Accessing the CpArNi(I) Synthon: Reactions with N‑Heterocyclic Carbenes, TEMPO, Sulfur, and Selenium
journal contributionposted on 02.05.2016, 18:04 by Uttam Chakraborty, Franziska Urban, Bernd Mühldorf, Christophe Rebreyend, Bas de Bruin, Niels van Velzen, Sjoerd Harder, Robert Wolf
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.