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-in denyl)ethane (10). Treatment of the dilithio salt of 10 with either me thyl iodide or benzyl bromide gives the corresponding dialkylated bis( indene) in high yield. Titanium complexation of the dimethyl and diben zyl bis(indene) derivatives affords [ethylenebis[(eta(5)-1-methyl-2-in denyl)]titanium dichloride(14) and [ethylenebis[(eta 5-1-benzyl-2-inde nyl)]titanium dichloride(15), respectively. In each case, the ansa-tit anocene is obtained as a mixture of meso and racemic isomers. Treatmen t of the dilithio salt of 10 with trimethylsilyl chloride results in a mixture of bis(trimethylsilyl) derivatives. Attempted titanium comple xation of the silylated bis(indene) mixture results in an intramolecul ar 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 ebis(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 a nd are presented. Examination of ethylene-bridged bis(2-indenyl) ansa- titanocenes as catalysts for the epoxidation of unfunctionalized alken es was conducted using the representative titanocenes 9, 14, 15, and 1 7. The catalytic ability of this new class of. ansa-titanocenes in the epoxidation study was found in some cases to exceed the activity of e xistent titanocene complexes.