Die Fulven-Route zum Pentaisopropylcyclopentadienid / The Fulvene Route to Pentaisopropylcyclopentadienide

Sodium tetraisopropylcyclopentadienide (2) is attacked selectively in 5-position by tosyl azide with formation of 5-diazo-1,2,3,4-tetraisopropylcyclopentadiene (1) and also by the iminium salt [Me 2 NC(H)OMe] + MeOSO 3 - to yield 1,2,3,4-tetraisopropyl-6-dimethylamino-pentafulvene (3) with concomitant methanol elimination. In a one pot reaction 3 adds methyllithium to form a cyclopentadienide intermediate (4) which is converted in situ to 1,2,3,4- tetraisopropyl-6-methyl-pentafulvene (5) with dimethylchlorosilane. By the same procedure with 1,4-dilithiobutane instead of methyllithium two tetraisoproylfulvene moieties are linked to the bis-fulvene 8 with a -(CH 2 ) 4 - backbone. 3 can be converted directly to 1,2,3,4- tetraisopropylpentafulvene (7) with diisobutylaluminum hydride. 5 again adds methyllithium to give lithium pentaisopropylcyclopentadienide (6) or can be deprotonated at the 6-methyl group with potassium hydride. The intermediate potassium salt gives 1,2,3,4-tetraisopropyl- 6-trimethylsilylmethyl-pentafulvene (9) with trimethylchlorosilane. The fulvene 7 could be η 6 -coordinated to the tricarbonyl chromium complex 10 with [Cr(CO) 3 (NCEt) 3 ], 5 and 7 yield the molybdenum analogues 11 and 12 with [Mo(CO) 3 (NCEt) 3 ].