- Hydrolytic Studies on (η5-C5Me5)TiMe3; X-Ray Structure of 5-C5Me5)TiMe(μ-O)>3 containing a Ti3O3 Ring
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Successive hydrolysis of (η5-C5Me5)TiMe3 (2) gives first 5-C5Me5)TiMe2>2(μ-O) (3) and then 5-C5Me5)TiMe(μ-O)>3 (4); the crystal structure of (4) reveals a Ti3O3 ring.
- Blanco, Severino Garcia,Sal, M. Pilar Gomez,Carreras, Sagrario Martinez,Mena, Miguel,Royo, Pascual,Serrano, Ricardo
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- Pentamethylcyclopentadienylmethyltitanium silsesquioxanes and their zwitterionic complexes with tris(pentafluorophenyl)borane
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Reaction of [(η5-C5Me5)TiMe 3] with [(c-C5H9)7Si 8O12(OH)] (SIPOSS) or [(c-C5H9) 7Si7O9(OSiMe3)(OH)2)] (DIPOSS') affords stoichiometrically the half-sandwich titanium-disiloxy-methyl complexes [(η5-C5Me5){(c-C5H 9)7Si8O12O)2TiMe] (1) and [(η5-C5Me5){(c-C5H 9)7Si7O9(OSiMe3)O 2)TiMe] (2), respectively. Compound 2 consists of the two stereoisomers possessing the (η5-C5Me5) ligand and OSiMe3 group in syn- (2a) and anti-position (2b). The more abundant 2a (2a/2b ≈2:1) was isolated by fractional crystallization. Compounds 1 and 2a reacted rapidly with B(C6F5) 3 to give zwitterionic complexes [(η5-C 5Me5){(c-C5H9)7Si 8O12O}2Ti](+)[(μ-Me)B(C 6F5)3](-) (3) and syn-[(η5C5Me5){(c-C5H 9)7Si7O9(OSiMe3)O 2}Ti]{+)[(μ-Me)B(C6F5) 3](-) (4a), respectively. Infrared spectra proved that 3 and 4a were thermally stable in the solid state and the structure of 4a was determined by X-ray single-crystal analysis. In contrast, 1H, 13C and 19F NMR spectra of 3 in toluene C 7D8 revealed that it was completely dissociated into initial components at 25 °C; however, the features of 3 were dominating already at -35 °C. On the other hand, 4a was dissociated only slightly at 25 °C. Stable ionic complexes 7 and 8 were prepared by reacting [PhNHMe 2]+[B(C6F5)4] - with 1 and 2, respectively. Both 7 and 8 contained the molecule PhNMe2 coordinated to the titanium cation and 8 consisted of the syn- and anti-isomers 8a and 8b in abundances found for 2a/2b. Analogous reaction of 1 and 2 with [Ph3C]+[B(C6F5) 4]- afforded impure ionic complexes 9 and 10. When dissolved in the presence of PhNMe2, the amine coordinated to the titanium cations, thus reproducing complexes 7 and 8a/8b, identified by 1H NMR spectra. All compounds 1-10 were inactive in polymerization of styrene to syndiotactic polymer. A low activity was achieved by adding of 2 equiv of AlMe3 to 3 or 4.
- Varga, Vojtech,Pinkas, Jiri,Cisarova, Ivana,Horacek, Michal,Mach, Karel
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p. 6944 - 6956
(2010/04/04)
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- Synthesis, structure, and ethylene/α-olefin polymerization behavior of (cyclopentadienyl)(nitroxide)titanium complexes
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Mono-Cp titanium coordination compounds bearing monoanionic ligands derived from stable nitroxyl radicals have been synthesized by two methods: (i) trapping of CpTi(III) species with the stable nitroxyl radical TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) to provide Cp′TiCl2(TEMPO) (Cp′ = Cp (1) and Cp* (2)) and (ii) salt metathesis of Ti(IV) halides with a nitroxide anion generated by the in situ methylation of tert-butyl-α-phenylnitrone. Alkylation of these complexes with MeLi or MeMgBr furnishes Cp*TiMe2(TEMPO) (3) and Cp′TiMe2(ON(tBu)(CHMePh)) (Cp′ = Cp(4) and Cp* (5)). The molecular structure of 2 has been determined by X-ray crystallography to reveal a monoanionic η1-TEMPO ligated to titanium. Complexes 3 and 4 activated with iprAFPB (2,6,-diisopropyl-N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate) efficiently copolymerize ethylene and 1-hexene to provide copolymers having higher 1-hexene contents and higher productivities than the related Cp*Ti(CH2Ph)3 under identical conditions. Comparison of structural and electronic features as well as the ethylene/1-hexene copolymerization behavior of 3 and 4 with the constrained geometry catalyst [MeSi2(η5-Me4Cp)(η1-N-tBu)]T iMe2 (6) provides insights into factors governing high comonomer incorporation by mono-Cp titanium complexes.
- Mahanthappa, Mahesh K.,Cole, Adam P.,Waymouth, Robert M.
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p. 836 - 845
(2008/10/09)
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- Electron-deficient (pentamethylcyclopentadienyl)titanium trialkyls: Evidence of Ti?H-C and Ti?C-C interactions. Crystal and molecular structure of μ-[o-(CH2)2C6H4]{(η 5-C5Me5)Ti[o-(CH2)2C 6H4]}2
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(η5-C5Me5)TiCl3 (1) reacts with 3 equiv of lithium or Grignard reagents to form (η5-C5Me5)TiR3 (R = Me, CH2Ph, CH2SiMe3, and C6F5) and with 2 equiv to give (η5-C5Me5)TiClR2 (R = Me, CH2Ph, and CH2SiMe3). If 1 is reacted with [o-(CH2)2C6H4]Mg(THF)2 in a 2:3 molar ratio, μ-[o-(CH2)2C6H4]{(η 5-C5Me5)Ti[o-(CH2)2C 6H4]}2 is obtained; its structure has been fully elucidated by X-ray diffraction methods. Crystals are monoclinic of space group P21/a with Z = 4 in a unit cell of dimensions a = 11.207 (1) A?, b = 34.520 (6) A?, c = 10.460 (1) A?, and β = 113.83 (1)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by blocked-matrix least squares to R = 0.0694 and Rw = 0.0743 for 2096 observed reflections. Of the three o-xylylene groups two act as chelating ligands to the Ti atoms, while the third one acts as a bridge between the two metals. An interaction between the Ti atoms and the C ring atoms of the chelating o-xylylene groups is evident. This situation is compared with that of (η5-C5Me5)Ti(CH2Ph)3, where an agostic interaction has been proposed.
- Mena, Miguel,Royo, Pascual,Serrano, Ricardo,Pellinghelli, Maria Angela,Tiripicchio, Antonio
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p. 476 - 482
(2008/10/08)
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- Preparation of Titanium Pentamethylcyclopentadienyl Trialkyls and Crystal Structure of Tribenzylpentamethylcyclopentadienyltitanium, showing Some Evidence of a CH2...Ti Interaction
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Titanium pentamethylcyclopentadienyl trialkyls (η5-C5Me5)TiR3 (R = Me, CH2SiMe3, C6F5, and CH2Ph) are easily obtained by conventional alkylation of the trichloro analogue; the structure of the tribenzyl derivative, determined by X-ray methods, shows some evidence of CH2...Ti interaction.
- Mena, Miguel,Pellinghelli, Maria Angela,Royo, Pascual,Serrano, Ricardo,Tripicchio, Antonio
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p. 1118 - 1119
(2007/10/02)
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