New carbonyl derivatives of niobium(I) and tantalum(I)
Abstract
The hexacarbonylmetalates(1–) of niobium and tantalum are oxidised by H+ and halogens to give the [M2X3(CO)8]– anions (X = Cl, Br, or I). By exchange reactions, the µ-acetato- and µ-methoxo-complexes (X = O2CMe or OMe) were also obtained. The crystal and molecular structure of [H(thf)2][Nb2Cl3(CO)8] was investigated by X-ray diffraction methods. Crystals are triclinic, space group P, with a= 16.283(3), b= 9.293(2), c= 9.050(2)Å, α= 113.01(2), β= 96.56(2), γ= 98.39(2)°, U= 1 224.7 Å3, Dc= 1.792 g cm–3(Z= 2), µ(Mo-Kα)= 12.2 Cm–1. The two niobium atoms of the dimeric anion are bridged by three chlorides located at the vertices of an approximately equilateral triangle perpendicular to the niobium-niobium vector [Nb ⋯ Nb 3.631 (1)Å]. The seven-co-ordination of niobium is completed by four carbonyl groups. The dimeric chloride-bridged complexes of niobium(I) and tantalum(I) undergo the following reactions: (a) reduction by sodium to the hexacarbonylmetalate(1 –); (b) chloride substitution by C5H5– to the cyclopentadienyl derivatives [M(η5-C5H5)(CO)4] in good yields and by arenes in the presence of aluminium bromide to the new cationic complexes [M (η6-arene)(CO)4]+ as their hexa(bromo)chlorodialuminate derivatives.