Interconversion of η<sup>3</sup>-H<sub>2</sub>SiRR′ σ-Complexes and 16-Electron Silylene Complexes via Reversible H–H or C–H Elimination
作者:Mark C. Lipke、Felix Neumeyer、T. Don Tilley
DOI:10.1021/ja501803w
日期:2014.4.23
Solid samples of eta(3)-silane complexes [PhBP3Ph](-) RuH(eta(3)-H2SiRR') (R,R' = Et-2, 1a; PhMe, 1b; Pb-2, 1c, MeMes, 1d) decompose when exposed to dynamic vacuum. Gas-phase H-2/D-2 exchange between isolated, solid samples of 1c-d(3) and 1c indicate that a reversible elimination of H-2 is the first step in the irreversible decomposition. An efficient solution-phase trap for hydrogen, the 16-electron ruthenium benzyl complex [PhBPPb3]Ru[eta(3)-CH2(3,5-Me2C6H3)] (3) reacts quantitatively with H2 in benzene via elimination of mesitylene to form the eta(5)-cyclohexadienyl complex [PhBP3Ph]Ru(eta(5)-C6H7) (4). This H2 trapping reaction was utilized to drive forward and quantify the elimination of H-2 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 [PhBP3Ph]Ru(mu-Cl)}(2) (2) with (THF)(2)Li(SiHMes(2)) forms a new eta(3)-H2Si species [PhBP3Ph]Ru[CH2(2-(eta(3)-H(2)SiMes)-3,5-Me2C6H2)] (5) which reacts with H-2 to form the eta(3)-H(2)SiMes(2) complex [PhBP3Ph]RuH(eta(3)-H(2)SiMes(2)) (1e). Complex 1e was identified by NMR spectroscopy prior to its decomposition by elimination of Mes(2)SiH(2) to form 4. DFT calculations indicate that an isomer of 5, the 16-electron silylene complex [PhBP3Ph]Ru(mu-H)(= SiMes(2)), is only 2 kcal/mol higher in energy than 5. Treatment of 5 with XylNC (Xyl = 2,6-dimethylphenyl) resulted in trapping of [PhBP3Ph]Ru(mu-H)(=SiMes(2)) to form the 18-electron silylene complex [PhBP3Ph]Ru(CNXyl)(mu-H)(=SiMes(2)) (6). A closely related germylene complex [PhBP3Ph]Ru[CN(2,6-diphenyl-4-MeC6H2)](H)(=(GeHBu)-Bu-t) (8) was prepared from reaction of (BuGeH3)-Bu-t with the benzyl complex [PhBP3Ph]Ru[CN(2,6-diphenyl-4-MeC6H2)][eta(1)-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 (BuGeH3)-Bu-t to form ((BuGeH2)-Bu-t)(2) (85% yield) and H-2.