Synthesis of 1,3-Dialkylimidazol-2-ylidene Boranes from 1,3-Dialkylimidazolium Iodides and Sodium Borohydride

1,3-Dialkylimidazol-2-ylidene boranes have been made in moderate yields (typically 23-53%) from the corresponding N-alkyl imidazole, an alkylating agent (usually MeI), and sodium borohydride (NaBH4). The two-step, one-pot reaction sequence takes about 1 day to perform. The reagents are inexpensive, and the reactions are easy to conduct. The synthesis of 1,3-dimethylimidazol-2-ylidene borane has been conducted on scales up to 100 mmol and is especially convenient because the pure product can be isolated by direct recrystallization from water.