Takaya Mise

Preparation and structure of the first ansa-molybdenocene and tungstenocene derivatives. Reaction of [O(SiMe2C5H4)2]MoH2 with methyl methacrylate to probe the olefin attacking site

Abstract Bridged-bis(cyclopentadienyl) molybdenum and tungsten dihydrides and their derivatives have been synthesized for the first time. [(1,1,3,3-Tetramethyldisiloxane-1,3-diyl)bis(η5-cyclopentadienyl)lmolybdenum dihydride (1a) and tungsten dihydride (1b) were prepared by sodium borohydride reduction of [O(SiMe2C5H4)2]MCl2 (2a: M  Mo, 2b: M  W) which was obtained by the reaction of disodium 1,1,3,3-tetramethyl-1,3-bis(cyclopentadienyl)disiloxane with MCl4(thf)2 (M  Mo, W). The dichlorides 2 reacted with ZnMe2 and NaSEt to afford [O(SiMe2C5H4)2]MMe2 (3a: M  Mo, 3b: M  W) and [O(SiMe2C5H4)2]M(SEt)2 (4a: M  Mo, 4b: M  W), respectively. Photolysis of 1b in benzene gave [O(SiMe2C5H4)2]WH(C6H5) (5b). An X-ray crystal analysis of 3a has proved that the bridging chain blocks one of the side positions of the complex, the siloxy unit being present at one side of the MeMoMe bisector. Consistent with side position attack by olefins, the reaction rate of 1a with methyl methacrylate was found to be nearly one half that of the parent Cp2MoH2 (6a).

Stereospecific polymerization of 1-hexene catalyzed by ansa-metallocene/methylaluminoxane systems under high pressures

Stereospecific polymerization of 1-hexene under high pressures (up to 1,000 MPa = ca. 10,000 atm) using metallocene/methylaluminoxane (MAO) catalysts was investigated. Several C 2 -symmetric ansa-metallocenes, their meso-isomers, and two C s -symmetric ansa-metallocenes were employed as catalyst precursors. In the course of this study, novel C 2 -symmetric germylene-bridged ansa-metallocenes, (rac-[Me 2 Ge(η 5 -C 5 H-2,3,5-Me 3 ) 2 MCl 2 ] (M = Zr, rac-4a; M = Hf, rac-4b), have been prepared. High pressures induced enhancement of the catalytic activity and the molecular weight of the polymers in most of the catalysts. The maximum of both the catalytic activity and the molecular weight of the polymers was mostly observed at 100-500 MPa in each catalyst, although the enhanced ratio was smaller than that observed for nonbridged metallocenes. Isospecificity of the C 2 -symmetric ansa-metallocene catalysts was essentially maintained even under high pressure. Highly isotactic polyhexene ([mmmm] = 91.6%) with very high molecular weight (M w = 2,360,000) was achieved by rac-4b under 250 MPa. High pressures slightly decreased syndiotacticity when the C s -symmetric ansa-metallocene, isopropylidene(1-η 5 -cyclopentadienyl)(9-H 5 -fluorenyl)zirconium dichloride 5, was employed.

Rhodium carbonyl-catalyzed carbonylation of unsaturated compounds: III. Synthesis of α,β-unsaturated ethyl ketones by cross-hydrocarbonylation of acetylenes and ethylene with carbon monoxide and hydrogen

Abstract Rhodium carbonyl-catalyzed cross-hydrocarbonylation of acetylenes and ethylene with carbon monoxide and hydrogen gives α,β-unsaturated ethyl ketones. Under CO (10 kg cm −2 ) and H 2 (50 kg cm −2 ) at 90°C the reaction of diphenylacetylene with ethylene in the presence of Rh 4 (CO) 12 catalyst gave ( E )-1,2-diphenyl-1-penten-3-one ( 3a ) in 91% yield. Under similar conditions phenylacetylene ( 1d ), 1-hexyne ( 1e ), 3,3-dimethyl-1-butyne ( 1f ), and trimethylsilylacetylene ( 1g ) gave ( E )-1-phenyl-1-penten-3-one ( 3d ), ( E )-4-nonen-3-one ( 3e ), ( E )-6,6-dimethyl-4-hepten-3-one ( 3f ), and ( E )-1-trimethylsilyl-1-pentene-3-one ( 3g ) in 76, 68, 93, and 62% yields, respectively. Thus, the reaction of terminal acetylenes proceeds with high stereo- and regioselectivity: the propionyl group is introduced to the less-sterically hindered acetylenic carbon atom. By comparison of the regioselectivity with that in the formation of 5-ethyl-2(5 H )-furanone ( 2 ), which is obtained in the presence of a hydrogen donor such as alcohol, these reactions are assumed to include a β-acylvinylrhodium complex as the common key intermediate.

Synthesis and some reactions of n5-pentamethylcyclopentadienylnickel complexes

Reaction of Me5C5Li and Ni(CO)4 gave [(n5-Me5C5)Ni(CO)]2 (I) in 40 % yield. Reaction of I with iodine followed by addition of a tertiary phosphine or reaction of (PPh3)2NiX2 with Me5C5Li or Me5C5SnBu3 gave (n5-Me5C5)Ni(L)X (II) (L = tertiary phosphine, X = halogen). Treatment of II with RLi (R = Me, PhCC) afforded (n5-Me5C5)Ni(L)R (III). The spectroscopic properties and the reactivities of n5-pentamethylcyclopentadienylnickel complexes indicate that the n5-Me5C5 ligand is more electron-donating and a sterically more bulky than the n5-C5H5 ligand.

