Synthesis,Structure And Catalytic Behavior Of Aromatic-ring-bridged Salicylaldiminato Binuclear Titanium And Vanadium Complexes

Because of their excellent performances in olefin polymerization,non-metallocene early transition dinuclear metal complexes have attracted a great deal of attention.Salicylaldiminato metallic complexes are stable,simple to synthesize,and with open coordination space.Presently,very few bimetallic non-metallocene titanium complexes have appeared in literature and bimetallic vanadium complexes have never been reported.In this work,threearomatic-ring-bridged salicylaldiminato[O^-NS]tridentatebimetallic titanium complexes 8a-8cand nine aromatic-ring-bridged salicylaldiminato[NO]bidentate vanadium complexes 11a-11iwere designed and prepared.The structures of these complexes were characterized and verified by various analytical techniques.We also investigated their catalytic performance for ethylene polymerization and copolymerization with?-olefins,cyclic olefins.The main content is described in the following:1.Aromatic-ring-bridgedsalicylaldiminato tridentate[O^-NS]bimetallic titanium complexes 8a-8c and[NO]bidentate bimetallicvanadium complexes 11a-11i were synthesized by a one-pot method.All the ligands and complexes were characterized and verified by IR and ¹HNMR Spectra.As further revealed by XRD analysis,complex8b demonstrated C2 symmetry,with each titanium coordinated with six atoms and formed a distorted octahedral configuration;while the two metal centers were also bridged by a Oatom,forming a relatively stable macrocyclic structure.Bimetallicvanadium complexs 11a and 11b were of distorted trigonal bipyramidal geometry.Nevertheless,the two metal centers are rather close to each other,resulting in large steric hindrance of the tetrahydrofuran ligand,and the subsequent elimination of a butene to form V=O bond.2.When activated by MMAO,bimetallic titanium complex8b demonstrated high activity for ethylene polymerization.The highest activity reached141.1kg/mol Ti.h.atm.In the presence of Et₂Al Cl,all the bimetallicvanadium complexes also demonstrated high activity for ethylene polymerization.The activity increased with the increase of fluorine substitution on the aromatic ring.the complex contained five F atoms on iminoaryl ring demonstrated the highest activity,reaching10.98×10⁶g/mol V.h.atm?3.We also investigated the catalytic performance of bimetallicvanadium complexes for ethylene copolymerization with 1-hexene and norbornene.These complexes showed high activity for copolymerization with norbornene,the highest activity reached 16.2×10⁶g/mol V.h.atm.When catalyzing copolymerization with1-hexene,the incorporation of hexene by complexes 11d-11i which contain F atoms is higher than that by complex 11a.The highest incorporation ratio increased by 54%.With the increase of F substitution,the activity firstly increased,then decreased,with complex 11g which contain two F atoms on iminoaryl ring demonstrated highest activity.