N-Heterocyclic Carbene Palladium Pincer ComplexesSynthesis, Aggregations and Catalytic Applications
N-Heterocyclic Carbene Palladium Pincer Complexes
Synthesis, Aggregations and Catalytic Applications
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DissertationPrüfungsdatum
20.10.2011Datum der Veröffentlichung
29.11.2011Erstgutachter
Dötz, Karl HeinzZweitgutachter
Lützen, ArneMetadaten
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The work presented herein describes an investigation of a new class of pyridine-bridged bis- (benz)imidazolium salts and N-heterocyclic pincer carbene complexes derived there from, as well as their implication as homogenious catalysis in Heck and Suzuki cross coupling reactions and their aggregation to liquid crystals and organometallic gels.
The novel pyridine bridged bis-benzimidazolylidene pincer palladium complex 6 is readily accessible by the amination of 2,6-difluoropyridine with benzimidazole, followed by N-alkylation with n-alkylhalide. The cyclometalation with palladium acetate under microwave conditions leads to palladium carbene complex 6. The palladium atom was strongly bound to two carbene molecules and coordinated with a pyridine molecule leading to the CNC carbene complex. The palladium carbene complex 6 is an efficient catalyst towards the Heck and Suzuki cross-coupling reactions even with catalyst loadings as low as 0.1 to 1 ppm. The scope of aryl halides as reaction proceeding is not significantly hampered by electronic or steric effects. The carbene complex is stable against air, moisture and high temperature.
A new class of conjugated palladium pincer bis-imidazolylidene complexes 12a,b were synthesised according to a modified procedure. Conjugated dibromopyridine was prepared through Arbuzov reaction, followed by cross coupling with imidazole under copper catalysis. The cyclometalated palladium complexes were prepared according to a standard procedure. A short C4 alkyl chain complex 12a shows strong catalytical activity towards cross coupling reactions. The C16 long alkyl chain complex 12b efficiently gelates polar organic solvents. A co-solvent effect is also playing a key role towards gelation. A stable and transparent gel was observed in DMSO at 0.5 wt%. The thermal stability of the gel increases with the gelator concentration.
According to the similar procedure the π-extended conjugated palladium pincer bis-benzimidazolylidene complexes 15a, b were prepared. Compared to bis-imidazolylidene complex 12a, C4 the short alkyl chain palladium complex 15a shows a strong catalytical activity towards cross-coupling reactions due to the σ-donor ability of the NHC ligand which increases the electron density on the palladium center. The extended π-system complex 15b strongly gelates polar, apolar and chlorinated solvents. With the strong coordinating polar solvents thin film TEM images were observed, while long helical fiber (P and M) networks were observed in apolar solvents, which are quite rarely observed in gel networks, formed from achiral gelators. A stable and transparent gel was observed in DMSO at 0.3 wt%. Again the thermal stability of the gel increases with the gelator concentration.
Tuning property of molecules from gels to liquid crystalline behaviour is a challenge towards the design of target oriented synthesis. The highly extended conjugated pyridine-bridged bis-benzimidazolium salt is readily accessible according to modified procedure in quantitative yields. The extended π-system in pyridine-bridged bis-benzimidazolium salts 5a-d efficiently gelates aprotic solvents; however the conjugated pyridine-bridged bis-(benz)imidazolium salts 11b, 14b do not show any significant effect towards gelation. The highly extended pyridine-bridged bis-benzimidazolium salt 19 behaves like liquid crystalline materials at higher temperature. Fan-shaped textures of 19 were observed at 200° C under crossed polarized optical microscopy. Due to the lack of sufficient van der Waals interactions at orthogonal direction, at the isotropic point electron rich salt 19 was undergoes polymerisation leading to plastic crystalline materials.
The oligovinylene materials have been pain to much attention due to strong π-π stacking, hydrogen bonding ionic and van der Waals interactions towards self-assembly. The self-assembly of the highly conjugated pyridine-bridged bis-imidazolium salt 28 behaves like thermoreversible liquid crystalline materials. Compared to bis-benzimidazolium salt 19, strong van der Waals interactions in orthogonal direction of 28 allow to pack the molecules in three-dimensional directions to optimize liquid crystalline properties at 100o C. The investigation of mesomorphic properties of 28 by POM and DSC revealed that the thermoreversible liquid crystalline materials are regaining their original property even after cooling from isotropic phase.
