The supported titanium catalyst s(FI)Ti, generated by adding (FI)TiCl 3 to MAO-treated SiO 2 (FI ... more The supported titanium catalyst s(FI)Ti, generated by adding (FI)TiCl 3 to MAO-treated SiO 2 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2′-(2″-methoxyphenyl)anilinato), effects the selective trimerization of the linear α-olefins (LAOs) propene, 1-pentene, 1-hexene, and 1-decene, with >95% selectivity for trimers and ∼85% selectivity to a single isomer thereof (2,3,5-trialkyl-1-hexene). Mechanistic interpretations are offered for the high regioselectivity as well as for some unusual kinetics behavior, including third-order dependence on LAO concentration and nearly identical initial rates at 0 and 25 °C.
Highly crystalline poly(hydroxybutyrate) suffers from high melting point and entanglement molecul... more Highly crystalline poly(hydroxybutyrate) suffers from high melting point and entanglement molecular weight. This leads to low melt strength, limits processing through regular techniques, and precludes many applications. In this work we report a series of racemic and enantiopure zinc catalysts supported by variously substituted diaminophenolate ancillary ligands which form high melt strength PHBs with different molecular weights and microstructure. These complexes are active for the highly controlled polymerization of β-butyrolactone (BBL); some can polymerize 2000 equiv of BBL in less than 30 min. Changing the steric bulk of the ligand forms PHBs of varied syndiotacticity (P r = 0.75 to 0.55). These are highly robust systems capable of polymerizing an unprecedented 20000 equiv of BBL in the presence of 5000 equiv of benzyl alcohol. Thermorheological investigations reveal that the synthesized PHBs have surprisingly high melt strength at above the melting point. For processable PHBs, high density of entanglements and relatively low crystallinity are crucial. We show that the best PHBs should have high molecular weight and moderate syndiotacticity.
Linear low-density polyethylene (LLDPE) is produced from an ethylene-only feed over a tandem cata... more Linear low-density polyethylene (LLDPE) is produced from an ethylene-only feed over a tandem catalyst system consisting of a phenoxy−imine titanium trimerization catalyst and a silylene-linked cyclopentadienyl/amido titanium polymerization catalyst cosupported on the same methylaluminoxane/ silica particles. The level of 1-hexene incorporation can be controlled by varying the ethylene pressure. P roduction of linear low-density polyethylene (LLDPE) by copolymerization of ethylene with an α-olefin is an important industrial process. 1 As currently practiced, ethylene is catalytically oligomerized to the α-olefin, principally 1-hexene or 1-octene, which is isolated and copolymerized with ethylene in a separate reactor, using a different catalytic system. 2 Orthogonal tandem catalysis, 3 where two independent catalysts operate together to perform consecutive transformations in a single reactor, offers the potential for a more efficient and economical process; a supported version would be of particular interest. Supported catalysts are widely used industrially in polyolefin synthesis, as they favor highly uniform particle morphology and free-flowing product without undesired " fines " (small polyethylene particles) and/or sticky ethylene copoly-mers with high 1-alkene content that adhere to reactor components, thus allowing for easy product isolation and preventing reactor fouling. 4 Several tandem catalyst systems for the synthesis of LLDPE have been reported 5 (to the best of our knowledge, none of these are in commercial use), including two supported systems. 5d,g In those examples, the two catalysts are on separate supports, 6 which can cause undesirable issues in an industrial process, such as catalyst segregation and inhomogeneity in the reactor over time. Supporting both catalysts on the same solid material would avoid such problems. It could also offer other potential advantages (e.g., more efficient tandem behavior resulting from proximity) as well as difficulties, such as reduced activity due to mutual interference; both of these have been observed with a covalently linked homogeneous tandem catalyst. 5f Here we report the first successful generation of a tandem LLDPE catalyst by cosupporting both trimerization and polymerization catalysts on the same silica particles. We previously reported that the ethylene trimerization precatalyst initially developed by Fujita et al., (FI)TiCl 3 (FI = (N-(5-methyl-3-(1-adamantyl)-salicylidene)-2′-(2″-methoxyphenyl)anilinato), 7 can be effectively used in a methylaluminoxane (MAO)/silica-supported form, called s-(FI)Ti. 8 A tandem catalyst with cosupported (Cp*SiNR)TiCl 2 (Cp*SiNR = (η 5-C 5 Me 4)Me 2 Si(η 1-NCMe 3), originally reported by Okuda et al. 9 and Dow Chemical Company, 10 as the copolymerization component, was generated by addition of a solution of the two catalysts to a toluene slurry of MAO/silica (Scheme 1). Co-supported systems with y/x = 1−10 were prepared in this manner. In all instances, the Al:Ti ratio (300:1) and the total titanium loading (0.018 mmol/g of MAO/silica) were kept the same. The cosupported catalyst systems thus obtained are yellow free-flowing, pyrophoric solids, highly sensitive toward air and moisture.
