Cooperative B–H and Si–H Bond Activations by κ²‑N,S‑Chelated Ruthenium Borate Complexes

Cooperative E–H (E = B, Si) bond activations employing κ²-N,S-chelated ruthenium borate species, [PPh₃{κ²-N,S-(NS₂C₇H₄)}­Ru­{κ³-H,S,S′-H₂B­(NC₇H₄S₂)₂}], (1) are established. Treatment of 1 with BH₃·SMe₂ yielded the six-membered ruthenaheterocycle [PPh₃{κ²-S,H-(BH₃NS₂C₇H₄)}­Ru­{κ³-H,S,S’-H₂B­(C₇H₄NS₂)₂}] (2) formed by a hemilabile ring opening of a Ru–N bond and capturing of a BH₃ unit coordinated in an “end-on” fashion. On the other hand, the bulky borane H₂BMes shows different reactivity with 1 that led to the formation of the two dihydroborate complexes [{κ³-S,H,H-(NBH₂Mes)­(S₂C₇H₄)}­Ru­{κ³-H,S,S’-H₂B­(C₇H₄NS₂)₂}] (3) and [PPh₃{κ³-S,H,H-(NBH₂Mes)­(S₂C₇H₄)}­Ru­(κ²-N,S-C₇H₄NS₂)] (4), in which H₂BMes has been inserted into the Ru–N bond of the initial κ²-N,S-chelated ligand. In an attempt to directly activate hydrosilanes by 1, reactions were carried out with H₂SiPh₂ that yielded two isomeric five-membered ruthenium silyl complexes, namely [PPh₃{κ²-S,Si-(NSiPh₂)­(S₂C₇H₄)}­Ru­{κ³-H,S,S’-H₂B­(C₇H₄NS₂)₂}] (5a,b), and the hydridotrisilyl complex [Ru­(H)­{κ²-S,Si-(SiPh₂NC₇H₄S₂}₃] (6). These complexes were generated by Si–H bond activation with the release of H₂ and the formation of N–Si and Ru–Si bonds. When the reaction of 1 was carried out in the presence of PhSiH_3, the reaction only produced the analogous complexes [PPh₃{κ²-S,Si-(NSiPhH)­(S₂C₇H₄)}­Ru­{κ³-H,S,S’-H₂B­(C₇H₄NS₂)₂}] (5a′,b′). Density functional theory (DFT) calculations have been used to probe the bonding modes of boranes/silane with the ruthenium center.