Swollen Polyhedral Volume of the anti-B18H22 Cluster via Extensive Methylation: anti-B18H8Cl2Me12

Methylation of anti B18H22 (1) affords the first example of alkyl substitution of terminal hydrogen atoms on the fluorescent octadecaborane-22 molecule to give highly methylated 2,2'-Cl-2-1,1',3,3',4,4',7,7',8,8',10,10'-Me-12 anti B18H8 (2). This extensive chemical substitution leads to a swelling in the polyhedral volume of the 18-vertex boron atomic skeleton of the molecule and an enhancement of the absorption and solubility characteristics of this highly fluorescent molecule. We propose this swollen polyhedral volume to be the result of a marked increase in the relative positivity of the cluster-only total charge of the boron atomic skeleton caused by the combined electron-withdrawing capacity of the 12 methyl groups. Enhancement in the absorption and solubility properties may be crucial in the design of new borane-based laser materials.