Aqueous Organometallic Chemistry. 2. <sup>1</sup>H NMR Spectroscopic, Synthetic, and Structural Study of the Chemo- and Diastereoselective Reactions of [Cp*Rh(H<sub>2</sub>O)<sub>3</sub>]<sup>2+</sup> with Nitrogen Ligands as a Function of pH OgoSeiji ChenHong OlmsteadMarilyn M. FishRichard H. 1996 The reactions of a new Cp*Rh aqua synthon, [Cp*Rh(H<sub>2</sub>O)<sub>3</sub>]<sup>2+</sup> (<b>1</b>), at acidic pH values (2−6) with aniline (<b>2</b>), pyridine (<b>3</b>), and l-phenylalanine (<b>4</b>) have provided interesting chemo- and diastereoselectivities as studied by <sup>1</sup>H NMR, FAB/MS, and single-crystal X-ray crystallography. The reaction of <b>2</b> and aqua complex <b>1</b>, at pH values from 4 to 6, quantitatively provided [Cp*Rh(η<sup>6</sup>-aniline)]<sup>2+</sup> (<b>5</b>); the structure of <b>5</b> was unequivocally determined by a single-crystal X-ray analysis, which also showed an approximate 25% η<sup>5</sup> component. Compound <b>3</b> reacted with <b>1</b>, at pH 2−6, to selectively provide [Cp*Rh(η<sup>1</sup>-pyridine)<i><sub>n</sub></i>(H<sub>2</sub>O)<sub>3</sub><sub>-</sub><i><sub>n</sub></i>]<sup>2+</sup> (<i>n</i> = 1−3) complexes <b>6a</b><b>−</b><b>c </b>as a function of pH. Surprisingly, complex <b>1</b> reacted with <b>4</b>, from pH 4 to 6, to provide only one diastereomer of the known cyclic trimer [(Cp*Rh)(μ-η<sup>1</sup>-(<i>OCO</i>):η<sup>2</sup>-(<i>N</i>,<i>OCO</i>)-l- phenylalanine)]<sub>3</sub><sup>3+</sup> (<b>7</b>; <i>S</i><sub>C</sub>,<i>S</i><sub>C</sub>,<i>S</i><sub>C</sub>,<i>S</i><sub>Rh</sub>,<i>S</i><sub>Rh</sub>,<i>S</i><sub>Rh</sub>), an example of a <i>one</i>-<i>step</i>, highly diastereoselective reaction in H<sub>2</sub>O.