Mixed-dicyclopentadienyl niobium and tantalum complexes: synthesis and reactivity X-ray molecular structures of Ta( η5-C 5Me 5)( η5-C 5H 4SiMe 3)Cl 2 and Ta( η5-C 5Me 5){ η5-C 5H 3(SiMe 3) 2}H 3

Abstract

MCp ∗ Cl 4, ( Cp ∗ = η 5- C 5 Me 5 ) reacts with LiCp (Cp = C 5H 4(SiMe 3)(Cp′); C 5H 3(SiMe 3) 2 (Cp″)) and sodium amalgam, in 1:1:1 molar ratio to give the paramagnetic dicyclopentadienyl niobium and tantalum(IV) complexes, MCp ∗ CpCl 2, (M = Nb, Cp = Cp′ 1; Cp″ 2; M = Ta, Cp = Cp′ 3; Cp″ 4). Reactions of 3 and 4 with 1 2 equivalent of PCl 5 afford the diamagnetic trichlorocomplexes TaCp ∗ CpCl 3, (Cp = Cp′ 5; Cp″ 6), while oxidation with dry O 2 gives the diamagnetic dinuclear complexes [TaCp ∗ CpCl 2] 2(μ-O), (Cp = Cp′ 7; Cp″ 8), 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 3 (Cp = Cp′ 11; Cp″ 12). The trihydrido complex 12 reacts with two-electron donor ligands on heating to yield the hydrido tantalum(III) compounds TaCp ∗ Cp″H(L) (L = CO 13, C 2H 4 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 12 12 1, with Z = 4 in a unit cell of dimensions a = 11.775(5) A ̊ , b = 12.821(1) A ̊ , c = 13.037(7) A ̊ . Crystals of 12 are triclinic, space group P 1 with Z = 2 in a unit cell of dimensions a = 7.384(4) A ̊ , b = 10.861(2) A ̊ , c = 16.731(3) A ̊ , α = 75.94(2)°, β = 84.75(3)° and γ = 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 w values of 0.040 and 0.064 ( 3) and 0.022 and 0.033 ( 12) respectively.