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.
Dynamic stereochemistry of ligand substitution at a chiral titanium center. Synthesis of asymmetrical halidopseudohalidotitanocene complexes
Abstract Two new ligand exchange reactions (i and ii) at a chiral titanium center have been studied: These two reactions are selective but only the second is stereospecific. Reaction ii is shown to involve retention at the titanium atom. By use of these reaction, the first pairs of asymmetrical halidopseudohalido titanocene complexes have been isolated, and their relative configurations are suggested.
Simultaneous Asymmetric Hydrogenation and Hydroformylation by Chiral Platinum Complexes
An asymmetric induction of 37.6% has been obtained in the asymmetric hydrogenation of α-ethylstyrene with the [(−)-DIOP]-PtCl2/SnCl2 catalytic system. When carbon monoxide is present, both hydrogenation and hydroformylation of the substrate occur. The prevailing antipode arises from the opposite prochiral face of the olefin in hydrogenation and hydroformylation respectively.