Why do many C-2-symmetric bisphosphine ligands fail in asymmetric hydroformylation? Theory in front of experiment

Supported by a pure QM and MM treatment, stereoselectivities of rhodium sys tems containing the C-2-symmetric ligands CHIRAPHOS (2,3-bis(diphenylphosph ino)butane; 2), BINAP (2,2'-bis(diphenylphosphino)-1,1'-binaphthyl; 3), DIO P (2,2-dimethyl-4,5-bis((diphenylphosphino)methyl)-1,3-dioxolane; 4), and N APHOS (2,2'-bis((diphenylphosphino)methyl)-1,1'-binaphthyl; 5) have been ca lculated with a combined QM/MM method. On the basis of the RSAI (requiremen t of synchronous asymmetric inductions), which states that all ligand coord ination modes favor transition states with the same asymmetric induction, w e demonstrate that the performance of C-2-symmetric bidentate phosphine lig ands is governed by two interdependencies, namely induction influence of th e chelate ring and backbone flexibility. In a further step, the NAPHOS deri vatives 6 (2,2'-bis((2-dinaphthylphosphino)-methyl)-1,1'-binaphthyl) and 7 (2,2'-bis((1-dinaphthylphosphino)methyl)-1,1'-binaphthyl) which to our know ledge have not been tested experimentally up to now, have been investigated in the same manner. 7 fulfills the RSAI and will be tested experimentally. Our explanations and predictions release asymmetric hydroformylation from its predominantly empirical character, although the magic formula for ligan d development is still unknown.