Synthesis, structural characterization, and some properties of 2-acylmethyl-6-ester group-difunctionalized pyridine-containing iron complexes related to the active site of [Fe]-hydrogenase

Abstract

As biomimetic models for [Fe]-hydrogenase, the 2-acylmethyl-6-ester group-difunctionalized pyridine-containing iron(II) complexes 1–4 have been successfully prepared via the following three separate steps. In the first step, the acylation or esterification of difunctionalized pyridine 2-(p-MeC₆H₄SO₃CH₂)-6-HOCH₂C₅H₃N with acetyl chloride or benzoic acid gives the corresponding pyridine derivatives 2-(p-MeC₆H₄SO₃CH₂)-6-RCO₂CH₂C₅H₃N (A, R = Me; B, R = Ph). The second step involves reaction of A or B with Na₂Fe(CO)₄ followed by treatment of the intermediate Fe(0) complexes [Na(2-CH₂-6-RCO₂CH₂C₅H₃N)Fe(CO)₄] (M₁, R = Me; M₂, R = Ph) with iodine to afford 2-acylmethyl-6-acetoxymethyl or 6-benzoyloxymethyl-difunctionalized pyridine-containing Fe(II) iodide complexes [2-C(O)CH₂-6-RCO₂CH₂C₅H₃N]Fe(CO)₂I (1, R = Me; 3, R = Ph). Finally, when 1 or 3 is treated with sodium 2-mercaptopyridinate, the corresponding difunctionalized pyridine-containing Fe(II) mercaptopyridinate complexes [2-C(O)CH₂-6-RCO₂C₅H₃N]Fe(CO)₂(2-SC₅H₄N) (2, R = Me; 4, R = Ph) are produced. While the structures of model complexes 1–4 are confirmed by X-ray crystallography, the electrochemical properties of 2 and 4 are compared with those of the two previously reported models. In addition, complexes 2 and 4 have been found to be catalysts for H₂ production in the presence of TFA under CV conditions.