11 research outputs found

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

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    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

    Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes

    No full text
    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 ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes

    No full text
    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

    Efficient Separation of Diastereomeric Mixtures of <i>syn</i>- and <i>anti</i>-2,4-Pentanediol

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    A simple and practical process was developed for the efficient separation of diastereomeric <i>syn</i>- and <i>anti</i>-2,4-pentanediol by selective acetalization of a diastereomeric mixture of the 2,4-pentanediols and selective hydrolysis of the corresponding acetals. The process relies upon the reaction rate differences of <i>syn</i>-2,4-pentanediol (<i>syn</i>-diol) and <i>anti</i> 2,4-pentanediol (<i>anti</i>-diol) in acetalization and of the corresponding acetals in hydrolysis: the <i>syn</i>-diol reacts faster to form a more stable acetal than the <i>anti</i>-diol, which in turn is more susceptible to hydrolysis by Brønsted acid. Acetalization of a 2,4-pentanediol diastereomeric mixture (<i>syn</i>/<i>anti</i> = 45:55) with acetophenone (0.95 equiv relative to <i>syn</i>-diol) leads to the formation of a <i>syn</i>-enriched acetal mixture with a <i>syn</i>/<i>anti</i> diastereomeric ratio (dr<sub><i>s</i>/<i>a</i></sub>) of 6:1, leaving an <i>anti</i>-enriched diol mixture (dr<sub><i>s</i>/<i>a</i></sub> = 1:7). Subsequent kinetic resolution via selective hydrolysis of the minor <i>anti</i>-acetal with a catalytic amount of 1.0 N HCl at ambient temperature affords the pure <i>syn</i>-acetal (dr<sub><i>s</i>/<i>a</i></sub> > 99:1) in the organic phase and the <i>anti</i>-enriched 2,4-pentanediols (dr<sub><i>s</i>/<i>a</i></sub> = 1:6) in the aqueous phase, which are conveniently separated by a phase cut. Hydrolysis of the <i>syn</i>-acetal is facile in alcohol solvents at elevated temperatures (60–80 °C), yielding the pure <i>syn</i>-diol. A second acetalization of the <i>anti</i>-enriched 2,4-pentanediols leads to the pure <i>anti</i>-2,4-pentanediol. This separation gives the <i>syn</i>-diol in 75–79% yield with dr<sub><i>s</i>/<i>a</i></sub> > 99:1 and the <i>anti</i>-diol in 79–85% yield with dr<sub><i>a</i>/<i>s</i></sub> > 98:2. Additionally, the acetophenone used for the acetalization can be recovered in 88–92% yield, and therefore, the overall process is high-yielding, atom-economical, and potentially recyclable

    Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes

    No full text
    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 ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes

    No full text
    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 ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes

    No full text
    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 ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes

    No full text
    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 ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes

    No full text
    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

    Catalytic Production of Isocyanates via Orthogonal Atom and Group Transfers Employing a Shared Formal Group 6 M(II)/M(IV) Redox Cycle

    No full text
    Under an atmosphere of CO, the Mo­(IV) imido complex Cp*Mo­[N­(<sup>i</sup>Pr)­C­(Me)­N­(<sup>i</sup>Pr)]­(NSiMe<sub>3</sub>) (Cp* = η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>) (<b>1</b>) serves as a catalyst for production of an isocyanate via metal-mediated nitrene group transfer in benzene solution under mild conditions (55 °C, 10 psi) according to RN<sub>3</sub> + CO → N<sub>2</sub> + RNCO. Mechanistic and structural studies support a catalytic cycle for nitrene group transfer involving formal Mo­(II) monocarbonyl and Mo­(IV) (κ<sup>2</sup>-<i>C,N</i>)-isocyanate intermediates. These results complement an earlier finding that catalytic production of isocyanates can alternatively proceed through oxygen-atom transfer and an isomeric Mo­(IV) (κ<sup>2</sup>-<i>C,O</i>)-isocyanate according to N<sub>2</sub>O + CNR → N<sub>2</sub> + RNCO
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