The multiredox catalytic activity of late 2nd and 3rd row transition metal complexes can be understood in terms of their capacity to undergo cooperative two-electron transfer events coupled to bond-making and bond-breaking steps.  The cooperativity arises from the stability of the d6- and d8-electron configurations with respect to the intermediate d7-electron configuration, which can be expected to manifest as an inversion of the one-electron reduction potentials: E1�'(d7/d8)>E2�'(d6/d7).  Fine tuning these redox potentials and electron-transfer kinetics is a potential strategy for improving catalysts and rationally designing new catalysts.  However, attempts to investigate the thermodynamics and kinetics of these electron-transfer reactions are severely hampered by the fact that these reactions are typically irreversible because of the accompanying drastic changes in the metal coordination sphere.  To address this problem, we have designed a series of platinum and palladium complexes that undergo cooperative, outer-sphere and reversible two-electron transfer.  An important architectural element of these molecules is a ligand scaffold capable of stabilizing the square planar coordination geometry preferred by a d8-electron metal centre and the octahedral geometry of d6-electron metal centre.  Here we will describe the synthesis, spectroscopy, structures, and reactivity of these complexes, as well as current understanding of the mechanism of electron transfer.

Coooperative and reversible outer-sphere two-electron transfer reactions of late transition metal complexes

246th National Meeting (2013)

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