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 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)(μ-η¹-(OCO):η²-(N,OCO)-l- phenylalanine)]₃³⁺ (7; S_C,S_C,S_C,S_Rh,S_Rh,S_Rh), an example of a one-step, highly diastereoselective reaction in H₂O.