Synthesis of Meso-phenyl-4,6-dipyrrins, Preparation of their Cu(II), Ni(II) and Zn(II) Chelates, and Structural Characterization of Bis[meso-phenyl-4,6-dipyrrinato]Ni(II)
Bruckner, C., Karunaratne, V., Rettig, S., and David Dolphin
Can. J. Chem.
Meso-Phenyldipyrromethanes can be oxidized by 2,6-dicyano-3,5-dichloro-para-benzoquinone (DDQ) to the corresponding meso-phenyldipyrrins. As expected, these novel, stable bipyrrolic pigments readily form metal chelates with Cu(II), Ni(II), and Zn(II). Their UV-visible spectra are compared with known alkyl-substituted dipyrrin chelates and, based on the UV-visible spectral anal., the dihedral angle between the two ligands in the bis[meso-phenyldipyrrinato]Ni(II) complex is 42o. The molecular structure of this complex was determined by x-ray crystallography, essentially confirming the calculations. Crystals of C30H22N4Ni are orthorhombic, a 17.156(3), b 35.217(1), c 7.886(1) Å, Z = 8, space group Fddd. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R = 0.040 and Rw = 0.031 for 1058 reflections with I ? 3σ (F2). The central Ni is coordinated in a distorted square-planar fashion by four nitrogens. The pair of the planar dipyrrinato ligands enclose a dihedral angle of 38.5o. This is the lowest angle reported for Ni(II) complexes of this kind. As a result of this, and in sharp contrast to previously described Ni(II) dipyrrin chelates, the central metal is diamagnetic.