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

•Open shell (S = 3/2) heterobimetallic Cr/Rh and Cr/Ir complexes are reported.•These complexes feature the shortest Cr–Rh and Cr–Ir distances reported to date.•DFT calculations suggest a relatively covalent metal–metal interaction.•A metal–metal bond order of 0.5 between Cr and Rh or Ir is described.

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.

Graphical abstractA new chromium tris(phosphinoamide) precursor is used to synthesize open shell (S = 3/2) heterobimetallic Cr/Rh and Cr/Ir complexes featuring metal–metal bonds.Figure optionsDownload full-size imageDownload as PowerPoint slide