Dicyanomethylene groups

Oligomers with 11 thiophene units showed an absorption maximum at 462 nm (91JA5887). The terthiophene derivative 21 and some other oli-gothiophene derivatives were studied because the coexistence of an electron-rich moiety (the terthiophene spine) and electron-deficient moiety (the dicyanomethylene groups on either side of the molecule) is expected to cause intramolecular charge-transfer (89BCJ1539 95BCJ2363 ... 

The process developed by Edwards required elevated temperatures. A low-temperature process uses, instead of the usual dianhydrides, a monomer with two dicyanomethylene groups, which are more reactive toward nucleophiles. Polymerization affords a partially imidized product that readily cyclizes, with loss of malonitrile, to the polyimide119. 

The synthetic utility of this method is increased by intercepting the oxazolinium salts with various nucleophiles to prepare lactams that bear an (o-fiinctionalized carbon chain. It is also possible to form azacycles containing a 2-dicyanomethylene group. Direct reduction of the oxazolinium salts with NaBH gives amines. ... 

Disubstituted-2-methyl-1,2,3-triazinium iodides 114a-c are demethylated to the triazines 17m,s,u by reaction with formamide and diammonium persulfate (Equation 92) < 1991H(32)2015>. This special case has already been mentioned in Section 9.01.5.6 together with the removal of 2-dicyanomethylene groups from the 1,2,3-triazinium dicyanomethylides 34 (R = H R, R = Me, Et, Ph) under the same conditions see also <1996CHEC-11(6)483>. Cycloadditions of 2-ethyl-1,2,3-triazinium tetrafluoroborates and 1,2,3-triazinium 2-dicyanomethylides have been treated in Section 9.01.5.7. 

The structure of 54 was supported by analysis of its (symmetry seen) and H NMR spectra and showed less negative charge delocalized onto the central carbon of the dicyanomethylene group as compared to the starting dichloride used to prepare it. A significant barrier to rotation of the pyrrolidino groups was observed as four separate and well-defined carbon resonances (66.1, 65.7, 48.4, 45.6 ppm) were observed, whereas the starting dichloride had only two resonances (66.1, 48.6 ppm). 

T. Takahashi, K. Matsuoka, K. Takimiya, T. Otsubo and Y. Aso, Extensive quinoidal oligothiophenes with dicyanomethylene groups at terminal positions as highly amphoteric redox molecules, J. Am. Chem. Soc., 127, 8928-8929 (2005). 

The synthesis of anionic compounds derived from squaric acid possessing one or more jt-delocalized substituents, such as dicyanomethylene groups. 

Numerous studies have been conducted on the synthesis of compounds substituted by dicyanomethylene groups, as shown in Figure 5.8 [1, 48b, 82]. Malononitrile is often used in substitution reactions of oxocarbon systems, especially in the croconate and squarate series [83], as shown in Schemes 5.2 and 5.5. 

In addition to the two crystal structures obtained in this study, six other coordination compounds have been synthesized and characterized [73, 84]. A complete spectroscopic study was performed involving squaraines 1,3- and 1,2-disubstituted with dicyanomethylene groups and four different transition metals cobalt, manganese, zinc, and nickel. The Raman and infrared spectra of all these complexes with both ligands reveal that the ligands exhibit an inverted symmetry element, meaning that the bands which are seen with one technique are not seen with the other, and vice versa. The complexation did not affect the molecular symmetry (in the case of the trans dianion) or the solid-state structure (in the case of the cis dianion). 

From previous studies [87,88] it is known that the excess electron density in the TCNQ anions is located at the dicyanomethylene groups. Consequently, the first syntheses of 7r-extended systems were carried out on different polycyclic hydrocarbon skeletons bearing the dicyanomethylene units on the terminal positions. Thus, during the 1970s and early 1980s, novel acceptor structures such as 9,9,10,10-tetracyanonaphtho-... 

Cl 1,C12,C13,C19 (13.2(1)°). The dicyanomethylene group contiguous to the sulphur atom is more coplanar with the rings than the other dicyanomethylene group, due to the absence of peri hydrogens (Figure 1.30). 

These moieties are predicted to be planar except for the anion of 92 for which the TCNQ ring remains largely folded. For 92 , the dicyanomethylene groups are twisted out of the molecular plane and permit the TCNQ ring to achieve planarity. The lack of planarity in 92 destabilizes the anion and justifies the obtention of a unique reduction wave to the dianion for 92. 

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