The reactions of trifluoromethyl and pentafluorophenyl cyanides with BCl3, BBr3, TiCl4, and SnCl4 have been investigated and the compounds [TiCl4(C6F5·CN)2], [BX3(C6F5·CN)], and {CF3·C(X)NBX2}2(X = Cl or Br) are described. The ethylideneamino-boranes were produced by the novel insertion of a cyano-group into a boron–halogen bond. 11B- and 19F-Nuclear magnetic resonance and infrared spectral data are recorded.