The novel N-heterocyclic carbenes receive much attention due to their strong σ-donor and π-acceptor ligand ability and their metal complexes are widely applied in catalysis and material science. A new class of six-membered NHC ligands derived from perimidinium salts show stronger σ-donor ability compared to five-membered NHC ylidenes derived from (benz)imidazolium salts. For the making of novel pyridine bridged bis-perimidiniylidene complex 32 was synthesised according to modified procedure. Under copper catalyzed cross coupling reactions pyridine bridged bis-perimidine was prepared in moderate yields, followed by N-alkylation with n-alkyl halides. The in-situ generation of carbene was stabilized by intramolecular delocalisation leading to urea type molecule; however no cyclometalation product 32 was formed.
The lutidine- bridged bis-(benz)imidazolium and perimidinium salts 33, 34, 38 were prepared according to the reported procedure. The in-situ generation of the palladium catalyst by treatment of equimolar amounts of salts and palladium acetate, subjected to the cross coupling reactions. At 5 ppm catalyst loadings the high efficient catalyst shows strong significant effect towards the Heck and Suzuki cross-coupling reactions leading to high turnover numbers. The precatalysts are generated from bis-(benz) imidazolium salts are less effective compared to bis-perimidinum salt due to week σ-donor and π-acceptor ability.
Phosphine-free palladium catalysed cross-coupling reactions are very attractive towards regio- and chemoselective C-arylation on thiophene ring with haloarenes. A selective catalytic C-H activation at 5-position of the thiopehene ring with iodoarene with palladium acetate under inert conditions leads to 2, 5-diarylthiophenes with high yields. The cross-coupling is compatible with both electron-donating and electron accepting substituents in the iodoarene and also conducted in an either inter- or intramolecular fashion. The novel protocol is applied to the synthesis of arylthiophenes as relevant for the development of both bioactive compounds and functional materials, such as in electronic devices or liquid crystals.
The novel pyridine bridged bis-benzimidazolylidene pincer palladium complex 6 is readily accessible by the amination of 2,6-difluoropyridine with benzimidazole, followed by N-alkylation with n-alkylhalide. The cyclometalation with palladium acetate under microwave conditions leads to palladium carbene complex 6. The palladium atom was strongly bound to two carbene molecules and coordinated with a pyridine molecule leading to the CNC carbene complex. The palladium carbene complex 6 is an efficient catalyst towards the Heck and Suzuki cross-coupling reactions even with catalyst loadings as low as 0.1 to 1 ppm. The scope of aryl halides as reaction proceeding is not significantly hampered by electronic or steric effects. The carbene complex is stable against air, moisture and high temperature.
A new class of conjugated palladium pincer bis-imidazolylidene complexes 12a,b were synthesised according to a modified procedure. Conjugated dibromopyridine was prepared through Arbuzov reaction, followed by cross coupling with imidazole under copper catalysis. The cyclometalated palladium complexes were prepared according to a standard procedure. A short C4 alkyl chain complex 12a shows strong catalytical activity towards cross coupling reactions. The C16 long alkyl chain complex 12b efficiently gelates polar organic solvents. A co-solvent effect is also playing a key role towards gelation. A stable and transparent gel was observed in DMSO at 0.5 wt%. The thermal stability of the gel increases with the gelator concentration.
According to the similar procedure the π-extended conjugated palladium pincer bis-benzimidazolylidene complexes 15a, b were prepared. Compared to bis-imidazolylidene complex 12a, C4 the short alkyl chain palladium complex 15a shows a strong catalytical activity towards cross-coupling reactions due to the σ-donor ability of the NHC ligand which increases the electron density on the palladium center. The extended π-system complex 15b strongly gelates polar, apolar and chlorinated solvents. With the strong coordinating polar solvents thin film TEM images were observed, while long helical fiber (P and M) networks were observed in apolar solvents, which are quite rarely observed in gel networks, formed from achiral gelators. A stable and transparent gel was observed in DMSO at 0.3 wt%. Again the thermal stability of the gel increases with the gelator concentration.
