SYNTHESIS OF ANSA-TITANOCENES FROM 1,2-BIS(2-INDENYL)ETHANE AND STRUCTURAL COMPARISONS IN THE CATALYTIC EPOXIDATION OF UNFUNCTIONALIZED ALKENES

Novel ansa-titanocene dichlorides have been prepared from 1,2-bis(2-indenyl)ethane (10). Treatment of the dilithio salt of 10 with either methyl iodide or benzyl bromide gives the corresponding dialkylated bis(indene) in high yield. Titanium complexation of the dimethyl and dibenzyl bis(indene) derivatives affords [ethylenebis[(eta(5)-1-methyl-2-indenyl)]titanium dichloride(14) and [ethylenebis[(eta 5-1-benzyl-2-indenyl)]titanium dichloride(15), respectively. In each case, the ansa-titanocene is obtained as a mixture of meso and racemic isomers. Treatment of the dilithio salt of 10 with trimethylsilyl chloride results in a mixture of bis(trimethylsilyl) derivatives. Attempted titanium complexation of the silylated bis(indene) mixture results in an intramolecular oxidative coupling of the C(3) and C(3') positions to yield a trans-6,7-dihydroindeno[2,1-c]fluorene derivative, 16. [Ethylenebis(eta(5)-2-indenyl)]titanium dichloride (9) is hydrogenated to yield tethylenebis(eta(5)-4,5,6,7-tetrahydro-2-indenyl)]titanium dichloride (17). The crystal structures of rac-l4 and 17 were determined by X-ray crystallography and are presented. Examination of ethylene-bridged bis(2-indenyl) ansa-titanocenes as catalysts for the epoxidation of unfunctionalized alkenes was conducted using the representative titanocenes 9, 14, 15, and 17. The catalytic ability of this new class of. ansa-titanocenes in the epoxidation study was found in some cases to exceed the activity of existent titanocene complexes.