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Issue 3, 2016
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Highly functionalizable penta-coordinate iron hydrogen production catalysts with low overpotentials

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Abstract

Penta-coordinate iron carbonyl complexes that are built around the rigid Fe(PNP) motif (PNP = (C6H5)2PN(R)P(C6H5)2) are synthesized and structurally and spectroscopically characterized. These complexes allow for facile customization of the secondary ligand sphere with various types of linkers and functional groups. The new [Fe(S2C6H4)(PNP)(CO)] complexes show dihydrogen production electrocatalysis at overpotentials of 0.09–0.21 V vs. Pt under mildly acidic conditions (and activities from 0.28 to 3.51 s−1). The most active compound exhibits a turnover frequency (TOF) of 3.51 s−1 at an overpotential of only 0.15 V vs. Pt. Trends in activity are further analyzed. It is found that (a) a decrease in overpotential correlates strongly with the electron withdrawing strength of the PNP amine substituent, and (b) aliphatic substituents give comparatively higher TOFs than aromatic ones. An EC-type mechanism is shown to proceed by initial reduction of the FeII metal center and proposed formation of an FeIII hydride intermediate. Analogous cobalt compounds were synthesized and characterized, but were found to have low stability in acidic media under turnover conditions, and hence, are unsuitable as catalysts for proton reduction.

Graphical abstract: Highly functionalizable penta-coordinate iron hydrogen production catalysts with low overpotentials

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Supplementary files

Article information


Submitted
25 Sep 2015
Accepted
18 Nov 2015
First published
23 Nov 2015

Dalton Trans., 2016,45, 1138-1151
Article type
Paper
Author version available

Highly functionalizable penta-coordinate iron hydrogen production catalysts with low overpotentials

S. C. Eady, T. Breault, L. Thompson and N. Lehnert, Dalton Trans., 2016, 45, 1138
DOI: 10.1039/C5DT03744A

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