Bis(μ-oxo)dimetal “Diamond” Cores in Copper and Iron Complexes Relevant to Biocatalysis

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Abstract
Although quite a familiar feature in high‐valent manganese chemistry, the M2(μ‐O)2 diamond core motif has only recently been found in synthetic complexes for M=Cu or Fe. Structural and spectroscopic characterization of these more reactive Cu2(μ‐O)2 and Fe2(μ‐O)2 compounds has been possible through use of appropriately designed supporting ligands, low‐temperature handling methods, and techniques such as electrospray ionization mass spectrometry and X‐ray crystallography with area detector instrumentation for rapid data collection. Despite differences in electronic structures that have been revealed through experimental and theoretical studies, Cu2(μ‐O)2 and Fe2(μ‐O)2 cores exhibit analogously covalent metal–oxo bonding, remarkably congruent Raman and extended X‐ray absorption fine structure (EXAFS) signatures, and similar tendencies to abstract hydrogen atoms from substrates. Core isomerization is another common reaction attribute, although different pathways are traversed; for Fe, bridge‐to‐terminal oxo migration has been discovered, while for Cu, reversible formation of an O−O bond to yield a peroxo isomer has been identified. Our understanding of biocatalysis has been enhanced significantly through the isolation and comprehensive characterization of the Cu2(μ‐O)2 and Fe2(μ‐O)2 complexes. In particular, it has led to the development of new mechanistic notions about how non‐heme multimetal enzymes, such as methane monooxygenases, fatty acid desaturase, and tyrosinase, may function in the activation of dioxygen to catalyze a diverse array of organic transformations.