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 TMSCF2H (TMS=trimethylsilyl) and potassium tert‐butoxide were allowed to react with pinBPh (Me4C2O2BPh) in the presence of 18‐crown‐6 to give the corresponding borate compound [pinB(Ph)CF2H]−K+(18‐crown‐6) as an air‐ and moisture‐tolerant solid. The unambiguously determined crystal structure of [pinB(Ph)CF2H]−K+(18‐crown‐6) revealed that the difluoromethylborate unit partially coordinated on the potassium ion. Reaction of [pinB(Ph)CF2H]–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 [F3BCF2H]–K+(18‐crown‐6) in a good yield. The crystal structure of air‐ and moisture‐tolerant [F3BCF2H]–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), CF2H, and BF3 units. The difluoromethylsilicate species generated from TMSCF2H KOtBu reacts with pinB−Ph in the presence of 18‐crown‐6 to give [pinB(Ph)CF2H]−K+(18‐crown‐6) as an air‐ and moisture‐tolerant solid. Subsequent reaction of [pinB(Ph)CF2H]−K+(18‐crown‐6) with KHF2 in acetic acid gave the difluoromethylated trifluoroborate [F3BCF2H]−K+(18‐crown‐6) showing the polyrotaxane‐like linear structure.