Reactivity and catalytic activity of heteronuclear clusters. 1. Fluxional decapping of the heterometallic moiety in H3Ru4(CO)12MPR3 (M = Au, Cu) and the Crystal Structure of H3Ru4(CO)12AuPPh3

Article abstract of DOI:10.1021/om00147a018

IR and variable-temperature ¹H and ³¹P NMR studies have indicated that the PR₃-promoted dissociation of a copper site from H₃Ru₄(CO)₁₂CuPR₃ to form [Cu(PR₃)₃]⁺[H₃Ru ₄(CO)₁₂]^- occurs as a fluxional process. The equilibrium and rate constants for the process at 285 K have been estimated for H₃Ru₄(CO)₁₂CuPPh₃ as 1300 M^-2 and 30 s^-1, respectively, and for H₃Ru₄(CO)₁₂CuP(p-MeC₆H ₄)₃ as 174 M^-2 and 30 s^-1 respectively, at cluster and phosphine concentrations of 0.029 M. Increasing the steric bulk of the phosphine to that of P(o-MeC₆H₄)₃ retards the intermolecular exchange process as does the change in the heterometal atom from copper to gold. The X-ray structure of H₃Ru₄(CO)₁₂AuPPh₃ is reported: the compound crystallizes in the triclinic system, space group P1, Z = 2, with cell dimensions a = 9.428 (1) ?, b = 11.718 (2) ?, c = 17.230 (1) ?, α = 107.36 (9)°, β = 105.52 (1)°, and γ = 89.84 (1)°; R = 0.0347 from 5326 reflections (F > 3σ(F)). An approximately tetrahedral Ru4 cluster has an edge-bridged AuPPh₃ grouping (Ru-Au = 2.809 (1), 2.723 (1) ?; Au-P = 2.305 (2) ?). There are two edge-bridging (μ₂-H) hydride atoms and one face-bridging (μ₃-H) hydride atom; the gold atom is not involved in hydride coordination.