Synthesis and characterisation of polymeric materials consisting of {Fe2(CO)5}-unit and their relevance to the diiron sub-unit of [FeFe]-hydrogenase

Abstract

By using "click" chemistry between a diazide and a diiron model complex armed with two alkynyl groups, two polymeric diiron complexes (Poly-Py and Poly-Ph) were prepared. The two polymeric complexes were investigated using infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), Mössbauer spectroscopy, and cyclic voltammetry (Poly-Py only, due to the insolubility of Poly-Ph). To probe the coordinating mode of the diiron units in the two polymeric complexes, two control complexes (3 and 4) were also synthesised using a monoazide. Complexes 3 and 4 were well characterised and the latter was further crystallographically analysed. It turns out that in both complexes (3 and 4) and the two polymeric diiron complexes, one of the two iron atoms in the diiron unit coordinates with one of the triazole N atoms. Our results revealed that both morphologies and properties of Poly-Py and Poly-Ph are significantly affected by the organic moiety of the diazide. Compared to the protonating behaviour of the complexes 3 and 4, Poly-Py exhibited proton resistance. In electrochemical reduction, potentials for the reduction of the diiron units in Poly-Py and hence its catalytic reduction of proton in acetic acid-DMF shifted by over 400 mV compared to those for complexes 3 and 4. It is likely that the polymeric nature of Poly-Py offers the diiron units a "protective" environment in an acidic medium and more positive reduction potential.

Diiron Complexes with Pendant Phenol Group(s) as Mimics of the Diiron Subunit of [FeFe]‐Hydrogenase: Synthesis, Characterisation, and Electrochemical Investigation

“…Electrochemistry was performed as described elsewhere. [23,28,33,36] All potentials were quoted against the ferrocenium/ferrocene couple, F C + /F C . The microanalysis service was provided by the Centre of Analysis and Testing at Nanchang University and Nanjing University.…”

“…The structure proposed is based on the facts that the anti form is dominant in complexes of this type and that it is not unprecedented that one of the phenolate groups coordinates the iron atom in a basal position rather than in an axial position. [26,33] Plotting the absorption bands of a known diiron tetracarbonyl complex against the bands of the product produces a linear correlation ( Figure S2), which serves as further support for the proposed tetracarbonyl product. Despite our attempts at using bulky organic cations, for example, Ph 4 PBr or But 4 NBF 4 , isolating this product was not successful because of its instability as we observed previously for the monophenolate analogue.…”

Introducing polyethyleneimine (PEI) into the electrospun fibrous membranes containing diiron mimics of [FeFe]-hydrogenase: Membrane electrodes and their electrocatalysis on proton reduction in aqueous media

“…To this end, we have tried a number of strategies to develop polymeric materials functionalised with diiron mimics, (ⅰ) directly polymerising diiron model complexes containing an alkynyl group [44,45]; (ⅱ) using "click chemistry" reaction between an alkynyl and an organic azide [46]; (ⅲ) chemically immobilising diiron mimics onto commercially available polymers such as PVC (polyvinyl chloride) and PEI (polyenthylenimine) [36,47]; (ⅳ) incorporating a diiron mimic into fibrous membranes via electrospinning technique [48].…”

Using polyethyleneimine (PEI) as a scaffold to construct mimicking systems of [FeFe]‐hydrogenase: preparation, characterization of PEI‐based materials, and their catalysis on proton reduction

“…Further improvement was achieved by anchoring diiron models into pro‐polymerized polypyrrole film via diffusion and then chemical reaction . Recently, we reported polymeric systems functionalized with diiron mimics prepared either by polymerizing diiron models possessing alkynyl group(s) or by joining the model to an organic diazide via ‘click’ chemistry . Those functionalized polymers were successfully employed to construct film electrodes that exhibited electrochemical responses in the presence or absence of an acid.…”