Synthesis of poly-1,1′-ferrocenylenesvia ferrocenylenecuprates(1)

Summary The solution polycondensation of TMEDA-chelated 1,1-dilithioferrocene in the presence of Cu⁺ ion, leading to polyferrocenylenes, is explored, the cupration stoichiometry (CuLi=ca. 0.5) being such as to favor the intermediacy of ferrocenylenecuprates, R₂CuLi (R=0.5 ferrocenylene unit). In the first series of experiments, the cuprate intermediates are allowed to undergo thermal or oxidative poly-coupling; in subsequent experiments, they are copolymerized with 1,1-diiodoferrocene. Both reaction sequences result in the formation of linear oligomeric and polymeric coupling products essentially identical in composition and spectroscopic properties with the poly-1,1-ferrocenylenes of previous investigations. Best results are obtained in the copolymerizations with the diiodo derivative, which give higher overall yields (70–75%) and molecular masses (typically 4000 for the first fraction) than attained in earlier work. In addition, whereas previous syntheses involving either the oxidative coupling of the dilithioferrocene with Cu²⁺ ion or the oxidative-thermal coupling of ferroceny-lenecopper(I) intermediates gave large quantities of the dinuclear 0.0]-ferrocenophane at the expense of linear polyferrocenylenes, the copolymerizations with diiodoferrocene distinctly favor linear propagation, and yields of the ferrocenophane are less than one percent. The organocuprate/organoiodide coupling reaction thus constitutes a preparative approach to polyferrocenylenes superior to previous syntheses described.