Reactions of Dinuclear Niobium(III) and Tantalum(III) Compounds with Alkyl Isocyanides To Give Dinuclear Products with Dimerized Isocyanides

Article abstract of DOI:10.1021/ja00335a021

Reactions of Nb2Cl6(SMe2)3 and Ta2Cl6(SMe2)3 with the isocyanides Me3CNC, Me2CHNC, and c-C6H11NC have been carried out under conditions where the products are all of the composition M2Cl6(RNC)6.All products have been characterized by elemental analysis and IR spectroscopy, and two compounds, Nb2Cl6(t-BuNC)6 (1) and Ta2Cl6(i-PrNC)6 (2), have been further studied by X-ray crystallography.Each of these compounds contains a tetradentate ligand, RNCCNR, formed by dimerization of the isocyanide; this ligand is bonded by its two central carbon atoms to a MCl2(CNR)4 group and through its nitrogen atoms to a MCl4 group.The first metal atom has roughly pentagonal bipyramidal coordination geometry with one Cl and the pair of carbon atoms at apical positions, while the second metal atom has essentially octahedral coordination geometry with the nitrogen atoms in cis positions.Crystallographic results are as follows.For 1: Pn; a = 14.102 (2) Amgstroem, b = 13.486 (5) Amgstroem, c = 11.157 (4) Amgstroem, β = 93.26 (2) deg, V = 2118 (1) Amgstroem³, Z = 2, R₁ = 0.0543, R₂ = 0.0727.For 2: P2₁/c; a = 18.014 (8) Amgstroem, b = 11.862 (4) Amgstroem, c = 17.948 (5) Amgstroem, β = 98.23 (3) deg, V = 3796 (4) Amgstroem³, Z = 4, R₁ = 0.0621, R₂ = 0.0741.The compounds are diamagnetic, and this is explained by using an MO scheme that leads to the occupation of a delocalized ? MO by both of the metal d electrons.