Study On The Homogeneous Catalytic Reaction Of Br(?)nsted Acid In Cooperation With Titanocene Lewis Acid

A binary acid cooperative catalytic system of Lewis acid and Br(?)nsted acid has become a powerful strategy to access unique reactivity and selectivity in synthetic organic chemistry.We developed stable titanocene dichloride as organometallic precursor to combine with simple organic Br(?)onsted acids,thus designed synergistic binary acids system.The Mannich reactions,Diels-Alder reactions and Friede?-Crafts reactions of indoles were employed as model reactions to evaluate the dramatic synergistic effects of conventional Br(?)onsted acids on organometallic Lewis acids.Analysis on the coordination of 5-sulfosalicylic acid,salicylic acid,anthranilic acid,8-hydroxyquinoline with titanocene dichloride showed the cooperative binary acid activation,by which the structure,coordination behavior of these complexes in the solution,and their catalytic performance were studied.The synergistic effect of Br(?)ensted acid on Lewis acidity of titanocenereveals the law of activation of these binary acid catalyst system.The main contents are included as follows:(1)We investigated the catalytic efficiency of three-component Mannich reaction of acetone,aromatic amine and aromatic aldehyde.The binary acid catalyst composed of[Cp2TiCl2]and salicylic acid was successfully applied in the Mannich reactions,which afforded 97%yield.The structure of complex,coordination,and catalytic performance of titanocene dichloride and salicylic acids were tested by 1H NMR spectroscopy analysis,X-ray structure analyses as well as active species control experiments,respectively.The mechanistic experimentation demonstrated bis-salicylato titanocene(VI)as the catalytically active species.These findings led us to explore the first protocol for the organometallic binary-acid-catalysed direct three-component Mannich reaction.(2)5-sulfosalicylic acid/titanocene dichloride were evaluated in the Diels-Alder reaction.We prepared the water-soluble titanocene complexes[Cp2Ti(H2O)2]2+(O3SC6H3-2-(OH)CO2H)2·4H2O(?)through a simple aqueous-organic two-phase method.This is the first case that water-soluble titanium complexes have both organic metal Lewis acid sites and Br(?)nsted acid sites.This synthetic method avoids the use of expensive silver halides,and it can perform in the air.Complexes ? catalyzed aromatic amines,aromatic aldehyde and ketone of Diels-Alder reaction with high yield and unexpected endo-selectivity.(3)Friedel-Crafts reaction was selected as model reaction.The screening of different ligands tune the synergistic acidity of titanocene which selectively catalyze the reactions of indoles,aldehydes and amine.Friedel-Crafts mono-and double substituted products were selectively obtained with optimize the reaction conditions.We further investigated the behavior of the coordination of 8-hydroxyquinoline,anthranilic acid with titanocene dichloride catalyst reaction.The results show that 8-hydroxyquinoline and anthranilic acid have different activation effect on titanocene dichloride.The selectivity of indole reaction was regulated by ligands,indicating the theoretical basis of different ligands on the controllable catalysis of organic metal Lewis acid.