Structural and spectroscopic investigations of 1,1,3,3-tetrakis(alkylamino)allyl cations, methylene-bis(N,N′-dialkylformamidinium) dications and related formamidine derivatives

Abstract

Treatment of pentachlorocyclopropane under basic conditions with either of the primary amines, Pr i NH 2 or Bu t NH 2 , displaces all the chlorine atoms and yields methylene-bis(N,N′-dialkylformamidine), CH 2 {C(NR)NHR} 2 (R=Pr i or Bu t ). A facile protonation converts the molecule into the 1,1,3,3-tetrakis(alkylamino)allyl cation, [CH{C(NHR) 2 } 2 ] + to which a further proton can be added to generate the corresponding methylene-bis(N,N′-dialkylformamidinium) ion. Barriers to rotation about the partial CN double bonds of these dications, [CH 2 {C(NHR) 2 } 2 ] 2 (R=Pr i or Bu t ), of 80 and 74 kJ mol -1 , respectively, are deduced from variable temperature NMR data. 1 H and 13 C NMR studies of the kindred methylene-bis(formamidine) molecules show evidence of tautomerism as well as conformational changes in solution. Hydrolysis of methylene-bis(N,N′-di-tert-butylfor mamidine) gives N,N′-di-tert-butylformamidine. The crystallographically determined structure of N,N′-di-tert-butylformamidinium chloride, [CH(NHBu t ) 2 ]Cl, is compared with other members of this series.