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

Abstract

The reaction of the cobalt bis(dicarbollide)(1-)() ion in the presence of t-butylbromide, acting as a potent Lewis acid activator, leads to the clean substitution of by the N-atom of acetonitrile (or benzonitrile), thus resulting in the smooth formation of [(8-RCN)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))-3,3'-Co(iii)](0) (R = CH(3) or C(6)H(5)) ( and ). 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[triple bond, length as m-dash]N- bond in and is prone to the facile addition of nucleophiles. Thus, alkaline hydrolysis of and in aqueous alcohols furnishes high yields of the corresponding B(8)-N-alkylamides [(8-RC(O)=NH)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))-3,3'-Co(iii)](-), where R = CH(3) or C(6)H(5) ( and ). The reactions with butyl and diethyl amine result in the high-yield formation of 8-alkylamidine derivatives [(8-(3)R(2)RNH-(1)RC[double bond, length as m-dash]N)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))-3,3'-Co(iii)](0), where (1)R = CH(3), (2)R = H, (3)R = C(4)H(9), (), (1)R = C(6)H(5), (2)R = (3)R = C(2)H(5) () or (1)R = C(6)H(5), (2)R = (3)R = C(2)H(5) (). Hydrazinolysis of provides a high yield of the zwitterionic [(8-H(3)N)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))-3,3'-Co(iii)](0) (), whereas reduction of the nitrile group in and using BH(3).SMe(2) affords the respective alkylammonium derivatives [(8-RH(2)N)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))-3,3'-Co(iii)](0), where R = -C(2)H(5) () or -CH(2)C(6)H(5) () in moderate yields. Compound can also be prepared by alkylation of along with dibenzylderivative (). 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-O(3)SC(3)H(6)NH(2))-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))-3,3'-Co(iii)](-) () All new compounds were characterized by multinuclear NMR spectroscopy and mass spectrometry and the structures of compounds , , and were established by X-ray crystallography.