Convenient Preparation and Structure Determination of Air- and Moisture-Tolerant Difluoromethylborates.

Convenient and reliable synthetic methods for difluoromethylborates have been established. The intermediary generated difluoromethylsilicate species from TMSCF2 H (TMS=trimethylsilyl) and potassium tert-butoxide were allowed to react with pinBPh (Me4 C2 O2 BPh) in the presence of 18-crown-6 to give the corresponding borate compound [pinB(Ph)CF2 H]- K+ (18-crown-6) as an air- and moisture-tolerant solid. The unambiguously determined crystal structure of [pinB(Ph)CF2 H]- K+ (18-crown-6) revealed that the difluoromethylborate unit partially coordinated on the potassium ion. Reaction of [pinB(Ph)CF2 H]- K+ (18-crown-6) with potassium difluoride (KHF2 ) in acetic acid enabled substitution of the pinacol unit and phenyl group with fluorides, and gave (difluoromethyl)trifluoroborate [F3 BCF2 H]- K+ (18-crown-6) in a good yield. The crystal structure of air- and moisture-tolerant [F3 BCF2 H]- K+ (18-crown-6), which would be a promising reagent for synthesis of various difluoromethylboron species, showed a polyrotaxane-like polymeric structure based on the K⋅⋅⋅F interactions between the K+ (18-crown-6), CF2 H, and BF3 units.