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) 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.