Probing Cu(I) in homogeneous catalysis using high-energy-resolution fluorescence-detected X-ray absorption spectroscopy.

Metal-to-ligand charge transfer excitations in Cu(I) X-ray absorption spectra are introduced as spectroscopic handles for the characterization of species in homogeneous catalytic reaction mixtures. Analysis is supported by correlation of a spectral library to calculations and to complementary spectroscopic parameters.

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 metal­ligand covalency of the Ir­S 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 S­S 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 diffraction, X-ray absorption spectroscopy, optical spectroscopy, magnetometry, density functional theory, and spectroscopy-oriented configuration interaction calculations. Spectroscopic and theoretical analyses suggest that the stability of [Ir(mnt)3]2­ may be attributed to dilution of ligand radical character by a high degree of Ir 5d character in the singly occupied molecular orbital.