Boron(8) substituted nitrilium and ammonium derivatives, versatile cobalt bis(1,2-dicarbollide) building blocks for synthetic purposes

The reaction of the cobalt bis(dicarbollide)(1-)(1) ion in the presence of t-butylbromide, acting as a potent Lewis acid activator, leads to the clean substitution of 1 by the N-atom of acetonitrile ( or benzonitrile), thus resulting in the smooth formation of [(8-RCN)-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'Co(III)](0) (R = CH3 or C6H5) (2 and 3). These compounds can serve as versatile precursors for the generation of a variety of other synthetically useful functional groups. The nitrogen atom of the nitrile C N-bond in 2 and 3 is prone to the facile addition of nucleophiles. Thus, alkaline hydrolysis of 2 and 3 in aqueous alcohols furnishes high yields of the corresponding B(8)-N-alkylamides [(8-RC(O)=NH)-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co(III)](-), where R = CH3 or C6H5 (4 and 5). The reactions with butyl and diethyl amine result in the high-yield formation of 8-alkylamidine derivatives [(8-(RRNH)-R-3-R-2-(RC)-R-1= N)-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co(III)](0), where R-1 = CH3, R-2 = H, R-3 = C4H9, (6), R-1 = C6H5, R-2 = R-3 = C2H5 (7) or R-1 = C6H5, R-2 = R-3 = C2H5 (8). Hydrazinolysis of 2 provides a high yield of the zwitterionic [(8-H3N)-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co(III)](0) (9), whereas reduction of the nitrile group in 2 and 3 using BH3 center dot SMe2 affords the respective alkylammonium derivatives [(8-RH2N)-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co(III)](0), where R = -C2H5 (10) or -CH2C6H5 (11) in moderate yields. Compound 11 can also be prepared by alkylation of 9 along with dibenzylderivative (12). A further example of alkylation is the ring cleavage of the 3-hydroxypropanesulfonic acid gamma-sultone producing a compound with alkyl ammonium sulfonic acid substitution [(8-O3SC3H6NH2)-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co(III)](-) (13) All new compounds were characterized by multinuclear NMR spectroscopy and mass spectrometry and the structures of compounds 2, 6, 7 and 12 were established by X-ray crystallography.