Terminal phosphinidene complexes Cp^R(L)M=PAr of the group 9 transition metals cobalt, rhodium, and iridium. Synthesis, structures, and properties

Novel terminal rhodium- and cobalt-complexed phosphinidenes, Cp*(PR₃)Rh=PAr (3-5) and Cp(PPh₃)Co=PAr (8), were obtained by dehydrohalogenation of the primary phosphine complexes Cp*RhCl₂(PH₂Ar) (2) and CpCoI₂(PH₂Ar) (7) in the presence of a phosphine. X-ray crystal structures are reported for Cp*(PPh₃)Rh=PMes* (3) and Cp(PPh₃)Co=PMes* (8). A comparative reactivity study and a computational survey were performed on the Co-, Rh-, and Ir-containing phosphinidene complexes. All react with organic dihalides to form phosphaalkenes, with the rhodium congener being far more reactive than the iridium and cobalt complexes. Density functional theory calculations give geometrical parameters and ³¹P NMR chemical shifts in good agreement with experimental data. The rhodium congeners exhibit the most pronounced charge separation of the Rh=P bond, which may explain its higher reactivity. The M-L bond is strong in all Cp(L)M=PH (M = Co, Rh, Ir) complexes and inhibits reactivity at the metal center. Comparisons with the Zr-containing complex Cp₂(PH₃)Zr-PH are made.