2‐(2′‐Pyridyl)‐4,6‐diphenylphosphinine versus 2‐(2′‐Pyridyl)‐4,6‐diphenylpyridine: Synthesis, Characterization, and Reactivity of Cationic Rh^III and Ir^III Complexes Based on Aromatic Phosphorus Heterocycles

<jats:title>Abstract</jats:title><jats:p>The bidentate P,N hybrid ligand <jats:bold>1</jats:bold> allows access for the first time to novel cationic phosphinine‐based Rh<jats:sup>III</jats:sup> and Ir<jats:sup>III</jats:sup> complexes, broadening significantly the scope of low‐coordinate aromatic phosphorus heterocycles for potential applications. The coordination chemistry of <jats:bold>1</jats:bold> towards Rh<jats:sup>III</jats:sup> and Ir<jats:sup>III</jats:sup> was investigated and compared with the analogous 2,2′‐bipyridine derivative, 2‐(2′‐pyridyl)‐4,6‐diphenylpyridine (<jats:bold>2</jats:bold>), which showed significant differences. The molecular structures of [RhCl(Cp*)(<jats:bold>1</jats:bold>)]Cl and [IrCl(Cp*)(<jats:bold>1</jats:bold>)]Cl (Cp*=pentamethylcyclopentadienyl) were determined by means of X‐ray diffraction and confirm the mononuclear nature of the <jats:italic>λ</jats:italic><jats:sup>3</jats:sup>‐phosphinine–Rh<jats:sup>III</jats:sup> and Ir<jats:sup>III</jats:sup> complexes. In contrast, a different reactivity and coordination behavior was found for the nitrogen analogue <jats:bold>2</jats:bold>, especially towards Rh<jats:sup>III</jats:sup> as a bimetallic ion pair [RhCl(Cp*)(<jats:bold>2</jats:bold>)]<jats:sup>+</jats:sup>[RhCl<jats:sub>3</jats:sub>(Cp*)]<jats:sup>−</jats:sup> is formed rather than a mononuclear coordination compound. [RhCl(Cp*)(<jats:bold>1</jats:bold>)]Cl and [IrCl(Cp*)(<jats:bold>1</jats:bold>)]Cl react with water regio‐ and diastereoselectively at the external PC double bond, leading exclusively to the <jats:italic>anti</jats:italic>‐addition products [MCl(Cp*)(<jats:bold>1</jats:bold>H<jats:bold>⋅</jats:bold>OH)]Cl as confirmed by X‐ray crystal‐structure determination.</jats:p>