George Rodriguez

SYNTHESIS OF TWO TANTALUM COMPLEXES BEARING CYCLOPENTADIENYL ANALOGS

Abstract Reaction of Li[C 5 H 5 B-NMe 2 ] with (TBM)TaMe 2 Cl (TBM = tribenzylidenemethane) gives (TBM)[C 5 H 5 B-NMe 2 ]TaMe 2 ( 1 ). A single crystal diffraction study revealed a metallocene-like environment with the metal binding more strongly to the boratabenzene ring carbons furthest from the boron atom. Cp ∗ [ C 4 H 4 B - N ( CHMe 2 ) 2 ] Ta (η 4 - C 4 H 6 ) ( 2 ) (Cp ∗ = C 5 Me 5 ) is obtained from the reaction of Cp ∗ [C 4 H 4 B-N(CHMe 2 ) 2 ]TaCl 2 and (C 4 H 6 Mg)(THF) 2 . The diene fragment binds in a trans configuration. The oxidation state of tantalum in 2 can be considered as I, III or V if all resonance contributions are taken into account.

Triazamethylenemethane complexes of zirconium and tantalum

Abstract Addition of [Li 2 (THF) 4 ][C(NPh) 3 ] ( 2 ) to a THF solution of Cp * ZrCl 3 (Cp * =C 5 Me 5 ) yields, after recrystallization in Et 2 O, the zwitterionic species Cp * [C(NPh) 3 ]ZrCl 2 Li(Et 2 O)(THF) ( 3 ). Treating 3 with excess methylaluminoxane (MAO) affords a homogeneous Ziegler–Natta catalyst for ethylene polymerization. Addition of LiNPh 2 to 3 allows for Cl substitution to give the new product Cp * [C(NPh) 3 ]Zr(NPh 2 )ClLi(THF) 2 ( 4 ). A single crystal diffraction study of 4 reveals that the [C(NPh) 3 ] ligand is η 2 -bound. The group 5 complex Cp * [C(NPh) 3 ]TaMe 2 ( 5 ) was prepared by addition of 2 to Cp * TaMe 2 Cl(OSO 3 CF 3 ). The X-ray diffraction structure of 5 shows that the [C(NPh) 3 ] ligand is η 2 -bound to tantalum and that, when compared to 4 , there is less electron delocalization across the inner core of [C(NPh) 3 ].

A tribenzylidenemethane–tantalum compound: some experiences with `inversion twinning'

The six-electron-donating ligand tribenzylidenemethandiide has been used to form a tantalum (group 5) mimic, (η^5-cyclopentadienyl)(η^4-tribenzylidenemethandiide)dimethyltantalum, of a group 4 bent metallocene. The material crystallizes with two molecules in the asymmetric unit with quite different packing arrangements, although the overall structures of the two are similar. The Cp and methyl ligands are disordered about a threefold axis. Crystal data: [Ta{(C_7H_6)_3C}(C_5H_5)(CH_3), trigonal P31c, with a = 12.681 (3), c = 16.124 (5) A, V = 2245.5 (7) A^3, T = 293 K, Z = 4, M_r = 558.47, D_x = 1.65 g cm^(-3), F(000) = 1104, Mo Kα, λ = 0.71073 A, µ = 4.91 mm^(-1), R = 0.020 for 1319 reflections with F_o > 4σ(F_o); S = 2.18. Because of crystal decay, three separate crystals were needed for a full data set. These polar (but achiral) crystals showed apparently differing amounts of inversion twinning, leading to problems in accurately merging the three data sets and refining the structure. These problems are discussed briefly.