Small molecule activation by multimetallic active sites depends on subtle interplays of cluster geometry, electronic structure, and cooperative reactivity that are difficult to elucidate in a site-specific manner with traditional spectroscopic techniques. An emerging tool for gaining site-specific information within multinuclear clusters is high-resolution multiwavelength anomalous diffraction (MAD), a single-crystal experiment that enables deconvolution of X-ray absorption profiles with atomic precision. Our group has previously studied [Cu4(µ4-S)L4]2+ clusters [L = Ph2PCH2PPh2 (1) or Ph2PNHPPh2 (2)] that structurally mimic the CuZ catalytic site of nitrous oxide reductase. Recently, we identified conditions under which 2 mediates 2H+/2e- reduction of N2O to N2 and H2O while 1 is unreactive. In this presentation, the differences between these two complexes will be mapped atomistically using MAD and accompanying techniques. Subtle geometric differences between 1 and 2 and corresponding impacts on electron density were correlated to reactivity differences, allowing for a comprehensive elucidation of structural, electronic, and cooperative effects that enable activation of the inert N2O molecule in a site-specific manner. Calibrated by experimental observations, computational modeling of N2O binding to a site-differentiated cluster geometry provided further insight into the cluster/N2O interactions necessary for N-O bond cleavage.

Atomistic elucidation of N2O binding to a tetracopper-sulfur cluster

ACS Spring 2022

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