E-H Bond Cleavage Processes in Reactions of Heterometallic Phosphinidene-Bridged MoRe and MoMn Complexes with Hydrogen and p-Block Element Hydrides.

Reactions of complexes [MoMCp(μ-PMes*)(CO)] with H and several p-block element (E) hydrides mostly resulted in the cleavage of E-H bonds under mild conditions [M = Re () and Mn (); Mes* = 2,4,6-CHBu]. The reaction with H (ca. 4 atm) proceeded even at 295 K to give the hydrides [MoMCp(μ-H)(μ-PHMes*)(CO)]. The same result was obtained in the reactions with HSiPh and, for , upon reduction with Na(Hg) followed by protonation of the resulting anion [MoReCp(μ-PHMes*)(CO)]. The latter reacted with [AuCl{P(-tol)}] to yield the related heterotrimetallic cluster [MoReAuCp(μ-PHMes*)(CO){P(-tol)}]. The reaction of with thiophenol gave the thiolate-bridged complex [MoReCp(μ-PHMes*)(μ-SPh)(CO)], which evolved readily to the pentacarbonyl derivative [MoReCp(μ-PHMes*)(μ-SPh)(CO)]. In contrast, no P-H bond cleavage was observed in reactions of complexes with PHCy, which just yielded the substituted derivatives [MoMCp(μ-PMes*)(CO)(PHCy)]. Reactions with HSnPh again resulted in E-H bond cleavage, but now with the stannyl group terminally bound to M, while reacted with BH·PPh to give the hydride-bridged derivatives [MoReCp(μ-H)(μ-PHMes*)(CO)(PPh)] and [MoReCp(μ-H){μ-P(CHCMe)CHBu}(CO)(PPh)], which follow from hydrogenation, C-H cleavage, and CO/PPh substitution steps. Density functional theory calculations on the PPh-bridged analogue of revealed that hydrogenation likely proceeds through the addition of H to the Mo=P double bond of the complex, followed by rearrangement of the Mo fragment to drive the resulting terminal hydride into a bridging position.