Early transition metal derivatives stabilised by the phenylenediamido 1,2-C6H4(NCH2tBu)2 ligand: Synthesis, characterisation and reactivity studies: Crystal structures of [Ta{1,2-C6H4(NCH2tBu)2}2Cl] and [Zr{(1,2-C6H4(NCH2tBu)2}(NMe2)(μ-NMe2)]2

Li2[1,2-C6H4(NCH2tBu)2] reacts with one equiv of [TiCl4(THF)2] in refluxing toluene to give the chelate compound [Ti{1,2-C6H4(NCH2tBu)2}Cl2(THF)] (1), isolated as a black product, while the reaction of the dilithio diamido salt with one equiv of [ZrCl4(THF)2] in refluxing toluene affords the dinuclear zirconium derivative [Zr{1,2-C6H4(NCH2tBu)2}Cl(THF)(μ-Cl)]2 (2), obtained as an orange solid. Treatment of the dilithio diamido salt with TaCl5 in a 2:1 molar ratio in toluene yields [Ta{1,2-C6H4(NCH2tBu)2}2Cl] (3) as a red product. The reaction of 1,2-C6H4(NHCH2tBu)2 with [Zr(NMe2)4] in toluene at room temperature affords the dinuclear zirconium complex [Zr{1,2-C6H4(NCH2tBu)2}(NMe2)(μ-NMe2)]2 (4). The dibenzyl derivative [Ti{1,2-C6H4(NCH2tBu)2}(CH2Ph)2] (5) is obtained by the reaction of 1 with 2 equiv of Mg(CH2Ph)Cl at −78 °C. Compound 1 reacts with the lithium amide reagent LiN(SiMe3)2 to afford [Ti{1,2-C6H4(NCH2tBu)2}Cl{N(SiMe3)}] (6). The μ-oxo titanium derivative [(Ti{1,2-C6H4(NCH2tBu)2}{CH2Ph})2(μ-O)] 7 is precipitated when compound 5 is maintained in solution. The tendency of these compounds to coordinate donor ligands and their reactivity with Lewis acid reagents are described. All compounds were analytically and spectroscopically characterised and the molecular structures of the diamine 1,2-C6H4(NHCH2tBu)2 and the complexes 3 and 4 were established by single-crystal X-ray diffraction studies. The lack of correlation between the degree of metallacycle folding and phenylene ring distortion is observed in the solid state structures. The performance of precursors 1, 3 and 5 were evaluated in ethylene polymerisation upon activation with B(C6F5)3, methylaluminoxane (MAO) and sMAO as cocatalysts, with very modest activities.

Graphical abstractA series of phenylenediamido titanium, zirconium and tantalum derivatives have been prepared by different synthetic pathways and have been fully characterised. Reactions with alkylating reagents, the tendency to coordinate donor ligands and their reactivity with Lewis acid reagents are described.Figure optionsDownload full-size imageDownload as PowerPoint slide