The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Shigetoshi Takahashi - One of the best experts on this subject based on the ideXlab platform.
-
stereoselective ligand exchange reaction of planar chiral Cyclopentadienyl ruthenium complexes thermodynamic control of configuration at a stereogenic metal center
Dalton Transactions, 2004Co-Authors: Yuji Matsushima, Kiyotaka Onitsuka, Shigetoshi TakahashiAbstract:The reaction of planar-chiral Cyclopentadienyl–ruthenium complexes with Bu4NI resulted in the formation of iodo complexes with high diastereoselectivity (up to >99%de). The stereochemistry of the ruthenium center in the starting material did not influence the diastereoselectivity of the products. Epimerization of a diastereomerically pure sample gave a mixture of two diastereomers in the same ratio as with the ligand-exchange reaction, suggesting that the selectivity is determined by the difference in thermodynamic stability between the diastereomeric pair of iodo complexes. The ratio of the products depends on the nature of the substituent on the Cyclopentadienyl ring and P ligands on the ruthenium atom. A combination of small substituents on the Cyclopentadienyl Group and small P ligands with strong electron-donating ability favored the formation of 2-I. The bulkiness of the substituents on the Cyclopentadienyl Group or of the P ligands, and low electron-donating ability of the P ligands increased the ratio of 2-II complexes to 2-I isomer.
-
Stereoselective ligand-exchange reaction of planar-chiral Cyclopentadienyl–ruthenium complexes: thermodynamic control of configuration at a stereogenic metal center
Dalton transactions (Cambridge England : 2003), 2004Co-Authors: Yuji Matsushima, Kiyotaka Onitsuka, Shigetoshi TakahashiAbstract:The reaction of planar-chiral Cyclopentadienyl-ruthenium complexes with Bu4NI resulted in the formation of iodo complexes with high diastereoselectivity (up to >99%de). The stereochemistry of the ruthenium center in the starting material did not influence the diastereoselectivity of the products. Epimerization of a diastereomerically pure sample gave a mixture of two diastereomers in the same ratio as with the ligand-exchange reaction, suggesting that the selectivity is determined by the difference in thermodynamic stability between the diastereomeric pair of iodo complexes. The ratio of the products depends on the nature of the substituent on the Cyclopentadienyl ring and P ligands on the ruthenium atom. A combination of small substituents on the Cyclopentadienyl Group and small P ligands with strong electron-donating ability favored the formation of 2-I. The bulkiness of the substituents on the Cyclopentadienyl Group or of the P ligands, and low electron-donating ability of the P ligands increased the ratio of 2-II complexes to 2-I isomer.
-
Control of Stereochemistry at the Metal Center in Planar-Chiral Cyclopentadienyl Ruthenium Complexes with Anchor Phosphine on Complexation with Salicylideneaminato Ligands
Organometallics, 2001Co-Authors: Kiyotaka Onitsuka, Yoshiki Ajioka, And Yuji Matsushima, Shigetoshi TakahashiAbstract:Reactions of planar-chiral Cyclopentadienyl-phosphine ruthenium complexes [η5,η1-{C5H2(Me)(R)COO(CH2)2PPh2}Ru(MeCN)2][PF6] (1a, R = Me; 1b, R = Ph) with sodium salicylideneaminato (2) led to the formation of salicylideneaminato complexes (3 and 4, R = Me; 5 and 6, R = Ph) inducing metal-centered chirality with a high selectivity (up to >99% de). The diastereoselectivity of products did not depend on the substituent on aromatic ring of salicylideneaminato ligands, but upon the substituents on the Cyclopentadienyl Group and on nitrogen of the imino Group. X-ray diffraction and NMR studies including NOE measurements revealed that the configuration of the major isomers is SCpRRu/RCpSRu. Similar reactions of planar-chiral Cyclopentadienyl ruthenium complexes [η5-{C5H2(Me)(R)COOEt}Ru(PPh3)(MeCN)2][PF6] (7) (7a, R = Me; 7b, R = Ph) having no anchor phosphine ligands with 2 also gave salicylideneaminato complexes (8 and 9) with a low selectivity. Epimerization of a pure sample of the major product 5a into a diast...
Kotohiro Nomura - One of the best experts on this subject based on the ideXlab platform.
