The detailed dissociation mechanism of diborane (B~2H~6) in vacuum or in tetrahydrofuran (THF) media has been studied at B3LYP/6-31G^* level with dimethyl ether to simulate the involved THF. All the calculations indicate a two-step mechanism for the dissociation. Only one H-bridge bond is broken and one B－O bond is formed in the each S~N-2 like step. Comparing with the dissociation of B~2H~6 in vacuum or in hydrocarbon media, participation of Me~2O significantly lowers the activation barriers in the process. The barriers are further lowered when solvent effect is taken into account (28.03 kJ·mol^-^1 for the first step and 21.00kJ·mol^-^1 for the second one).

Key words: DIBORANE, DIMETHYL ETHER, DECOMPOSITION, SOLVENT EFFECT