A compound containing two tantalum atoms in oxidation states separated by six units

Reaction of [Et4N][Ta(CO)(6)] (1) and Hhpp, Hhpp = 1,3,4,6,7,8-hexahydro-2H -pyrimido[1,2-a] gives a mixed-valent tantalum compound [Ta(hpp)(4)][Ta(CO) (6)] (2). It contains the eight-coordinate Ta(V) cation [Ta(hpp)(4)](+), ac companied by the homoleptic hexacarbonyltantalate(- I) anion from the start ing material. Thus, the oxidation numbers fdr the tantalum atoms span a ran ge of six units. This is the first complex containing four chelating hpp an ions. Crystal structures of 1, 2 and [Ph4P][Ta(CO)(6)] (3) were determined by X-ray crystallography. (C) 2000 Elsevier Science S.A. All rights reserve d.