Aqueous organometallic chemistry .2. H-1 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: H-1 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(eta(6)-aniline)](2+) (5); the structure of 5 was unequivocally determined by a;single-crystal X-ray analysis, which also showed an approximate 25% eta(5) component. Compound 3 reacted with 1, at pH 2-6, to selectively provide [Cp*Rh(eta(1)-pyridine)(n)(H2O)(3-n)](2+) (n = 1-3) complexes 6a-c 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)(mu-eta(1)-(OCO):eta(2)-(N,OCO)-L-phenylalanine)] (3+)(3) (7; S-C,S-C,S-C,S-Rb,S-Rh,S-Rh), an example of a one-step, highly diastereoselective reaction in H2O.