Synthesis Of Novel Nickel And Palladium Catalysts And Their Application For Ethylene Homo And Co-Polymerization With Polar Monomers

After the discovery of Nobel laureate Ziegler and Natta's catalysts,transition metal catalyzed olefin polymerization has gained so much attraction both by industrial and academic researchers.Brookhart's seminal discovery of ?-diimine nickel and palladium catalysts which possessed great functional group tolerance and ability to incorporate polar monomers,further enlightened this field in 1990s.The most prominent feature of this type of catalyst is the chain walking property,in which the metal center moves along the polymer chain by ?-H elimination and reinsertion with opposite regiochemistry.During this process,ethylene trapping of the migrated intermediate is responsible for the generation of branches and affords various polymer topologies.Despite these unique features,many of the initially reported ?-diimine catalysts possess low thermal stability,as evidenced by quick decomposition and greatly reduced molecular weight at elevated temperatures.This limitation has led to numerous researches to improve these types of catalysts.In this context,ligand steric and electronic effects are two of the most important factors responsible for the control of important parameters,such as catalyst stability,polymer molecular weight,and polymer branching density.Sterically bulky substituents on the ortho-position of aniline or on the ligand backbone can strategically block the axial sites of the metal center and suppress chain transfer,leading to high thermal stability and high polymer molecular weight,whereas ligand electronic effect influences not only catalyst stability but also polymer topology,through perturbations on the relative rates of insertion and chain walking.Furthermore,polyolefin branching and topology are directly related to rheological and mechanical properties.1.In this thesis,our major work deals with ?-diimine nickel and palladium catalysts.So the chapter one contained a detailed literature survey not only related to structural improvements of catalysts but also their effects on ethylene polymerization and co-polymerization2.Despite copious studies on individual tuning of ligand sterics or electronics,there have been few studies on the simultaneous tuning of these two factors.So in the second part,we introduced a strategy in which both ligand sterics and electronics factors operate in a concerted fashion.For this purpose,2,6-Dibenzhydryl-3,4,5-trimethoxyaniline,2,6-Dibenzhydryl-3,4,5-trifluoroaniline,and their corresponding ?-diimine nickel and palladium catalysts have been synthesized and characterized by 1HNMR,13CNMR,EI-MS,MALDI-TOF-MS and XRD.The presence of three methoxy or fluoro groups has more dramatic influences on ligand electronics.Moreover,it was proved by crystallographic data,the interaction of the two meta-substituted groups with the benzhydryl moieties is responsible to lock substituent rotation and result in an increased steric hindrance over the axial position of the metal center compared to those catalysts without substituents at meta-position.In ethylene polymerization,this concurrent tuning of electronic and steric effects led to simultaneous enhancement of several parameters such as activity up to 50 × 105 g/mol Pd·h,stability up to 100?,polymer molecular weight up to 256.29×104,melting point up to 112.2?,and branching density up to 13/1000C.In the case of ethylene copolymerization with MA and AA,the co-monomer incorporation was greatly reduced because of the ligand steric effect.Expressively better mechanical properties were observed for the palladium generated polyethylene samples.The fluoro substituted nickel and palladium catalysts were found to be inactive in ethylene polymerization,which might be because of six electron-withdrawing fluoro groups and corresponding catalyst decomposition.3.In third part,a series of unsymmetrical ?-diimine palladium catalysts bearing ortho-funcationalized dibenzhydryl moieties has been synthesized by multi-step synthetic procedure and characterized by 1HNMR,13CNMR,COSY,HSQC EI-MS,MALDI-TOF-MS and XRD.Two types of functionalities varying in quantity such as methoxy as an H-bond acceptor and hydroxyl as an H-bond donner at the ortho-position of dibenzhydryl groups has been introduced.It was observed that these moieties have some long-distance secondary interactions with metal center.It was observed that the catalytic performances were improved by introducing more ortho-substituents.All of these catalysts exhibit high activities at 80?(up to 8.8 × 105 g mol-1 h-1),producing high molecular weight polyethylenes(Mn up to 3.93 × 104 g mol-1).The catalysts also exhibited good thermal stabilities at high temperatures,producing branched polyethylenes.The catalysts bearing hydroxyl groups possessing intramolecular H-bonding,resulted in slightly higher incorporation ratios of MA unit compared with the catalysts bearing methoxy groups that might be because of some interactions of MA with hydroxyl groups.Nevertheless,it can also be due to the less steric-hinerance effect associated with the hydroxyl groups.4.In the fourth part,a ligand-metal secondary interaction effect has been studied and elaborated in Phosphine-Sulfonate based palladium and nickel catalyzed ethylene polymerization and co-polymerization.In this contribution,some phosphine-sulfonate Pd and Ni catalysts,bearing sp2 hybrid N based aromatic carbazolyl and pyrrolyl units in the ligand framework,have been designed,synthesized and characterized by 1HNMR,13CNMR,31PNMR EI-MS,MALDI-TOF-MS and XRD.It was examined that the N-heterocyclic unit can interact with the Pd or Ni center,thus inducing ligand-metal secondary interaction effect.Moreover,this secondary interaction also has been modulated by the addition of Lewis acid regent.The Pd catalysts showed high activities in ethylene polymerization and copolymerization with a variety of polar comonomers(methyl acrylate,acrylic acid,6-chloro-1-hexene,10-undecenol,10-undecenoic acid and methyl 10-undecenoate),resulting in high molecular weight(co)polymers.The Ni catalysts show low activities,affording low molecular weight(co)polymers.Both the Pd and the Ni catalysts demonstrate enhanced thermal stability versus the analogues devoid of the ligand-metal interaction.The addition of Lewis acidic additive such as B(C6F5)3 resulted in an increase of activity and decrease of molecular weight.More interestingly it was noticed that a 670-fold increase chain transfer rate can be achieved in Pd catalyzed ethylene polymerization.In Ni catalyzed ethylene polymerization,polymer microstructures highly influenced by the Lewis acid.The combination of ligand-metal secondary interaction effect with Lewis acid modulation makes this strategy highly versatile and potentially applicable to other catalytic processes.