ELECTRON-TRANSFER PROCESSES WITH SUBSTITUTED GROUP-5 METAL-CARBONYLS - SYNTHESIS, CRYSTAL AND MOLECULAR-STRUCTURE OF AG3M3(CO)12(ME2PCH2CH2PME2)3, M=NB, TA, THE 1ST STRUCTURALLY CHARACTERIZED CARBONYL DERIVATIVES OF NIOBIUM(0) AND TANTALUM(0)

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, CoCp2{black star}, carries out the two-electron transfer to form [CoCp2{black star}][M(CO)4dppe]. Finally, oxidation of the [M(CO)4dmpe]- anion, M = Nb, Ta, with the silver(I) salts AgNO2 and AgBF4 gave the hexanuclear mixed metal clusters Ag3M3(CO)12(dmpe)3, which were studied by X-ray diffraction methods. Crystals of Ag3Nb3(CO)12(dmpe)3 are rhombohedric, space group R3c, hexagonal setting, No. 167, a 14.323(1), c 44.772(4) Å, V 7954.6 Å3, Z = 6, Dcalc 1.739 g cm-3, μ(Cu-Kα) 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 Å3, Z = 6, Dcalc 2.095 g cm-3, μ(Mo-Kα) 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). © 1990.