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

[Image: see text] Reactions of complexes [MoMCp(μ-PMes*)(CO)(6)] with H(2) and several p-block element (E) hydrides mostly resulted in the cleavage of E–H bonds under mild conditions [M = Re (1a) and Mn (1b); Mes* = 2,4,6-C(6)H(2)(t)Bu(3)]. The reaction with H(2) (ca. 4 atm) proceeded even at 295 K to give the hydrides [MoMCp(μ-H)(μ-PHMes*)(CO)(6)]. The same result was obtained in the reactions with H(3)SiPh and, for 1a, upon reduction with Na(Hg) followed by protonation of the resulting anion [MoReCp(μ-PHMes*)(CO)(6)](−). The latter reacted with [AuCl{P(p-tol)(3)}] to yield the related heterotrimetallic cluster [MoReAuCp(μ-PHMes*)(CO)(6){P(p-tol)(3)}]. The reaction of 1a with thiophenol gave the thiolate-bridged complex [MoReCp(μ-PHMes*)(μ-SPh)(CO)(6)], which evolved readily to the pentacarbonyl derivative [MoReCp(μ-PHMes*)(μ-SPh)(CO)(5)]. In contrast, no P–H bond cleavage was observed in reactions of complexes 1a,b with PHCy(2), which just yielded the substituted derivatives [MoMCp(μ-PMes*)(CO)(5)(PHCy(2))]. Reactions with HSnPh(3) again resulted in E–H bond cleavage, but now with the stannyl group terminally bound to M, while 1a reacted with BH(3)·PPh(3) to give the hydride-bridged derivatives [MoReCp(μ-H)(μ-PHMes*)(CO)(5)(PPh(3))] and [MoReCp(μ-H){μ-P(CH(2)CMe(2))C(6)H(2)(t)Bu(2)}(CO)(5)(PPh(3))], which follow from hydrogenation, C–H cleavage, and CO/PPh(3) substitution steps. Density functional theory calculations on the PPh-bridged analogue of 1a revealed that hydrogenation likely proceeds through the addition of H(2) 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.