ORGANOTRANSITION-METAL METALLACARBORANES .15. REGIOSPECIFIC B-ALKYLATION OF (ARENE)FE(ET2C2B3H5), (ARENE)RU(ET2C2B3H5) AND (C5ME5)CO(ET2C2B3H5) SANDWICH COMPLEXES

The controlled introduction of hydrocarbon substituents onto specific boron locations in nido-metallcarborane complexes of the title classes has been achieved via bridge deprotonation followed by reaction with alkyl or arylalkyl halides. The monodeprotonated complex anions react with MeI, EtBr, p-MeC6H4CH2Br, or p-BrCH2C6H4CH2Br in THF to generate exclusively the B(5)-substituted derivative in each case. This pattern differs strikingly from the corresponding reactions of nido-R2C2B4H5- carborane anions, which had been shown in an earlier study to give the B(4)- (and equivalent B(6)-) alkylated products with 99% regiospecificity. In the present work, the B(5)-methyl complexes of Fe, Ru, and Co were each further alkylated via deprotonation/alkyl halide treatments, to give successively the B(4,5)-dimethyl and B(4,5,6)-trimethyl derivatives as desired. The alkylated products were isolated in generally high yields; for the three compound classes studied, the B-monomethyl complexes are extremely air-stable, but the sensitivity to air increases on further alkylation. Reactions of the (C6Me6)Fe(Et2C2B3H3)2- and (C5Me5)Co(Et2C2B3H3)2- dianions with alkyl iodides result in partial iodination at the B(4) position. © 1990, American Chemical Society. All rights reserved.