A new route to achiral and chiral 1,2-bis(phosphino)ethanes, 1-arsino-2-phosphinoethanes, and 1,3-bis(phosphino)propanes and the molecular structure and catalytic activity of some rhodium(I) complexes derived thereof.

A series of unsymmetrical 1,2-bis(phosphino)ethanes R2PCH2CH2PR′2 (2a–d) and 1-arsino-2-phosphinoethanes R2AsCH2CH2PR′2 (3a–c) mainly with bulky substituents R and R′ were prepared from the cyclic sulfate 1 by stepwise cleavage of the carbon–oxygen bonds by LiPR2 and LiPR′2 or LiAsR2 and LiPR′2, respectively. Analogously, racemic mixtures of R2PCH2CH(Me)PPh2 (R = iPr 5a, Cy 5b) as well as the enantiomers (R)-5a, (R)-5b and (R)-tBu2PCH2CH(Me)PPh2 (R)-5c were obtained from the corresponding unsymmetrical cyclic sulfates 4 and (S)-4. On a similar route, the racemates of the 1,3-bis(phosphino)propanes R2PCH2CH2CH(Me)PPh2 (R = iPr 7, tBu 8), optically pure (R)-8 and (S,S)-iPr2PCH(Me)CH2CH(Me)PPh2 (S,S)-10 were prepared. The reaction of [{RhCl(η4-C8H12)}2] with chelating ligands L–L, where L–L is R2PCH2P(men)2 (R = iPr, Ph; men = (1S,2R,5S)-menthyl), Cy2AsCH2P(men)2, or (R)-5a, (R)-5b, (R)-5c, (R)-8 and (S,S)-10, in the presence of AgPF6, gave the complexes [Rh(η4-C8H12)(L–L)]PF6 (12a–h) which were used as pre-catalysts in the hydrogenation of the methyl ester of α-acetamidocinnamic acid (ACM). Depending on L–L, the solvent, the temperature and the pressure of H2, optical yields of up to 69% ee were achieved. For two of the rhodium complexes, 12c and 12d, the molecular structures were determined by X-ray crystallography.