title: Are methyl groups electron-donating or electron-withdrawing in boron clusters? Permethylation of o-carborane.
abstract: That methyl groups attached to carbon atoms are electron donors must not be generally assumed. In boron clusters, Me groups on boron are electron withdrawing. At the B3LYP/6-31G* level of theory, it has been proven that the Mulliken charge on each boron after substitution of -H by -Me increases by +0.18 unit. This leads to a high build-up of positive charge upon permethylation, then hampering it. Experimentally, this is proven by the synthesis of 9-I0.707H0.293-12-Cl0.566H0.434-3,4,5,6,7,8,10,11-Me8-1,2-C2B10H2, in which positions 9 and 12 were first methylated and then attacked by nucleophiles. This is substantiated by the synthesis of 3,6,8,9,10,12-Me6-1,2-C2B10H6 under the same experimental conditions but with time control.
authors: Institut de Ciència de Materials de Barcelona (CSIC), Campus U.A.B., E-08193 Bellaterra, Spain.
authors: Francesc
authors: F
authors: Teixidor
authors: Gemma
authors: G
authors: Barberà
authors: Albert
authors: A
authors: Vaca
authors: Raikko
authors: R
authors: Kivekäs
authors: Reijo
authors: R
authors: Sillanpää
authors: Josep
authors: J
authors: Oliva
authors: Clara
authors: C
authors: Viñas