Zirconium Complexes Bearing [ONNO]-Type Bis(phenolate) Ligands: Synthesis, Characterization And Catalytic Properties For Alkene Polymerization

Olefin coordination polymerization catalysis is the basis of the development of polyolefin industry.The development of polyolefin catalyst is the key to the development of polyolefin industry.Starting from the 1960s,olefin polymerization catalysts mainly experienced several stages in the past 60 years,including Ziegler-Natta catalyst,Phillips catalyst,metallocene catalyst and non-metallocene catalyst.Among them,non-metallocene catalysts are occupying more and more market shares and playing an increasingly important role in the field of petroleum industry due to their simple synthesis method and superior catalytic performance.There is no doubt that the development prospects of non-metallocene catalysts are very optimistic.Using metallocene catalysts to catalyze the polymerization of olefin monomers,polyolefin products with excellent properties can be obtained,such as low density polyethylene products,high density polyethylene products,isotactic polypropylene products,syndiotactic polypropylene products,syndiotactic polystyrene products,ethylene and cyclic olefin copolymerization products.As non-metallocene catalysts have considerable advantages in the synthesis of polyolefin products,it is necessary for us to continue to explore and improve the effect of substituents on non-metallocene catalysts in catalyzing olefin polymerization.At the same time,we expect to further optimize the structure of the catalyst and the polymerization conditions to synthesize polyolefin products with better performance.In this paper,a series of tetradentate[ONNO]-type dichlorozirconium complexesbearingdiamine-bis?phenolate?ligands,[2,2'-?OC6H2-4-^tBu-6-R?2CH2NMe?CH2?n NMeCH2]ZrCl2[R=CMe3,n=2,?1?;R=CMe2Ph,n=2,?2?;R=CMePh2,n=2,?3?;R=CMe3,n=3,?4?;R=CMe2Ph,n=3,?5?;R=CMePh2,n=3,?6?;R=CMe3,n=4,?7?;R=CMe2Ph,n=4,?8?;R=CMePh2,n=4,?9?],have been synthesized in moderate yields by reactions of ZrCl4?THF?2 with 1 eq.of disodium salts of the corresponding ligand precursors in THF.The dichlorozirconium complexes were characterized by ¹H and ¹³C NMR,and elemental analyses.While for complexes 3–6,8 and 9 single C1-symmetric isomers were observed in solution at room temperature,and a molecular C2-symmetry was observed at ambient temperature for complex 7.Complexes 1 and 2 formed as a mixture of cis-??C2-symmetry,trans?O,O?-cis?N,N???1a and 2a?and cis-??C1-symmetry,cis?O,O?-cis?N,N??isomers?1b and 2b?.The molecular structures of complexes 1b,3 and 7 were determined by single-crystal X-ray crystallography.The crystallographic analysis indicated that complexes 1b and 3 adopt the cis?O,O?-cis?N,N?C1-symmetrical structure,while complex 7 adopts the trans?Cl,Cl?C2-symmetrical structure.Upon activation with MAO or AlⁱBu3/Ph3CB?C6F5?4,complexes 1–9 exhibit moderate to high catalytic activities for ethylene polymerization and ethylene/1-hexene copolymerization,producing polyethylenes with moderate to high molecular weights and poly?ethylene-co-1-hexene?s with moderate comonomer incorporation which are typical linear low-density polyethylenes?LLDPE?.