Fluorine-substituted tetraazaannulene complexes: syntheses and characterizations

Abstract

The syntheses of two new fluorine-substituted tetraazaannulene macrocyclic complexes have been accomplished. A mixture of the cis- and trans-bis(trifluoromethyl) substituted macrocycles, 5,7-bis(trifluoromethyl)-12,14-dimethyldibenzo[ b, i][1,4,8,11]- tetraaza[14]annulene nickelate, [Ni( cis-BTDMTAA)], and 5,12-bis(trifluoromethyl)-7,14-dimethyldibenzo[ b, i][1,4,8,11]-tetraaza[14]annulene nickelate, [Ni( trans-BTDMTAA)], results in low yield from the reaction of 1,1,1-trifluoro-2,4-pentanedione and 1,2-diaminobenzene in the presence of nickel(II) acetate tetrahydrate. The two one-electron oxidations observed for the corresponding Ni(II) complex of the tetramethyltetraazaannulene are shifted to significantly more positive values (+0.85 and + 1.15 V). The macrocyclic complexes do not display the characteristic electropolymerization of other tetraazaannulenes, which suggests that the second oxidation is not associated with the oxidation of a coupled dimer. The bis(trifluoromethyl) derivatives do bind CO 2 in solution and catalyze the electrochemical reduction to formate. The reduction occurs at −1.06 V, almost 0.5 V more positive than the value observed for the electropolymerized tetramethyl complex. An octafluorotetramethyltetraazaannulene, prepared by the reaction of 3,4,5,6-tetrafluoro-l,2-diaminobenzene with 2,4-pentanedione, is also reported.