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Download fileRole of Anation on the Mechanism of Proton Reduction Involving a Pentapyridine Cobalt Complex: A Theoretical Study
journal contribution
posted on 2018-07-03, 13:19 authored by Murugesan Panneerselvam, Madhavan JaccobKinetic
and thermodynamic aspects of proton reduction involving pentapyridine
cobalt(II) complex were investigated with the help of quantum chemical
calculations. Free energy profile of all possible mechanistic routes
for proton reduction was constructed with the consideration of both
anation and solvent bound pathways. The computed free energy profile
shows that acetate ion plays a significant role in modulating the
kinetic aspects of Co(III)–hydride formation which is found
to be the key intermediate for proton reduction. Upon replacing solvent
by acetate ion, one electron reduction and protonation of CoI species become more rapid along with slow displacement reaction.
Most favorable pathways for hydrogen evolution from Co(III)–hydride
species is also investigated. Among the four possible pathways, reduction
followed by protonation of Co(III)–hydride (RPP) is found to
be the most feasible pathway. On the basis of QTAIM and NBO analyses,
the electronic origin of most favorable pathway is explained. The
basicity of cobalt center along with thermodynamic stability of putative
CoIII/II–H species is essentially a prime factor
in deciding the most favorable pathway for hydrogen evolution. Our
computed results are in good agreement with experimental observations
and also provided adequate information to design cobalt-based molecular
electrocatalysts for proton reduction in future.