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Structural and Electronic Influences on Rates of Tertpyridine−Amine Co III −H Formation During Catalytic H 2 Evolution in an Aqueous Environment
Author(s) -
DiMarco Brian N.,
Polyansky Dmitry E.,
Grills David C.,
Wang Ping,
Kuwahara Yutaka,
Zhao Xuan,
Fujita Etsuko
Publication year - 2021
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.202100295
Subject(s) - chemistry , catalysis , protonation , radiolysis , aqueous solution , solvolysis , catalytic cycle , amine gas treating , medicinal chemistry , reaction rate constant , inorganic chemistry , reaction intermediate , reaction mechanism , photochemistry , kinetics , ion , organic chemistry , hydrolysis , physics , quantum mechanics
Abstract In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co II −Cl] + species results in the formation of [Co II (κ 4 ‐L)(OH 2 )] 2+ . Further reduction produces [Co I (κ 4 ‐L)(OH 2 )] + , which undergoes a rate‐limiting structural rearrangement to [Co I (κ 5 ‐L)] + before being protonated to form [Co III −H] 2+ . The rate of [Co III −H] 2+ formation is similar for all complexes in the series. Using E 1/2 values of various Co species and p K a values of [Co III −H] 2+ estimated from PR experiments, we found that while the protonation of [Co III −H] 2+ is unfavorable, [Co II −H] + reacts with protons to produce H 2 . The catalytic activity for H 2 evolution tracks the hydricity of the [Co II −H] + intermediate.