11 research outputs found
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)Â(2,4-dimethylquinolin-8-yl)Âamino)Âtribenzylhafnium
(<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
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
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
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
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
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
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
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
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
Under
an atmosphere of CO, the MoÂ(IV) imido complex Cp*MoÂ[NÂ(<sup>i</sup>Pr)ÂCÂ(Me)ÂNÂ(<sup>i</sup>Pr)]Â(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 MoÂ(II) monocarbonyl and
MoÂ(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 MoÂ(IV) (κ<sup>2</sup>-<i>C,O</i>)-isocyanate
according to N<sub>2</sub>O + CNR → N<sub>2</sub> + RNCO