The mechanism of the reaction of 9-chloro-9-borafluorene and NaBH₄ has been investigated by density functional theory. The optimized geometries of ten intermediates and twelve transition states were obtained and possible reaction pathways were found. Calculation results indicate that the more possible reaction pathway includes six intermediates and five transition states, the higtest active energy E_a which decides the reaction velocity is 80.35 kJ•mol^－1, and that 9-borafluorene is not the most stable intermediate. The reason that the intermediate 9-borafluorene can not be successfully separated experimentally is explained.

Key words: 9-chloro-9-borafluorene, NaBH₄, DFT, reaction mechanism