176247-96-4Relevant academic research and scientific papers
Interconversion between zwitterionic and cationic rhodium(I) complexes of demonstrated value as catalysts in hydroformylation, silylformylation, and hydrogenation reactions. Dynamic 31P{1H} NMR studies of (η6-PhBPh3)-Rh+(DPPB) and [Rh(DPPB)2]+BPh4- in solution
Zhou, Zhongxin,Facey, Glenn,James, Brian R.,Alper, Howard
, p. 2496 - 2503 (2008/10/08)
Treatment of an orange solution of [Rh(COD)(DPPB)]+BF4- (2) in MeOH with 2 equiv of NaBPh4 at room temperature (RT) afforded an orange precipitate, [Rh(COD)(DPPB)]+BPh4- (3), in 94% yield. Reaction of the cationic rhodium complex 3 with H2 under ambient conditions in CH2Cl2 for 1 h gave the zwitterionic complex (η6-PhBPh3)-Rh+(DPPB) (4) in quantitative yield. Although 3 is stable in the solid state, it has the propensity in solution to convert to the zwitterionic complexes (η6-PhBPh3)-Rh+(COD) (1) and (η6-PhBPh3)-Rh+-(DPPB) (4) along with a small amount of [Rhx(DPPB)2x]x+[BPh4 -]x. Addition of 1, 2, and 4 equiv of DPPB to the CD2Cl2 solution of (η6-PhBPh3)-Rh+(NBD) (6) under N2 resulted in the formation of [Rh(NBD)(DPPB)]+BPh4- (7) and [Rh(DPPB)2]+BPh4- (5) in ratios of 90/ 10, 57/43, and 0/100, respectively, while addition of 2 equiv of DPPB to the CD2Cl2 solution of 6, under an atmosphere of H2 at RT, gave 4 and 5 in an ratio of 35/65. Slowed η6-PhBPh3- rotation about the (η6-PhBPh3)--Rh bond axis in (η6-PhBPh3)-Rh+(DPPB) (4) was established by a variable-temperature 31P{1H} NMR study. Variable-temperature 31P{1H} NMR spectra of [Rh(DPPB)2]+BPh4- (5) along with the low-temperature 31P{1H} COSY and EXSY NMR spectra demonstrated the presence of an equilibrium between [Rh(DPPB)2]+ (5α) and [Rh(DPPB)(μ-DPPB)]22+ (5β).
