A zirconium dichloro complex supported by an ancillary stereorigid tetradentate bis(phenoxo-imino) Schiff-base-donor ligand: Evidence for a conformational equilibrium between two solution stereoisomers

Reaction of the dilithium salt of the Schiff-base N,N′-o-phenylene-bis(3,5-di-tert-butyl-salicylidene-imine) (tBu4salophenH2) with 1 equiv. of ZrCl4(THF)2 in toluene at −78 °C affords the dichloro complex ZrCl2[C6H4-1,2-{NCH-(3,5-tBu2C6H2-2-O)}2], isolated as a mixture of the C2v-(3a) and C2-(3b) symmetry isomers. Thermodynamic and kinetic parameters for the equilibrium between 3a and 3b have been determined and studied by 1H NMR spectroscopy. Reactions of ZrCl2[C6H4-1,2-{NCH-(3,5-tBu2C6H2-2-O)}2] with alkylating reagents gave an intractable, unidentified mixture of products from which the NMR spectra in C6D6 solution are unusable.

Graphical abstractThe synthesis of the bis(phenoxo-imino) zirconium dichloro derivative ZrCl2[C6H4-1,2-{NCH-(3,5-tBu2C6H2-2-O)}2] is described. This compound has been spectroscopically characterized as a mixture of the C2v- and C2-symmetry derivatives. The interconversion between these two species is observed in toluene and chloroform solution and interpreted as a result of the intramolecular isomerization of the ligand. Thermodynamic and kinetic parameters for the equilibrium between 3a and 3b have been determined. The alkylation reaction of the bis(phenoxo-imino) zirconium dichloro complex using various alkylation agents under different reaction conditions has been studied.Figure optionsDownload full-size imageDownload as PowerPoint slide