Effect of methoxy groups in a 1,3-diazaphenalenyl π-system: Electronic-spin structure of 4,9-dimethoxy-1,3-diazaphenalenyl

Recently our synthesis and isolation of tert-butylated 1,3-diazaphenalenyl radical has demonstrated heteroatomic effects of nitrogen atoms introduced into parent phenalenyl π-system on its stability, π-electronic and crystal structure. For further development of electronically-modified new azaphenalenyl systems, we have designed 4,9-dimethoxy-substituted 1,3-diazaphenalenyl radical as the first example of azaphenalenyl system having alkoxy substituents. Generation of the radical was accomplished by treatment of the corresponding 1,3-diazaphenalene derivative with an excess amount of p-chloranil or PbO2 in degassed toluene solution. The stability of the radical in the solution and solid state was found to be lower than that of the parent tert-butylated 1,3-diazaphenalenyl. The electronic-spin structure of the 4,9-dimethoxy-substituted 1,3-diazaphenalenyl radical has been determined by ESR/ENDOR/TRIPLE spectroscopies and density functional theory calculations. By comparing the spin densities of the radical with those of the parent 1,3-diazaphenalenyl radical, it has turned out that the spin densities of 6- and 7-positions decrease and conversely the spin densities at 1- and 3-positions (on nitrogen atoms) increase.

Graphical abstractA derivative of 4,9-dimethoxy-substituted 1,3-diazaphenalenyl radical has been synthesized and characterized for evaluating the heteroatomic effects on phenalenyl π-system. In comparison with the parent 1,3-diazaphenalenyl radical, it turns out that the title radical significantly undergoes spin redistribution; the spin densities on the 6,7-positions decrease, while those on the 1,3-positions increase.Figure optionsDownload full-size imageDownload as PowerPoint slide