: The synthesis of the first alkoxide-bridged indium complex supported
by a chiral dinucleating l... more : The synthesis of the first alkoxide-bridged indium complex supported by a chiral dinucleating ligand platform (1), along with its zinc analogue (2), is reported. Both complexes are synthesized in a one-pot reaction starting from a chiral dinucleating bis(diamino)phenolate ligand platform, sodium ethoxide, and respective metal salts. The dinucleating indium analogue (7) based on an achiral ligand backbone is also reported. Indium complexes bearing either the chiral or achiral ligand catalyze the ring-opening polymerization of racemic lactide (rac-LA) to afford highly heterotactic poly(lactic acid) (PLA; Pr > 0.85). The indium complex bearing an achiral ligand affords essentially atactic PLA from meso-LA. The role of the dinucleating ligand structure in catalyst synthesis and polymerization activity is discussed
Treatment of dry silica with methylaluminoxane (MAO) followed by (FI)TiCl3 (FI = (N-(5-methyl-3-(... more Treatment of dry silica with methylaluminoxane (MAO) followed by (FI)TiCl3 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2′-(2′′-methoxyphenyl)anilinato) gives a heterogeneous supported ethylene trimerization catalyst, s(FI)Ti, which exhibits productivity more than an order of magnitude higher than its homogeneous analogues. This increase in productivity is attributed to a decreased rate of catalyst decomposition, a process that is proposed to occur via comproportionation to an inactive Ti(III) species; immobilization retards this process. In addition, s(FI)Ti catalyzes trimerization of α-olefins with high selectivity. Based on regioisomer distributions, catalysis by s(FI)Ti involves the same active species as the previously reported homogeneous systems (FI)TiR2 Me/B(C6F5)3(R = Me, CH2SiMe3,CH2CMe3).
A methodology for controlling aggregation in highly active and isoselective indium catalysts for ... more A methodology for controlling aggregation in highly active and isoselective indium catalysts for the ring opening polymerization of racemic lactide is reported. A series of racemic and enantiopure dinuclear indium ethoxide complexes bearing salen ligands [(ONNO R )InOEt] 2 (R ¼ Br, Me, admantyl, cumyl, t -Bu) were synthesized and fully characterized. Mononuclear analogues (ONNO R )InOCH 2 Pyr (R ¼ Br, t -Bu, SiPh 3 ) were synthesized by controlling aggregation with the use of chelating 2-pyridinemethoxide functionality. The nuclearity of metal complexes was con fi rmed using PGSE NMR spectroscopy. Detailed kinetic studies show a clear initiation period for these dinuclear catalysts, which is lacking in their mononuclear analogues. The polymerization behavior of analogous dinuclear and mononuclear compounds is identical and consistent with a mononuclear propagating species. The isotacticity of the resulting polymers was investigated using direct integration and peak deconvolution methodologies and the two were compared.
Chiral indium salen complexes are highly active, isoselective catalysts for the ring opening poly... more Chiral indium salen complexes are highly active, isoselective catalysts for the ring opening polymerization of racemic lactide. The polymerizations are well controlled and polymers with high molecular weights and low molecular weight distributions are obtained. Preliminary kinetic investigations with the enantiopure complex confirm enantiomorphic site control as the dominant contributor to selectivity and formation of block copolymers.
