Chiral diphosphinites derived from 2,2-biphosphole as a new class of stereodynamic ligands for enantioselective hydrogenation

Abstract

New stereodynamic diphosphinites derived from 2,2'-biphosphole, were synthesised by introduction of a linker obtained from chiral diols between the two phosphorus atoms and used for catalytic hydrogenation through a dual chirality control induced by Rh-coordination. The application of these ligands in hydrogenation of dimethyl itaconate shows that the enantioselectivity strongly depends on steric and electronic properties of the chiral linker whereas the sense of enantioselection is determined by the configuration of these stereocentres. These stereodynamic diphosphinites induce higher enantioselectivities than the analogous stereodynamic diphosphanes derived from 2,2-biphosphole.

Phosphole-based ligands in catalysis

“…Starting from DMPP, L30 were obtained by asymmetric alkylation of the dianion, resulting from the cleavage of the two phosphorusphosphorus bonds of the tetraphosphole, using various enantiomerically pure diol ditosylates (or dimesylates), 138 whereas L31 were prepared by nucleophilic substitution of the dicycano intermediate using enantiomerically pure diols, as described in Scheme 78. 139 These tropos diphosphines and diphosphinites, L30 and L31, are able to provide diastereo-and enantiopure complexes of palladium, platinum and rhodium by a kinetic dynamic resolution upon coordination on a metal center. Their potential was demonstrated in particular for Pdcatalyzed allylic substitution and Rh-catalyzed hydrogenation reactions.…”

“…Starting from DMPP , L30 were obtained by asymmetric alkylation of the dianion, resulting from the cleavage of the two phosphorus–phosphorus bonds of the tetraphosphole, using various enantiomerically pure diol ditosylates (or dimesylates), 138 whereas L31 were prepared by nucleophilic substitution of the dicycano intermediate using enantiomerically pure diols, as described in Scheme 78. 139…”

Chiral diphosphines and diphosphinites derived from 2,2-biphosphole: Stereodynamic ligands for asymmetric catalysis

“…Indeed, the three diastereoisomers (C, D and E [or F] forms) are observed in solution as an equilibrium mixture at room temperature. The isomerization process, studied by desulfurization of diphosphine sulfides using a fully stereoselective method [14] that affords, at low temperature, chiral phosphines with retention of configuration, occurs at temperature below À60 8C. Since the chiral bridge prevents the formation of A and B forms, the only possible pathway for this isomerisation process requires a phosphorus-inversion 4 inducing atropo-inversion, the driving force being the pyramidal inversion barrier of the phosphorus atom as illustrated in Fig.…”

“…Molecular view of R[Sp,Sp,Sc]-2a space group: P2 1 2 1 2 1 , Flack's parameter: 0.06(14) 7. p-donor substituents on the phosphorus of phospholes do not affect the activation barrier according to experimental measurements and calculations.…”