Titanium‐Catalyzed Norbornene Oligomerization. Isolation of a Crystalline Heptamer with a 2,3‐exo‐Disyndiotactic Structure

Abstract Summary: Norbornene (NB) was oligomerized at 0 °C using AlEt 2 Cl‐TiCl 4 at a monomer/titanium molar ratio of about 11. The oligomerization product consists of a fraction soluble in diethyl ether, amorphous by X‐ray examination, and of a crystalline fraction, insoluble in diethyl ether. The crystalline fraction was shown by powder X‐ray diffraction to consist of a NB heptamer. Single‐crystal X‐ray analysis indicated that the heptamer had a stereoregular 2,3‐ exo ‐disyndiotactic structure. The heptamer adopts a strained, highly irregular, folded conformation in the crystalline state. Structural differences with respect to NB oligomers obtained with zirconocene catalysts are discussed. A view of the molecular structure of the crystalline NB heptamer. magnified image A view of the molecular structure of the crystalline NB heptamer.