Synthesis, Structure Determination, and Reactivity of C2-Symmetrical Ethylene-Bridged ansa-Bis(DiMeBCOCp)titanium Dichlorides

The bridging of C 2 -symmetric 8,10-dimethyltricyclo[5.2.2.0 2,6 ]-2,5-undecadiene (DMeBCOCpH) by silicon, methylene, and ethylene was investigated. The dimethylsilyl-bridged bis(BCOCp) ligand was accessible but could not be converted to its titanium, zirconium, or niobium chloride complexes. 8,10-Dimethyl-4-(1-methylethylidene)tricyclo[5.2.2.0 2,6 ]-2,5-undecadiene (DMeBCOCp-dimethylfulvene) was formed, but did not react with cyclopentadienyl anions. A regioisomeric mixture of 1,2-bis[( 1R,7R,8R,10R )-8,10-dimethyltricyclo[5.2.2.0 2,6 ]-2,5-undecadienyl]ethane [en(DMeBCOCpH)] ligands could be formed and metalated to form (+)-[ethylene-1,2-bis[η 5 -( 1R,7R,8R,10R )-8,10-dimethyltricyclo[5.2.2.0 2,6 ]-2,5-undecadien-4-yl]]titanium dichloride [(+)-β,β-en(DMeBCOCp) 2 TiCl 2, (+)- 11 ] along with its α,α- and α,β-bridged regioisomeric titanocene dichlorides. (+)- 11 is unique in that it is a chiral ethylene-bridged ansa -metallocene which contains only homotopic cyclopentadienyl faces. (+)- 11 was characterized by X-ray crystallography and was applied as a catalyst for the enantioselective isomerization of alkenes. (+)- 11 was less active and less enantioselective than a known chiral ansa -bis(indenyl)titanium catalyst for the enantioselective alkene isomerization.