Niobium isocyanide complexes,Nb(CNAr)6, with Ar = 2,6‐dimethylphenyl (Xyl), a diamagnetic dimer containing four reductively coupled isocyanides,and Ar = 2,6‐diisopropylphenyl (Dipp), a paramagnetic monomer analogous to the highly unstable hexacarbonylniobium(0)

Treatment of bis(mesitylene)niobium(0) with 6–7 equivalents of 2,6‐dimethylphenyl isocyanide (CNXyl) affords two products with the empirical formula Nb(CNXyl)_n (n = 7 or 6), which have been shown to be the diamagnetic dimers bisμ‐N,N′,N′′,N′′′‐tetrakis(2,6‐dimethylphenyl)squaramidinato(2?)]bispentakis(2,6‐dimethylphenyl isocyanide)niobium(I)], Nb₂(C₉H₉N)₁₀(C₃₆H₃₆N₄)] or Nb(CNXyl)₅]₂μ‐C₄(NXyl)₄]·xSolvent, 1 , and bisμ‐N,N′,N′′,N′′′‐tetrakis(2,6‐dimethylphenyl)squaramidinato(2?)]bistetrakis(2,6‐dimethylphenyl isocyanide)niobium(I)] tetrahydrofuran trisolvate, Nb₂(C₉H₉N)₈(C₃₆H₃₆N₄)]·3C₄H₈O or Nb(CNXyl)₄]₂μ‐C₄(NXyl)₄]·3THF (THF = tetrahydrofuran), 2 . Each contains Nb^I bound to either five or four terminal isocyanides, respectively, and to an unprecedented bridging tetraarylsquaramidinate(2?) unit, coordinated as a bidentate ligand to each niobium center, symmetrically due to the crystallographic inversion center that coincides with the centroid of the central C₄ unit. Thus, in the presence of CNXyl, the bis(mesitylene)niobium(0) is oxidized to niobium(I), resulting in the facile loss of both mesitylene groups and the reductive coupling of two CNXyl groups per niobium to provide the first examples of tetraarylsquaramidinate(2?) ligands, cyclo‐C₄N₄Ar₄]^2?, coordinated to metals. In contrast, bis(mesitylene)niobium(0) reacts with the more crowded 2,6‐diisopropylphenyl isocyanide (CNDipp) to afford the paramagnetic monomer hexakis(2,6‐diisopropylphenyl isocyanide)niobium(0), Nb(C₁₃H₁₇N)₆] or Nb(CNDipp)₆, 3 , the first zero‐valent niobium isocyanide analog of the highly unstable Nb(CO)₆, which is presently only known to exist in an argon matrix at 4.2 K.