Abstract
The stable nickel(III) complex [NiIII(H2IMe)(P(o-C6H3-3-SiMe3-2-S)3)] (1) (H2IMe = 1,3-dimethylimidazole-2-ylidene) was isolated from the reaction of [PPN][NiIII(OMe)(P(o-C6H3-3-SiMe3-2-S)3)] with 1,3-dimethylimidazolium iodide. Complex 1, characterized by UV-vis, EPR, SQUID, CV, and single-crystal X-ray diffraction, has a five-coordinate distorted trignoal bypyramidal geometry in Ni(III) center. Reaction of complex 1 and KC8 in THF-MeCN at ambient temperature led to the isolation of Ni(II) complex [K-18-crown-6-ether][NiII(H2IMe)(P(o-C6H3-3-SiMe3- 2-S)3)] (2). Interestingly, complex 2 is not EPR-silent. The unpaired electron probably delocalizes both on the Ni center and the NHC ligand. The Ni(IV) complex [NiIV(H2IMe)(P(o-C6H3-3-SiMe3-2-S)3)][BF4] (5) was synthesized by reaction of complex 1 and nitrosonium tetrafluoroborate ([NO][BF4]). The oxidation state of Ni center and the central metal coordinating environment of complex 5 were characterized by X-ray absorption (Ni K-edge) of XANES and EXAFS, respectively. Bubbling dry and high-purity carbon dioxide gas into the stirring THF-DMF solution of complex 2 at room temperature for minutes led to the formation of complex 1.