Aqueous Organometallic Chemistry. 2. 1H NMR Spectroscopic, Synthetic, and Structural Study of the Chemo- and Diastereoselective Reactions of [Cp*Rh(H2O)3]2+ with Nitrogen Ligands as a Function of pH

The reactions of a new Cp*Rh aqua synthon, [Cp*Rh(H2O)3]2+ (1), at acidic pH values (2−6) with aniline (2), pyridine (3), and l-phenylalanine (4) have provided interesting chemo- and diastereoselectivities as studied by 1H NMR, FAB/MS, and single-crystal X-ray crystallography. The reaction of 2 and aqua complex 1, at pH values from 4 to 6, quantitatively provided [Cp*Rh(η6-aniline)]2+ (5); the structure of 5 was unequivocally determined by a single-crystal X-ray analysis, which also showed an approximate 25% η5 component. Compound 3 reacted with 1, at pH 2−6, to selectively provide [Cp*Rh(η1-pyridine)n(H2O)3-n]2+ (n = 1−3) complexes 6ac as a function of pH. Surprisingly, complex 1 reacted with 4, from pH 4 to 6, to provide only one diastereomer of the known cyclic trimer [(Cp*Rh)(μ-η1-(OCO):η2-(N,OCO)-l- phenylalanine)]33+ (7; SC,SC,SC,SRh,SRh,SRh), an example of a one-step, highly diastereoselective reaction in H2O.