Formation and reactions of metal–metal bonded heterobimetallic (C5H4PR2)-bridged (Zr–Ir) and (Zr–Rh) complexes: evidence for the participation of metal hydride intermediates

Abstract

Treatment of the complexes [(C₅H₄PR₂)₂Zr(CH₃)₂] 1 (b: R = isopropyl; c: R = cyclohexyl) with the reagent HIr(CO)(PPh₃)₃ (2b) yield the heterobimetallic complexes [(µ-C₅H₄PR₂)₂(H₃C–Zr–Ir(CO)(PPh₃))] (4b, 4c) with evolution of methane. The reaction of the –PPh₂ substituted analogue 1a with 2b initially yields an intermediate [(H₃C)₂Zr(µ-C₅H₄PPh₂)₂Ir(H)(CO)(PPh₃)] 5a, that still contains both methyl groups at zirconium and does not contain a metal–metal bond. At room temperature, the intermediate 5a reacts further with methane formation to eventually yield the (Zr–Ir) complex 4a. The corresponding [(µ-C₅H₄PR₂)₂(H₃C–Zr–Rh(CO)(PPh₃))] complexes 3a (R = Ph) and 3b (R = isopropyl) react cleanly with isopropyl alcohol to liberate methane and yield the corresponding [(µ-C₅H₄PR₂)₂(Me₂CHO–Zr–Rh(CO)(PPh₃))] products (7a, 7b). Carefully monitoring the reaction of 3b with Me₂CHOH by NMR revealed that the Zr–Rh functionality is attacked first to give the intermediate [Me(Me₂CHO)Zr(µ-C₅H₄PR₂)₂Rh(H)(CO)(PPh₃)] (6b). This intermediate then reacts further to cleave off methane and re-form the (Zr–Rh) metal–metal bond to yield the product 7b. The tetrametallic µ-oxo-(Zr–Rh) metallocene derivate 11a was obtained starting from the (Zr–Rh) complex 3a and it was characterized by X-ray diffraction. It may be that this reaction is also initiated by H–OH addition to the [Zr–Rh] metal–metal bond.