Chelating Diphosphines That Contain a Rhenium Stereocenter in the Backbone: Applications in Rhodium-Catalyzed Enantioselective Ketone Hydrosilylations and Alkene Hydrogenations

Rhodium chelate complexes of the title diphosphines, (( S )- 5, n = 0; ( S )- 6, n /R = 1/H; ( S Re S C )- and ( S Re R C )- 7, n /R = 1/Ph), are catalyst precursors (1.0 mol %, 24−26 °C) for additions of Ph 2 SiH 2 to the ketones PhCOCH 2 R (R = H, CH 3, CH 2 CH 3, CH 2 CH 2 Cl; 93−77% conversions). Hydrolyses give the alcohols ( R )-HOCH(Ph)CH 2 R in 83−60% isolated yields; configurations correlate with the relative rhenium configurations of the catalysts. The ee values with ( S )- 6 (63/62/60/92%) exceed those of ( S )- 5 (44/38/47/48%); ee values of ( S Re R C )- 7 (41/46/62/58%) are higher than those of the diastereomer ( S Re S C )- 7 (23/11/15/35%). The alkenes ( Z )-RCH C(NHCOCH 3 )CO 2 R‘ (R/R‘ = H/H, Ph/H, Ph/CH 3 ) and H 2 (1 atm) react in the presence of ( S Re S C )- and ( S Re R C )- 7 (0.5 mol %, 30 °C) to give the protected amino acids RCH 2 CH(NHCOCH 3 )CO 2 R‘ in 85−92% yields. The ee values with ( S Re S C )- 7 (37/62/61%) are lower than those found earlier for ( S )- 6 (62/72/65%) or ( S )- 5 (92/93/88%), with S enantiomers dominant in all cases. Surprisingly, ( S Re R C )- 7 gave much higher ee values (93/94/97%), but with R enantiomers dominant. Hence, the carbon stereocenter of 7 controls the product configuration.