Metal Complex of Hydrogenase Active Sites

Abstract

This article reviews the synthesis and chemistry of complexes that are of relevance to the structure and catalysis observed at the active sites of [NiFe], [FeFe] and [Fe] hydrogenase enzymes. Both structural and functional modelling of these biosites has been accomplished using ligand design to assemble low molecular weight metal complexes incorporating polythiolate coordination at the metal centre, coupled to appropriate amine, phosphine, cyanide and CO co-ligands. Exchange of ligands and the use of alternative metal centres, particularly Ru and Co, are discussed, and recent developments leading to the incorporation of proton relays and photoactive moieties are highlighted as strategies to generate photocatalysts for hydrogen production and oxidation for use in fuel cells.

Synthetic Designs and Structural Investigations of Biomimetic Ni–Fe Thiolates

“…20 To generate Fe−Ni complexes, reactions of [Ni(NS 3 )] − with cyclopentadienyl iron complexes were investigated. 27,28 Treatment of Na[Ni(NS 3 ] or Ph 4 P[Ni(NS 3 )] with [CpFe-(CO) 2 (thf)]BF 4 gave an immediate reaction. The deep brown product exhibited a pair of ν CO bands, shifted by 25−30 cm −1 to lower energy with respect to the cationic precursor (Figure S15).…”

Functional Model for the [Fe] Hydrogenase Inspired by the Frustrated Lewis Pair Concept

“…In view of the world’s ever increasing demand for energy, and powered by the search for a sustainable energy supply, dihydrogen is seen among the promising energy carriers of the future. , However, the efficient production, storage, and splitting of dihydrogen still poses a significant challenge. Nature provides valuable inspiration for the development of H 2 formation and activation catalysts as embodied by a unique class of metalloenzymes called hydrogenases, which efficiently catalyze the reversible formation and heterolytic cleavage of H 2 . − Well-known and extensively characterized are the binuclear [FeFe] and [NiFe] hydrogenases, − for which a large body of biomimetic model complexes has been developed. − A third phylogenetically unrelated type, the [Fe] hydrogenase (Hmd), has been discovered more recently and has attracted wider attention only in the past few years. − While [Fe] hydrogenase was initially thought to be a purely organic hydrogenation catalyst, , subsequent investigations revealed a unique mononuclear iron-guanylylpyridinol (FeGP) cofactor. , As in the other hydrogenases it features an Fe II (CO) moiety, but in [Fe] hydrogenase this is bound to one cysteine sulfur atom, an sp 2 -hybridized pyridine nitrogen atom and an acyl carbon atom, thus representing a rather unusual organometallic binding motif in biological systems . In many methanogenic archea, [Fe] hydrogenase catalyzes the reversible reduction of methenyltetrahydromethanopterin (methenyl-H 4 MPT + ) to methylenetetrahydromethanopterin (methylene-H 4 MPT), thereby splitting the H 2 molecule heterolytically and transferring a hydride ion stereospecifically to the pro-R site of the acceptor molecule (Scheme ) …”

Molecular Concepts of Water Splitting: Nature's Approach

“…However, these criteria are not easy to meet in model systems [150]. The work on biomimetic models for [NiFe] and [FeFe] hydrogenase has been described in several review articles [150][151][152][153][154][155][156][157][158]. In this work, many of the structural features important for proper function found in the native systems have been successfully incorporated -for example, the bimetallic Ni-Fe or Fe-Fe core with rather short metalmetal distances and an open coordination site at one metal, the sulfur-rich environment (terminal and bridging thiolate ligands), CO/CN ligation of the iron(s), and the incorporation of a base for acceptance of the proton and, more recently, of hydride bridges.…”