Reactions of Pyridyl-Functionalized, Chelating λ³-Phosphinines in the Coordination Environment of Rh^III and Ir^III

Graphical Abstract

Rh^III and Ir^III complexes based on the λ³-P,N hybrid ligand 2-(2′-pyridyl)-4,6-diphenylphosphinine (1) react selectively at the PC double bond to give chiral coordination compounds of the type [(1H⋅OH)Cp*MCl]Cl, which can be deprotonated to form [(1H⋅O)Cp*IrCl] and [(1⋅OH)Cp*RhCl] (see figure). These new transformations in the coordination environment of Rh^III and Ir^III provide an easy and general access to new transition-metal complexes containing λ⁵σ⁴-phosphinine ligands.

Abstract

Rh^III and Ir^III complexes based on the λ³-P,N hybrid ligand 2-(2′-pyridyl)-4,6-diphenylphosphinine (1) react selectively at the PC double bond to chiral coordination compounds of the type [(1H⋅OH)Cp*MCl]Cl (2,3), which can be deprotonated with triethylamine to eliminate HCl. By using different bases, the pK_a value of the POH group could be estimated. Whereas [(1H⋅O)Cp*IrCl] (4) is formed quantitatively upon treatment with NEt₃, the corresponding rhodium compound [(1H⋅O)Cp*RhCl] (5) undergoes tautomerization upon formation of the λ⁵σ⁴-phosphinine rhodium(III) complex [(1⋅OH)Cp*RhCl] (6) as confirmed by single-crystal X-ray diffraction. Blocking the acidic POH functionality in 3 by introducing a POCH₃ substituent leads directly to the λ⁵σ⁴-phosphinine iridium(III) complex (8) upon elimination of HCl. These new transformations in the coordination environment of Rh^III and Ir^III provide an easy and general access to new transition-metal complexes containing λ⁵σ⁴-phosphinine ligands.