2-(2′-Pyridyl)-4,6-diphenylphosphinine versus 2-(2′-Pyridyl)-4,6-diphenylpyridine: Synthesis, Characterization, and Reactivity of Cationic RhIII and IrIII Complexes Based on Aromatic Phosphorus Heterocycles

The bidentate P,N hybrid ligand 1 allows access for the first time to novel cationic phosphinine‐based RhIII and IrIII complexes, broadening significantly the scope of low‐coordinate aromatic phosphorus heterocycles for potential applications. The coordination chemistry of 1 towards RhIII and IrIII was investigated and compared with the analogous 2,2′‐bipyridine derivative, 2‐(2′‐pyridyl)‐4,6‐diphenylpyridine (2), which showed significant differences. The molecular structures of [RhCl(Cp*)(1)]Cl and [IrCl(Cp*)(1)]Cl (Cp*=pentamethylcyclopentadienyl) were determined by means of X‐ray diffraction and confirm the mononuclear nature of the λ3‐phosphinine–RhIII and IrIII complexes. In contrast, a different reactivity and coordination behavior was found for the nitrogen analogue 2, especially towards RhIII as a bimetallic ion pair [RhCl(Cp*)(2)]+[RhCl3(Cp*)]− is formed rather than a mononuclear coordination compound. [RhCl(Cp*)(1)]Cl and [IrCl(Cp*)(1)]Cl react with water regio‐ and diastereoselectively at the external PC double bond, leading exclusively to the anti‐addition products [MCl(Cp*)(1H⋅OH)]Cl as confirmed by X‐ray crystal‐structure determination. A bidentate P,N hybrid ligand allows for access to cationic phosphinine‐based RhIII and IrIII complexes, broadening significantly the scope of low‐coordinate aromatic phosphorus heterocycles for potential applications (see figure). The coordination chemistry of this ligand towards RhIII and IrIII was investigated and compared with 2‐(2′‐pyridyl)‐4,6‐diphenylpyridine, which showed remarkable differences between the structurally related heterocycles.