Perhaloaryl-metal chemistry III. σ-(trichloro-2-thienyl) derivatives of transition metals and related studies

Polychloroheteroaromatic Compounds

“…143) [113,[140][141][142]. With tetrahydrofuran as the solvent and one equivalent of ethylene bromide as the entrainer, the yield of the Grignard compound is essentially quantitative [142].…”

“…With one equivalent of n-butyl-lithium in ether [141,[143][144][145] or tetrahydrofuran [1461 at _70 0 , or methyl-, t-butyl-, or phenyllithium in tetrahydrofuran at _70 0 (146], tetrachlorothiophen gives trichloro-2-thienyl-lithium. In the case of t-butyl-lithium, the lithium compound is formed exclusively in tetrahydrofuran but, with methyl-or n-butyl-lithium in the same solvent, considerable ringfragmentation also occurs [146].…”

“…Trichloro-2-thienyl-lithium reacts normally with acid [143,145], carbon dioxide [141, 143-146, 148, 149], acetaldehyde [141], acetone [141], benzophenone [143], mercuric chloride [143], various chlorosilanes [145,146,149], and chlorodiphenylphosphine [143, 1451. With various transition metal halides, it gives a-bonded (trichloro-2-thienyl) derivatives, for example compound (81), which show enhanced thermal and oxidative stabilities relative to their hydrocarbon analogues [143].…”

“…Attempts to eliminate lithium chloride from trichloro-2-thienyllithium have failed [143], presumably because the expected product, 4,5-dichloro-2,3-dehydrothiophen is a highly strained ring-system. An ethereal solution of this lithium compound remains essentially unchanged after 4 days at 0 0 • Pyrolysis of the mercury derivative (82) (see later) in the presence of tetraphenylcyclopentadienone gives a high yield of the benzo [b ] thiophen (83), but this reaction is…”

“…more likely to proceed via initial addition of the cyclopentadienone to the mercury compound (82) rather than via formation of 4,5-dichloro-2,3-dehydrothiophen [143] .…”