Synthesis And Characterization Of Zirconium Complexes Supported By Aminophonolato Ligands And Their Catalytic Behavior Toward Alkylation Of Indoles

A series of amine-bridged aryloxy-stabilized zirconium complexes were synthesized and characterized.The catalytic properties of these complexes were investigated and found to catalyze the C7-alkylation of N-alkylindoles,exhibiting excellent catalytic activity and regioselectivity.1.Synthesis and characterization of the zirconium complexesIn order to synthesize amine-bridged bis（phenolato）-zirconium complexes with different steric and electronic properties,ligand precursors L¹H₂-L⁵H₂ and L⁶H with different bridges and substituents were synthesized.Amine-bridged bis（phenolato）-zirconium complexes 1-6 were synthesized and characterized.Among them,complexes 1,2 and 6 are zirconium dibenzyl complexes stabilized by tridentate ligands-,3 and 4 are zirconium dibenzyl complexes stabilized by tetradentate ligands-,and 5 is a zirconium tribenzyl complex stabilized by a bidentate ligand-.Furthermore,a hexa-nuclear zirconium magnesium complex 7 was synthesized by reaction tris（phenols）with tetrabenzylzirconium and benzylmagnesium chloride.2.C7-alkylation of N-alkyl indole catalyzed by cationic zirconium complexesThe catalytic properties of cationic zirconium complexes which are in situ formed by amine bridged bis（phenolato）zirconium complexes 1-4 and[Ph₃C][B（C₆F₅）₄]（TB）were studied.These cationic complexes were found to be efficient in catalyzing the alkylation of N-alkylindole with alkenes.It is worth noting that,compared to previous reports,the products obtained by the reaction are mainly C7-alkylated products,without introducing complex directing group.The substrate scope of the reaction was investigated,and C7-alkylation products were obtained in 25-90%yields.The reaction mechanism was explored by control experiments.The results show that the progress of the reaction is promoted by the Br（?）nsted acid formed by the reaction of the cationic zirconium complex with indole.