The reactivity of two dinuclear SalBinam indium compounds for the ring-opening
polymerization of ... more The reactivity of two dinuclear SalBinam indium compounds for the ring-opening polymerization of lactide was investigated. Examination of the polymerization behavior of two complexes and the reaction equilibrium between the two illustrates the importance of aggregation in indium salen complexes compared to their aluminum counterparts.
A series of (±)- and (R,R)-tridentate diamino, ortho/para disubstituted phenolate proligands H(NN... more A series of (±)- and (R,R)-tridentate diamino, ortho/para disubstituted phenolate proligands H(NNOR) with various phenolate substituents was synthesized and used to prepare indium dichloride complexes (NNOR)InCl2via salt metathesis of the deprotonated ligands with indium trichloride. These complexes are dinuclear in the solid state, in contrast to previously reported complexes with t-butyl or methyl phenolate substituents. Solution state 1H and PGSE NMR spectroscopy suggests that a fast exchange between the monomeric and dimeric forms of these complexes may exist in solution and is likely influenced by the chirality of the complexes undergoing aggregation. The indium dichloride complexes were utilized to synthesize dinuclear indium ethoxide complexes via salt metathesis with sodium ethoxide. These complexes were active for the polymerization of lactide. In situ and bulk polymerization data confirmed differences in the activity and selectivity of these systems based on the phenolate substituents as well as the ligand chirality.
The nature of the central amine donor may play a role in tuning the reactivity of dinuclear indiu... more The nature of the central amine donor may play a role in tuning the reactivity of dinuclear indium catalysts for the ring opening polymerization of lactide. Catalysts with central secondary amine donors are 2 orders of magnitude more reactive than those with central tertiary amine donors.
The supported titanium catalyst s(FI)Ti, generated by adding (FI)TiCl 3 to MAO-treated SiO 2 (FI ... more The supported titanium catalyst s(FI)Ti, generated by adding (FI)TiCl 3 to MAO-treated SiO 2 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2′-(2″-methoxyphenyl)anilinato), effects the selective trimerization of the linear α-olefins (LAOs) propene, 1-pentene, 1-hexene, and 1-decene, with >95% selectivity for trimers and ∼85% selectivity to a single isomer thereof (2,3,5-trialkyl-1-hexene). Mechanistic interpretations are offered for the high regioselectivity as well as for some unusual kinetics behavior, including third-order dependence on LAO concentration and nearly identical initial rates at 0 and 25 °C.
Highly crystalline poly(hydroxybutyrate) suffers from high melting point and entanglement molecul... more Highly crystalline poly(hydroxybutyrate) suffers from high melting point and entanglement molecular weight. This leads to low melt strength, limits processing through regular techniques, and precludes many applications. In this work we report a series of racemic and enantiopure zinc catalysts supported by variously substituted diaminophenolate ancillary ligands which form high melt strength PHBs with different molecular weights and microstructure. These complexes are active for the highly controlled polymerization of β-butyrolactone (BBL); some can polymerize 2000 equiv of BBL in less than 30 min. Changing the steric bulk of the ligand forms PHBs of varied syndiotacticity (P r = 0.75 to 0.55). These are highly robust systems capable of polymerizing an unprecedented 20000 equiv of BBL in the presence of 5000 equiv of benzyl alcohol. Thermorheological investigations reveal that the synthesized PHBs have surprisingly high melt strength at above the melting point. For processable PHBs, high density of entanglements and relatively low crystallinity are crucial. We show that the best PHBs should have high molecular weight and moderate syndiotacticity.
