New C2-symmetric diphosphite ligands derived from carbohydrates: Effect of the remote stereocenters on asymmetric catalysis

Abstract

The synthesis of new modular chiral diphosphite ligands with C 2-symmetry and carbohydrate backbone is reported. We also report here the synthesis of the corresponding rhodium complexes [Rh(COD)(L)]BF4 (L = diphosphite). All these species have been characterised in solution by NMR spectroscopy and in some cases in the solid state by X-ray diffraction. The solution structures of the hydridorhodiumcarbonyl species [RhH(CO) 2(L)], where L = diphosphites 12a-14a, 12b, have been studied using high-pressure NMR spectroscopy. The configuration and substitution of the remote stereocentres in positions 2 and 5 of the tetrahydrofuran ring of the diphosphite ligands were observed to have a considerable influence on the results obtained in the rhodium-catalysed hydroformylation and hydrogenation reactions. Thus, the configuration of the major isomer obtained in the hydroformylation reaction may be controlled by changing the configuration of these stereocentres. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.