The deprotonation of 1-(1H-benzimidazol-2-yl)-3-methylbenzimidazolium hexafluorophosphate (2(Me)H(2)[PF6]) and 1-(1H-benzimidazol-2-yl)-3-isopropylbenzimidazolium hexafluorophosphate (2(iPr)H(2)[PF6]) with potassium tert-butoxide in THF afforded the benzimidazolium-benzimidazolates 2(Me)H and 2(iPr)H. The instant carbene behavior of these conjugated mesomeric betaines was demonstrated by trapping their carbenic tautomers 2'H-Me and 2'H-iPr with elemental sulfur and selenium, which afforded the corresponding thio- and selenourea derivatives 2'(HE)-H-Me and 2'(HE)-H-iPr (E = S, Se). The treatment of 2(Me)H and 2(iPr)H with nickelocene furnished the nickel(II) complexes [NiCp(2'(Me))] and [NiCp(2'(iPr))], which contain an anionic C,N-amido-chelating NHC ligand. The electronic structure and redox behavior of the nickel(II) chelates were investigated, as well as those of the closely related chelates [NiCp(1'(Me))] and [NiCp(1'(iPr))] derived from the corresponding imidazolium-benzimidazolates 1(Me)H and 1(iPr)H. According to DFT calculations, the highest occupied molecular orbital (HOMO) is located over the NiCp moiety and the pi system of the chelate ligand with a large contribution from the (benz-)imidazolate moiety. Cyclic voltammetry revealed a reversible oxidation to the monocation [NiCp(L)](+) (E-1/2 = 0.315, 0.222, 0.396, 0.265 V vs ferrocene/ferrocenium for L = 1'(Me), 1'(iPr), 2'(Me), 2'(iPr), respectively) in CH2Cl2/0.1 M n-Bu4N[B(Ar-F)(4)] (B(Ar-F)(4)(-) = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), and isosbestic behavior was found in UV-vis-NIR spectroelectrochemical experiments. The different redox potentials reflect the different donor/acceptor properties of the NHC part of the chelate ligands, with 1'(iPr) being the strongest and 2'(Me) the weakest net electron donor. The EPR spectroscopic signature of [NiCp(2'(Me))](+) in CH2Cl2/0.1 M n-Bu4N[B(Ar-F)(4)] at 100 K is consistent with a chelate-ligand-based radical with strong spin-orbit coupling to the Ni center. In contrast, the EPR spectra of [NiCp(1'(Me))]+, [NiCp(1'(iPr))]+, and [NiCp(2'(iPr))]+ indicate that these monocations are best described as Ni-III complexes, the comparatively higher contribution of the Ni-III(L) vs the Ni-II(L center dot+) valence tautomer being supported by the results of open-shell DFT calculations.