Yukio Imanishi

Recent developments in olefin polymerizations with transition metal catalysts

Abstract Discovery of effective homogeneous transition metal catalysts for olefin polymerization must be one of the most dramatic technologies for polymer synthesis in the 1980s. Especially, development of group 4-metallocene catalysts not only improved the property of manufactured polyolefins but also made us possible to synthesize new type polyolefins. A large number of studies have also been made on structure and property of the resultant polyolefins with the advance of catalyst technology. Over the past few years, trend in catalyst development has moved from modification of group 4-metallocene catalysts to search for new generation catalysts, such as non-metallocene catalysts and late transition-metal catalysts. Some of the new catalysts can proceed specific polymerizations, which are not achieved with existent olefin polymerization catalysts. Although, there are some subjects for the manufacturing of new catalysts and polyolefins, the technologies are progressing rapidly. In this review, we highlight not only the development of polymerization catalysts but also the polyolefins obtained with the new catalysts in the last decade.

Ruthenium catalyzed hydrogenation of methyl phenylacetate under low hydrogen pressure

Abstract PhCH2CO2Me has been efficiently hydrogenated to yield PhCH2CH2OH (1) and PhCH2CO2CH2CH2Ph (2) even under relatively low hydrogen pressure (

Negative surface potential produced by self-assembled monolayers of helix peptides oriented vertically to a surface

Abstract Self-assembled monolayers (SAMs) of helix peptides oriented vertically to a gold surface were prepared and the surface potential measured using the Kelvin technique up to 140°C. Negative surface potentials of a few hundred millivolts were observed for the helix peptide SAMs, indicating the occurrence of the large dipole moment of the helices directing toward the surface. The longer the helix peptide, the larger was the negative surface potential obtained. The absolute value of the surface potential decreased with increase in temperature due to thermal perturbation in the helical structure. However, Fourier transform infrared reflection–absorption spectroscopy revealed that perturbation is not significant and the α-helical conformation is stable even at 140°C.

Copolymerization of ethylene and cyclopentene with zirconocene catalysts: Effect of ligand structure of zirconocenes

Copolymerization of ethylene and cyclopentene (CPE) was carried out with various non-bridged and bridged zirconocene catalysts using methylaluminoxane as a cocatalyst. Non-bridged metallocene catalysts effected ethylene homopolymerization without copolymerization. On the other hand, bridged zirconocene catalysts produced copolymers containing cis-1,2-cyclopentane units. Among the used catalysts, rac-ethylenebis(indenyl)zirconium dichloride [Et(Ind) 2 ZrCl 2 ] gave copolymers containing the highest amount of CPE units by 1,2- insertion or 1,3-insertion. Temperature-rising elution fractionation of the copolymers using 1,2-dichlorobenzene as a solvent showed a broad distribution of copolymer composition in copolymers obtained by specific zirconocene catalysts.

Direct synthesis of 2-phenylethanol by hydrogenation of methyl phenylacetate using homogeneous ruthenium-phosphine catalysis under low hydrogen pressure

Methyl phenylacetate could be efficiently hydrogenated to yield 2-phenylethanol under lower hydrogen pressure (<10 atm) by using ruthenium-phosphine catalysis composed of Ru(acac)3, P(n-C8H17)3 in the presence of Zn. Effect of both phosphine and Zn plays an crucial role in order for this hydrogenation to proceed under mild conditions.

Copolymerization of ethylene and 1,7-octadiene, 1,9-decadiene with zirconocene catalysts

