Synthetic and structural studies on new vinylcyclopentadienyl derivatives of titanium, iron and thallium

An improved procedure for the preparation of vinylcyclopentadienyllithium (1) from 6-methylfulvene and lithium diisopropylamide in THF solution has been developed. Reaction of 1 with thallium ethoxide in THF has produced vinylcyclopentadienylthallium (3). Compounds 1 and 3 have been used in the synthesis of vinyl- (4) and 1,1′-divinyltitanocene dichloride (5). Treatment of 1,2,3,4,6-pentamethylfulvene with lithium diisopropylamide in THF solution has afforded vinyltetramethylcyclopentadienyllithium (2) in high yield. Reactions of 2 with FeCl₂ or TiCl₄ have led to bis(η⁵-vinyltetramethylcyclopentadienyl)iron (7) and (η⁵-vinyltetramethylcyclopentadienyl)titanium trichloride (8), respectively. Compound 8 reacts with (η⁵-C₅H₅)T1 to produce 1-vinyl-2,3,4,5-tetramethyltitanocene dichloride (9) in high yield. The crystal structure of 5 has been determined. 5 is monoclinic, C2₁/c, with a = 14.420(3), b = 6.610(2), c = 14.111(3) Å, β = 102.18(2)° and D_calc = 1.52 g cm^-3 for Z = 4. The Ti atom resides on a crystallographic two-fold axis. The η⁵-vinylcyclopentadienyl groups are slightly staggered with the carbons bonded to the vinyl groups next to one another and between the ClTiCl bond. The TiC(η⁵) separations range from 2.343(4) to 2.450(3) Å, the latter values for the carbon atoms bonded to the vinyl group.