Dimeric rhodium(II) complexes containing bridging mandelate ligands

The syntheses and characterization of some dimeric rhodium(II) complexes containing bridging mandelato ligands and a metal–metal bond are described. The compounds isolated are Rh2(O2CR)4(H2O)2, previously described by Shchelokov and coworkers, and derivatives of the type Rh2(O2CR)2(N—N)2X2•nH2O (R = (R)—CH(OH)Ph, N—N = o-phenanthroline or 2,2′-dipyridyl, X = Cl, Br, I, and n is 4, 2, or 1). A mixture of species containing both bridged acetate and mandelate was isolated also. Infrared and electronic spectral data are reported. The chloride ligands of the dimers are displaced readily by alcohols, phosphines, phosphites, and amines; the metal centre also may be reduced by alcohols, P(OEt)3, and nBu2NH. Preliminary studies point to the conditions necessary for the rhodium(II) mandelate and derivatives (phosphine or (N—N) substituted) to activate H2 for catalytic hydrogenation of olefins and ketones, including prochiral substrates.