Synthesis and Characterization of a Series of (Diphenyldipyrazolylmethane)copper Complexes as Possible Precursors to Type I Blue Copper Protein Active Site Models

A series of copper complexes employing the neutral, bidentate, pyrazole‐based ligand diphenyldipyrazolylmethane was synthesized and fully characterized by various techniques, including elemental analysis, EPR, and structure elucidation by single‐crystal X‐ray diffraction. The structures of compounds 3−8 reveal variable coordination environments at the copper center, ranging from square pyramidal to tetrahedral, depending on the steric bulk at the pyrazole periphery and on the identity of the counterion. Cyclic voltammetry data on these compounds show a positively shifted reduction potential as compared to those observed employing the negatively charged pyrazolylborates or β‐diketiminates. These results indicate that these compounds may lead to (thiol)copper complexes that more accurately reproduce the reduction potentials observed during electron‐transfer processes in blue copper proteins. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)