Mixed-dicyclopentadienyl niobium and tantalum complexes: synthesis and reactivity X-ray molecular structures of Ta(η-C5Me5)(η5-C5H4SiMe3)Cl2 and Ta(η5-C5Me5){η5-C5H3(SiMe3)2}H3

Abstract

MCp* Cl,, (Cp* = $-C,Me,) reacts with LiCp (Cp = C,H,(SiMe,) (Cp’); C,H,(SiMe,), (Cp”)) and sodium amalgam, in I : I : 1 molar ratio to give the paramagnetic dicyclopentadienyl niobium and tantalum(W) complexes, MCp * CpCI,, (M = Nb, Cp = Cp’ 1; Cp” 2; M = Ta, Cp = Cp’ 3; Cp” 4). Reactions of 3 and 4 with l/2 equivalent of PCl, afford the diamagnetic trichlorocomplexes TaCp* CpCI,, (Cp = Cp’ 5; Cp” 6). while oxidation with dry 0, gives the diamagnetic dinuclear complexes [TaCp* CpCI,],( p-O>, (Cp = Cp’ 7; Cp” S), and with air are transformed into the corresponding oxoderivatives TaCp * CpCl(O), (Cp = Cp’ 9; Cp” 10). Treatment of compounds 3 and 4 with a slight excess of lithium aluminium hydride affords the trihydrido complexes TaCp” CpH, (Cp = Cp’ 11; Cp” 12). The trihydrido complex 12 reacts with two-electron donor ligands on heating to yield the hydrido tantalum(II1) compounds TaCp* Cp”H(L) (L = CO 13, C,H, 14, RNC 15). All the new complexes were characterized by usual IR and NMR spectroscopic methods. The crystal structures of 3 and 12 were determined by X-ray diffraction studies. Crystals of 3 are orthorhombic, space group P2,2,2,, with Z= 4 in a unit cell of dimensions a = 11.775(5) A, b = 12.821(l) A, c = 13.037(7) A. Crystals of 12 are triclinic, space group Pi with Z = 2 in a unit cell of dimensions a = 7.384(4) A, b = 10.861(2) A, c = 16.731(3) A, LY = 75.94(2)“, p = 84.75(3)” and y = 72.57(4)‘. Both structures were solved from diffractometer data by a combination of direct and Fourier methods and refined by full-matrix least squares fit on the basis of 4088 (3) and 4594 (12) observed reflections to R and R,. values of 0.040 and 0.064 (3) and 0.022 and 0.033 (12) respectively.