Structural, Spectroscopic, and Theoretical Characterization of Bis(μ-oxo)dicopper Complexes, Novel Intermediates in Copper-Mediated Dioxygen Activation

A description of the structure and bonding of novel bis(μ-oxo)dicopper complexes and their bis(μ-hydroxo)dicopper decomposition products was derived from combined X-ray crystallographic, spectroscopic, and ab initio theoretical studies. The compounds [(LCu)2(μ-O)2]X2 were generated from the reaction of solutions of [LCu(CH3CN)]X with O2 at −80 °C (L = 1,4,7-tribenzyl-1,4,7-triazacyclononane, LBn3; 1,4,7-triisopropyl-1,4,7-triazacyclononane, LiPr3; or 1-benzyl-4,7-diisopropyl-1,4,7-triazacyclononane, LiPr2Bn; X = variety of anions). The geometry of the [Cu2(μ-O)2]2+ core was defined by X-ray crystallography for [(d21-LBn3Cu)2(μ-O)2](SbF6)2 and by EXAFS spectroscopy for the complexes capped by LBn3 and LiPr3; notable dimensions include short Cu−O (∼1.80 A) and Cu···Cu (∼2.80 A) distances like those reported for analogous M2(μ-O)2 (M = Fe or Mn) rhombs. The core geometry is contracted compared to those of the bis(μ-hydroxo)dicopper(II) compounds that result from decomposition of the bis(μ-oxo) complexes upon...