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.

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.