para-Chlorotetrafluorophenyl-boranes – syntheses and structures of a series of mono- and bidentate Lewis acids

Mono- and bidentate tri-coordinated boron compounds bearing the yet unexplored para-chlorotetrafluorophenyl substituent have been synthesized and structurally investigated. The acidity of tris(para-chlorotetraphenyl)borane (7) was shown to exceed that of the widely used tris(pentafluorophenyl)borane (BCF) according to the Gutmann-Beckett method. Acid-base adducts of 7 with diethyl ether and triethylphosphine oxide were crystallized. Dihydrogen splitting at room temperature was observed with a Frustrated Lewis Pair consisting of 7 and 2,2,6,6-tetramethylpiperidine (TMP). The hydrogen adduct was isolated and characterized by NMR, SC-XRD and elemental analysis. Its solid-state structure contains a H⋯H distance on the verge of dihydrogen bonding (2.28(6) Å). Bis(para-chlorotetrafluorophenyl)hydridoborane was prepared in situ and shown to be applicable in hydroboration reactions similarly to Piers' borane.