Tuning property of molecules from gels to liquid crystalline behaviour is a challenge towards the design of target oriented synthesis. The highly extended conjugated pyridine-bridged bis-benzimidazolium salt is readily accessible according to modified procedure in quantitative yields. The extended π-system in pyridine-bridged bis-benzimidazolium salts 5a-d efficiently gelates aprotic solvents; however the conjugated pyridine-bridged bis-(benz)imidazolium salts 11b, 14b do not show any significant effect towards gelation. The highly extended pyridine-bridged bis-benzimidazolium salt 19 behaves like liquid crystalline materials at higher temperature. Fan-shaped textures of 19 were observed at 200° C under crossed polarized optical microscopy. Due to the lack of sufficient van der Waals interactions at orthogonal direction, at the isotropic point electron rich salt 19 was undergoes polymerisation leading to plastic crystalline materials.
The oligovinylene materials have been pain to much attention due to strong π-π stacking, hydrogen bonding ionic and van der Waals interactions towards self-assembly. The self-assembly of the highly conjugated pyridine-bridged bis-imidazolium salt 28 behaves like thermoreversible liquid crystalline materials. Compared to bis-benzimidazolium salt 19, strong van der Waals interactions in orthogonal direction of 28 allow to pack the molecules in three-dimensional directions to optimize liquid crystalline properties at 100o C. The investigation of mesomorphic properties of 28 by POM and DSC revealed that the thermoreversible liquid crystalline materials are regaining their original property even after cooling from isotropic phase.
The novel N-heterocyclic carbenes receive much attention due to their strong σ-donor and π-acceptor ligand ability and their metal complexes are widely applied in catalysis and material science. A new class of six-membered NHC ligands derived from perimidinium salts show stronger σ-donor ability compared to five-membered NHC ylidenes derived from (benz)imidazolium salts. For the making of novel pyridine bridged bis-perimidiniylidene complex 32 was synthesised according to modified procedure. Under copper catalyzed cross coupling reactions pyridine bridged bis-perimidine was prepared in moderate yields, followed by N-alkylation with n-alkyl halides. The in-situ generation of carbene was stabilized by intramolecular delocalisation leading to urea type molecule; however no cyclometalation product 32 was formed.
The lutidine- bridged bis-(benz)imidazolium and perimidinium salts 33, 34, 38 were prepared according to the reported procedure. The in-situ generation of the palladium catalyst by treatment of equimolar amounts of salts and palladium acetate, subjected to the cross coupling reactions. At 5 ppm catalyst loadings the high efficient catalyst shows strong significant effect towards the Heck and Suzuki cross-coupling reactions leading to high turnover numbers. The precatalysts are generated from bis-(benz) imidazolium salts are less effective compared to bis-perimidinum salt due to week σ-donor and π-acceptor ability.
Phosphine-free palladium catalysed cross-coupling reactions are very attractive towards regio- and chemoselective C-arylation on thiophene ring with haloarenes. A selective catalytic C-H activation at 5-position of the thiopehene ring with iodoarene with palladium acetate under inert conditions leads to 2, 5-diarylthiophenes with high yields. The cross-coupling is compatible with both electron-donating and electron accepting substituents in the iodoarene and also conducted in an either inter- or intramolecular fashion. The novel protocol is applied to the synthesis of arylthiophenes as relevant for the development of both bioactive compounds and functional materials, such as in electronic devices or liquid crystals.
