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

• Published in: Organometallics 2023-10, Vol.42 (19), p.2826-2838
• Main Authors: Alvarez, M. Angeles, García, M. Esther, García-Vivó, Daniel, Ruiz, Miguel A., Vega, Patricia
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.3c00295

Reactions of complexes [MoMCp­(μ-PMes*)­(CO)6] with H2 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-C6H2 t Bu3]. The reaction with H2 (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 H3SiPh 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 PHCy2, which just yielded the substituted derivatives [MoMCp­(μ-PMes*)­(CO)5(PHCy2)]. Reactions with HSnPh3 again resulted in E–H bond cleavage, but now with the stannyl group terminally bound to M, while 1a reacted with BH3·PPh3 to give the hydride-bridged derivatives [MoReCp­(μ-H)­(μ-PHMes*)­(CO)5(PPh3)] and [MoReCp­(μ-H)­{μ-P­(CH2CMe2)­C6H2 t Bu2}­(CO)5(PPh3)], which follow from hydrogenation, C–H cleavage, and CO/PPh3 substitution steps. Density functional theory calculations on the PPh-bridged analogue of 1a revealed that hydrogenation likely proceeds through the addition of H2 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.