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

Ten branched polymeric materials (PEI‐P‐Fe 2 s) derived from polyethyleneimine (PEI) functionalized with [Fe 2 (CO) 5 ]‐units to mimic [FeFe]‐hydrogenase were prepared. Before the functionalization , PEI was first premodified using diphenylphosphinamine (NPPh 2 ) group. In the premodification, three approaches were employed: (i) using PEI with an average molecular weight of 1800 and 600, respectively; (ii) grafting NPPh 2 group by either direct reaction of chlorodiphenylphosphine with PEI or Br(CH 2 ) 11 OPPh 2 ; and (iii) further premodification with BrCH 2 COOH after immobilization of the NPPh 2 group. Reaction of the premodified PEI with diiron hexacarbonyl complexes, [Fe 2 (μ‐S) 2 (CO) 6 ] (1), or [Fe 2 (μ‐S 2 C 2 H 4 )(CO) 6 ] (3) produced 10 functionalized materials, PEI‐P‐Fe 2 s. These materials were characterized using a variety of spectroscopic techniques, FTIR, NMR, TGA, and cyclic voltammetry. Spectral comparison with two control complexes, [Fe 2 (μ‐S) 2 (CO) 5 PPh 3 ] (2) and [Fe 2 (μ‐S 2 C 2 H 4 )(CO) 5 PPh 3 ] (4), suggested that the immobilized diiron units of PEI‐P‐Fe 2 s were dominantly pentacarbonyl analogous to complexes 2 and 4, although tetracarbonyl units may also exist because the amine groups of PEI could also be involved in substituting CO, as was the NPPh 2 group. The catalysis of these materials on proton reduction was examined in 0.1 mol l −1 [NBut 4 ]BF 4 /DMF containing acetic acid by using cyclic voltammetry. Our results indicated that both the presence of carboxylic acid and dangling the diiron units at the end of a long aliphatic chain improved catalytic efficiency by one‐fold. The improvement was attributed to the increase in flexibility of the catalytic center and enhancement of proton transfer during the catalysis . Copyright © 2013 John Wiley & Sons, Ltd.