Phosphinodi(benzylsilane) PhP{( o -C 6 H 4 CH 2 )SiMe 2 H} 2 : A Versatile “PSi 2 H x ” Pincer-Type Ligand at Ruthenium
Résumé
The synthesis of the new phosphinodi(benzylsilane) compound PhP{(o-C6H4CH2)SiMe2H}2 (1) is achieved in a one-pot reaction from the corresponding phenylbis(o-tolylphosphine). Compound 1 acts as a pincer-type ligand capable of adopting different coordination modes at Ru through different extents of Si–H bond activation as demonstrated by a combination of X-ray diffraction analysis, density functional theory calculations, and multinuclear NMR spectroscopy. Reaction of 1 with RuH2(H2)2(PCy3)2 (2) yields quantitatively [RuH2{[η2-(HSiMe2)-CH2-o-C6H4]2PPh}(PCy3)] (3), a complex stabilized by two rare high order ε-agostic Si–H bonds and involved in terminal hydride/η2-Si–H exchange processes. A small free energy of reaction (ΔrG298 = +16.9 kJ mol–1) was computed for dihydrogen loss from 3 with concomitant formation of the 16-electron species [RuH{[η2-(HSiMe2)-CH2-o-C6H4]PPh[CH2-o-C6H4SiMe2]}(PCy3)] (4). Complex 4 features an unprecedented 29Si NMR decoalescence process. The dehydrogenation process is fully reversible under standard conditions (1 bar, 298 K).