Syntheses and Characterization of (C 2 F 5 ) 3 BCO and (C 3 F 7 ) 3 BCO

The new tris(perfluoroalkyl)borane carbonyls, (C 2 F 5 ) 3 BCO and (C 3 F 7 ) 3 BCO, were prepared by means of a novel synthetic route using commercially available precursors by reacting K[(C 2 F 5 ) 3 BCOOH] and K[(C 3 F 7 ) 3 BCOOH] with concentrated sulfuric acid in the last step. The carboxylic acids, K[(C 2 F 5 ) 3 BCOOH] and K[(C 3 F 7 ) 3 BCOOH], were prepared by oxidative cleavage of the CC triple bonds in Cs[(C 2 F 5 ) 3 BCCPh] and Cs[(C 3 F 7 ) 3 BCCPh] in a two‐step process to yield K[(C 2 F 5 ) 3 BCOCOPh] and K[(C 3 F 7 ) 3 BCOCOPh] as isolable intermediates. Crystal structures were obtained of K[(C 2 F 5 ) 3 BCOCOPh], K[(C 2 F 5 ) 3 BCOOH] ⋅ H 2 O, (C 2 F 5 ) 3 BCO, K[(C 3 F 7 ) 3 BCOOH] ⋅ 2 H 2 O, and (C 3 F 7 ) 3 BCO. In the crystal structures of (C 2 F 5 ) 3 BCO and (C 3 F 7 ) 3 BCO the CO bond lengths are 1.109(2) and 1.103(5) Å, respectively, which are among the shortest observed to date. Tris(pentafluoroethyl)borane carbonyl and (C 3 F 7 ) 3 BCO slowly decompose at room temperature to yield CO, difluoroperfluoroalkylboranes and perfluoroalkenes. The decomposition of (C 2 F 5 ) 3 BCO was found to follow a first‐order rate law with E a =107 kJ mol −1 .