Synthesis and characterisation of labelled diphenylcarboranes

Abstract The synthesis, by either acid-catalysed electrophilic substitution or recapitation, and characterisation of four new B-labelled diphenyl carboranes is described. Two of these, 1,2-Ph 2 -9,12-I 2 -1,2- closo -C 2 B 10 H 8 ( 1 ) and 1,2-Ph 2 -3-Me-1,2- closo -C 2 B 10 H 9 ( 2 ) were subjected to crystallographic study, whilst the 3-Et ( 3 ) and 3-F ( 4 ) analogues of 2 were studied spectroscopically. Decapitation of the mono-iodo analogue of 1 affords [5-I-7,8-Ph 2 -7,8- nido -C 2 B 9 H 9 ] − , isolated as [HNEt 3 ] + ( 5a ) [HNMe 3 ] + ( 5b ) and [C 6 H 5 CH 2 NMe 3 ] + ( 5c ) salts, the last of which was subjected to crystallographic analysis. Decapitation of 3 and 4 selectively removes B6, yielding the 3-labelled nido -carboranes [3-Et-7,8-Ph 2 -7,8- nido -C 2 B 9 H 9 ] − and [3-F-7,8-Ph 2 -7,8- nido -C 2 B 9 H 9 ] − , respectively, both isolated as [HNMe 3 ] + salts ( 6a and 7 ). The ethyl species was also prepared as the [HNEt 3 ] + salt ( 6b ), and was structurally characterised. Salts 5b , 6a and 7 are all afforded in good yield and the anions are ideal candidates for subsequent deprotonation and metallation, which should result in low-temperature isomerisation of the transient 3,1,2-MC 2 B 9 species thereby produced, and thereby yield important, robust, mechanistic information on the rearrangement process.