Functional Hydride Transfer by a Thiolate‐Containing Model of Mono‐Iron Hydrogenase featuring an Anthracene Scaffold

Abstract

We report the synthesis, X-ray structure and functional biomimetic activity of a model complex of mono-iron hydrogenase (Hmd). To achieve the desired biomimetic fac-CNS(thiolate) ligation motif, an anthracene framework is used to provide the requisite donors in a single chelate. A bulky aryl thiolate (ortho dimethylphenyl) is included to achieve mononuclearity. In addition to exhibiting structural (X-ray) and spectroscopic (NMR, IR) similarity to the enzyme, the complex is competent for H activation (heterolysis) and hydride transfer to a model substrate-mimicking the functional behavior of the enzyme in a biomimetic CNS coordination sphere for the first time.

Biomimetic Hydrogenation Catalyzed by a Manganese Model of [Fe]‐Hydrogenase

“…However, the Fe‐acyl moiety was prone to decomposition via decarbonylation so that catalysis could not be achieved. Two Fe models supported by an anthracene‐bridged NCS ligand could also activate H 2 . Notably these two models contained a carbamoyl donor, instead of the acyl donor found in the enzyme.…”

“…Notably these two models contained a carbamoyl donor, instead of the acyl donor found in the enzyme. Among them, the neutral derivative 3 (Figure d) mediated the hydrogenation of 2,6‐difluoro(phenyl)‐2‐(4‐ethyl)imidazolium cation, a model of methenyl‐H 4 MPT + . Despite this progress, none of the previous Fe models achieved turnovers in hydrogenation reactions.…”

Scaffold-based [Fe]-hydrogenase model: H2 activation initiates Fe(0)-hydride extrusion and non-biomimetic hydride transfer

“…Complex 2 with base. Provided our previous work, 18 we postulated that an extra equivalent of base in solution would drive H 2 activation and prevent protonation of the methine-C responsible for ligand loss. Therefore, 1 was rst treated with two equiv.…”

“…It is proposed that Hmd utilizes the pendant pyridonate-O as a proton acceptor to facilitate heterolytic cleavage of H 2 . Due to the absence of this basic functionality in the present ligand design, we previously reported 18 Extraction of the resulting powder into MeCN produced Xray quality crystals at À20 C. The resulting structure (Fig. 2) revealed a remarkable result: a dimeric complex in which two iron centers bridge via the formation of a new Fe-C bond between the deprotonated methine-C (formerly the methylene unit) of adjacent, identical units.…”

“…Hu and coworkers developed functional systems derived from hybrid molecule|protein systems 15 and a small molecule system that incorporates an abiotic diphosphine ligand with a pendant amine base. 16 Our group has reported model systems capable of hydride abstraction 17 (the enzymatic ‘reverse’ reaction) and hydride transfer 18 (enzymatic ‘forward’ reaction) with biomimetic substrates. However, both of our reported systems replicated the strong trans influence of the Fe–C acyl σ bond in the form of ‘carbamoyl’ ligation ( i.e.…”