Klassifikation (DDC)
540 ChemieJagadeesh, Malineni: N-Heterocyclic Carbene Palladium Pincer Complexes : Synthesis, Aggregations and Catalytic Applications. - Bonn, 2011. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5N-27094
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5N-27094
@phdthesis{handle:20.500.11811/5071,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5N-27094,
author = {{Malineni Jagadeesh}},
title = {N-Heterocyclic Carbene Palladium Pincer Complexes : Synthesis, Aggregations and Catalytic Applications},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2011,
month = nov,
note = {The work presented herein describes an investigation of a new class of pyridine-bridged bis- (benz)imidazolium salts and N-heterocyclic pincer carbene complexes derived there from, as well as their implication as homogenious catalysis in Heck and Suzuki cross coupling reactions and their aggregation to liquid crystals and organometallic gels.
The novel pyridine bridged bis-benzimidazolylidene pincer palladium complex 6 is readily accessible by the amination of 2,6-difluoropyridine with benzimidazole, followed by N-alkylation with n-alkylhalide. The cyclometalation with palladium acetate under microwave conditions leads to palladium carbene complex 6. The palladium atom was strongly bound to two carbene molecules and coordinated with a pyridine molecule leading to the CNC carbene complex. The palladium carbene complex 6 is an efficient catalyst towards the Heck and Suzuki cross-coupling reactions even with catalyst loadings as low as 0.1 to 1 ppm. The scope of aryl halides as reaction proceeding is not significantly hampered by electronic or steric effects. The carbene complex is stable against air, moisture and high temperature.
A new class of conjugated palladium pincer bis-imidazolylidene complexes 12a,b were synthesised according to a modified procedure. Conjugated dibromopyridine was prepared through Arbuzov reaction, followed by cross coupling with imidazole under copper catalysis. The cyclometalated palladium complexes were prepared according to a standard procedure. A short C4 alkyl chain complex 12a shows strong catalytical activity towards cross coupling reactions. The C16 long alkyl chain complex 12b efficiently gelates polar organic solvents. A co-solvent effect is also playing a key role towards gelation. A stable and transparent gel was observed in DMSO at 0.5 wt%. The thermal stability of the gel increases with the gelator concentration.
According to the similar procedure the π-extended conjugated palladium pincer bis-benzimidazolylidene complexes 15a, b were prepared. Compared to bis-imidazolylidene complex 12a, C4 the short alkyl chain palladium complex 15a shows a strong catalytical activity towards cross-coupling reactions due to the σ-donor ability of the NHC ligand which increases the electron density on the palladium center. The extended π-system complex 15b strongly gelates polar, apolar and chlorinated solvents. With the strong coordinating polar solvents thin film TEM images were observed, while long helical fiber (P and M) networks were observed in apolar solvents, which are quite rarely observed in gel networks, formed from achiral gelators. A stable and transparent gel was observed in DMSO at 0.3 wt%. Again the thermal stability of the gel increases with the gelator concentration.
Tuning property of molecules from gels to liquid crystalline behaviour is a challenge towards the design of target oriented synthesis. The highly extended conjugated pyridine-bridged bis-benzimidazolium salt is readily accessible according to modified procedure in quantitative yields. The extended π-system in pyridine-bridged bis-benzimidazolium salts 5a-d efficiently gelates aprotic solvents; however the conjugated pyridine-bridged bis-(benz)imidazolium salts 11b, 14b do not show any significant effect towards gelation. The highly extended pyridine-bridged bis-benzimidazolium salt 19 behaves like liquid crystalline materials at higher temperature. Fan-shaped textures of 19 were observed at 200° C under crossed polarized optical microscopy. Due to the lack of sufficient van der Waals interactions at orthogonal direction, at the isotropic point electron rich salt 19 was undergoes polymerisation leading to plastic crystalline materials.
The oligovinylene materials have been pain to much attention due to strong π-π stacking, hydrogen bonding ionic and van der Waals interactions towards self-assembly. The self-assembly of the highly conjugated pyridine-bridged bis-imidazolium salt 28 behaves like thermoreversible liquid crystalline materials. Compared to bis-benzimidazolium salt 19, strong van der Waals interactions in orthogonal direction of 28 allow to pack the molecules in three-dimensional directions to optimize liquid crystalline properties at 100o C. The investigation of mesomorphic properties of 28 by POM and DSC revealed that the thermoreversible liquid crystalline materials are regaining their original property even after cooling from isotropic phase.
