Stuart J. Smith

Bridge vs. terminal protonation of isostructural Mo–Pt and W–Pt heterobimetallic compounds

Protonation of the complexes cp(OC)2[graphic omitted](CO)(PPh3)(cp = cyclopentadienyl) exhibits an M-dependent site selectivity, with protonation occurring at the metal–metal bond for M = Mo to give [cp(OC)2Mo(µ-PPh2)(µ-H)-Pt(CO)PPh3]+ whilst for M = W protonation occurs directly at he tungsten to give a terminal hydrido cation [cp-(OC)2H[graphic omitted](CO)PPh3]+.

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

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.