Synthesis and structural studies of rhodium(I)-catalytic precursors containing two furanoside diphosphines
作者:Montserrat Diéguez、Oscar Pàmies、Aurora Ruiz、Carmen Claver
DOI:10.1016/s0022-328x(01)00819-1
日期:2001.6
We have prepared new rhodium(I) complexes with two furanoside diphosphines, 3,5,6-trideoxy-3,5-bis-diphenylphosphine-1, 2-O-isopropylidene-beta -L-idofuranose (1) and 3,5,6-trideoxy-3,5-bis-diphenylphosphine-1,2-O-isopropylidene-alpha -L-glucofuranose (2), which form six-membered chelate rings when they coordinate to rhodium. NMR spectroscopy of the Rh complexes and molecular mechanics calculations showed that the configuration of the stereocenter C-5 greatly influences the structure of these complexes, and thus their enantioselectivity. The pre-catalyst [Rh(cod)(2)]BF4, which gives the highest enantioselectivities in the asymmetric hydrogenation of alkenes, adopts the twist-lambda conformation. By changing the configuration of the C-5, the complex becomes fluxional at room temperature and enantioselectivity drops considerably. (C) 2001 Elsevier Science B.V. All rights reserved.