Di- and Trinuclear Mixed-Valence Copper Amidinate Complexes from Reduction of Iodine

Abstract

Molecular examples of mixed-valence copper complexes through chemical oxidation are rare but invoked in the mechanism of substrate activation, especially oxygen, in copper-containing enzymes. To examine the cooperative chemistry between two metals in close proximity to each other we have begun to study the reactivity of a dinuclear Cu(I) amidinate complex. The reaction of [(2,6-Me2C6H3N)2C(H)]2Cu2, 1, with I2 in THF, CH3CN, and toluene affords three new mixed-valence copper complexes, [(2,6-Me2C6H3N)2C(H)]2Cu2(μ2-I3)(THF)2, 2, [(2,6-Me2C6H3N)2C(H)]2Cu2(μ2-I)(NCMe)2, 3, and [(2,6-Me2C6H3N)2C(H)]3Cu3(μ3-I)2, 4, respectively. The first two compounds have been characterized by UV-Vis and EPR spectroscopy and their molecular structure determined by X-ray crystallography. Both di- and trinuclear mixed-valence intermediates have been characterized for the reaction of compound 1 to compound 4 and the molecular structure of 4 has been determined by X-ray crystallography. The electronic structure of each of these complexes has also been investigated using density functional theory.

Topological analysis of the metal-metal bond: A tutorial review

“…At the MP2 level, their strength has been calculated three times weaker than aurophilic interactions [314]. However, the oxidation of one Cu(I) centre involved in the cuprophilic interaction, results in the formation of a stronger single Cu(II)-Cu(I) bond in the corresponding mixed-valence complex [315,316].…”

Triggering Redox Activity in a Thiophene Compound: Radical Stabilization and Coordination Chemistry

“…Thep aramagnetism of Cu 2 I 2 (LC)could conceivably arise from either the presence of the ligand radical LC and two Cu I centers,o rf rom an anionic ligand with delocalized Cu I /Cu II mixed-valence cations. Although mixed-valence Cu complexes have been reported and are seen to adopt pseudotetrahedral geometries in the solid state, [18] the fluid-solution EPR spectrum of Cu 2 I 2 (LC) shows ar esonance at g = 1.9958 that is consistent with al igand-based radical. Thel owering of the g-value as compared to LC is ascribed to spin-orbit contributions from the iodo atoms,which reduce all g-values to slightly less than g e ,a sd escribed by the frozen-solution spectrum (see .…”

Triggering Redox Activity in a Thiophene Compound: Radical Stabilization and Coordination Chemistry

“…The paramagnetism of Cu2I2(L • ) could conceivably arise from either the presence of the ligand radical L • and two Cu(I) centers, or from an anionic ligand with delocalized Cu(I)/Cu(II) mixed-valence cations. While mixed-valence Cu complexes have been reported and are seen to adopt pseudo-tetrahedral geometries in the solid state, [17] the fluid-solution EPR spectrum of Cu2I2(L • ) shows a resonance at g = 1.9958 that is consistent with a ligand-based radical. The lowering of the g-value compared to L • is ascribed to spin-orbit contributions from the copper atoms which reduce all gvalues to slightly less than ge, as described by the frozen-solution spectrum ( Figure S8).…”

“…and two Cu I centers, or from an anionic ligand with delocalized Cu I /Cu II mixed‐valence cations. Although mixed‐valence Cu complexes have been reported and are seen to adopt pseudotetrahedral geometries in the solid state, the fluid‐solution EPR spectrum of Cu 2 I 2 ( L . ) shows a resonance at g= 1.9958 that is consistent with a ligand‐based radical.…”