Mechanistic aspects of Ru(BINAP)-catalysed asymmetric hydrogenation of vinylcarboxylic acid derivatives
Journal
Inorganica Chimica Acta
Journal Volume
234
Journal Issue
1-2
Pages
95-100
Date Issued
1995
Author(s)
Abstract
The mechanism of the RuII(BINAP)-catalysed hydrogenation of vinylcarboxylic acids has been investigated via detailed deuterium labelling studies. The activation of H2 by the Ru catalyst was found to be via a heterolytic splitting route. The regioselectivity of the hydride migration step strongly correlates to the stability of the resulting metal-alkyl intermediate. When an α,β-unsaturated carboxylic acid such as 2-(6-methoxy-2-naphthyl)acrylic acid is used as the substrate, the hydrite migrates exclusively to the α position, forming a metal-primary alkyl intermediate. In the case of a β,γ-unsaturated carboxylic acid with an electron-withdrawing group attached to the β-carbon, the hydrite migrates exlusively to the γ-carbon, forming a five-membered ring metal-alkyl intermediate with the β-carbon coordinated to the metal. The product formation step involves two competing routes: the hydrogenolysis and the solvolysis of the metal-alkyl intermediates. The choice of each route is highly dependent on the reaction conditions. The solvolysis route is significant if the reaction is carried out under low H2 pressure and the reaction medium is more acidic. Under high H2 pressure, hydrogenolysis becomes the dominant route. Under basic conditions, the solvolysis route is essentially shut off and only the hydrogenolysis product is obtained. A unified mechanism which explains all of the known experimental results is proposed. © 1995.
SDGs
Type
journal article