Structural characterization of ansa-zirconocene dichloride bearing a vicinal di-tert-butylcyclopentadienyl ligand and high pressure polymerization of 1-hexene catalyzed by sterically hindered zirconocene complexes

Abstract An ansa -zirconocene complex having a vicinally di- tert -butyl-substituted cyclopentadienyl ligand, Me 2 Si(C 5 H 4 )(C 5 H 2 -3,4- t -Bu 2 )ZrCl 2 ( 1 ), has been synthesized and characterized by X-ray diffraction (orthorhombic, space group: Pbca , a =18.3690(8), b =18.0749(12), c =13.2039(9) A, V =4383.9(4) A 3 , Z =8, R =0.0283, R w =0.0291). Complex 1 has a very much twisted structure due to its steric repulsion. In solution, however, the two tert -butyl groups are magnetically equivalent even at −80°C, indicating very fast oscillation of the bridged cyclopentadienyl unit with respect to the metal center. Complex 1 and nonbridged zirconocene dichlorides with tert -butyl-substituted cyclopentadienyl ligands, (C 5 H 4 - t -Bu) 2 ZrCl 2 ( 2 ), (C 5 H 3 -1,2- t -Bu 2 ) 2 ZrCl 2 ( 3 ) and (C 5 H 3 -1,3- t -Bu 2 ) 2 ZrCl 2 ( 4 ), have been employed as methylaluminoxane (MAO)-activated catalysts for polymerization of 1-hexene under high pressure conditions (100–750 MPa=ca. 1000–7500 atm). Comparison with some non and methyl-substituted metallocenes are also discussed.

Rhodium carbonyl-catalyzed carbonylation of unsaturated compounds: V. Cross-hydrocarbonylation of 1-alkyne and ethylen by rhodium carbonyl catalyst modified with phosphines

Abstract In the presence of RH4(CO)12 catalyst modified with triphenylphosphine the cross-hydrocarbonylation of 1-alkyne (RC2H; R = Me, Et, nPr, nBu, and tBu) and ethylene using 2-propanol as the hydrogen donor gives 3-alkyl-5-ethyl-2(5H)-furanone (4, 44–69%), along with a small amount of 4-alkyl-5-ethyl-2(5H-foranone (5, 1–8%). When acetylene itself is used, γ-caprolactone (6a, which is the hydrogenation product of the expected 5-ethyl-2(5H)-furanone (4a), is obtained. The yield of 6a depends on the nature of the phosphine employed and decreases in the following order: PR3 = P(C6H4F-4)3 > P(C6H4OMe-p)3 > PPh2Et > PPhEt2 > PEt3.

37. Propylene Polymerizations with Silylene-Bridged Metallocene Catalysts

New C 2 -symmetric silylene-bridged metallocene compounds, [Me 2 Si(R n -C 5 H 4-n )(R′ m -C 5 H 4-m )]MCl 2 (M=Zr, Hf; R n , R′ m =Me, t-Bu, 2,4-Me 2 , 2,3,5-Me 3 ), were synthesized together with C ° -symmetric compounds (M=Zr, Hf; R n =2,3,5-Me3, 2,4-Me 2 , 3,4-Me 2 , t-Bu, Me; R′ m =Me,H) for comparison and employed as the catalysts for isotactic polymerization of propylene in combination with methylaluminoxane. The C 2 -symmetric metallocenes bearing methyl groups at the 2- or 5-positions gave polymers of the highest melting point (160–163 °C) and stereoregularity ([mmmm]=97–99%).

Polymerization of hex-1-ene by homogeneous zirconocene and hafnocene catalysts in compressed solution

Poly(hexene) with very high molecular weight is produced at 250 MPa (2500 atm) with (C5HMe4)2HfCl2–methyl aluminoxane (MAO) as catalyst; the dependence of the polymerization on the reaction pressure (0.1 MPa–1.5 GPa) and the substituent pattern of a zirconocene catalyst is described.

Ruthenium-catalyzed ring-closing reaction of α,ω-bis(vinylsilyl) compounds via a silyl transfer mechanism

Compounds having a vinyldimethylsilyl group at both terminals have been successfully cyclized by ruthenium hydride catalysts to give selectively disilacycles of various ring sizes via a metathetical reaction, i.e. ethene elimination from the two terminal vinyl groups, not involving metallocarbene–metallacyclobutane type intermediates.

Olefin Polymerization under High-pressure: Formation of Super-high Molecular Weight Polyolefins

Polymerization of 1-hexene under high-pressures (100-1,000 MPa) was investigated using permethylated ansa-metallocenes/ methylaluminoxane (MAO) as catalysts. Five types of ansa-metallocenes, R2E(ŋ5-C5Me4)2MCl2 (R = Me, Et, vinyl; E = Si, Ge, M = Zr, Hf), and their heterobimetallic derivatives (ŋ5-C9H7)Rh(rh((ŋ2-CH2=CH)2Si(ŋ5-C5Me4)2MCl2 (M = Zr, Hf) were synthesized and used as catalyst precursors. These complexes exhibited remarkably enhanced catalytic activity under high pressures despite their very congested structures and gave poly( 1-hexene) of unprecedented high molecular weight (M w = 1.02 x107 , M w/M n = 3.79, by GPC). Studies on termination processes revealed that s-hydrogen transfer to olefin is much accelerated under 500 MPa in the zirconocene complex, while the chain-tranfer reactions are little affected by pressure in the hafnocene.