Abstract:
The reaction of dilithiated thiophene and
thiophene derivatives with group 6 transition metal carbonyl
precursors and subsequent alkylation afforded linearly
arranged Fischer 2,5-bis-carbene and the rare unsymmetrical
2,3-bis-carbene chelated complexes. The latter requires a
second lithiation to occur at an adjacent, less reactive site on the thiophene ring. The control of reactivity sites was investigated
and achieved by either blocking more reactive positions with substituents or activating less reactive positions by lithium−halogen
exchange reactions. A series of Fischer bis-carbene chelates were synthesized by manipulating the above variables. Structural
features of Fischer mono-carbene, mononuclear bis-carbene, and bis-carbene chelated complexes were studied by IR, NMR, and
single-crystal X-ray diffraction
