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

abstract

  • Rhodium chelate complexes of the title diphosphines, [η5-C5H4PPh2)Re(NO)(PPh3 )(M-(CHR)nPPh2)Rh(NBD)]+PF6- ((S)-5, n = 0; (S)-6, n/R = 1/H; (SReSc)- and (SReRc)-7, n/R = 1/Ph), are catalyst precursors (1.0 mol %, 24-26 °C) for additions of Ph2SiH2 to the ketones PhCOCH2R (R = H, CH3, CH2CH3, CH2CH2Cl; 93-77% conversions). Hydrolyses give the alcohols (R)-HOCH(Ph)CH2R 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 (SReRc)-? (41/46/62/58%) are higher than those of the diastereomer (SReSc)-7 (23/11/15/35%). The alkenes (Z)-RCH=C(NHCOCH3)CO2R′ (R/R′ = H/H, Ph/H, Ph/CH3) and H2 (1 atm) react in the presence of (SReSc)- and (SReAc)-7 (0.5 mol %, 30 °C) to give the protected amino acids RCH2CH(NHCOCH3)CO2R′ in 85-92% yields. The ee values with (SRe-Sc)-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, (SReAc)-7 gave much higher ee values (93/94/97%), but with R enantiomers dominant. Hence, the carbon stereocenter of 7 controls the product configuration.

author list (cited authors)

  • Kromm, K., Osburn, P. L., & Gladysz, J. A.

citation count

  • 43

publication date

  • August 2002