SYNTHESIS OF [AMINE(TERT-BUTYLISONITRILE) DIHYDROBORON(III)] CATIONS VIA THE ANTIMONY PENTACHLORIDE COMPLEXES OF AMINE-DIHYDROCYANOBORANES - A NEW ROUTE TO AMINE-CARBOXYBORANES

The reaction of the cyanoborane complexes L.BH2CN [where L = R3N (R = Me, Et, Pr, Bu); quinuclidine (Q) and Ph3P] with SbCl5 in CCl4 afforde d 1:1 complexes. Coordination of antimony to the nitrogen atom of the cyano group was clearly implied by the 35-42 cm-1 shift of the nu(CN) cyano resonances towards the higher wavenumbers. The L.BH2CN.SbCl5 com plexes, carrying a bridge-head CN function, readily transformed with B u(t)Cl into the [BH2(L)CNBu(t)]SbCl6 tert-butylnitrilium salts with hi gh crystallization ability. In the case of L = R3N and Q substituents partial chlorination of the B-H 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 v alues observed for nu(CN), 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 Bu(t)NC. The synthetic utility of related complexes was shown by the highly efficient transfo rmation of [BH2(L)CNBu(t)]SbCl6 into Me3.BH2C(O)NHBu(t) in an alkaline mediUM, whose acid hydrolysis furnishes Me3N.BH2COOH, a well-known an d important compound in boron chemistry with high yield. Preparation o f this substance with the presented new process, via the tert-butylnit rilium salt, is much more efficient than by means of the previously re ported procedures employing the ethylnitrilium salt. The proposed stru ctures of the new compounds L.BH2CN-SbCl5, [BH2(L)CNBu(t)]SbCl6 and Me 3.BH2C(O)NHBu(t) were derived from IR, H-1 and B-11 NMR spectral data.