Pincer-Ligated Iridium Complexes with Low-Field Ancillary Ligands: Complexes of (iPrPCP)IrCl2 and Comparison with (iPrPCP)IrHCl

Abstract

Pincer-ligated iridium complexes have been widely developed, and (pincer)Ir(III) complexes, particularly five-coordinate, are central to their chemistry. Such complexes typically bear two formally anionic ligands in addition to the pincer ligand itself. Yet despite the prevalence of halides as anionic ligands in transition metal chemistry, there are relatively few examples in which both of these ancillary anionic ligands are halides or even other monodentate low-field anions. We report a study of the fragment (^iPrPCP)IrCl₂ (^iPrPCP = κ³-2,6-C₆H₃(CH₂PⁱPr₂)) and adducts thereof. These species are found to be thermodynamically disfavored relative to the corresponding hydridohalides. For example, DFT calculations and experiments indicate that one Ir–Cl bond of (^iPrPCP)IrCl₂ complexes will undergo reaction with H₂ to give (^iPrPCP)IrHCl or an adduct thereof. In the presence of aqueous HCl, (^iPrPCP)IrCl₂ adds a chloride ion to give an unusual example of an anionic transition metal complex ((^iPrPCP)IrCl₃^–) with a Zundel cation (H₅O₂⁺). (^iPrPCP)IrCl₂ is not stable as a monomer at room temperature but exists in solution as a mixture of clusters which can add various small molecules. DFT calculations indicate that dimerization and trimerization of (^iPrPCP)IrCl₂ are more favorable than the analogous reactions of (^iPrPCP)IrHCl, in accord with cluster formation being observed only for the dichloride complex.