Nickel(II) and Copper(II) Complexes of β-Unsubstituted 5,15-Diazaporphyrins and Pyridazine-Fused Diazacorrinoids: Metal-Template Syntheses and Peripheral Functionalizations

The present paper reports the first comprehensive study on the synthesis, structures, optical and electrochemical properties, and peripheral functionalizations of nickel(II) and copper(II) complexes of beta-unsubstituted 5,15-diazaporphyrins (M-DAP; M=Ni, Cu) and pyridazine-fused diazacorrinoids (Ni-DACX; X=N, O). These two classes of compounds were constructed starting from mesityldipyrromethane by a metaltemplate method. Ni-DAP and Cu-DAP were prepared in high yields by the reaction of the respective metalbis(dibromodipyrrin) complexes with NaN3CuX (X=I, Br), whereas Ni-DACN and Ni-DACO were formed as predominant products by the reaction with NaN3. In both cases, the metal centers change their geometry from tetrahedral to square planar during the aza-annulation; X-ray crystallographic analyses of M-DAPs showed highly planar diazaporphyrin p planes. The Q band of Ni-DAP was redshifted and intensified compared with that of a nickelporphyrin reference, due to the involvement of electronegative nitrogen atoms at the meso positions. It was found that the peripheral bromination of Ni-DAP and Ni-DACO occurred regioselectively to afford Ni-DAP-Br4 and Ni-DACO-Br, respectively. These brominated derivatives underwent Stille reactions with tributyl(phenyl)stannane to give the corresponding phenylated derivatives, Ni-DAP-Ph4 and Ni-DACO-Ph. On the basis of the absorption spectra and X-ray analysis, it has been concluded that the attached phenyl groups efficiently conjugate with the diazaporphyrin p system. The present results unambiguously corroborate that the beta-unsubstituted DAPs and DACXs are promising platforms for the development of a new class of p-conjugated azaporphyrin-based materials.