Linear low-density polyethylene (LLDPE) is produced from an ethylene-only feed over a tandem cata... more Linear low-density polyethylene (LLDPE) is produced from an ethylene-only feed over a tandem catalyst system consisting of a phenoxy−imine titanium trimerization catalyst and a silylene-linked cyclopentadienyl/amido titanium polymerization catalyst cosupported on the same methylaluminoxane/ silica particles. The level of 1-hexene incorporation can be controlled by varying the ethylene pressure. P roduction of linear low-density polyethylene (LLDPE) by copolymerization of ethylene with an α-olefin is an important industrial process. 1 As currently practiced, ethylene is catalytically oligomerized to the α-olefin, principally 1-hexene or 1-octene, which is isolated and copolymerized with ethylene in a separate reactor, using a different catalytic system. 2 Orthogonal tandem catalysis, 3 where two independent catalysts operate together to perform consecutive transformations in a single reactor, offers the potential for a more efficient and economical process; a supported version would be of particular interest. Supported catalysts are widely used industrially in polyolefin synthesis, as they favor highly uniform particle morphology and free-flowing product without undesired " fines " (small polyethylene particles) and/or sticky ethylene copoly-mers with high 1-alkene content that adhere to reactor components, thus allowing for easy product isolation and preventing reactor fouling. 4 Several tandem catalyst systems for the synthesis of LLDPE have been reported 5 (to the best of our knowledge, none of these are in commercial use), including two supported systems. 5d,g In those examples, the two catalysts are on separate supports, 6 which can cause undesirable issues in an industrial process, such as catalyst segregation and inhomogeneity in the reactor over time. Supporting both catalysts on the same solid material would avoid such problems. It could also offer other potential advantages (e.g., more efficient tandem behavior resulting from proximity) as well as difficulties, such as reduced activity due to mutual interference; both of these have been observed with a covalently linked homogeneous tandem catalyst. 5f Here we report the first successful generation of a tandem LLDPE catalyst by cosupporting both trimerization and polymerization catalysts on the same silica particles. We previously reported that the ethylene trimerization precatalyst initially developed by Fujita et al., (FI)TiCl 3 (FI = (N-(5-methyl-3-(1-adamantyl)-salicylidene)-2′-(2″-methoxyphenyl)anilinato), 7 can be effectively used in a methylaluminoxane (MAO)/silica-supported form, called s-(FI)Ti. 8 A tandem catalyst with cosupported (Cp*SiNR)TiCl 2 (Cp*SiNR = (η 5-C 5 Me 4)Me 2 Si(η 1-NCMe 3), originally reported by Okuda et al. 9 and Dow Chemical Company, 10 as the copolymerization component, was generated by addition of a solution of the two catalysts to a toluene slurry of MAO/silica (Scheme 1). Co-supported systems with y/x = 1−10 were prepared in this manner. In all instances, the Al:Ti ratio (300:1) and the total titanium loading (0.018 mmol/g of MAO/silica) were kept the same. The cosupported catalyst systems thus obtained are yellow free-flowing, pyrophoric solids, highly sensitive toward air and moisture.
: The synthesis of the first alkoxide-bridged indium complex supported
by a chiral dinucleating l... more : The synthesis of the first alkoxide-bridged indium complex supported by a chiral dinucleating ligand platform (1), along with its zinc analogue (2), is reported. Both complexes are synthesized in a one-pot reaction starting from a chiral dinucleating bis(diamino)phenolate ligand platform, sodium ethoxide, and respective metal salts. The dinucleating indium analogue (7) based on an achiral ligand backbone is also reported. Indium complexes bearing either the chiral or achiral ligand catalyze the ring-opening polymerization of racemic lactide (rac-LA) to afford highly heterotactic poly(lactic acid) (PLA; Pr > 0.85). The indium complex bearing an achiral ligand affords essentially atactic PLA from meso-LA. The role of the dinucleating ligand structure in catalyst synthesis and polymerization activity is discussed
Treatment of dry silica with methylaluminoxane (MAO) followed by (FI)TiCl3 (FI = (N-(5-methyl-3-(... more Treatment of dry silica with methylaluminoxane (MAO) followed by (FI)TiCl3 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2′-(2′′-methoxyphenyl)anilinato) gives a heterogeneous supported ethylene trimerization catalyst, s(FI)Ti, which exhibits productivity more than an order of magnitude higher than its homogeneous analogues. This increase in productivity is attributed to a decreased rate of catalyst decomposition, a process that is proposed to occur via comproportionation to an inactive Ti(III) species; immobilization retards this process. In addition, s(FI)Ti catalyzes trimerization of α-olefins with high selectivity. Based on regioisomer distributions, catalysis by s(FI)Ti involves the same active species as the previously reported homogeneous systems (FI)TiR2 Me/B(C6F5)3(R = Me, CH2SiMe3,CH2CMe3).
