Hafnium Amidoquinoline Complexes: Highly Active Olefin Polymerization Catalysts with Ultrahigh Molecular Weight Capacity

The preparation and characterization of a new class of polyolefin procatalysts is described. Hafnium tribenzyl procatalysts, supported by amidoquinoline ligands, were prepared in two steps from commercially available materials. Solid-state structures, determined by single-crystal X-ray analyses, revealed that all the hafnium complexes display approximate trigonal-bipyramidal geometry around the metal center. The complexes were evaluated in an ethylene/1-octene copolymerization study and were found to be highly active at elevated temperatures (120 °C). The best catalyst, derived from ((2,6-dimethylphenyl)­(2,4-dimethylquinolin-8-yl)­amino)­tribenzylhafnium (<b>6d</b>), compares favorably to previously reported systems supported by bidentate nitrogen-based ligands. In particular, this catalyst exhibits very high molecular weight capacity and high catalytic activity, with a moderate 1-octene response. Alkyl substitution at the carbon <i>ortho</i> to the quinolino nitrogen was found to be an important factor for improving polymer compositional homogeneity, as evidenced by a narrowing of the polydispersity index and a single melting temperature in the resulting copolymer

Copolymerization of Ethylene and 1,4–Pentadiene: Structure Characterization and Reaction Mechanism

Copolymerization of ethylene and 1,4-pentadiene was conducted by using a homogeneous catalyst to understand the insertion mode of 1,4-pentadiene. The polymer microstructure of the synthesized material was subjected to structural characterization using quantitative NMR spectroscopy, diffusometry, two-dimensional correlation spectroscopy, and selectively refocused insensitive nuclei enhanced by polarization transfer (Sel-RINEPT). The multimodal NMR characterization allows effective differentiation of chain ends and backbone signals, filters irrelevant spectral information, and provides site-specific information to achieve unambiguous structural elucidation. The experimental results reveal that pentadiene has been primarily converted to cis- and trans-dialkyl-substituted cyclohexane moieties along the polymer backbone over the course of polymerization. The analysis also confirms that unreacted pendant allyl groups from pentadiene remain at a concentration that is significantly lower than the cyclic structures. In comparison to the literature results, some discrepancies in structural assignment have been identified and the results will be discussed. Detailed molecular structure elucidation provides critical insights into advancing the understanding of the reaction mechanism

Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe₃ and HfMe₃ Complexes

A novel strategy for polyolefin catalyst development was explored, in which imino–enamido zirconium and hafnium trimethyl complexes were used as synthons to produce a diverse array of new dimethyl derivatives. Specifically, reactions of the trimethyl precursors with protic reagents (i.e., imidazolimines, phosphinimines, and phenols) or unsaturated organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide) resulted in the formation of new complexes wherein a single methyl group is replaced by a heteroatom-based ligand. In total, ten new dimethyl complexes were prepared and isolated in high yields utilizing these synthetic approaches. The new complexes were evaluated as precatalysts in ethylene/1-octene copolymerization reactions at 120 °C. Seven complexes were found to be competent catalysts under these conditions, and the resulting copolymers comprised a wide range of molecular weights and octene contents. The best catalysts of the series comprised imino–enamido complexes containing a phosphine-imidato ligand, which exhibited remarkably high activities, had high ethylene selectivities, and produced ethylene/1-octene copolymers with exceptionally high molecular weights. This work demonstrates that the replacement of one of the alkyl groups from trialkyl complexes can be a very effective approach for accessing a variety of new dialkyl precatalysts that can exhibit diverse polymerization behavior

Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe₃ and HfMe₃ Complexes

A novel strategy for polyolefin catalyst development was explored, in which imino–enamido zirconium and hafnium trimethyl complexes were used as synthons to produce a diverse array of new dimethyl derivatives. Specifically, reactions of the trimethyl precursors with protic reagents (i.e., imidazolimines, phosphinimines, and phenols) or unsaturated organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide) resulted in the formation of new complexes wherein a single methyl group is replaced by a heteroatom-based ligand. In total, ten new dimethyl complexes were prepared and isolated in high yields utilizing these synthetic approaches. The new complexes were evaluated as precatalysts in ethylene/1-octene copolymerization reactions at 120 °C. Seven complexes were found to be competent catalysts under these conditions, and the resulting copolymers comprised a wide range of molecular weights and octene contents. The best catalysts of the series comprised imino–enamido complexes containing a phosphine-imidato ligand, which exhibited remarkably high activities, had high ethylene selectivities, and produced ethylene/1-octene copolymers with exceptionally high molecular weights. This work demonstrates that the replacement of one of the alkyl groups from trialkyl complexes can be a very effective approach for accessing a variety of new dialkyl precatalysts that can exhibit diverse polymerization behavior

Synthesis and Scale-up of Imino–Enamido Hafnium and Zirconium Olefin Polymerization Catalysts

New imino–enamido hafnium and zirconium trimethyl complexes were prepared in high yield by reacting a mixture of an imino–enamine ligand and hafnium or zirconium tetrachloride with four equivalents of methylmagnesium bromide in toluene. A significantly improved imine formation reaction in the final step of the ligand synthesis was developed that involves the reaction between the keto–enamine and a reagent formed <i>in situ</i> by mixing 0.55 equivalents of titanium tetrachloride and 5.5 equivalents of <i>n</i>-butylamine. Ethylene/1-octene polymerization evaluations at 120 °C revealed that polymerization characteristics of the imino–enamido hafnium and zirconium trimethyl derivatives were very similar to those of the tribenzyl analogues. A scale-up of the hafnium trimethyl derivative, performed on a 255 g scale, was accomplished in an overall yield of 57% in four steps starting with commercially available cyclohexa-1,2-dione. Hafnium and zirconium complexes derived from two isomeric imino–enamine ligands each resulted in very high molecular weight ethylene/1-octene copolymers, which differ significantly, however, in the level of incorporated octene. These features make these new catalysts good candidates for the preparation of olefin block copolymers via chain-shuttling polymerization

Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe₃ and HfMe₃ Complexes

A novel strategy for polyolefin catalyst development was explored, in which imino–enamido zirconium and hafnium trimethyl complexes were used as synthons to produce a diverse array of new dimethyl derivatives. Specifically, reactions of the trimethyl precursors with protic reagents (i.e., imidazolimines, phosphinimines, and phenols) or unsaturated organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide) resulted in the formation of new complexes wherein a single methyl group is replaced by a heteroatom-based ligand. In total, ten new dimethyl complexes were prepared and isolated in high yields utilizing these synthetic approaches. The new complexes were evaluated as precatalysts in ethylene/1-octene copolymerization reactions at 120 °C. Seven complexes were found to be competent catalysts under these conditions, and the resulting copolymers comprised a wide range of molecular weights and octene contents. The best catalysts of the series comprised imino–enamido complexes containing a phosphine-imidato ligand, which exhibited remarkably high activities, had high ethylene selectivities, and produced ethylene/1-octene copolymers with exceptionally high molecular weights. This work demonstrates that the replacement of one of the alkyl groups from trialkyl complexes can be a very effective approach for accessing a variety of new dialkyl precatalysts that can exhibit diverse polymerization behavior

Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe₃ and HfMe₃ Complexes

A novel strategy for polyolefin catalyst development was explored, in which imino–enamido zirconium and hafnium trimethyl complexes were used as synthons to produce a diverse array of new dimethyl derivatives. Specifically, reactions of the trimethyl precursors with protic reagents (i.e., imidazolimines, phosphinimines, and phenols) or unsaturated organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide) resulted in the formation of new complexes wherein a single methyl group is replaced by a heteroatom-based ligand. In total, ten new dimethyl complexes were prepared and isolated in high yields utilizing these synthetic approaches. The new complexes were evaluated as precatalysts in ethylene/1-octene copolymerization reactions at 120 °C. Seven complexes were found to be competent catalysts under these conditions, and the resulting copolymers comprised a wide range of molecular weights and octene contents. The best catalysts of the series comprised imino–enamido complexes containing a phosphine-imidato ligand, which exhibited remarkably high activities, had high ethylene selectivities, and produced ethylene/1-octene copolymers with exceptionally high molecular weights. This work demonstrates that the replacement of one of the alkyl groups from trialkyl complexes can be a very effective approach for accessing a variety of new dialkyl precatalysts that can exhibit diverse polymerization behavior

Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe₃ and HfMe₃ Complexes

A novel strategy for polyolefin catalyst development was explored, in which imino–enamido zirconium and hafnium trimethyl complexes were used as synthons to produce a diverse array of new dimethyl derivatives. Specifically, reactions of the trimethyl precursors with protic reagents (i.e., imidazolimines, phosphinimines, and phenols) or unsaturated organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide) resulted in the formation of new complexes wherein a single methyl group is replaced by a heteroatom-based ligand. In total, ten new dimethyl complexes were prepared and isolated in high yields utilizing these synthetic approaches. The new complexes were evaluated as precatalysts in ethylene/1-octene copolymerization reactions at 120 °C. Seven complexes were found to be competent catalysts under these conditions, and the resulting copolymers comprised a wide range of molecular weights and octene contents. The best catalysts of the series comprised imino–enamido complexes containing a phosphine-imidato ligand, which exhibited remarkably high activities, had high ethylene selectivities, and produced ethylene/1-octene copolymers with exceptionally high molecular weights. This work demonstrates that the replacement of one of the alkyl groups from trialkyl complexes can be a very effective approach for accessing a variety of new dialkyl precatalysts that can exhibit diverse polymerization behavior

Synthesis and Scale-up of Imino–Enamido Hafnium and Zirconium Olefin Polymerization Catalysts

New imino–enamido hafnium and zirconium trimethyl complexes were prepared in high yield by reacting a mixture of an imino–enamine ligand and hafnium or zirconium tetrachloride with four equivalents of methylmagnesium bromide in toluene. A significantly improved imine formation reaction in the final step of the ligand synthesis was developed that involves the reaction between the keto–enamine and a reagent formed <i>in situ</i> by mixing 0.55 equivalents of titanium tetrachloride and 5.5 equivalents of <i>n</i>-butylamine. Ethylene/1-octene polymerization evaluations at 120 °C revealed that polymerization characteristics of the imino–enamido hafnium and zirconium trimethyl derivatives were very similar to those of the tribenzyl analogues. A scale-up of the hafnium trimethyl derivative, performed on a 255 g scale, was accomplished in an overall yield of 57% in four steps starting with commercially available cyclohexa-1,2-dione. Hafnium and zirconium complexes derived from two isomeric imino–enamine ligands each resulted in very high molecular weight ethylene/1-octene copolymers, which differ significantly, however, in the level of incorporated octene. These features make these new catalysts good candidates for the preparation of olefin block copolymers via chain-shuttling polymerization

Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe₃ and HfMe₃ Complexes

A novel strategy for polyolefin catalyst development was explored, in which imino–enamido zirconium and hafnium trimethyl complexes were used as synthons to produce a diverse array of new dimethyl derivatives. Specifically, reactions of the trimethyl precursors with protic reagents (i.e., imidazolimines, phosphinimines, and phenols) or unsaturated organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide) resulted in the formation of new complexes wherein a single methyl group is replaced by a heteroatom-based ligand. In total, ten new dimethyl complexes were prepared and isolated in high yields utilizing these synthetic approaches. The new complexes were evaluated as precatalysts in ethylene/1-octene copolymerization reactions at 120 °C. Seven complexes were found to be competent catalysts under these conditions, and the resulting copolymers comprised a wide range of molecular weights and octene contents. The best catalysts of the series comprised imino–enamido complexes containing a phosphine-imidato ligand, which exhibited remarkably high activities, had high ethylene selectivities, and produced ethylene/1-octene copolymers with exceptionally high molecular weights. This work demonstrates that the replacement of one of the alkyl groups from trialkyl complexes can be a very effective approach for accessing a variety of new dialkyl precatalysts that can exhibit diverse polymerization behavior