Oxidative Cleavage of Cellobiose by Lytic PolysaccharideMonooxygenase (LPMO)-Inspired Copper Complexes

The potentially tridentate ligand bis[(1-methyl-2-benzimidazolyl)ethyl]amine (2BB) was employed to prepare copper complexes [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 as bioinspired models of lytic polysaccharide copper-dependent monooxygenase (LPMO) enzymes. Solid-state characterization of [(2BB)CuI]OTf revealed a Cu(I) center with a T-shaped coordination environment and metric parameters in the range of those observed in reduced LPMOs. Solution characterization of [(2BB)CuII(H2O)2](OTf)2 indicates that [(2BB)CuII(H2O)2]2+ is the main species from pH 4 to 7.5; above pH 7.5, the hydroxo-bridged species [{(2BB)CuII(H2O)x}2(μ-OH)2]2+ is also present, on the basis of cyclic voltammetry and mass spectrometry. These observations imply that deprotonation of the central amine of Cu(II)-coordinated 2BB is precluded, and by extension, amine deprotonation in the histidine brace of LPMOs appears unlikely at neutral pH. The complexes [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 act as precursors for the oxidative degrada...