NEW ELECTRON-ACCEPTORS - SYNTHESIS, ELECTROCHEMISTRY, AND RADICAL-ANIONS OF N,7,7-TRICYANOQUINOMETHANIMINES AND X-RAY CRYSTAL-STRUCTURES OF THE TRIMETHYL AND TETRAMETHYL DERIVATIVES

The reaction of a range of quinones 3 with malononitrile in the presence of titanium tetrachloride/pyridine yields dicyanoquinomethides 4, which on reaction with N,N'-bis(trimethylsilyl)carbodiimide are converted into the corresponding N,7,7-tricyanoquinomethanimines 6. The solution electrochemical redox properties of compounds 6 have been studied by cyclic voltammetry; they are strong acceptors which readily form radical anions and dianions. The radical anions of N,7,7-tricyanoquinodimethanimine 6a and the tetra-, tri- and dimethyl derivatives 6c, 6d, and 6e, respectively, have been studied by ESR and ENDOR spectroscopy. X-ray crystal structure analysis reveals that trimethyl derivative 6d is planar, whereas the tetramethyl derivative 6c is strongly deformed with the ring existing in a boat conformation, similar to that found previously for tetrasubstituted TCNQ derivatives.