Synthesis and properties of new derivatives of 4,5-dicyanoimidazole and 4,4′,5,5′-tetracyano-2,2′-biimidazole

Article abstract of DOI:10.1021/ja00016a038

The synthesis and properties of new derivatives of 4,5-dicyanoimidazole (1, HDcim) and 4,4′,5,5′-tetracyano-2,2′-biimidazole (2, H₂Tcbiim) are reported. Conditions for selective metalation at the 2-position of N-protected 4,5-dicyanoimidazoles are described. Various protecting groups were used. Oxidative coupling of N-protected 2-lithio-4,5-dicyanoimidazoles with cupric chloride gives new 1,1′-disubstituted derivatives of 4,4′,5,5′-tetracyano-2,2′-biimidazole (13-15, R₂Tcbiim where R = CH₃, CH₂OCH₃, CH₂Ph). Ullmann coupling of 1-methyl-2-bromo-4,5-dicyanoimidazole (6) gives (CH₃)₂Tcbiim (13). Deprotection of R₂Tcbiim (when R = CH₃ or CH₂OCH₃) gives H₂Tcbiim (2). Several new routes to H₂Tcbiim are now available. Reaction of H₂Tcbiim with 1 ,n-dihaloalkanes (n = 2, 3, and 4) gives the corresponding 1,1′-alkyl-bridged derivatives 16-18 or (CH₂)_nTcbiim (n = 2, 3, and 4). (CH₂)₂Tcbiim (16) has also been synthesized via an intramolecular Ullmann coupling reaction of 19. The physical, structural, and electronic properties of these new cyanoimidazoles have been investigated by using UV-visible spectroscopy and cyclic voltammetry. Dicyanoimidazoles and tetracyanobiimidazoles are moderate to weak electron acceptors. (CH₂)₂Tcbiim (16) forms a 1:1 complex with tetrathiafulvalene (TTF). The donor (D)-acceptor (A) complex, [TTF][(CH₂)₂Tcbiim], forms as red needles from acetonitrile solution. X-ray crystallography of [TTF] [(CH₂)₂Tcbiim] shows extended alternate or "mixed" stacking (...DADADA...). The photoluminescence spectrum of the complex shows an emission band centered at 660 nm with onset of emission at 530 nm.