Abstract:
Initial stages of two representative Ni-catalysed asymmetric hydrogenations were investigated computationally featuring the formation of the active catalytic species [R,R-BenzP*NiH]+ from R,R-BenzP*Ni(OAc)2 and [S,S-Ph-BPENiH]+ from S,S-Ph-BPENi(OAc)2. Among several computed pathways the most feasible is dissociation of acetic acid from (ligand)NiH(HOAc) formed by H2 metathesis in the (ligand)Ni(H2)(OAc)2. The rate-limiting step is the initial metathesis of H2 requiring high effective activation barriers of 28.3 and 26.6 kcal mol–1, in accord with high pressures and elevated temperatures essential for the Ni-catalysed hydrogenations.
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