Niobium isocyanide complexes, Nb(CNAr), 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 hexacarbonyln

Author(s) Kucera, B.E.; Roberts, C.J.; Young, V.G.; Brennessel, W.W.; Ellis, J.E.
Journal Acta Crystallogr C Struct Chem
Date Published 2019 09 01
Abstract

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 = 7 or 6), which have been shown to be the diamagnetic dimers bis[μ-N,N',N'',N'''-tetrakis(2,6-dimethylphenyl)squaramidinato(2-)]bis[pentakis(2,6-dimethylphenyl isocyanide)niobium(I)], [Nb(CHN)(CHN)] or [Nb(CNXyl)][μ-C(NXyl)]·xSolvent, 1, and bis[μ-N,N',N'',N'''-tetrakis(2,6-dimethylphenyl)squaramidinato(2-)]bis[tetrakis(2,6-dimethylphenyl isocyanide)niobium(I)] tetrahydrofuran trisolvate, [Nb(CHN)(CHN)]·3CHO or [Nb(CNXyl)][μ-C(NXyl)]·3THF (THF = tetrahydrofuran), 2. Each contains Nb 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 C 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-CNAr], 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(CHN)] or Nb(CNDipp), 3, the first zero-valent niobium isocyanide analog of the highly unstable Nb(CO), which is presently only known to exist in an argon matrix at 4.2 K.

DOI 10.1107/S205322961901101X
ISSN 2053-2296
Citation Kucera BE, Roberts CJ, Young VG, Brennessel WW, Ellis JE. Niobium isocyanide complexes, Nb(CNAr), 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 hexacarbonyln. Acta Crystallogr C Struct Chem. 2019;75(Pt 9):1259-1265.

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