Modular chiral diphosphite derived from l-tartaric acid. Applications in metal-catalyzed asymmetric reactions

A new family of C2-symmetric chiral diphosphites was synthesized using two different chiral backbones derived from tartaric acid, combined with chiral binaphthyls or non-chiral substituted biphenyl moieties. Diphosphites were applied to Rh-catalyzed hydroformylation of styrene producing good conversions in mild conditions, fair regioselectivities but low enantioselectivities in all cases. Ligands were also essayed in Pd-catalyzed allylic substitution reactions of linear and cyclic substrates using dimethyl malonate as nucleophile. Conversion rates up to 7200 h−1 were reached, while moderated ee's were attained. In this reaction, a kinetic resolution of rac-1,3-diphenyl-3-acetoxyprop-1-ene was observed, leading to 99% ee of for the unreacted S-substrate and 60% ee of S-alkylated product. Coordination properties of diphosphites in rhodium and palladium complexes related to catalytic species involved in the two previous reactions were investigated. Some ligands form equatorial-equatorial chelates in pentacoordinated complexes [RhH(CO)(PPh3)(diphosphite)], while other act as bridge between two metal atoms. In the catalytic active species [Pd(η3-PhCHCHCHPh)(diphosphite)]PF6 one or two diastereoisomers are formed, depending on the diphosphite structure.

New chiral diphosphite ligands have been synthesized and applied in asymmetric hydroformylation and asymmetric allylic alkylation. Rhodium and palladium complexes related to the catalytically active species were also investigated.Figure optionsDownload high-quality image (109 K)Download as PowerPoint slide