title: A Theoretical Investigation of the Ni(II)-Catalyzed Hydrovinylation of Styrene.
abstract: We report a detailed and full computational investigation on the hydrovinylation reaction of styrene with the Ni(II)-phospholane catalytic system, which was originally presumed to proceed through a cationic mechanism involving a nickel hydride intermediate. The following general features emerge from this study on a specific catalyst complex that was found to give quantitative yield and moderate selectivity: (a) the activation barrier for the initiation (18.8 kcal/mol) is higher than that for the reaction due to a low-lying square-planar pentenyl chelate intermediate originating from a Ni(II)-allyl catalyst precursor. Consequently there is an induction period for the catalysis; (b) the exit of product from the catalyst is via a β-H-transfer step instead of the usual β-H elimination pathway, which has a very high activation energy due to a trans effect of the phospholane ligand; (c) the turnover-limiting and enantio- determining transition state is also the β-H-transfer; (d) because of the absence of a hydride intermediate, the unwanted isomerization of the product is prevented; (e) since the enantio-discrimination is decided at the H-transfer stage itself, the configuration of the product in a catalytic cycle influences the enantioselectivity in the subsequent cycle; (f) the trans effect of the sole strong ligand in the d8 square-planar Ni(II), the stability of the η(3)-benzyl intermediate, and the availability of three coordination sites enable regioselective hydrovinylation over the possible oligomerization/polymerization of the olefin substrates and linear hydrovinylation. This work has also confirmed the previously recognized role of the hemilabile group at various stages in the mechanism.
authors.affiliation: School of Chemistry, University of Hyderabad, Central University P. O., Hyderabad 500046, India, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India, Indian Institute of Science Education and Research, Thiruvananthapuram, CET Campus, Kerala 695016, India, and Department of Chemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210.
authors.forename: Jorly
authors.initials: J
authors.lastname: Joseph
authors.forename: T V
authors.initials: TV
authors.lastname: Rajanbabu
authors.forename: Eluvathingal D
authors.initials: ED
authors.lastname: Jemmis