Novel rubredoxin model tetrathiolato iron(II) and cobalt(II) complexes containing intramolecular single and double NH•••S hydrogen bonds

Simple rubredoxin model complexes with o-(acylamino)benzenethiolato and 2,6 -(diacylamino)benzenethiolato were synthesized and characterized by H-1 NMR, IR, and electrochemical properties. The structures of (NEt4)(2)-[Fe-II(S-o-t-BuCONHC6H4] . 2EtCN (3a), (NEt4)(2)[Co-II(S-o-t-BuCONHC6H4)(4)]. 2EtCN (3b), and (PPh4)(2)[Co-II{S-2,6-(CF3CONH)(2)C6H3}(4)] . Et2O (5b') were determined by X-ray analysis. The complexes have intramolecular single or double NH ... S hydrogen bonds. The mean Fe-S and Co-S distances are significantly shorter than those of non-hydrogen-bonding complexes, [M(SPh)(4)](2-)(M = Fe(II), Co(LI)), by 0.024 Angstrom (3a), 0.032 Angstrom (3b), and 0.029 Angstrom (5b'), respectively. (NMe4)(2)[Fe-II(S-o-CH3CONHC6H4)(4)] (2a) and (NMe4)(2)[Fe-II{S-2,6-(CH3CONH)(2)C6H3}4] (6a) have remarkably positive shifted Fe(III)/Fe(II) redox couples by the single and double NH ... S hydrogen bond, respectively. The shifts are +0.25 for 2a and +0.56 for 6a from the redox potential of [Fe-II(SPh)(4)](2-), which indicate additivity of the effect of the NH ... S hydrogen bond. The formation and the structure of a novel chelating amido(thiolato) complex (PPh4)(2)[Co-II{S-2,6-(CF3CONH)(2)C6H3}(2)(S-2-CF3CONH-6-CF3CONC6H3)]. Et2O (9) are also described.