A methodology for controlling aggregation in highly active and isoselective indium catalysts for ... more A methodology for controlling aggregation in highly active and isoselective indium catalysts for the ring opening polymerization of racemic lactide is reported. A series of racemic and enantiopure dinuclear indium ethoxide complexes bearing salen ligands [(ONNO R )InOEt] 2 (R ¼ Br, Me, admantyl, cumyl, t -Bu) were synthesized and fully characterized. Mononuclear analogues (ONNO R )InOCH 2 Pyr (R ¼ Br, t -Bu, SiPh 3 ) were synthesized by controlling aggregation with the use of chelating 2-pyridinemethoxide functionality. The nuclearity of metal complexes was con fi rmed using PGSE NMR spectroscopy. Detailed kinetic studies show a clear initiation period for these dinuclear catalysts, which is lacking in their mononuclear analogues. The polymerization behavior of analogous dinuclear and mononuclear compounds is identical and consistent with a mononuclear propagating species. The isotacticity of the resulting polymers was investigated using direct integration and peak deconvolution methodologies and the two were compared.
Chiral indium salen complexes are highly active, isoselective catalysts for the ring opening poly... more Chiral indium salen complexes are highly active, isoselective catalysts for the ring opening polymerization of racemic lactide. The polymerizations are well controlled and polymers with high molecular weights and low molecular weight distributions are obtained. Preliminary kinetic investigations with the enantiopure complex confirm enantiomorphic site control as the dominant contributor to selectivity and formation of block copolymers.
The reactivity of two dinuclear SalBinam indium compounds for the ring-opening
polymerization of ... more The reactivity of two dinuclear SalBinam indium compounds for the ring-opening polymerization of lactide was investigated. Examination of the polymerization behavior of two complexes and the reaction equilibrium between the two illustrates the importance of aggregation in indium salen complexes compared to their aluminum counterparts.
A series of (±)- and (R,R)-tridentate diamino, ortho/para disubstituted phenolate proligands H(NN... more A series of (±)- and (R,R)-tridentate diamino, ortho/para disubstituted phenolate proligands H(NNOR) with various phenolate substituents was synthesized and used to prepare indium dichloride complexes (NNOR)InCl2via salt metathesis of the deprotonated ligands with indium trichloride. These complexes are dinuclear in the solid state, in contrast to previously reported complexes with t-butyl or methyl phenolate substituents. Solution state 1H and PGSE NMR spectroscopy suggests that a fast exchange between the monomeric and dimeric forms of these complexes may exist in solution and is likely influenced by the chirality of the complexes undergoing aggregation. The indium dichloride complexes were utilized to synthesize dinuclear indium ethoxide complexes via salt metathesis with sodium ethoxide. These complexes were active for the polymerization of lactide. In situ and bulk polymerization data confirmed differences in the activity and selectivity of these systems based on the phenolate substituents as well as the ligand chirality.
The nature of the central amine donor may play a role in tuning the reactivity of dinuclear indiu... more The nature of the central amine donor may play a role in tuning the reactivity of dinuclear indium catalysts for the ring opening polymerization of lactide. Catalysts with central secondary amine donors are 2 orders of magnitude more reactive than those with central tertiary amine donors.
