Molecular and Electronic Structures of One‐Electron Oxidized Ni^II–(Dithiosalicylidenediamine) Complexes: Ni^III–Thiolate versus Ni^II–Thiyl Radical States

Abstract

The dithiosalicylidenediamine Ni II complexes [Ni(L)] (R=tBu, R'=CH2C(CH3)2CH2 1, R'=C6H4 2; R=H, R'=CH2C(CH3)2CH2 3, R'=C6H4 4) have been prepared by transmetallation of the tetrahedral complexes [Zn(L)] (R=tBu, R'=CH2C(CH3)2CH2 7, R'=C6H4 8; R=H, R'=CH2C(CH3)2CH2 9, R'=C6H4 10) formed by condensation of 2,4-di-R-thiosalicylaldehyde with diamines H2N-R'-NH2 in the presence of Zn II salts. The diamagnetic mononuclear complexes [Ni(L)] show a distorted square-planar N2S2 coordination environment and have been characterized by 1H- and 13C NMR and UV/Vis spectroscopies and by single-crystal X-ray crystallography. Cyclic voltammetry and coulombic measurements have established that complexes 1 and 2, incorporating tBu functionalities on the thiophenolate ligands, undergo reversible one-electron oxidation processes, whereas the analogous redox processes for complexes 3 and 4 are not reversible. The one-electron oxidized species, 1+ and 2+, can be generated quantitatively either electrochemically or chemically with 70 % HClO4. EPR and UV/Vis spectroscopic studies and supporting DFT calculations suggest that the SOMOs of 1+ and 2+ possess thiyl radical character, whereas those of 1(py)2 + and 2(py)2 + possess formal Ni III centers. Species 2+ dimerizes at low temperature, and an X-ray crystallographic determination of the dimer [(2)2](ClO4)2.2 CH2Cl2 confirms that this dimerization involves the formation of a S-S bond (S...S=2.202(5) A).

A Bio‐Inspired Switch Based on Cobalt(II) Disulfide/Cobalt(III) Thiolate Interconversion

“…Such a phenomenon has been described for a mononuclear Ni II thiyl radical complex, which rapidly undergoes an irreversible dimerization process involving the formation of an SÀS bond. [12] Two conditions seem to be required for such metal-based disulfide/thiolate interconversion process to occur reversibly. First, the redox potential of the RSSR/2RS À and M n+ /M (nÀ1)+ redox couples should be close enough to allow a small structural modification to address the direction of the internal electron transfer between the ligand and the metal.…”

Aromatic Versus Heteroradialene Character in Extended Thiophloroglucinol Ligands and their Trinuclear Nickel(II) Complexes

“…[108][109][110][111][112][113] The CS resonances in the thiophloroglucinol systems shift from about 189 to about 155 ppm on complexation, whereas the CO resonances in the phloroglucinol systems shift from about 185 to about 170 ppm. [108][109][110][111][112][113] The CS resonances in the thiophloroglucinol systems shift from about 189 to about 155 ppm on complexation, whereas the CO resonances in the phloroglucinol systems shift from about 185 to about 170 ppm.…”

“…Comparisons for the evaluation of the change in the heteroradialene character in the thiophloroglucinol ligands on complexation are limited, as the chemical shifts for the mononuclear Ni II thiosalen complexes are not assigned if provided at all. [108][109][110][111][112][113] The CS resonances in the thiophloroglucinol systems shift from about 189 to about 155 ppm on complexation, whereas the CO resonances in the phloroglucinol systems shift from about 185 to about 170 ppm. This much Scheme 3.…”

Subkomponenten‐Selbstorganisation und Transmetallierung zweikerniger Helikate

“…[16] ¾hnliches Verhalten wurde bereits zuvor für Transmetallierungen einkerniger Zink-, Nickel- [17] und Palladiumkomplexe [18] …”

“…Als thermodynamische Triebkraft dieser Metallaustauschreaktionen kann die bevorzugte Koordination der weichen N,S-Bindungsgruppen an das weichere Metallzentrum angenommen werden. [16] ¾hnliches Verhalten wurde bereits zuvor für Transmetallierungen einkerniger Zink-, Nickel- [17] und Palladiumkomplexe [18] mit Schwefel-Stickstoff-Koordination beobachtet. Um ein besseres Verständnis für die Prinzipien der Transmetallierungen zu erhalten, wurden Austauschreaktionen zwischen den Helikaten 3, 4 und 5 untersucht.…”