The proton-coupled electron transfer (PCET) reaction of [Co(Cp)(dppe)]+ (Cp = cyclopentadienyl, dppe = 1,2-bis(diphenylphosphino)ethane) to form the corresponding cobalt(III)-hydride proceeds via a stepwise electron-transfer, proton-transfer process in acetonitrile. With weak acids, a linear free energy relationship between the second order rate constant for proton transfer and acid pKa is observed. However, when the acid strength is increased, the second order rate constant becomes acid pKa-independent (2.1 x 107 M-1 s-1). When acids with steric bulk around the acidic proton are utilized, rate constants do not clearly correlate with pKa. In order to more deeply understand the proton-coupled electron transfer reactivity giving rise to these trends, we examined a series of complexes with various phosphine substituents to reveal how pKa–depenent and pKa––independent reactivity is influenced by structural and electronic factors. These data have revealed the rich PCET reactivity associated with protonation of transition metal centers.

Structural and thermochemical parameters influencing the PCET formation of a cobalt(III)-hydride

255th National Meeting (2018)

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