Several New [Fe]Hydrogenase Model Complexes with a Single Fe Center Ligated to an Acylmethyl(hydroxymethyl)pyridine or Acylmethyl(hydroxy)pyridine Ligand

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Abstract

We have developed two novel synthetic methods, by which two types of mononuclear Fe model complexes for the active site of [Fe]hydrogenase are successfully synthesized. The first type of 2-acylmethyl-6-hydroxymethylpyridine-containing complexes, [2-COCH2-6-HOCH2C5H3N]Fe(CO)2G (1, G = PhCO2; 2, PhCOS; 3, PhCS2; 4, 2-S-6-MeC5H3N), were prepared by a “one-pot” method involving reaction of 2-TsO-6-HOCH2C5H3N (Ts = 4-MeC6H4SO2) with Na2Fe(CO)4 followed by treatment of the resulting Fe(0) intermediate [Na(2-CH2-6-HOCH2C5H3N)Fe(CO)4] (M1) with (PhCO2)2, (PhCOS)2, (PhCS2)2, and (2-S-6-MeC5H3N)2 in 49–72% yields, respectively. The second type of 2-acylmethyl-6-hydroxypyridine-containing complexes, (2-COCH2-6-HOC5H3N)Fe(CO)2(2-SCO-6-RC5H3N) (9a, R = MeO; 9b, R = PhS), could be prepared via a multiple-step synthetic method. This method involves (i) treatment of 2-ClCO-6-RC5H3N (R = MeO, PhS) with NaSH followed by acidification with diluted HCl to give 2-HSCO-6-RC5H3N (5a, R = MeO; 5b, R = PhS); (ii) further treatment of 5a,b with KOH to afford 2-KSCO-6-RC5H3N (6a, R = MeO; 6b, R = PhS); (iii) treatment of 2-TsOCH2-6-PMBOC5H3N (PMB = 4-MeOC6H4CH2) with Na2Fe(CO)4 followed by treatment of the resulting Fe(0) intermediate [Na(2-CH2-6-PMBOC5H3N)Fe(CO)4] (M2) with Br2 or I2 to produce (2-COCH2-6-PMBOC5H3N)Fe(CO)3X (7a, X = Br; 7b, X = I); (iv) further treatment of 7a,b with 6a,b to yield (2-COCH2-6-PMBOC5H3N)Fe(CO)2(2-S-6-RC5H3N) (8a, R = MeO; 8b, R = PhS); and (v) finally, removal of the PMB groups from 8a,b under the action of deprotecting reagent CF3CO2H/EtSH to give complexes 9a,b. All compounds 1–4 and 5a,b–9a,b with the exception of 7b are new and have been characterized by elemental analysis, spectroscopy, and, particularly for 1, 4, and 7a–9a, X-ray crystallography.

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