PHENYL-INDUCED 3,1,11-REARRANGEMENT IN THE SYNTHESIS OF MIXED PYRROLYL DICARBOLLIDE COBALTADICARBABORANES/

Mixed pyrrolide cobaltadicarbollides have been prepared from the react ion involving potassium pyr pyrrolide, anhydrous CoCl2 and the [7,8-(C 6H5)(2)-nido-7,8-C2B9H10](-) anion in dimethoxyethane. An alternative and higher-yield route consists in the reaction between 1,2-(C6H5)(2)- closo-1,2-C2B10H10 and potassium pyrrolide in the presence of anhydrou s CoCl2. As confirmed by the X-ray diffraction ana lysis of a(5)-NC4H4 )-1,11-(C6H5)(2)-closo-3,1,11-CoC2B9H9], the phenyl rings were found t o enhance the rearrangement of the metallacarborane cluster carbons to produce the 3,1,11-isomer instead of the expected 3,1,2-derivative. A s suggested by H-1 and C-13 NMR spectroscopy, the electron-withdrawing properties and steric requirements of the phenyl rings facilitate the rearrangement.