Synthesis and investigation of the metal–metal interactions in heterobimetallic Cr/Rh and Cr/Ir complexes

Abstract

The chromium(III) tris(phosphinoamide) precursor Cr(iPrNPiPr2)3 (1) has been used to synthesize Cr/Rh and Cr/Ir heterobimetallic complexes. Treatment of [MCl(COD)]2 with 1 affords the open shell S=3/2 complexes ClCr(μ-iPrNPiPr2)2M(η2-iPrNPiPr2) (M=Rh (2), Ir (3)). Instead of simple coordination of the late transition metal fragment to the C3-symmetric tris(phosphinoamide) binding pocket, the preference of RhI and IrI for a square planar environment leads to a chloride/amide ligand exchange process. Complexes 1–3 have been structurally characterized using X-ray crystallography, revealing short Cr–Rh and Cr–Ir distances (2.6095(3)Å (2); 2.6064(4)Å (3)) indicative of metal–metal bonds. A computational investigation of the electronic structures of 2 and 3 reveals substantial metal–metal orbital overlap, but the high spin nature of the CrIII center leads to population of metal–metal antibonding orbitals and relatively weak metal–metal bonding. The effects of the metal–metal interaction on the redox properties of the CrIII center are investigated using cyclic voltammetry.