N. Beach, Kenneth D. Camm, D. E. Fogg
Aug 2, 2010
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0
Influential Citations
33
Citations
Journal
Organometallics
Abstract
An unexpected “generation gap” is uncovered between the Grubbs catalysts RuCl2(L)(PCy3)(═CHPh) (1a, L = PCy3; 1b, L = IMes, N,N′-bis(mesityl)imidazol-2-ylidene) in their reactions with hydrogen versus methanol, in the presence of base. Treatment of the first-generation catalyst 1a with H2 and NEt3 (CH2Cl2, 60 °C, 1000 psi H2) affords RuHCl(H2)(PCy3)2 (2a) in 75% yield within 30 min, as determined by in situ NMR analysis. Complex 2a is in turn efficiently converted (96%; 2 h) into the important hydrogenation catalyst RuHCl(CO)(PCy3)2 (3a) by mild thermolysis with methanol and NEt3 (4:1 CH2Cl2−MeOH, 60 °C), 72% net yield for the 1a−3a transformation. In comparison, subjecting the second-generation catalyst 1b to this two-step process effects <40% net conversion to RuHCl(CO)(IMes)(PCy3) (3b) (hydrogenolysis of 1b: ca. 60% RuHCl(H2)(IMes)(PCy3) (2b) (1 h); carbonylation of isolated 2b: 65% 3b (2.5 h)), owing to the susceptibility of the dihydrogen derivative 2b to disproportionation and decomposition. The opp...