The novel N-heterocyclic carbenes receive much attention due to their strong σ-donor and π-acceptor ligand ability and their metal complexes are widely applied in catalysis and material science. A new class of six-membered NHC ligands derived from perimidinium salts show stronger σ-donor ability compared to five-membered NHC ylidenes derived from (benz)imidazolium salts. For the making of novel pyridine bridged bis-perimidiniylidene complex 32 was synthesised according to modified procedure. Under copper catalyzed cross coupling reactions pyridine bridged bis-perimidine was prepared in moderate yields, followed by N-alkylation with n-alkyl halides. The in-situ generation of carbene was stabilized by intramolecular delocalisation leading to urea type molecule; however no cyclometalation product 32 was formed.
The lutidine- bridged bis-(benz)imidazolium and perimidinium salts 33, 34, 38 were prepared according to the reported procedure. The in-situ generation of the palladium catalyst by treatment of equimolar amounts of salts and palladium acetate, subjected to the cross coupling reactions. At 5 ppm catalyst loadings the high efficient catalyst shows strong significant effect towards the Heck and Suzuki cross-coupling reactions leading to high turnover numbers. The precatalysts are generated from bis-(benz) imidazolium salts are less effective compared to bis-perimidinum salt due to week σ-donor and π-acceptor ability.
Phosphine-free palladium catalysed cross-coupling reactions are very attractive towards regio- and chemoselective C-arylation on thiophene ring with haloarenes. A selective catalytic C-H activation at 5-position of the thiopehene ring with iodoarene with palladium acetate under inert conditions leads to 2, 5-diarylthiophenes with high yields. The cross-coupling is compatible with both electron-donating and electron accepting substituents in the iodoarene and also conducted in an either inter- or intramolecular fashion. The novel protocol is applied to the synthesis of arylthiophenes as relevant for the development of both bioactive compounds and functional materials, such as in electronic devices or liquid crystals.},
url = {https://hdl.handle.net/20.500.11811/5071}
}
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5N-27094,
author = {{Malineni Jagadeesh}},
title = {N-Heterocyclic Carbene Palladium Pincer Complexes : Synthesis, Aggregations and Catalytic Applications},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2011,
month = nov,
note = {The work presented herein describes an investigation of a new class of pyridine-bridged bis- (benz)imidazolium salts and N-heterocyclic pincer carbene complexes derived there from, as well as their implication as homogenious catalysis in Heck and Suzuki cross coupling reactions and their aggregation to liquid crystals and organometallic gels.
The novel pyridine bridged bis-benzimidazolylidene pincer palladium complex 6 is readily accessible by the amination of 2,6-difluoropyridine with benzimidazole, followed by N-alkylation with n-alkylhalide. The cyclometalation with palladium acetate under microwave conditions leads to palladium carbene complex 6. The palladium atom was strongly bound to two carbene molecules and coordinated with a pyridine molecule leading to the CNC carbene complex. The palladium carbene complex 6 is an efficient catalyst towards the Heck and Suzuki cross-coupling reactions even with catalyst loadings as low as 0.1 to 1 ppm. The scope of aryl halides as reaction proceeding is not significantly hampered by electronic or steric effects. The carbene complex is stable against air, moisture and high temperature.
A new class of conjugated palladium pincer bis-imidazolylidene complexes 12a,b were synthesised according to a modified procedure. Conjugated dibromopyridine was prepared through Arbuzov reaction, followed by cross coupling with imidazole under copper catalysis. The cyclometalated palladium complexes were prepared according to a standard procedure. A short C4 alkyl chain complex 12a shows strong catalytical activity towards cross coupling reactions. The C16 long alkyl chain complex 12b efficiently gelates polar organic solvents. A co-solvent effect is also playing a key role towards gelation. A stable and transparent gel was observed in DMSO at 0.5 wt%. The thermal stability of the gel increases with the gelator concentration.
