afford the substitution products CpMoIr₃(μ-CO)₃(CO)_8-x(L)_x (L = PPh₃, x = 1 (2), 2 (3); L = PMe₃, x = 1 (4), 2 (5), 3 (6)) in fair to good yields (23-54%); the yields of both 3 and 6 are increased on reacting 1 with excess phosphine. Products 2-5 are fluxional in solution, with the interconverting isomers resolvable at low temperatures. A structural study of one isomer of 2 reveals that the three edges of an MoIr₂ face of the tetrahedral core are spanned by bridging carbonyls, and that the indium-bound triphenylphosphine ligates radially and the molybdenum-bound cyclopentadienyl coordinates axially with respect to this MoIr₂ face. Information from this crystal structure, ³¹P NMR data (both solution and solid-state), and results with analogous tungsten-triiridium and tetrairidium clusters have been employed to suggest coordination geometries for the isomeric derivatives.