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 [RhClACHTUNGTRENUNG(Cp*)(1)]Cl and [IrClACHTUNGTRENUNG(Cp*)(1)]Cl (Cp*=pentamethylcyclopentadienyl) were determined by means of X-ray diffraction and confirm the mononuclear nature of the l3-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 [RhClACHTUNGTRENUNG(Cp*)(2)]+ ACHTUNGTRENUNG[RhCl3ACHTUNGTRENUNG(Cp*)] is formed rather than a mononuclear coordination compound. [RhClACHTUNGTRENUNG(Cp*)(1)]Cl and [IrClACHTUNGTRENUNG(Cp*)(1)]Cl react with water regio- and diastereoselectively at the external P=C double bond, leading exclusively to the antiaddition products [MClACHTUNGTRENUNG(Cp*)- ACHTUNGTRENUNG(1H·OH)]Cl as confirmed by X-ray crystal-structure determination.