Diiron azadithiolates with hydrophilic phosphatriazaadamantane ligand as iron-only hydrogenase active site models: Synthesis, structure, and electrochemical study

Abstract

Three novel complexes (μ-adt)[Fe 2(CO) 5PTA] ( 2-PTA), (μ-adt)[Fe 2(CO) 4PTA 2] ( 2-PTA 2 ) and (μ-adt)[Fe 2(CO) 5DAPTA] ( 2-DAPTA), where adt is SCH 2N(CH 2CH 2CH 3)CH 2S, PTA stands for 1,3,5-triaza-7-phosphaadamantane and DAPTA is 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, were prepared as the models of the iron hydrogenase active site through controlled CO displacement of (μ-adt)[Fe 2(CO) 6] with PTA and DAPTA. The coordination configurations of 2-PTA and 2-PTA 2 were characterized by X-ray crystallography. The disubstituted diiron complex 2-PTA 2 features a basal/apical coordination mode, instead of the typical transoid basal/basal configuration. Protonation of three complexes only occurred at the bridging-N atom, rather than at the tertiary nitrogen atom on the PTA or DAPTA ligands. Electrochemical properties of the complexes were studied in acetonitrile or a mixture of acetonitrile and water in the presence of acetic acid, by cyclic voltammetry. The current sensitivity of the reduced species to acid concentration in the presence of H 2O is greater than in the pure CH 3CN solution.