Synthesis of heterocyclic analogues of Benzo-TCNQ
Crean, Colm (2002) Synthesis of heterocyclic analogues of Benzo-TCNQ. PhD thesis, Dublin City University.
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The combination of electron deficient and electron rich species to form charge transfer complexes has led to the observation of conductivity and superconductivity in organic and organometallic systems. Heterocyclic electron acceptors analogous to TCNQ are of particular interest, since heteroatoms can lead to greater planarity, which can increase dimensionality and ultimately improve conductivity.
The reaction of phthalonitrile and aqueous methylamine formed 2-methyl-3- methylimino-2,3-dihydroisoindol-l-one. Analogous reactions with aqueous cthylamine and benzylamine did not yield corresponding products. 1,3-Dialkyliminoisoindolines resulted from the reaction of ethylamine and benzylamine with phthalonitrile. Treatment o f 2-methyl-3-methylimino-2,3-dihydroisoindol-l-one in ethanol with malononitrile produced a methylammonium salt while a similar reaction in acetic acid yielded a monocondensation product 2-(2-methyl-3-oxo-2,3-dihydro-isoindol-l-ylidene)-malononitrile. An analogous mono-condensation product was obtained from 1,3-diethyliminoisoindoline and malononitrile in acetic acid.
The Mitsunobu reaction of 2-(3-dicyanomethylene-2,3-dihydro-isoindol-lylidene)- malononitrile with activated primary alcohols generated the desired N-alkylated tetra-cyano isoindolines. Similarly the Mitsunobu reaction of 2-(3-oxo-2,3-dihydroisoindol-l-ylidene)-malononitrile with various alcohols produced the desired N-alkylated products. The presence o f a carbonyl group meant that 2-(3-oxo-2,3-dihydro-isoindol-lylidene)-malononitrile would react with more alcohols than its tetra-cyano analogue. Treatment of 2-(3-oxo-2-pentyl-2,3-dihydro-isoindol-l-ylidene)-malononitrile and 2-(3-oxo-2-decyl-2,3-dihydro-isoindol-l-ylidene)-malononitrile with titanium tetrachloride and bis(trimethylsilyl)carbodiimide gave compounds that possessed both a dicyanomethylene group and a cyanoimino group.
Cyclic voltammetric analysis of these three families of compounds showed that they were all electrochemically reducible. Solid charge transfer complexes were formed between TTF and the N-alkylated tetra-cyano isoindolines and between TTF and Nalkylated isoindolines that contained a dicyanomethylene and a cyanomino group. X-ray crystallography showed that the CT complex between 2-(2-allyl-3-dicyanomethylene-2,3- dihydro-isoindol-l-ylidene)-malononitrile and TTF had a mixed stack arrangement.
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