-
half titanocenes containing anionic ancillary donor ligands as promising new catalysts for precise olefin polymerisation
Dalton Transactions, 2009Co-Authors: Kotohiro NomuraAbstract:Recent efforts concerning nonbridged half-titanocenes containing anionic donor ligand of the type, Cp′TiX2(Y) [Cp′ = Cyclopentadienyl Group; X = halogen, alkyl; Y = anionic ancillary donor ligands such as aryloxo, ketimide etc.], as new types of olefin polymerisation catalysts have been reviewed. It has been demonstrated that these complexes displayed unique characteristics especially for ethylene copolymerisation affording new polymers by efficient incorporation of bulky olefins (so called “traditionally unreactive” monomers in transition metal catalysed coordination polymerisation), that have not been attained by the ordinary catalysts.
-
Effects of Cyclopentadienyl fragment in ethylene, 1-hexene, and styrene polymerizations catalyzed by half-titanocenes containing ketimide ligand of the type, Cp′TiCl2(NCtBu2)
Catalysis Communications, 2004Co-Authors: Kotohiro Nomura, Kazuya Fujita, Michiya FujikiAbstract:Abstract Effects of substituents on Cyclopentadienyl Group for polymerization of ethylene, 1-hexene and styrene with a series of (Cyclopentadienyl)(ketimide)titanium(IV) complexes of type, Cp′TiCl2(NCtBu2) [Cp′=Cp (1), tBuC5H4 (2), C5Me5 (Cp∗, 3)], have been explored in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 1–3 showed high catalytic activities for ethylene polymerization regardless of kind of Cyclopentadienyl fragment, and the activity for 1-hexene polymerization increased in the order 1≫2>3. These complexes also showed catalytic activities for syndiospecific styrene polymerization, however, the observed activities were much lower than those with Cp∗TiCl3.
-
18 Effect of Cyclopentadienyl fragment in polymerization of ethylene, propylene, and styrene by nonbridged half-metalloce type titanium and zirconium complexes of the type, Cp'MCl2 [N(2,6-Me2 C6 H3) (SiMe3)], -MAO catalyst systems
Science and Technology in Catalysis 2002 Proceedings of the Fourth Tokyo conference on Advance Catalytic Science and Technology, 2003Co-Authors: Kotohiro Nomura, Kensaku FujiiAbstract:Abstract Various (anilide)(Cyclopentadienyl)titanium(IV) complexes of type, Cp'MCl2[N(2,6-Me2C6H3)-(SiMe3)] [M=Ti and Cp'=C5Me5 (Cp*, 1), 1,3-Me2C5H3 (2), C5H5 (Cp, 3); M=Zr and Cp'=Cp* (4)], have been chosen for polymerization of ethylene, propylene, and styrene in the presence of methylaluminoxane (MAO). 1 was found to exhibit the highest catalytic activity for ethylene polymerization whereas 3 showed the highest catalytic activity for syndiospecific styrene polymerization. These results clearly show that efficient catalyst for the desired polymerization can be modified only by changing the substituent on Cyclopentadienyl Group.
-
Ligand effect in olefin polymerization catalyzed by (Cyclopentadienyl)(aryloxy) titanium(IV) complexes, Cp′TiCl2(OAr)–MAO system.: Ethylene/1-hexene copolymerization by (1,3-tBu2C5H3)TiCl2(O-2,6-iPr2C6H3)–MAO catalyst system
Journal of Molecular Catalysis A: Chemical, 2000Co-Authors: Kotohiro Nomura, Takashi Komatsu, Yukio ImanishiAbstract:Abstract Effect of substituents on Cyclopentadienyl Group for catalytic activity in 1-hexene and 1-octene polymerization with the series of Cp′TiCl2(O-2,6-iPr2C6H3) [Cp′=Cp (1a), tBuC5H4 (2a), 1,3-Me2C5H3 (3a), 1,3-tBu2C5H3 (4a), and C5Me5 (5a)]–methylaluminoxane (MAO) catalysts have been explored, and the activity increased in the order: 4a (26 kg polymer/mol Ti·h) 5d (694)>5c (76)>5e (48)>5b (39). These orders are somewhat different from those in ethylene polymerization, and these differences observed here would be due to the steric bulk of monomer used as well as of substituents on both Cyclopentadienyl and aryloxy Groups. Although (1,3-tBu2C5H3)TiCl2(O-2,6-iPr2C6H3) (4a) showed the lowest catalytic activity for polymerization of both 1-hexene and 1-octene, 4a exhibited the significant activity for copolymerization of ethylene with 1-hexene, resulting in obtaining copolymer with relatively high 1-hexene contents (20.2–36.5 mol%) with relatively narrow molecular weight distributions.
Tomislav Rovis - One of the best experts on this subject based on the ideXlab platform.
-
Correction: Ligand design for Rh(iii)-catalyzed C-H activation: an unsymmetrical Cyclopentadienyl Group enables a regioselective synthesis of dihydroisoquinolones.
