Cyanide free contraction of disclosed 1,4-dioxane ring as a route to cobalt bis(dicarbollide) derivatives with short spacer between the boron cage and terminal functional group

Abstract

The 1,4-dioxane derivative of cobalt bis(dicarbollide) reacts with dialkylsulfides and triphenylphosphine to give the corresponding sulfonium and phosphonium derivatives [8-L(CH₂CH₂O)₂-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] (L = SMe₂, S(CH₂CH₂)₂O, PPh₃). The treatment of the triphenylphosphonium derivative with sodium hydroxide results in contraction of the side chain with formation of [8-HOCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻. The same product was obtained by treatment of the dimethylsulfonium derivative with the poorly nucleophilic base t-BuOK, whereas the stronger nucleophiles induce the sulfur demethylation to give [8-MeS(CH₂CH₂O)₂-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻. The alcohol was used for the synthesis of a series of other short-spacer functional derivatives [8-XOCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻ (X = NH₂, SH, N₃). A similar contraction of the disclosed 1,4-dioxane ring via the reactions with SMe₂ and PPh₃ can be used for the synthesis of short-spacer functional derivatives of nido-carborane, whereas the 1,4-dioxane derivatives of closo-decaborate and closo-dodecaborate anions, being stronger electron donors, are more stable and do not react with dimethylsulfide and triphenylphosphine.