Stabilizing Coordinated Radicals via Metal–Ligand Covalency: A Structural, Spectroscopic, and Theoretical Investigation of Group 9 Tris(dithiolene) Complexes

Proper assignment of redox loci in coordination complexes with redox-active ligands to either the metal or the ligand is essential for rationalization of their chemical reactivity. However, the high covalency endemic to complexes of late, third-row transition metals complicates such assignments. Herein, we systematically explore the redox behavior of a series of group 9 tris(dithiolene) complexes, [M(mnt)3]3– (M = Ir, Rh, Co; mnt = maleonitriledithiolate). The Ir species described comprise the first examples of homoleptic Ir dithiolene complexes. The enhanced metal–ligand covalency of the Ir–S interaction leads to remarkable reactivity of [Ir(mnt)3]3– and stabilization of mononuclear [Ir(mnt)3]2– complex ions as well as dimerized versions featuring weak, covalent, intermolecular S–S bonds. The dianionic Rh and Co analogues are, in contrast, highly unstable, resulting in the rapid formation of [Rh2(mnt)5]4– and [Co(mnt)2]22–, respectively. The synthesized complexes were studied by single-crystal X-ray diff...