Synthesis, crystal structure and reaction of differentially ring-substituted titanocene dichlorides
SummaryA new class of differentially ring-substituted titanocene dichlorides of the type Cp′Cp″TiCl2 has been prepared by reacting Cp″M (M=Li, K; Cp″=RC5H4) with Cp′TiCl3 (Cp′=MeOCH2CH2C5H4). The crystal structure of Cp′(PhCEt2C5H4)TiCl2, the first example, has been determined by x-ray diffraction and refined to a final R factor of 0.0532 for 2304 reflections. The crystal belongs to the monoclinic space group C2h5−P21/c with unit cell parameters:a 10.205(6),b 13.003(5),c 17.591(9) Å, β 101.91(4)°, V=2284 Å3, Z=4 and Dc=1.32 g/cm−3. Replacement of one neomenthyl in bis(neomenthyl-cyclopentadienyl)titanium dichloride by one MeOCH2CH2 — raises the e.e. value from 5.8% to 11.2% in the catalytic asymmetric hydrogenation of 2-phenyl-1-butene.
The influence of steric and electronic effects of substituents on the cyclopentadienyl ring on the behaviour of (CpR)2TiCl2 and (CpR)CpTiCl2/Et3Al2Cl3 catalysts in polymerization of ethene.
Abstract A range of (CpR)(CpR′)TiCl 2 complexes (R  R′  H, Me, Et, i Pr, t Bu, SiMe 3 , CMe 2 Ph, CO 2 Me and R  H, R′  Me, t Bu, SiMe 3 , CMe 2 Ph, CO 2 Me) have been synthesized. Ethylene polymerization studies (50°C, 10 bar) in the presence of Et 3 Al 2 Cl 3 as co-catalyst revealed catalyst activity of > 20 g polyethylene (mol Ti h) −1 when the combined Tolman cone angle for the two cyclopentadienyl rings was less than 260° and very low activity when the combined cone angle was larger. An analysis of available crystallographic data for (CpR) 2 TiCl 2 complexes revealed that the Cl TiCl angle decreases as the size of R increases. It thus appears that the steric influence of R may affect polymerization activity both by restricting access of reactants to the metal as well as by modifying metal-reactant (or polymer) interactions.
Mineral element analyses of various tropical forages in Guatemala and their relationship to soil concentrations
Determination de la composition minerale de differents fourrages dans 3 regions d'elevage du Guatemala et etude des relations entre la chimie des sols et la composition minerale des fourrages