C-arylation and C-heteroarylation of icosahedral carboranes via their copper(I) derivatives

Reaction between C-mono- or C,C′-di-copper(1) derivatives of 1,2-, 1,7-, or 1,12-dicarba-closo-dodecaborane(12) and aryl iodides in the presence of pyridine gives the corresponding C-mono- or C,C′-diaryl derivatives of 1,7- and 1,12-dicarba-closo-dodecaboranes(12); 1,2-dicarba-closo-dodecaborane(12) gives only the C-monoaryl product. Cyclic or linear arylene coupled systems are obtained when di-iodoarenes are used. Copper(I) derivatives may be generated from C-unsubstituted or C-monosubstituted carboranes using copper(I) t-butoxide when substituents incompatible with the use of C-lithio-intermediates are involved. The C-copper(I) derivative of 1,2-dicarba-closo-dodecaborane(12) gives 1,2-di-2′-pyridyl-1,2-dicarba-closo-dodecaborane(12) specifically with 2-bromopyridine. The (inferred) intermediate mono-2-pyridyl-derivative, obtained independently from 2-ethynylpyridine and the dimethylsulphide complex of decaborane, gives 1-phenyl-2,2′-pyridyl-1,2-dicarba-closo-dodecaborane(12) upon conversion into its copper(I) derivative and treatment with iododobenzene. However, the copper(I) derivative of 1-phenyl-1,2-dicarba-closo-dodecaborane(12) does not react to a significant extent with 2-bromopyridine.