Asymmetric Hydrogenation. Dimerization of Solvate Complexes: Synthesis and Characterization of Dimeric [Rh(DIPAMP)]₂²⁺, a Valuable Catalyst Precursor

The hydrogenation of [Rh(DIPAMP)(NBD)]BF4 (DIPAMP= 1,2-bis[(2-methoxyphenyl)(phenylphosphino)]ethane, NBD=2,5-norbornadiene) in methanol leads not only to the formation of the expected solvate complex [Rh(DIPAMP)(MeOH)(2)]BF4 but also to the arene-bridged dimeric species [Rh(DIPAMP)](2)(BF4)(2). The dimeric is characterized by X-ray analysis as well as by an extensive NMR solution study including H-1, P-31, and Rh-103 NMR. When used as a precursor for the asymmetric hydrogenation of prochiral olefins, [Rh(DIPAMP)](2)(BF4)(2) operates Without induction periods. It can be used for the formation of catalyst-substrate complexes such as [Rh(DIPAMP)(MAC)]BF4 (MAC = methyl (Z)-alpha-acetamidocinnamate).