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.
Substituent Effects on the Cleavage Rates of Titanocene Metallacyclobutanes
Effet des substituants des cyclopentadienyls sur la vitesse de reaction des t-butyl-3 di-η 5 -cyclopentadienyl-1,1 titanacyclobutanes avec le diphenylacetylene pour donner des di-η 5 -cyclopentadienyl-1,1 diphenyl-2,3 titanacyclobutenes-2 et le dimethyl-3,3 butene-1
Problems de stereochimie dynamique en serie du titanocene : II. Stereochimie dynamique de reactions déchange de ligands σ-lies
Two ligand exchange reactions at the titanium atom in quasi-tetrahedral titanocene complexes have been studied. The first is substitution of a Cl ligand by an aryloxy group starting from substrates η5-Cp-η5-Cp′Ti(Cl)OPh which have an planar chirality on the Cp′ ring. The second is the substitution of one of the aryloxy groups of the complexes η5-Cp-η5-Cp′Ti(OPh′)OPh by the action of HCl. In this case, the reaction is generally selective and has a high degree of stereo-specificity with retention at the titanium atom. This retention has been established by crystallographic analysis of two suitable substrates: diastereoisomer F. 171°C of η5-C5H5[η5-(1-Me-3-CHMe2C5H5)](2-ClC6H4O)(2,6-Me2C6H3O)Ti and diastereoisomer F. 134°C of η5-C5H5[η5-(1-Me-3-CHMe2C5H3)](2-ClC6H4O)TiCl.