THE FULVENE ROUTE TO PENTAISOPROPYLCYCLOP ENTADIENIDE

Sodium tetraisopropylcyclopentadienide (2) is attacked selectively in 5-position by tosyl azide with formation of 5-diazo-1,2,3,4-tetraisopr opylcyclopentadiene (1) and also by the iminium salt [Me2NC(H)OMe](+) MeOSO3- to yield 1,2,3,4-tetraisopropyl-6-dimethylaminopentafulvene (3 ) with concomitant methanol elimination. In a one pot reaction 3 adds methyllithium to form a cyclopentadienide intermediate (4) which is co nverted in situ to 1,2,3,4-tetraisopropyl-6-methyl-pentafulvene (5) wi th dimethylchlorosilane. By the same procedure with 1,4-dilithiobutane instead of methyllithium two tetraisoproylfulvene moieties an linked to the bis-fulvene 8 with a -(CH2)(4)-backbone. 3 can be converted dir ectly to 1,2,3,4-tetraisopropylpentafulvene (7) with diisobutylaluminu m hydride. 5 again adds methyllithium to give lithium pentaisopropylcy clopentadienide (6) or can be deprotonated at the 6-methyl group with potassium hydride. The intermediate potassium salt gives tetraisopropy l-6-trimethylsilylmethyl-pentafulvene (9) with trimethylchlorosilane. The fulvene 7 could be eta(6)-coordinated to the tricarbonyl chromium complex 10 with [Cr(CO)(3)(NCEt)(3)], 5 and 7 yield the molybdenum ana logues 11 and 12 with [Mo(CO)(3)(NCEt)(3)].