The reaction of the cyanoborane complexes L·BH2CN [where L = R3N (R = Me, Et, Pr, Bu); quinuclidine (Q) and Ph3P] with SbCl5 in CCl4 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 νCN cyano resonances towards the higher wave-numbers. The L·BH2CN·SbCl5 complexes, carrying a bridge-head CN function, readily transformed with ButCl into the [BH2(L)CNBut]SbCl6 tert-butylnitrilium salts with high crystallization ability. In the case of L = R3N and Q substituents partial chlorination of the BH bond accompanied the formation of the nitrilium salt. The relatively weak coordination of the ButNC ligand in the above antimony complexes was indicated by the 2282-2292 cm-1 values observed for νCN, unexpectedly high for isonitrile complexes, as well as by the exchange reactions with strong donors (i.e. Me2SO, Q, DMAP), giving rise to the liberation of the ButNC. The synthetic utility of related complexes was shown by the highly efficient transformation of [BH2(L)CNBut]SbCl6 into Me·BH2C(O)NHBut in an alkaline medium, whose acid hydrolysis furnishes Me3N·BH2COOH, 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·BH2CN·SbCl5, [BH2(L)CNBut]SbCl6 and Me3·BH2C(O)NHBut were derived from IR, 1H and 11B NMR spectral data.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry