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