Chiral biphosphines, rhodium complexes

At this point mechanistic studies have reached an impasse. All of the observable intermediates have been characterized in solution, and enamide complexes derived from diphos and chiraphos have been defined by X-ray structure analysis. Based on limited NMR and X-ray evidence it appears that the preferred configuration of an enamide complex has the olefin face bonded to rhodium that is opposite to the one to which hydrogen is transferred. There are now four crystal structures of chiral biphosphine rhodium diolefin complexes, and consideration of these leads to a prediction of the direction of hydrogenation. The crux of the argument is that nonbonded interactions between pairs of prochiral phenyl rings and the substrate determine the optical yield and that X-ray structures reveal a systematic relationship between P-phenyl orientation and product configuration. 

A fortunate feature of asymmetric catalysis is that chiral biphosphine rhodium diene complexes, especially with norbornadiene, crystallize well... 

Achiwa, K. (1976) Asymmetric hydrogenation with new chiral functionalized biphosphine- rhodium complexes, J. Am. Chem. Soc. 98,8265-8266. 

Morimoto T, Chiba M, Achiwa K. Efficient synthesis of natural (-f)-collinusin using catalytic asymmetric hydrogenation with a chiral biphosphine-rhodium(I) complex. Chem. Pharm. Bull. 1989 37(12) 3161-3163. 

Rhodium Complexes with Larger-ring Chelates of Chiral Biphosphines... 

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