Design Of Novel ?-diimine Ni(?) And Pd(?) Based-catalysts And Olefin Polymerization

The landmark disclosure of cationic ?-diimine nickel and palladium catalysts by Brookhart in 1995 opens the field of late-transition metal complexes for olefin homopolymerization and copolymerization with polar monomers.It was feasible to finely tailor the microstructure structure of polyolefins by unique "chain walking"mechanism and more importantly,to copolymerize olefin with polar monomers due to the weakly oxophilic nature of the active species.Despite of such great advances,a large number of the ?-diimine type nickel/palladium complexes still suffer from poor thermal stabilities at elevated temperatures,which significantly limits their applications in a broader scope,especially for future industrializations(70-110?).With this consideration,multiple strategies,i.e.,simultaneous enhancement for both axial and equatorial steric,unsymmetrical strategy,intra-ligand H…F noncovalent interaction and covalent linkage were employed to suppress the rotation of N-aryl.These novel ?-diimine type nickel/palladium complexes exhibit extraordinary performance in olefin polymerization and copolymerization with polar monomer.The details are listed as follows:1.Axial and equatorial bulkiness in the ?-diimine Ni/Pd type complexes are two crucial parameters that governs the catalytic activity,thermostability of the precatalysts and molecular weight as well as chain structure of the resulting polymers.In this contribution,we report the synthesis and characterization of a new family of ?-diimine nickel complexes that bearing axially bulky terphenyl group and equatorially bulky dibenzobarrelene group,and upon activation with MAO,these complexes not only displayed high activities towards ethylene polymerization,but also could give rise to ultra-high-molecular-weight polyethylenes(Mw as high as 174.8 ×104)due to the efficient retard of chain transfer rections for ethylene polymerization.Mechanical studies revealed that the resultant polyethylenes displayed typical elastomeric properties.2.Increasing the thermostability of ?-diimine late transition metal complexes and therefore rendering them higher active at higher temperature are of great importance yet challenging for olefin polymerization field.In the present research,a new family of ?-diimine palladium complexes that can promote norbornene polymerization at high temperature(up to 140?)is disclosed.Because of the conformational restriction by increasing axial and equatorial bulkiness,as well as the presence of intra-ligand H…F hydrogen bonds,N-aryl rotations can be efficiently restricted,which therefore is able to circumvent the deactivation of active species at high temperatures.At 80-140?,these complexes can catalyze norbornene homopolymerizations efficiently,giving high catalytic activities up to 5.65×107 g of PNB(mol of Ni)-1 h-1 and polymers with high molecular weights up to 37.2×104 g/mol,which are greatly superior than catalytic systems mediated by CF3-free complexes.Moreover,in the presence of polar 5-norbornene-2-carboxylic acid methyl ester(NB-COOCH3),these complexes could also afford medium catalytic activities.3.The novel ?-diimine ligands bearing half-sandwich macrocyclic configuration were synthesized.Single crystal X-ray crystallographic analysis revealed that the confined phenyl was nearly parallel with the coordination plane and strongly block the axial sites.The other phenyl lie almost perpendicular to the coordination plane and back off the axial site to afford more space for monomer insertion.Upon activation with MAO and AlEt2Cl these complexes showed high activities for ethylene polymerization and afforded polyethylenes with ultra high molecular weight(Mn up to 501.8×104 g/mol)and high branching degree.Furthermore for the ethylene/methyl undecenoate copolymerization,these complexes exhibited high activities,affording poly(ethylene-methyl undecenoate)s with relatively high comonomer incorporation(1.5-3.8%).4.A series of ?-diimine palladium complexes bearing axial and equatorial bulkiness were exhaustively explored in ethylene polymerization and copolymerization with methyl methacrylate.In contrast with the fluorine-free complex construction of the intra-ligand H…F noncovalent interaction effectively hindered the rotation of N-aryl and endowed the ?-diimine palladium complexes with high thermostability(up to 100?).By fixing the steric of one N-aryl with-CF3 substituted terphenyl systematacially varying the steric of the other N-aryl could produce polyethylene ranging from oligomer to high molecular polymer.These complexes was able to copolymerize ethylene and methyl methacrylate affording functional polyethylene.