Electronic Control of the Protonation Rates of Fe–Fe Bonds

Jablonskyte, Ausra, Webster, Lee R., Simmons, Trevor R., Wright, Joseph A. and Pickett, Christopher J. (2014) Electronic Control of the Protonation Rates of Fe–Fe Bonds. Journal of the American Chemical Society, 136 (37). pp. 13038-13044. ISSN 0002-7863

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Abstract

Protonation at metal–metal bonds is of fundamental interest in the context of the function of the active sites of hydrogenases and nitrogenases. In diiron dithiolate complexes bearing carbonyl and electron-donating ligands, the metal–metal bond is the highest occupied molecular orbital (HOMO) with a “bent” geometry. Here we show that the experimentally measured rates of protonation (kH) of this bond and the energy of the HOMO as measured by the oxidation potential of the complexes (E1/2ox) correlate in a linear free energy relationship: ln kH = ((F(c – βE1/2ox))/(RT)), where c is a constant and β is the dimensionless Brønsted coefficient. The value of β of 0.68 is indicative of a strong dependence upon energy of the HOMO: measured rates of protonation vary over 6 orders of magnitude for a change in E1/2ox of ca. 0.55 V (ca. 11 orders of magnitude/V). This relationship allows prediction of protonation rates of systems that are either too fast to measure experimentally or that possess additional protonation sites. It is further suggested that the nature of the bridgehead in the dithiolate ligand can exert a stereoelectronic influence: bulky substituents destabilize the HOMO, thereby increasing the rate of protonation.

Item Type: Article
Faculty \ School: Faculty of Science
Faculty of Science > School of Chemistry
Depositing User: Pure Connector
Date Deposited: 04 Nov 2014 11:56
Last Modified: 28 Oct 2019 15:50
URI: https://ueaeprints.uea.ac.uk/id/eprint/50630
DOI: 10.1021/ja506693m

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