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by a chiral dinucleating ligand platform (1), along with its zinc analogue (2), is reported. Both complexes are synthesized in a one-pot reaction starting from a chiral dinucleating bis(diamino)phenolate ligand platform, sodium ethoxide, and respective metal salts. The dinucleating indium analogue (7) based on an achiral ligand backbone is also reported. Indium complexes bearing either the chiral or achiral ligand catalyze the ring-opening polymerization of racemic lactide (rac-LA)
to afford highly heterotactic poly(lactic acid) (PLA; Pr > 0.85). The indium complex bearing an achiral ligand affords essentially atactic PLA from meso-LA. The role of the dinucleating ligand structure in catalyst synthesis and polymerization activity is discussed
comproportionation to an inactive Ti(III) species; immobilization retards this process. In addition, s(FI)Ti catalyzes trimerization of α-olefins with high selectivity. Based on regioisomer distributions, catalysis by s(FI)Ti involves the same active species as the previously reported homogeneous systems (FI)TiR2 Me/B(C6F5)3(R = Me, CH2SiMe3,CH2CMe3).
opening polymerization of racemic lactide is reported. A series of racemic and enantiopure dinuclear
indium ethoxide complexes bearing salen ligands [(ONNO
R
)InOEt]
2
(R
¼
Br, Me, admantyl, cumyl,
t
-Bu)
were synthesized and fully characterized. Mononuclear analogues (ONNO
R
)InOCH
2
Pyr (R
¼
Br,
t
-Bu,
SiPh
3
) were synthesized by controlling aggregation with the use of chelating 2-pyridinemethoxide
functionality. The nuclearity of metal complexes was con
fi
rmed using PGSE NMR spectroscopy. Detailed
kinetic studies show a clear initiation period for these dinuclear catalysts, which is lacking in their
mononuclear analogues. The polymerization behavior of analogous dinuclear and mononuclear
compounds is identical and consistent with a mononuclear propagating species. The isotacticity of the
resulting polymers was investigated using direct integration and peak deconvolution methodologies and
the two were compared.
polymerization of lactide was investigated. Examination of the polymerization behavior of
two complexes and the reaction equilibrium between the two illustrates the importance of
aggregation in indium salen complexes compared to their aluminum counterparts.
by a chiral dinucleating ligand platform (1), along with its zinc analogue (2), is reported. Both complexes are synthesized in a one-pot reaction starting from a chiral dinucleating bis(diamino)phenolate ligand platform, sodium ethoxide, and respective metal salts. The dinucleating indium analogue (7) based on an achiral ligand backbone is also reported. Indium complexes bearing either the chiral or achiral ligand catalyze the ring-opening polymerization of racemic lactide (rac-LA)
to afford highly heterotactic poly(lactic acid) (PLA; Pr > 0.85). The indium complex bearing an achiral ligand affords essentially atactic PLA from meso-LA. The role of the dinucleating ligand structure in catalyst synthesis and polymerization activity is discussed
comproportionation to an inactive Ti(III) species; immobilization retards this process. In addition, s(FI)Ti catalyzes trimerization of α-olefins with high selectivity. Based on regioisomer distributions, catalysis by s(FI)Ti involves the same active species as the previously reported homogeneous systems (FI)TiR2 Me/B(C6F5)3(R = Me, CH2SiMe3,CH2CMe3).
opening polymerization of racemic lactide is reported. A series of racemic and enantiopure dinuclear
indium ethoxide complexes bearing salen ligands [(ONNO
R
)InOEt]
2
(R
¼
Br, Me, admantyl, cumyl,
t
-Bu)
were synthesized and fully characterized. Mononuclear analogues (ONNO
R
)InOCH
2
Pyr (R
¼
Br,
t
-Bu,
SiPh
3
) were synthesized by controlling aggregation with the use of chelating 2-pyridinemethoxide
functionality. The nuclearity of metal complexes was con
fi
rmed using PGSE NMR spectroscopy. Detailed
kinetic studies show a clear initiation period for these dinuclear catalysts, which is lacking in their
mononuclear analogues. The polymerization behavior of analogous dinuclear and mononuclear
compounds is identical and consistent with a mononuclear propagating species. The isotacticity of the
resulting polymers was investigated using direct integration and peak deconvolution methodologies and
the two were compared.
polymerization of lactide was investigated. Examination of the polymerization behavior of
two complexes and the reaction equilibrium between the two illustrates the importance of
aggregation in indium salen complexes compared to their aluminum counterparts.