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)

Abstract

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(I1). Their UV-VIS spectra are compared with a series of known alkyl-substituted dipyrrin chelates and, based on the UV-VIS spectral analysis, the dihedral angle between the two ligands in the bis[mesophenyldipyrrinato]Ni(II) complex was calculated to be 42". The molecular structure of this complex was determined by X-ray crystallography, essentially confirming the calculation. Crystals of C3,H2,N4Ni are orthorhombic, a = 17.156(3), b = 35.217(1), c = 7.886(1) A, 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 R,, = 0.031 for 1058 reflections with I 2 ~u(F,). The central nickel is coordinated in a distorted square-planar fashion by four nitrogens. The pair of the planar dipymnato ligands enclose a dihedral angle of 38.5". This is the lowest angle reported for nickel(I1) complexes of this kind. As a result of this, and in sharp contrast to previously described nickel(I1) dipyrrin chelates, the central metal is diamagnetic.Key words: meso-phenyldipyrromethanes, meso-phenyldipymns, meso-phenyldipyrrinato transition metal chelates, X-ray crystallography.Resume : Sous l'influence de la 2,6-dicyano-3,5-dichloro-para-benzoquinone (DDQ), on peut oxyder les mksophCnyldipyrromCthanes en mkso-phCnyldipymnes correspondantes. Comme on pouvait s'y attendre, ces nouveaux pigments bipyrroliques stables forment des chClates mktalliques avec le cuivre(II), le nickel(I1) et le zinc(I1). On a comparC leurs spectres UV-VIS avec ceux d'une sCrie de chClates connus de dipymnes substitutkes par des groupes alkyles et, sur la base d'une analyse des spectres UV-VIS, on a calculC que l'angle dikdre entre les deux coordinats du complexe bis[miso-phCnyldipyrrinato]Ni(II) est de 42". La structure molCculaire de ce complexe, telle que dCterminCe par diffraction des rayons X, confirme essentiellement les conclusions obtenues par calculs. Les cristaux du C3&,,N4Ni sont orthorhombiques, groupe d'espace Fddd, avec a Le nickel central est coordinC d'une faqon plan carrC dCformCe par les quatre azotes. La paire de coordinats dipymnato plans forme un angle dikdrdre de 38,5". Cette valeur correspond h l'angle le plus faible rapport6 pour des complexes de nickel(II1) de cette espbce. I1 en rCsulte que, par opposition h ce qui a Ct C dCcrit anterieurement pour les chClates de nickel(I1) dipymne, le mCtal central est diamagnktique.

Structural Studies of the Self-Assemblies Created with Dipyrrins

“…The NMR spectra of the metal complexes 6-9 exhibit signals over a large chemicalshift range or completely disappeared due to the paramagnetism of the metal centers while the diamagnetic Zn complexes 5 shows typical chemical shifts in their NMR spectrum. As reported in previously, [31][32][33] the optical spectra of the metal complexes showed strong absorption bands newly appearing along with metal complexation. Similarly, the optical spectrum of the trivalent metal complexes 8 and 9 are also dramatically changed from that of the ligand.…”

Synthesis, Structure, and Spectroscopy of Phenylacetylenylene Rods Incorporating meso‐Substituted Dipyrrin Ligands

“…However the strong absorption features associated solely with the dipyrrin p ± p* transitions, centered at $ 435 nm is lost in favor of new features. The new bands are dependent on the nature of the metal center, [17,18] but not on the nature of the phenylacetylenylene group as would be anticipated for a metal ± dipyrrin charge transfer process. For the iron complexes, two new broad absorptions appear centered at around 444 and 490 nm.…”

“…Upon oxidation with DDQ, all of the compounds display a new absorption band centered around 435 nm, which is ascribed to the p ± p* transition of the dipyrrin aromatic system. [17,18] , as a shoulder feature of a more intense, higher energy absorption. These spectra indicate that this transition only appears in dipyrrins where the meso-phenyl group has para versus meta substitution, and that the feature is not solely due to the formation of a dipyrrin moiety.…”

“…Method 2 involved the preparation of an arylhalide-substituted dipyrromethane, followed by Sonogashira coupling [26] to phenylacetylenylene, and finally oxidation to the dipyrrin ligand. [17,18] Although a plausible route based on the large amounts of dipyrromethane that could be prepared (despite the modest yield), repeated attempts of the Sonogashira coupling were unsuccessful, presumably due to an incompatibility with the dipyrromethane moiety. Finally, method 3 was applied, which involves the synthesis of a phenylacetylenylene-extended aldehyde followed by subsequent preparation of the dipyrromethane and the dipyrrin, respectively.…”

Structural Control of the Photodynamics of Boron−Dipyrrin Complexes

“…We also synthesized and studied five analogs bearing alkyl groups rather than fluorine atoms on the boron (2a-Me 2 , 2a-Bu 2 , 2d-Me 2 , 2d-Bu 2 , 2d-BN). The fully unsubstituted dye (6), although unknown, is a benchmark for theoretical calculations.…”