Abstract
For the biomimetic nickel(II) thiolate-thiol and nickel (III)-thiolate complexes A series of mononuclear, distorted square planar complexes [NiII(X)(P(o-C6H4S)2(o-C6H4SH))]- (X = Se-p-C6H4-Cl (1), 2-S-C4H3S (2), Cl (9)) and [NiII(PPh3)(P(o-C6H4S)2(o-C6H4SH))] (5a)/(5b) with a S-H proton directly interacting with nickel atom or with both nickel and sulfur atoms were synthesized. The presence of intramolecular [Ni•••H-SR] interaction or combinations of intramolecular [Ni-S•••H-SR]/[Ni•••H-SR] interactions were verified in the solid state by the IR □SH stretching bands, the exo-thiol protons resonances of 1H NMR spectra and subsequently confirmed by single crystal X-ray diffraction studies. The exo-thiol proton in complexes 1, 2, and 5a was identified as a D2O exchangeable proton from NMR and IR studies. Based on the observations of IR νS-H stretching frequencies, the extent of interactions (exo-thiol interaction modes ([Ni-S…H-S], [Ni…H-S] or combinations)) was modulated by the electronic density surrounding nickel resulting from the distinct terminally-coordinated donor ligands [Se-p-C6H4-Cl]-, [SePh]-, [S-C4H3S]-, [Cl]-, and PPh3 in these NiII-exo-thiol complexes 1, 2, 5a, 5b, 8, and 9. Instead of the ligand-based oxidation to form dinuclear Ni(II) complexes and dichalcogenide, oxidation of THF-CH3CN solution of complexes 1 and 2 by O2 resulted in the formation of the mononuclear, distorted trigonal bipyramidal [NiIII(X)(P(o-C6H4S)3)]- (X = Se-p-C6H4-Cl (3), 2-S-C4H3S (4)) accompanied by byproduct H2O identified by 1H NMR. Also, the reaction of dry O2 with THF solution of complex 5a/5b afforded the mononuclear, distorted trigonal bipyramidal [NiIII(PPh3)(P(o-C6H4S)3)] (6). Reduction of complex 6 or deprotonation of complex 5a/5b yielded [NiII(PPh3)(P(o-C6H4S)3)]- (7), which also displayed the distorted trigonal bipyramidal geometry. The EPR spectra of complexes 3 and 4 exhibiting high rhombicities with three principal g values of 2.30, 2.09 and 2.0 are consistent with Ni(III) with the odd electron in the dz2 orbital. Complexes 3, 4, and 6 undergoes a reversible NiIII/II process at E1/2 = -1.17 V in CH3CN (complexes 3 and 4) and -0.865 V (complex 6) in CH2Cl2 (vs Cp2Fe/Cp2Fe+), respectively. In addition, the single crystal X-ray diffraction studies of complex [NiII(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] (10a/10b) give the evidence that the exo-thiol protons of the Ni(II) exo-thiol complexes 1, 2, 5a, 5b and 9 were attracted by nickel atom and sulfur atom of thiolate, resulting in the intramolecular interactions (combinations of [Ni-S…H-S]/[Ni…HS] or [Ni…HS]). Reaction of complex 10 with [SPh]- and [SePh]- led to the formation of [NiII(EPh)(P(o-C6H4S)2(o-C6H4-SCH3))]- (E = S (11); Se (12)). Combinations of 1H NMR spectra and single-crystal X-ray diffraction studies of mononuclear NiII exo-thioehter complexes 10a, 10b, 11, and 12 revealed that the intramolecular interaction between NiII and thioether sulfur atom became weaker when the temperature is increased or the more electron-donating terminal ligand is ligated to NiII center. For the iron-thiolate nitrosyl complexes The five-coordinated iron-thiolate nitrosyl complexes [PPN][Fe(NO)(S,S-C6H2-3,6-Cl2)2] (13), [PPN]2[Fe2(NO)2(S,SO2-C6H2-3,6-Cl2)2(S,S-C6H2-3,6-Cl2)2] (14), [PPN]2[(NO)Fe(S,S-C6H2-3,6-Cl2)2] (15), and [PPN]2[Fe(NO)(S,SO2-C6H2-3,6-Cl2)(S,S-C6H2-3,6-Cl2)] (16) have been isolated and characterized by IR, UV/vis, NMR spectra and X-ray crystallography. Upon contact with dry O2, iron-thiolate nitrosyl complex 13 containing {Fe(NO)}6 core trigger sulfur oxygenation to yield the S-bonded monosulfinate iron complex 14. Reduction of complex 13 by [EtS]- yields complex 15 with a bent Fe-N-O bond angle of 153.4□. Compared to the reaction of O2 with complex 13, there is to a certain extent an attack of O2 on the •NO radical of complex 15 containing {Fe(NO)}7 core leading to the formation of complex 13 accompanied by the minor products, [Fe(S,S-C6H4)2]22– and [NO3]–. Treatment of 1 equiv of [EtS]– and complex 14 in CH3CN-THF yields complex 16 along with (EtS)2 identified by 1H NMR. Compared to complex 15, complex 16 with the less electron-donating sulfinate ligand coordinated to {FeNO}7 core were oxidized by O2 to yield complex 14. Obviously, the electronic perturbation of the {Fe(NO)}7 core caused by the coordinated sulfinate in complex 16 may serve to regulate the reactivity of complex 16 toward O2. The iron-sulfinate nitrosyl species with {Fe(NO)}6/7 core exhibit the photolabilization of sulfur-bound [O] moiety under irradiation. The interconversion of complexes 13-14-16-15 may provide some clues to the transformation pathways between the active and inactive NO-bound forms of Fe-containing nitrile hydratase.