Synthesis and characterisation of heterotrinuclear transition metal complexes for biomimetic proton reduction

Selected structural, spectroscopic, electrochemical and photochemical properties of novel heterotrinuclear [FeFe]-hydrogenase enzyme model compounds carrying a catalytic iron sulfur cluster site directly coupled to different transition metal subunits are reported. Typical metal-to-ligand charge transfer (MLCT) chromophores based on electron donating copper(I), rhenium(l) and tungsten(0) complex fragments were selected to provide both long-wavelength spectral sensitization and photoredox activity. Photoinduced one-electron transfer from the MLCT donor subunit to the diiron acceptor site could be observed with an efficient steady-state accumulation of the corresponding charge-separated state. The reduced iron site of these deeply coloured heterotrinuclear [FeFe]-hydrogenase model systems has been shown to be electrocatalytically active for proton reduction in the presence of trifluoroacetic acid (TFA). However, a successful visible-light powered system for catalytic hydrogen release in homogeneous solution could not be achieved, and the reaction remained stoichiometric with all of the systems investigated. (C) 2017 Elsevier B.V. All rights reserved.