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 ų, D_c= 1.792 g cm^–3(Z= 2), µ(Mo-K_α)= 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.