333382-82-4Relevant academic research and scientific papers
Hydrogen transfer to carbonyls and imines from a hydroxycyclopentadienyl ruthenium hydride: Evidence for concerted hydride and proton transfer
Casey,Singer,Powell,Hayashi,Kavana
, p. 1090 - 1100 (2001)
Reaction of { [2,5-Ph2-3,4-Tol2(η5-C 4CO)]2H}Ru2(CO)4(μ-H) (6) with H2 formed [2,5-Ph2-3,4-Tol2(η5-C 4COH)Ru(CO)2H] (8), the active species in catalytic carbonyl reductions developed by Shvo. Kinetic studies of the reduction of PhCHO by 8 in THF at - 10 °C showed second-order kinetics with ΔH? = 12.0 kcal mol-1 and ΔS? = -28 eu. The rate of reduction was not accelerated by CF3CO2H, and was not inhibited by CO. Selective deuteration of the RuH and OH positions in 8 gave individual kinetic isotope effects kRuH/kRuD = 1.5 ± 0.2 and kOH/kOD = 2.2 ± 0.1 for PhCHO reduction at 0 °C. Simultaneous deuteration of both positions in 8 gave a combined kinetic isotope effect of kORuH/kODRuD = 3.6 ± 0.3. [2,5-Ph2-3,4-Tol2(η5-C 4COSiEt3) Ru(CO)2H] (12) and NEt4+[2,5-Ph2-3,4-Tol 2(η4-C4CO) Ru(CO)2H]- (13) were unreactive toward PhCHO under conditions where facile PhCHO reduction by 8 occurred. PhCOMe was reduced by 8 30 times slower than PhCHO; MeN=CHPh was reduced by 8 26 times faster than PhCHO. Cyclohexene was reduced to cyclohexane by 8 at 80 °C only in the presence of H2. Concerted transfer of a proton from OH and hydride from Ru of 8 to carbonyls and imines is proposed.
