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)

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 copper(II), nickel(II), and zinc(II). Their W-VIS spectra are compared with a series of blown alkyl-substituted dipyrrin chelates and, based oil the W-VIS spectral analysis, the dihedral angle between the two ligands iri the bis[meso-phenyldipyrrinato]Ni(II) complex was calculated to be 42 degrees. The molecular structure of this complex was determined by X-ray crystallography, essentially confirming the calculation. Crystals of C30H22N4Ni are orthorhombic, a = 17.156(3), b = 35.217(1), c = 7.886(1) Angstrom, Z = 8, space group Fddd. The structure was solved by direct methods and refined by hull-matrix least-squares procedures to R = 0.040 and R(W) = 0.031 for 1058 reflections with I greater than or equal to 3 sigma(F-2). The central nickel is coordinated in a distorted square-planar fashion by four nitrogens. The pair of the planar dipyrrinato ligands enclose a dihedral angle of 38.5 degrees. This is the lowest angle reported For nickel(II) complexes of this kind. As a result of this, and in sharp contrast ro previously described nickel(II) dipyrrin chelates, the central metal is diamagnetic.