Synthesis and structural characterization of novel organometallic dehydroannulenes with fused CpCo-cyclobutadiene and ferrocene units including a cyclic fullerenyne segment

The synthesis of fused organometallic dehydroannulenes containing cyclobutadiene(cyclopentadienyl)cobalt or ferrocene units separated by butadiyne linkers is presented. Starting from the corresponding 1,2-diethynylated sandwich complexes, either Eglinton, Hay, or Vogtle-type coupling furnishes the desired dehydroannulenes. The choice of the coupling variant is critical for the success of this reaction. It was found that for diethynylferrocene a variant of the classic Eglinton system utilizing a Cu2Cl2/CuCl2 mixture in pyridine works successfully, while for the case of the cyclobutadiene(cyclopentadienyl)cobalt complexes the Vogtle coupling utilizing Cu(OAc)(2) in acetonitrile gave the most impressive results, leading to a 87% yield of cyclized material. To obtain perethynylated organometallic dehydroannulenes, a novel synthesis of tetraethynylated cyclobutadiene complexes was developed. Flash vacuum pyrolysis of a bisbutadiynylated CpCo-ligated cyclobutadiene furnishes the desired tetraethynylated cyclobutadiene complex via a Bergman-type rearrangement. The two TMS and two TIPS substituents of the cyclobutadiene complex are oriented pairwise ortho with respect to each other. Removal of the TMS groups accesses a monomer, which under the conditions of the Vogtle coupling cyclizes to novel trimeric and tetrameric, perethynylated, cyclobutadieno fused, organometallic dehydroannulenes.