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.
Ring-opening metathesis polymerization of norbornene catalyzed by substituted titanocene complexes
The ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with 11 substituted titanocene dichlorides and MeLi as catalysts was studied. The substituent effect showed that the catalytic activity was generally decreased as the substituents were introduced into the Cp ring. The more bulky the substituents, the lower the activity and the bis-substituted titanocene appeared to have an even lower catalytic activity. The molecular weight of polynorbornene (PNBE) also decreased as substituents are introduced on the Cp ring. But the molecular weight distribution and cis structure content have no significant differences compared with non-substituted titanocene complex as catalyst.
Problemes de stereochimie dynamique en serie du titanocene
Abstract From the two dichlorides η5-Cp-η5-Cp′TiCl2 (Cp = C5H5; Cp′ = C5H3MeCHMe2-1,2 or -1,3), couples of diastereoisomeric chloroaryloxy [η5-Cp-η5-Cp′Ti(Cl)OPh] or of diastereoisomeric diaryloxy [η5-Cp-η5-Cp′Ti(OPh′)OPh], titanocene derivatives, are prepared in several ways. In each case, the diastereoisomeric complexes are separated and identified. These complexes are starting substrates which can be used for dynamic stereochemistry of the ligand substitution process which will be discussed in a following paper.