Interconversion of η3‑H2SiRR′ σ‑Complexes and 16-Electron Silylene Complexes via Reversible H–H or C–H Elimination

Solid samples of η3-silane complexes [PhBPPh3]­RuH­(η3-H2SiRR′) (R,R′ = Et2, 1a; PhMe, 1b; Ph2, 1c, MeMes, 1d) decompose when exposed to dynamic vacuum. Gas-phase H2/D2 exchange between isolated, solid samples of 1c-d3 and 1c indicate that a reversible elimination of H2 is the first step in the irreversible decomposition. An efficient solution-phase trap for hydrogen, the 16-electron ruthenium benzyl complex [PhBPPh3]­Ru­[η3-CH2(3,5-Me2C6H3)] (3) reacts quantitatively with H2 in benzene via elimination of mesitylene to form the η5-cyclohexadienyl complex [PhBPPh3]­Ru­(η5-C6H7) (4). This H2 trapping reaction was utilized to drive forward and quantify the elimination of H2 from 1b,d in solution, which resulted in the decomposition of 1b,d to form 4 and several organosilicon products that could not be identified. Reaction of {[PhBPPh3]­Ru­(μ-Cl)}2 (2) with (THF)2Li­(SiHMes2) forms a new η3-H2Si species [PhBPPh3]­Ru­[CH2(2-(η3-H2SiMes)-3,5-Me2C6H2)] (5) which reacts with H2 to form the η3-H2SiMes2 complex [PhBPPh3]­RuH­(η3-H2SiMes2) (1e). Complex 1e was identified by NMR spectroscopy prior to its decomposition by elimination of Mes2SiH2 to form 4. DFT calculations indicate that an isomer of 5, the 16-electron silylene complex [PhBPPh3]­Ru­(μ-H)­(SiMes2), is only 2 kcal/mol higher in energy than 5. Treatment of 5 with XylNC (Xyl = 2,6-dimethylphenyl) resulted in trapping of [PhBPPh3]­Ru­(μ-H)­(SiMes2) to form the 18-electron silylene complex [PhBPPh3]­Ru­(CNXyl)­(μ-H)­(SiMes2) (6). A closely related germylene complex [PhBPPh3]­Ru­[CN­(2,6-diphenyl-4-MeC6H2)]­(H)­(GeHtBu) (8) was prepared from reaction of tBuGeH3 with the benzyl complex [PhBPPh3]­Ru­[CN­(2,6-diphenyl-4-MeC6H2)]­[η1-CH2(3,5-Me2C6H3)] (7). Single crystal XRD analysis indicated that unlike for 6, the hydride ligand in 8 is a terminal hydride that does not engage in 3c-2e Ru–H → Ge bonding. Complex 1b is an effective precatalyst for the catalytic Ge–H dehydrocoupling of tBuGeH3 to form (tBuGeH2)2 (85% yield) and H2.