Copolymerizations of ethylene and 1,7-octadiene (OD) and 1,9-decadiene (DD) were investigated with various non-bridged and bridged zirconocene catalysts using methylisobutylaluminoxane as a cocatalyst. The resulting copolymers were extracted with boiling o-dichlorobenzene (ODCB), and the structure of the boiling ODCD-soluble part was studied by 1 H, 13 C NMR and DEPT (distortionless enhancement of polarization transfer) spectroscopy. In the case of ethylene/OD copolymerization, the ligand structure of the zirconocene catalysts strongly affected the propagation mode of OD. The zirconocene catalysts having cyclopentadienyl or pentamethylcyclopentadienyl ligands gave copolymers having 1-hexenyl and 1,3-disubstituted cycloheptane units, derived from 1,2-addition propagation and addition-cyclization propagatin of OD, respectively. On the other hand, the zirconocene catalysts with indenyl ligand produced the copolymers having exclusively 1,3-disubstituted cyclo-heptane units. Furthermore, the copolymer prepared by diphenylmethylene(cyclopentadienyl)(0-fluorenyl)zirconuim dichloride was crosslinked. The diastereostructure of the 1,3-disubstituted cycloheptane units in the copolymers was not influenced by the stereospecificity of the catalysts used, and a cis-structure was preferentially formed. In the case of the copolymerization of ethylene and DD, the C 2v -symmetric zirconocene catalysts produced the copolymers with 1-octenyl branches derived from 1,2-addition propagation of DD. Other C 2 - and C s -symmetric zirconocene catalysts with bulky ligands yielded copolymers with cross-linking structures derived form addition propagation of side-chain unsaturated bond of 1,2-added DD units.

Copolymerization of ethylene and 1,5-hexadiene with zirconocene catalysts

Copolymerization of ethylene and 1,5-hexadiene (HD) was carried out with non-bridged or bridged zirconocene catalysts using methylaluminoxane (MAO) as a cocatalyst. The resulting copolymers were extracted with boiling o-dichlorobenzene (ODCB) to fractionate into soluble and insoluble parts. The ligand structure of zirconocenes, the feed ratio of HD, and the catalyst concentration strongly affected the copolymer composition. In the copolymerization with non-bridged zirconocene catalysts, the amount of boiling ODCB-soluble part decreased with increasing HD content in the copolymer. On the other hand, with bridged zirconocene catalysts, it increased with increasing HD content in the copolymer. The bridged zirconocene catalysts were apt to take in more HD than non-bridged catalysts. Effect of catalyst concentration was investigated in relation to crosslinking reaction. Temperature-rising elution fractionation (TREF) of the boiling ODCB-soluble part was conducted to show the occurrence of heterogeneous composition in copolymers obtained with some specific zirconocene catalysts.

Polymerization of 1-hexene, 1-octene catalyzed by Cp′TiCl2(O-2,6-iPr2C6H3)–MAO system. Unexpected increase of the catalytic activity for ethylene/1-hexene copolymerization by (1,3-tBu2C5H3)TiCl2(O-2,6-iPr2C6H3)–MAO catalyst system

Abstract Although (1,3-tBu2C5H3)TiCl2(O-2,6-iPr2C6H3) (4) showed the lowest catalytic activity for polymerization of 1-hexene, 1-octene with the series of Cp′TiCl2(O-2,6-iPr2C6H3) [Cp′= Cp, tBuC5H4, 1,3-Me2C5H3, 1,3-tBu2C5H3, and C5Me5]–methylaluminoxane (MAO) catalysts, 4 exhibited the significant catalytic activity for copolymerization of ethylene with 1-hexene, resulting in obtaining a copolymer with relatively high 1-hexene content (20.2–36.5 mol%) with relatively narrow molecular weight distribution.

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

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.

Catalytic activity and conformation of chemically modified subtilisin Carlsberg in organic media

Subtilisin Carlsberg, an alkaline protease from Bacillus licheniformis, was modified with polyoxyethylene (PEG) or aerosol-OT (AOT), and the solubility, conformation, and catalytic activity of the modified subtilisins in some organic media were compared under the same conditions. The solubility of modified subtilisins depended on the solubility of the modifier. On the other hand, the conformational changes depended on the solubility, rather than the property, of the modifier. When the modified subtilisin was dissolved in water-miscible polar solvents such as dimethylsulfoxide, acetonitrile, and tetrahydrofuran, significant conformational changes occurred. When modified subtilisin was dissolved in water-immiscible organic solvents, such as isooctane and benzene, the solvent did not induce significant conformational changes. The catalytic activity in the transesterification reaction of the N-acetyl-L-phenylalanine ethylester of the modified subtilisin in organic solvents was higher than that of native subtilisin. The high activity of modified subtilisin was thought to be due to a homogeneous reaction by the dissolved enzymes.