Open AccessTheoretical Study of C–H Bond Cleavage via Concerted Proton-Coupled Electron Transfer in Fluorenyl-Benzoates
Author(s) -
Elvira R. Sayfutyarova,
Zachary K. Goldsmith,
Sharon HammesSchiffer
Publication year - 2018
Publication title -
journal of the american chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.115
H-Index - 612
eISSN - 1520-5126
pISSN - 0002-7863
DOI - 10.1021/jacs.8b10461
Subject(s) - chemistry , benzoates , cleavage (geology) , proton , bond cleavage , electron , proton coupled electron transfer , electron transfer , computational chemistry , photochemistry , organic chemistry , catalysis , nuclear physics , geotechnical engineering , fracture (geology) , engineering , physics
Developing new strategies to activate and cleave C-H bonds is important for a broad range of applications. Recently a new approach for C-H bond activation using multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an oxidant coupled to intramolecular proton transfer was reported. For a series of oxidants reacting with 2-(9 H-fluoren-9-yl)benzoate, experimental studies revealed an atypical Brønsted α, defined as the slope of the logarithm of the PCET rate constant versus the logarithm of the equilibrium constant or the scaled driving force. Herein this reaction is modeled with a vibronically nonadiabatic PCET theory. Hydrogen tunneling, thermal sampling of the proton donor-acceptor mode, solute and solvent reorganization, and contributions from excited vibronic states are found to play important roles. The calculations qualitatively reproduce the experimental observation of a Brønsted α significantly less than 0.5 and explain this shallow slope in terms of exoergic processes between pairs of electron-proton vibronic states. These fundamental mechanistic insights may guide the design of more effective strategies for C-H bond activation and cleavage.