New aspects of acid-assisted nucleophilic substitution reactions of 11-vertex nido-carboranes.

A comparative study of reactivity of nido -carboranes in acid-induced nucleophilic substitution reaction and unique behavior of carborane with covalently binded cage carbon atoms are presented. [Display omitted] Reactions of the nido -carborane salts Me 4 N[7,8-R,R-7,8- nido -C 2 B 9 H 10 ] (R,R = Me 2 ; R,R = o-C 6 H 4 (CH 2) 2) with Me 2 S in the presence of triflic acid give a mixture of isomeric carboranes 9-Me 2 S-7,8-R,R-7,8- nido -C 2 B 9 H 9 and 10-Me 2 S-7,8-R,R-7,8- nido -C 2 B 9 H 9. In contrast, Me 4 N[7,8-(CH 2) 3 –7,8- nido -C 2 B 9 H 10 ] affords the only isomer 10-Me 2 S-7,8-(CH 2) 3 –7,8- nido -C 2 B 9 H 9. Interaction of Me 4 N[7,8-(CH 2) 3 –7,8- nido -C 2 B 9 H 10 ] and dimethyl sulfoxide in acidic conditions leads to the formation of a product 10-Me 2 SO-7,8-(CH 2) 3 –7,8- nido -C 2 B 9 H 9 in which, according to the SC-XRD, dimethyl sulfoxide molecule attaches to nido -carborane cage through an oxygen atom. The half-peak potential of the first oxidation wave of nido -carboranes correlates well with their ability to undergo acid-assisted nucleophilic substitution reactions. Thermal isomerization of 10-Me 2 S substituted nido -carboranes to 9-Me 2 S isomers was observed at higher temperatures than acid-assisted nucleophilic substitution and could proceed with the formation of 11-vertex closo -carboranes as intermediates according to the DFT study. [ABSTRACT FROM AUTHOR]