Novel Rubredoxin Model Tetrathiolato Iron(II) and Cobalt(II) Complexes Containing Intramolecular Single and Double NH···S Hydrogen Bonds

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Abstract
Simple rubredoxin model complexes with o-(acylamino)benzenethiolato and 2,6-(diacylamino)benzenethiolato were synthesized and characterized by 1H NMR, IR, and electrochemical properties. The structures of (NEt4)2[FeII(S-o-t-BuCONHC6H4)4]·2EtCN (3a), (NEt4)2[CoII(S-o-t-BuCONHC6H4)4]·2EtCN (3b), and (PPh4)2[CoII{S-2,6-(CF3CONH)2C6H3}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(II)), by 0.024 Å (3a), 0.032 Å (3b), and 0.029 Å (5b ‘), respectively. (NMe4)2[FeII(S-o-CH3CONHC6H4)4] (2a) and (NMe4)2[FeII{S-2,6-(CH3CONH)2C6H3}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 [FeII(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[CoII{S-2,6-(CF3CONH)2C6H3}2(S-2-CF3CONH-6-CF3CONC6H3)]·Et2O (9) are also described.

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