Synthesis and site-selective protonation of MoPt and WPt bimetallic complexes

Abstract

The reaction of [M(cp)(CO)₃(PPh₃H)]PF₆1(M = Mo or W, cp =η-C₅H₅) with [Pt(C₂H₄)(PPh₃)₂] proceeds rapidly with a 1 : 2 (M : Pt) stoichiometry to give [(OC)₂(cp)[graphic omitted]t(CO)(PPh₃)]4 and [PtH(PPh₃)₃]PF₆5. However, using an initial 1 : 1 stoichiometry the final product is [(OC)₂(cp)M(µ-H)(µ-PPh₂)Pt(PPh₂)₂]PF₆8. The mechanisms of these reactions are shown to involve deprotonation of 1 to give [(OC)₃M(cp)(PPh₂)]2 followed by reaction of the latter with [Pt(C₂H₄)(PPh₃)₂] and subsequent transfer of CO from M to Pt to give 4. Protonation of 4 with HBF₄ is metal (M) dependent and proceeds to give [(OC)₂(cp)Mo(µ-H)(µ-PPh₂)Pt(CO)(PPh₃)]BF₄12a with M = Mo but for M = W the major product is [(OC)₂H(cp)[graphic omitted]t(CO)(PPh₃)]BF₄13b. Variable-temperature ¹H NMR studies show that the terminal hydride cation of 13b is rapidly equilibrating with a small amount of the hydride-bridged isomeric cation [(OC)₂(cp)W(µ-H)(µ-PPh₂)Pt(CO)(PPh₃)]⁺. Complex 4 reacts with PPh₃(60 °C) and 1,2-bis(diphenylphosphino)ethane (dppe) at 20 °C to give [(OC)₂(cp)[graphic omitted]t(PPh₃)₂]9 and [(OC)₂(cp)[graphic omitted]t(dppe)]10. On bubbling CO through a solution of 9(20 °C) complex 4 is rapidly regenerated. Reaction of 4 with HCl gives [(OC)₂(cp)M(µ-H)(µ-PPh₂)PtCl(PPh₃)]15. The molecular structure of [(OC)₂(cp)[graphic omitted]t(CO)(PPh₃)]4b has been determined by single-crystal X-ray diffraction.