Chemical science, 2016Co-Authors: Todd K. Hyster, Derek M. Dalton, Tomislav RovisAbstract:[This corrects the article DOI: 10.1039/C4SC02590C.].
-
ligand design for rh iii catalyzed c h activation an unsymmetrical Cyclopentadienyl Group enables a regioselective synthesis of dihydroisoquinolones
ChemInform, 2015Co-Authors: Todd K. Hyster, Derek M. Dalton, Tomislav RovisAbstract:The regioselectivity of the insertion reaction of (I) with terminal olefins is strongly dependent on the catalyst used.
-
Ligand Design for Rh(III)-Catalyzed C—H Activation: An Unsymmetrical Cyclopentadienyl Group Enables a Regioselective Synthesis of Dihydroisoquinolones.
ChemInform, 2015Co-Authors: Todd K. Hyster, Derek M. Dalton, Tomislav RovisAbstract:The regioselectivity of the insertion reaction of (I) with terminal olefins is strongly dependent on the catalyst used.
-
Correction: Ligand design for Rh(III)-catalyzed C–H activation: an unsymmetrical Cyclopentadienyl Group enables a regioselective synthesis of dihydroisoquinolones
Chemical science, 2015Co-Authors: Todd K. Hyster, Derek M. Dalton, Tomislav RovisAbstract:We report the regioselective synthesis of dihydroisoquinolones from aliphatic alkenes and O-pivaloyl benzhydroxamic acids mediated by a Rh(III) precatalyst bearing sterically bulky substituents. While the prototypical Cp* ligand provides product with low selectivity, sterically bulky Cpt affords product with excellent regioselectivity for a range of benzhydroxamic acids and alkenes. Crystallographic evidence offers insight as to the source of the increased regioselectivity.
-
correction ligand design for rh iii catalyzed c h activation an unsymmetrical Cyclopentadienyl Group enables a regioselective synthesis of dihydroisoquinolones
Chemical Science, 2015Co-Authors: Todd K. Hyster, Derek M. Dalton, Tomislav RovisAbstract:We report the regioselective synthesis of dihydroisoquinolones from aliphatic alkenes and O-pivaloyl benzhydroxamic acids mediated by a Rh(III) precatalyst bearing sterically bulky substituents. While the prototypical Cp* ligand provides product with low selectivity, sterically bulky Cpt affords product with excellent regioselectivity for a range of benzhydroxamic acids and alkenes. Crystallographic evidence offers insight as to the source of the increased regioselectivity.
Kiyotaka Onitsuka - One of the best experts on this subject based on the ideXlab platform.
-
stereoselective ligand exchange reaction of planar chiral Cyclopentadienyl ruthenium complexes thermodynamic control of configuration at a stereogenic metal center
Dalton Transactions, 2004Co-Authors: Yuji Matsushima, Kiyotaka Onitsuka, Shigetoshi TakahashiAbstract:The reaction of planar-chiral Cyclopentadienyl–ruthenium complexes with Bu4NI resulted in the formation of iodo complexes with high diastereoselectivity (up to >99%de). The stereochemistry of the ruthenium center in the starting material did not influence the diastereoselectivity of the products. Epimerization of a diastereomerically pure sample gave a mixture of two diastereomers in the same ratio as with the ligand-exchange reaction, suggesting that the selectivity is determined by the difference in thermodynamic stability between the diastereomeric pair of iodo complexes. The ratio of the products depends on the nature of the substituent on the Cyclopentadienyl ring and P ligands on the ruthenium atom. A combination of small substituents on the Cyclopentadienyl Group and small P ligands with strong electron-donating ability favored the formation of 2-I. The bulkiness of the substituents on the Cyclopentadienyl Group or of the P ligands, and low electron-donating ability of the P ligands increased the ratio of 2-II complexes to 2-I isomer.
-
Stereoselective ligand-exchange reaction of planar-chiral Cyclopentadienyl–ruthenium complexes: thermodynamic control of configuration at a stereogenic metal center
Dalton transactions (Cambridge England : 2003), 2004Co-Authors: Yuji Matsushima, Kiyotaka Onitsuka, Shigetoshi TakahashiAbstract:The reaction of planar-chiral Cyclopentadienyl-ruthenium complexes with Bu4NI resulted in the formation of iodo complexes with high diastereoselectivity (up to >99%de). The stereochemistry of the ruthenium center in the starting material did not influence the diastereoselectivity of the products. Epimerization of a diastereomerically pure sample gave a mixture of two diastereomers in the same ratio as with the ligand-exchange reaction, suggesting that the selectivity is determined by the difference in thermodynamic stability between the diastereomeric pair of iodo complexes. The ratio of the products depends on the nature of the substituent on the Cyclopentadienyl ring and P ligands on the ruthenium atom. A combination of small substituents on the Cyclopentadienyl Group and small P ligands with strong electron-donating ability favored the formation of 2-I. The bulkiness of the substituents on the Cyclopentadienyl Group or of the P ligands, and low electron-donating ability of the P ligands increased the ratio of 2-II complexes to 2-I isomer.
