Simple rubredoxin model complexes with o-(acylamino)benzenethiolato and 2,6-(diacylamino)benzenethiolato were synthesized and characterized by (1)H NMR, IR, and electrochemical properties. The structures of (NEt(4))(2)[Fe(II)(S-o-t-BuCONHC(6)H(4))(4)].2EtCN (3a), (NEt(4))(2)[Co(II)(S-o-t-BuCONHC(6)H(4))(4)].2EtCN (3b), and (PPh(4))(2)[Co(II){S-2,6-(CF(3)CONH)(2)C(6)H(3)}(4)].Et(2)O (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. (NMe(4))(2)[Fe(II)(S-o-CH(3)CONHC(6)H(4))(4)] (2a) and (NMe(4))(2)[Fe(II){S-2,6-(CH(3)CONH)(2)C(6)H(3)}(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 (PPh(4))(2)[Co(II){S-2,6-(CF(3)CONH)(2)C(6)H(3)}(2)(S-2-CF(3)CONH-6-CF(3)CONC(6)H(3))].Et(2)O (9) are also described.

Iron-sulfur clusters containing a singly or doubly NH.S hydrogen-bonded arenethiolate ligand, [Fe(4)S(4)(S-2-RCONHC(6)H(4))(4)](2)(-) (R = CH(3), t-Bu, CF(3)), [Fe(4)S(4){S-2,6-(RCONH)(2)C(6)H(3)}(4)](2)(-), [Fe(2)S(2)(S-2-RCONHC(6)H(4))(4)](2)(-) (R = CH(3), t-Bu, CF(3)), and [Fe(2)S(2){S-2,6-(RCONH)(2)C(6)H(3)}(4)](2)(-), were synthesized as models of bacterial [4Fe-4S] and plant-type [2Fe-2S] ferredoxins. The X-ray structures and IR spectra of (PPh(4))(2)[Fe(4)S(4){S-2,6-(CH(3)CONH)(2)C(6)H(3)}(4)].2CH(3)CN and (NEt(4))(2)[Fe(2)S(2){S-2,6-(t-BuCONH)(2)C(6)H(3)}(4)] indicate that the two amide NH groups at the o,o'-positions are directed to the thiolate sulfur atom and form double NH.S hydrogen bonds. The NH.S hydrogen bond contributes to the positive shift of the redox potential of not only (Fe(4)S(4))(+)/(Fe(4)S(4))(2+) but also (Fe(4)S(4))(2+)/(Fe(4)S(4))(3+) in the [4Fe-4S] clusters as well as (Fe(2)S(2))(2+)/(Fe(2)S(2))(3+) in the [2Fe-2S] clusters. The doubly NH.S hydrogen-bonded thiolate ligand effectively prevents the ligand exchange reaction by benzenethiol because the two amide NH groups stabilize the thiolate by protection from dissociation.