Electron-transfer processes with substituted group 5 metal carbonyls. Synthesis, crystal and molecular structure of Ag 3M 3(CO) 12(Me 2PCH 2CH 2PMe 2) 3, M = Nb, Ta, the first structurally characterized carbonyl derivatives of niobium(0) and tantalum(0)

Abstract

Some new tetracarbonyl derivatives of tantalum(I), TaI(CO) 4LL (LL = tmeda, dppm, 2,2′-dipy), have been obtained by diiodine oxidation of [Ta(CO) 6] − in the presence of the bidentate ligand. Dicyclopentadienylcobalt(II) does not react with the tetracarbonyl dppe derivatives of niobium(I) and tantalum(I), MI(CO) 4dppe, whereas the corresponding pentamethyl substituted complex, CoCp 2 ★, carries out the two-electron transfer to form [CoCp 2 ★][M(CO) 4dppe]. Finally, oxidation of the [M(CO) 4dmpe] − anion, M = Nb, Ta, with the silver(I) salts AgNO 2 and AgBF 4 gave the hexanuclear mixed metal clusters Ag 3M 3(CO) 12(dmpe) 3, which were studied by X-ray diffraction methods. Crystals of Ag 3Nb 3(CO) 12(dmpe) 3 are rhombohedric, space group R 3 c, hexagonal setting, No. 167, a 14.323(1), c 44.772(4) Å, V 7954.6 Å 3, Z = 6, D calc 1.739 g cm −3, μ(Cu- K α) 162.93 cm −1, F(000) = 4068; R = 0.044. Crystals of the tantalum derivative are isotypic: a 14.274(5), c 44.55(3) Å, V 7860.6 Å 3, Z = 6, D calc 2.095 g cm −3, μ(Mo- K α) 78.82 cm −1, F(000) = 4644, R = 0.029. The coordination geometry around the group 5 metal may be described as a distorted square antiprism, the coordination sites being filled with the four carbonyl groups, the two silver atoms and the two phosphorous atoms of the bidentate ligand. The central core of the clusters is constituted by two almost regular interpenetrated equilateral triangles of silver and niobium (or tantalum) atoms. Both metal clusters react with dry hydrogen iodide giving silver metal and MI(CO) 4(dmpe).