Author/s: A. V. Puga, F. Teixidor, R. Sillanpää, R. Kivekäs, M. Arca, G. Barbera and C. Viñas
Reference: Chemistry – A European Journal, 2009, 15, 9755 – 9763.

Abstract:

The incorporation of iodine atoms onto the boron vertices of the ocarborane framework causes, according to spectroscopic data, a uniform increase in the acidic character of the CcH (Cc = cluster carbon) vertices, whereas the incorporation of methyl groups onto the boron vertices of the o-carborane framework reduces their acidity. Methyl groups when attached to boron are electron-withdrawing in boron clusters, whereas iodine atoms bonded to boron act as electron donors. This has been proven on Bmethyl and B-iodinated o-carboranes with NMR spectroscopy measurements and DFT calculations of natural bond orbital (NBO) charges, which show a cumulative build-up of positive cluster only total charge (CTC) on B-methyl o-carboranes and a cumulative build-up of negative cluster-only total charge for B-iodinated o-carboranes.