Distorted electron acceptors: an unexpected reaction involving tetramethyl-TCNQ

Abstract

Reactions involving the donors N-methyl-2-methylbenzothiazolium – and N-(1-propyl)-2-methylbenzothiazolium iodide with the acceptor 2,3,5,6-tetramethyl-7,7,8,8-tetracyano-p-quinodimethane (TMTCNQ) in the presence of a suitable base lead to the isolation of novel [(Z)-β-(N-alkylbenzothiazol-3-ium-2-yl)-α-cyano-2,3,5,6-tetramethyl-4-styryl]dicyanomethanide chromophores. Under prolonged reaction periods, these first examples of charge transfer compounds incorporating the distorted TMTCNQ electron acceptor, undergo further reaction at the acrylonitrile functionality promoting the synthesis of novel thiomorpholine-based charge transfer compounds via a sulfur mediated cyclisation reaction. This second reaction illustrates a fundamentally new type of TCNQ-based chemistry as confirmed by X-ray crystallography and high-resolution mass spectrometry. A possible reaction mechanism for the formation of the thiomorpholine-based chromophores is considered.