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 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.