-
Control of Stereochemistry at the Metal Center in Planar-Chiral Cyclopentadienyl Ruthenium Complexes with Anchor Phosphine on Complexation with Salicylideneaminato Ligands
Organometallics, 2001Co-Authors: Kiyotaka Onitsuka, Yoshiki Ajioka, And Yuji Matsushima, Shigetoshi TakahashiAbstract:Reactions of planar-chiral Cyclopentadienyl-phosphine ruthenium complexes [η5,η1-{C5H2(Me)(R)COO(CH2)2PPh2}Ru(MeCN)2][PF6] (1a, R = Me; 1b, R = Ph) with sodium salicylideneaminato (2) led to the formation of salicylideneaminato complexes (3 and 4, R = Me; 5 and 6, R = Ph) inducing metal-centered chirality with a high selectivity (up to >99% de). The diastereoselectivity of products did not depend on the substituent on aromatic ring of salicylideneaminato ligands, but upon the substituents on the Cyclopentadienyl Group and on nitrogen of the imino Group. X-ray diffraction and NMR studies including NOE measurements revealed that the configuration of the major isomers is SCpRRu/RCpSRu. Similar reactions of planar-chiral Cyclopentadienyl ruthenium complexes [η5-{C5H2(Me)(R)COOEt}Ru(PPh3)(MeCN)2][PF6] (7) (7a, R = Me; 7b, R = Ph) having no anchor phosphine ligands with 2 also gave salicylideneaminato complexes (8 and 9) with a low selectivity. Epimerization of a pure sample of the major product 5a into a diast...
Yuji Matsushima - One of the best experts on this subject based on the ideXlab platform.
-
stereoselective ligand exchange reaction of planar chiral Cyclopentadienyl ruthenium complexes thermodynamic control of configuration at a stereogenic metal center
Dalton Transactions, 2004Co-Authors: Yuji Matsushima, Kiyotaka Onitsuka, Shigetoshi TakahashiAbstract:The reaction of planar-chiral Cyclopentadienyl–ruthenium complexes with Bu4NI resulted in the formation of iodo complexes with high diastereoselectivity (up to >99%de). The stereochemistry of the ruthenium center in the starting material did not influence the diastereoselectivity of the products. Epimerization of a diastereomerically pure sample gave a mixture of two diastereomers in the same ratio as with the ligand-exchange reaction, suggesting that the selectivity is determined by the difference in thermodynamic stability between the diastereomeric pair of iodo complexes. The ratio of the products depends on the nature of the substituent on the Cyclopentadienyl ring and P ligands on the ruthenium atom. A combination of small substituents on the Cyclopentadienyl Group and small P ligands with strong electron-donating ability favored the formation of 2-I. The bulkiness of the substituents on the Cyclopentadienyl Group or of the P ligands, and low electron-donating ability of the P ligands increased the ratio of 2-II complexes to 2-I isomer.
-
Stereoselective ligand-exchange reaction of planar-chiral Cyclopentadienyl–ruthenium complexes: thermodynamic control of configuration at a stereogenic metal center
Dalton transactions (Cambridge England : 2003), 2004Co-Authors: Yuji Matsushima, Kiyotaka Onitsuka, Shigetoshi TakahashiAbstract:The reaction of planar-chiral Cyclopentadienyl-ruthenium complexes with Bu4NI resulted in the formation of iodo complexes with high diastereoselectivity (up to >99%de). The stereochemistry of the ruthenium center in the starting material did not influence the diastereoselectivity of the products. Epimerization of a diastereomerically pure sample gave a mixture of two diastereomers in the same ratio as with the ligand-exchange reaction, suggesting that the selectivity is determined by the difference in thermodynamic stability between the diastereomeric pair of iodo complexes. The ratio of the products depends on the nature of the substituent on the Cyclopentadienyl ring and P ligands on the ruthenium atom. A combination of small substituents on the Cyclopentadienyl Group and small P ligands with strong electron-donating ability favored the formation of 2-I. The bulkiness of the substituents on the Cyclopentadienyl Group or of the P ligands, and low electron-donating ability of the P ligands increased the ratio of 2-II complexes to 2-I isomer.
