Accessing the CpArNi(I) Synthon: Reactions with N‑Heterocyclic Carbenes, TEMPO, Sulfur, and Selenium

A reactive “CpArNiI” surrogate (CpAr = C5(C6H4-4-Et)5) is accessible via the reduction of the dimer [CpArNi­(μ-Br)]2 with two equivalents of KC8. A trapping reaction with TEMPO afforded the new nickel­(II) complex [CpArNi­(η2-TEMPO)] (3), while the addition of N-heterocyclic carbenes gave the new nickel­(I) radicals [CpArNi­(IPr)] (4a, IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) and [CpArNi­(IiPr2Me2)] (4b, IiPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). EPR spectra supported by DFT calculations on 4a and 4b indicate that the spin density mainly resides at the nickel center. The reaction of the “CpArNi­(I) source” with yellow sulfur gave the Ni2S6 complex [(CpArNi)2(μ-S6)] (5); the “subselenide” [(CpArNi)2(μ-Se2)] (6) was formed in the analogous reaction with grey selenium. All new complexes were characterized by NMR, EPR, and UV–vis spectroscopy; their molecular structures were determined by X-ray crystallography.