Self-assembled biomimetic [2Fe2S]-hydrogenase-based photocatalyst for molecular hydrogen evolution

Abstract

The large-scale production of clean energy is one of the major challenges society is currently facing. Molecular hydrogen is envisaged as a key green fuel for the future, but it becomes a sustainable alternative for classical fuels only if it is also produced in a clean fashion. Here, we report a supramolecular biomimetic approach to form a catalyst that produces molecular hydrogen using light as the energy source. It is composed of an assembly of chromophores to a bis(thiolate)-bridged diiron ([2Fe2S]) based hydrogenase catalyst. The supramolecular building block approach introduced in this article enabled the easy formation of a series of complexes, which are all thoroughly characterized, revealing that the photoactivity of the catalyst assembly strongly depends on its nature. The active species, formed from different complexes, appears to be the [Fe 2(-pdt)(CO)4{PPh2(4-py)}2] (3) with 2 different types of porphyrins (5a and 5b) coordinated to it. The modular supramolecular approach was important in this study as with a limited number of building blocks several different complexes were generated.photocatalysis ͉ self-assembly ͉ supramolecular chemistry ͉ metalloporphyrin chromophore ͉ Stern-Volmer plot S upramolecular chemistry, defined by Nobel Prize Laureate Jean-Marie Lehn as the ''chemistry beyond the molecule,'' has changed the way we look at molecules (1). Besides exploring reactivity of molecules, interaction between molecules has become of dominant importance as it provides new means of controlling properties of chemical systems. Supramolecular chemistry has rapidly evolved into a mature field, and the implementation of supramolecular strategies has resulted in breakthroughs in several disciplines (2-4). The reversible character of noncovalent chemistry gives rise to concepts such as adaptation and self-correction, creating fundamentally different system properties compared with traditional covalent strategies. The modular character associated with the building block approach in supramolecular chemistry provides an easy strategy to generate large libraries of analogous structures of nanosize dimension. Such libraries are of interest in research areas where accurate prediction of particular properties of chemical systems is inadequate or impossible. For example, means to predict the selectivity provided by transition metal catalyst are lacking, and therefore high throughput screening of libraries of catalysts is still the most powerful method to find catalyst systems with desired selectivities. Indeed, we and others have introduced supramolecular ways to make transition metal catalysts and used the building block approach to create large libraries of related catalysts, some of which show unrivaled selectivities (5-9).Stimulated by these exciting results, we were wondering whether supramolecular strategies could also provide solutions to other challenges in catalysis. One of the greatest challenges our society is currently facing is the large-scale production of clean energy (10). Molecular hydrogen is e...

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

“…As compared with those reported in the literature [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] , the durability and activity of the present system are greatly increased; possibly as a result of the stabilization of the components by chitosan confinement leading to consecutive multi-step electron transfer in equilibrium. The importance of the stabilization was also analysed by exchanging chitosan for relatively small and loose aggregates, anionic SDS (0.166 mol l À 1 ) and cationic CTAB (0.055 mol l À 1 , cetyl trimethyl ammonium bromide) micelles 37 .…”

“…From a photochemical point of view, the electron transfer is triggered by the absorption of a photon by a photosensitizer [13][14][15][16][17][18][19][20][21][22][23][24][25] . Since the first attempt by Sun and Åkermark 34 to construct an artificial photocatalytic system for H 2 evolution in 2003, a large number of synthetic model complexes have been pursued to mimic the structure and functionality of the diiron subunit of the natural [FeFe]-H 2 ase H-cluster [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] . It is encouraging to see that the catalytic efficiency for H 2 evolution from artificial photocatalytic systems using mimics of the diiron subsite of [FeFe]-H 2 ase as catalysts has been increased from null to more than hundreds or thousands of turnover numbers (TON) under different irradiation conditions.…”

Light to Hydrogen: Photocatalytic Hydrogen Generation from Water with Molecularly-Defined Iron Complexes

“…It should be noted here that a direct comparison of turnover numbers is sometimes intricate as it depends on the concentration of the involved components, i.e., WRC, PS and SR. Inspired by the above-mentioned lead structure several groups, e.g., Wang and Sun [61,62], as well as Hammarström [23], Ott [63] and Reek [64] successfully developed a variety of Fe-based WRC, which resulted in catalyst turnover numbers of up to 466 regarding Fe (Scheme 2). An overview of the applied PS is provided in Scheme 3; selected conditions and TONs are listed in Table 1.…”

Bis-(thiosemicarbazonato) Zn(ii) complexes as building blocks for construction of supramolecular catalysts

“…[25][26][27] Recently we also took advantage of the chromophoric character of porphyrins: the assembly of Zn(II)porphyrins onto a functionalised bis (thiolate)-bridged ([2Fe2S]) diiron-based hydrogenase catalyst led to a supramolecular complex that displayed photo-activity forming molecular hydrogen upon exposure to light in the presence of a proton source. 28 Since the supramolecular approach to catalyst exploration is very versatile we aimed at extending the concept to other building blocks. We demonstrated that the pyridyl analogues of classical BIAN-ligands could be used as the template ligand, 29 and we also showed that Zn(II)salphen building blocks can be used analogously to Zn(II)porphyrins.…”