Stereochemistry at carbon upon protonolysis of a late transition metal-alkyl bond: a reaction of relevance to catalytic enantioselective hydrogenation of olefins

Abstract

Reaction of [Ru((R)-BINAP)(H)(MeCN)n(acetone)3–n](BF4) (where n = 0–3) (2) with 1 equiv of the olefin substrate methyl α-acetamidoacrylate (MAA) in acetone at room temperature immediately generated a mixture (72:28) of two diastereomers of the complex [Ru((R)-BINAP)(MeCN)(MAA(H))](BF4) (3). The olefin–hydride insertion reaction between 2 and MAA to generate 3 was regioselective, with transfer of the hydride to the β-olefinic carbon and transfer of ruthenium to the α-carbon in both diastereomers of 3. The two diastereomers of 3 differ by the absolute configuration at the α-carbon of MAA(H) ((SCα)-3 and (RCα)-3). The absolute configuration of the major ((SCα)-3) diastereomer was determined by X-ray diffraction in conjunction with NMR spectroscopic data. Protonolysis of the ruthenium–carbon bond in 3 and in the methyl α-acetamidocinnamate (MAC) analog ([Ru((R)-BINAP)(MeCN)((S)- MAC(H))](BF4) ((SCα)-4)) by addition of 2 equiv HBF4·Et2O in CH2Cl2 at room temperature was not stereospecific and did not occur with β-hydride elimination from the methyl or benzyl groups.Key words: ruthenium, BINAP, enantioselective, hydrogenation, catalysis.