The reaction of the cyanoborane complexes L·BH 2CN [where L = R 3N (R = Me, Et, Pr, Bu); quinuclidine (Q) and Ph 3P] with SbCl 5 in CCl 4 afforded 1:1 complexes. Coordination of antimony to the nitrogen atom of the cyano groupp was clearly implied by the 35–42 cm −1 shift of the ν CN cyano resonances towards the higher wave-numbers. The L·BH 2CN·SbCl 5 complexes, carrying a bridge-head CN function, readily transformed with Bu t Cl into the [BH 2(L)CNBu t ]SbCl 6 tert-butylnitrilium salts with high crystallization ability. In the case of L = R 3N and Q substituents partial chlorination of the BH bond accompanied the formation of the nitrilium salt. The relatively weak coordination of the Bu t NC ligand in the above antimony complexes was indicated by the 2282–2292 cm −1 values observed for ν CN, unexpectedly high for isonitrile complexes, as well as by the exchange reactions with strong donors (i.e. Me 2SO, Q, DMAP), giving rise to the liberation of the Bu t NC. The synthetic utility of related complexes was shown by the highly efficient transformation of [BH 2(L)CNBu t ]SbCl 6 into Me·BH 2C(O)NHBu t in an alkaline medium, whose acid hydrolysis furnishes Me 3N·BH 2COOH, a well-known and important compound in boron chemistry with high yield. Preparation of this substance with the presented new process, via the tert-butylnitrilium salt, is much more efficient than by means of the previously reported procedures employing the ethylnitrilium salt. The proposed structures of the new compounds L·BH 2CN·SbCl 5, [BH 2(L)CNBu t ]SbCl 6 and Me 3·BH 2C(O)NHBu t were derived from IR, 1H and 11B NMR spectral data.