New Phosphorous-Based [FeFe]-Hydrogenase Models

Florian Wittkamp,Ulf-Peter Apfel,Michael Roemelt,Esma Birsen Boydas

doi:10.3390/catal10050522

Abstract

[FeFe]-hydrogenases have attracted research for more than twenty years as paragons for the design of new catalysts for the hydrogen evolution reaction (HER). The bridging dithiolate comprising a secondary amine as bridgehead is the key element for the reactivity of native [FeFe]-hydrogenases and was therefore the midpoint of hundreds of biomimetic hydrogenase models. However, within those mimics, phosphorous is barely seen as a central element in the azadithiolato bridge despite being the direct heavier homologue of nitrogen. We herein synthesized three new phosphorous based [FeFe]-hydrogenase models by reacting dithiols (HSCH2)2P(O)R (R = Me, OEt, OPh) with Fe3(CO)12. All synthesized mimics show catalytic reactivity regarding HER and change their mechanisms depending on the strength of the used acid. In all presented mimics, the oxide is the center of reactivity, independent of the nature of the bridgehead. However, the phosphorous atom might be reduced by the methods we present herein to alter the reactivity of the model compounds towards protons and oxygen.

Highlights

IntroductionThe bridging dithiolate comprising a secondary amine as bridgehead is the key element for the reactivity of native [FeFe]-hydrogenases and was the midpoint of hundreds of biomimetic hydrogenase models
Lehrstuhl für Anorganische Chemie I, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Department of Electrosynthesis, Fraunhofer UMSICHT, Osterfelder Str. 3, 46047 Oberhausen, Germany
The phosphorous atom might be reduced by the methods we present to alter the reactivity of the model compounds towards protons and oxygen

Summary

Introduction

The bridging dithiolate comprising a secondary amine as bridgehead is the key element for the reactivity of native [FeFe]-hydrogenases and was the midpoint of hundreds of biomimetic hydrogenase models. Within those mimics, phosphorous is barely seen as a central element in the azadithiolato bridge despite being the direct heavier homologue of nitrogen. The other example is the formerly mentioned ADSe, in which the dithiolate bridge is replaced by a diselenolate bridge [8] This hybrid enzyme is active for proton reduction and H2 oxidation but is more biased towards the former. The chalcogenide exchange further results in a dramatically reduced oxygen stability and, an even more sensitive H-cluster than the native cofactor

Methods

Results

Conclusion