A simple route to (tetraethynylcyclobutadiene)cyclopentadienylcobalt

Reaction of 2-(trimethylsilylethynyl)-1,3-dioxane with CpCo(CO)2 followed by reaction with Me4NF in and NaH furnishes 1,2- and [1,3-bis[2-dioxanyl]cyclobutadienecyclopentadienylcobalt in an overall combined yield of 95% in a 3.5:1 ratio. Metalation of the 1,2-complex or the 1,3-complex by BuLi is followed by formylation. Transformation of the resulting aldehyde into an alkyne by CH3CO(CN2)PO(OEt)2 and repetition of the reaction sequence furnishes the 1,2-diethynyl- or [1,3-diethynyl(2-dioxanyl)cyclobutadiene]cyclopentadienylcobalt. Deketalization and subsequent Ohira reaction transforms these precursors into a host of different tetraethynylated CpCo-stabilized cyclobutadienes. The synthetic method is solution-phase based and circumvents the cumbersome flash-vacuum pyrolysis step hitherto necessary for the preparation of tetraethynylated CpCo-stabilized cyclobutadiene complexes.