128386-53-8Relevant academic research and scientific papers
Hydride transfer reactions of transition metal hydrides: Kinetic hydricity of metal carbonyl hydrides
Cheng, Tan-Yun,Brunschwig, Bruce S.,Bullock, R. Morris
, p. 13121 - 13137 (2007/10/03)
Hydride transfer from neutral transition metal hydrides (MH) to Ph3C+BF4- gives M-FBF3 and Ph3CH. The rate law -d[Ph3C+BF4-]/dt = k[Ph3C+BF4-][MH] was established from kinetic measurements using stopped- flow methods. Second-order rate constants determined in CH2Cl2 solution at 25 °C range from k(H) = 7.2 x 10-1 M-1 s-1 to k(H) = 4.6 x 106 M-1 s-1. The order of increasing kinetic hydricity is (C5H4-CO2Me)(CO)3 WH 5MnH 3CrH 3WH 3 4(PCy3)MnH 4(PPh3)MnH 5H4Me)(CO)3 WH 3MoH 3WH 3WH 5ReH 3MoH 4(PPh3)ReH 2WH 2(PCy3)MoH 2-(PPh3)MoH 2(PMe3)MoH (Cp = η5-C5H5, Cp* = η-C5Me5, Cy = cyclohexyl). Ranges of activation parameters for hydride transfer from trans- Cp(CO)2(PMe3)MoH, trans-Cp(CO)2(PCy3)MoH, cis-(CO)4(PPh3)ReH, and Cp*(CO)3MoH are ΔH(+)= 3.0 - 5.9 kcal mol-1 and ΔS(+) = -18 to -24 cal K-1 mol-1. The rate constant for hydride transfer (k(H)-) from cis- Cp(CO)2(PCy3)MoH at -55 °C is 3 orders of magnitude lower than that for trans-Cp(CO)2(PCy3)MoH. Phosphine substitution for CO generally enhances the kinetic hydricity, with trans-Cp(CO)2(PMe3)MoH being 104 times as reactive as Cp(CO)3MoH. The electronic effect of phosphine substitution is attenuated by steric factors when the phosphine is cis to the metal hydride. The hydride transfer kinetics reported here are interpreted to be single- step hydride transfers, rather than a multiple-step mechanism involving an initial electron transfer followed by hydrogen atom transfer. A distinction is made between hydricity and nucleophilicity of metal hydrides.
Kinetic hydricity of transition-metal hydrides toward trityl cation
Cheng,Bullock
, p. 4031 - 4033 (2008/10/09)
The kinetics of hydride transfer from a series of metal hydrides (MH) to Ph3C+BF4- (producing Ph3-CH and M - FBF3) have been studied by stopped-flow methods in CH2Cl3 solution. Second-order rate constants at 25°C span 5 orders of magnitude in kinetic hydricity, ranging from k = 5.0 × 101M-1 s-1 for HMn-(CO)5 to k = 4.6 × 105 M-1 s-1 for trans-HMo(CO)2-(PMe3)Cp.