According to the similar procedure the π-extended conjugated palladium pincer bis-benzimidazolylidene complexes 15a, b were prepared. Compared to bis-imidazolylidene complex 12a, C4 the short alkyl chain palladium complex 15a shows a strong catalytical activity towards cross-coupling reactions due to the σ-donor ability of the NHC ligand which increases the electron density on the palladium center. The extended π-system complex 15b strongly gelates polar, apolar and chlorinated solvents. With the strong coordinating polar solvents thin film TEM images were observed, while long helical fiber (P and M) networks were observed in apolar solvents, which are quite rarely observed in gel networks, formed from achiral gelators. A stable and transparent gel was observed in DMSO at 0.3 wt%. Again the thermal stability of the gel increases with the gelator concentration.
Tuning property of molecules from gels to liquid crystalline behaviour is a challenge towards the design of target oriented synthesis. The highly extended conjugated pyridine-bridged bis-benzimidazolium salt is readily accessible according to modified procedure in quantitative yields. The extended π-system in pyridine-bridged bis-benzimidazolium salts 5a-d efficiently gelates aprotic solvents; however the conjugated pyridine-bridged bis-(benz)imidazolium salts 11b, 14b do not show any significant effect towards gelation. The highly extended pyridine-bridged bis-benzimidazolium salt 19 behaves like liquid crystalline materials at higher temperature. Fan-shaped textures of 19 were observed at 200° C under crossed polarized optical microscopy. Due to the lack of sufficient van der Waals interactions at orthogonal direction, at the isotropic point electron rich salt 19 was undergoes polymerisation leading to plastic crystalline materials.
The oligovinylene materials have been pain to much attention due to strong π-π stacking, hydrogen bonding ionic and van der Waals interactions towards self-assembly. The self-assembly of the highly conjugated pyridine-bridged bis-imidazolium salt 28 behaves like thermoreversible liquid crystalline materials. Compared to bis-benzimidazolium salt 19, strong van der Waals interactions in orthogonal direction of 28 allow to pack the molecules in three-dimensional directions to optimize liquid crystalline properties at 100o C. The investigation of mesomorphic properties of 28 by POM and DSC revealed that the thermoreversible liquid crystalline materials are regaining their original property even after cooling from isotropic phase.
The novel N-heterocyclic carbenes receive much attention due to their strong σ-donor and π-acceptor ligand ability and their metal complexes are widely applied in catalysis and material science. A new class of six-membered NHC ligands derived from perimidinium salts show stronger σ-donor ability compared to five-membered NHC ylidenes derived from (benz)imidazolium salts. For the making of novel pyridine bridged bis-perimidiniylidene complex 32 was synthesised according to modified procedure. Under copper catalyzed cross coupling reactions pyridine bridged bis-perimidine was prepared in moderate yields, followed by N-alkylation with n-alkyl halides. The in-situ generation of carbene was stabilized by intramolecular delocalisation leading to urea type molecule; however no cyclometalation product 32 was formed.
The lutidine- bridged bis-(benz)imidazolium and perimidinium salts 33, 34, 38 were prepared according to the reported procedure. The in-situ generation of the palladium catalyst by treatment of equimolar amounts of salts and palladium acetate, subjected to the cross coupling reactions. At 5 ppm catalyst loadings the high efficient catalyst shows strong significant effect towards the Heck and Suzuki cross-coupling reactions leading to high turnover numbers. The precatalysts are generated from bis-(benz) imidazolium salts are less effective compared to bis-perimidinum salt due to week σ-donor and π-acceptor ability.
Phosphine-free palladium catalysed cross-coupling reactions are very attractive towards regio- and chemoselective C-arylation on thiophene ring with haloarenes. A selective catalytic C-H activation at 5-position of the thiopehene ring with iodoarene with palladium acetate under inert conditions leads to 2, 5-diarylthiophenes with high yields. The cross-coupling is compatible with both electron-donating and electron accepting substituents in the iodoarene and also conducted in an either inter- or intramolecular fashion. The novel protocol is applied to the synthesis of arylthiophenes as relevant for the development of both bioactive compounds and functional materials, such as in electronic devices or liquid crystals.},
url = {https://hdl.handle.net/20.500.11811/5071}
}
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