Biladienones from the Photooxidation of a meso-gem-Disubstituted Phlorin:  Crystal and Molecular Structures of the 3N + O Coordinated Nickel(II) and Copper(II) Complexes

Abstract

The photooxidation of a meso-gem-disubstituted phlorin gave two isomeric biladienones in an equilibrium involving a Z-E double bond photoisomerism. The structures of these bile pigments were elucidated using NMR techniques and show terminal benzoyl and pyrrolone moieties. Complexation with divalent cations (nickel(II), copper (II)) gave stable compounds whose crystal and molecular structure could be determined by X-ray diffraction. The metal is coordinated with three pyrrole nitrogen atoms and one oxygen atom of a terminal benzoyl group. In the crystal, the molecules are arranged in pairs through hydrogen bonds between the free terminal pyrrolones.

meso‐Diketopyripentaphyrin and Diketopyrihexaphyrin as Macrocyclic Tripyrrinone Ligands for NiII Ions

“…Similar bilinones are known as the photo‐oxidation products of meso ‐aryl porphyrinoids . In the degradation proces, the meso ‐pyrrole C−C bond was cleaved with molecular oxygen to furnish a meso‐ and α‐oxygenated linear tetrapyrrolic unit and it sometimes acts as an NNNO ligand . (Figure b)…”

Isolation of Phlorin‐Dipyrrin Conjugates from the Acid‐Catalyzed Condensation of Dipyrromethanes and Aldehydes

“…Our results show that the process of decompo-sition can be inhibited by placing only electron-withdrawing substituents on the meso-positions. Based on the decomposition products reported by Callot et al [12] (biladienones), we can assume that oxygen attack is the first step of this process, the same as that suggested for the decomposition of corroles. [22] Given that electron-withdrawing groups, which certainly increase the oxidation potential, stabilize corroles, [16] the mechanism of stabilization of phlorins might be analogous.…”

“…[1][2][3] Phlorins are nonaromatic isomers of chlorins produced either by reduction of porphyrins at one of the meso positions, or by the addition of nucleophiles to the porphyrin macrocycle. [4][5][6][7][8][9][10][11][12] The stability of most phlorins is limited, and only in a few favorable cases (usually when stabilized by steric hindrance) could these compounds be isolated in a pure state. [5,6,11] The main decomposition process relies on a simple oxidation to the parent porphyrin, but the irreversible meso addition of the carbon nucleophile does not allow this reaction to proceed.…”

Blue transition metal complexes of a natural bilin-type chlorophyll catabolite

“…11,16 Indeed, related spectral properties were also found in blue transition metal complexes of linear tetrapyrroles obtained via photooxygenolysis of porphyrins. [30][31][32] The spectroscopic behaviour of 1, and its metal complexes, also reminds of that of some articial tripyrrones, 16 as well as of prodigiosenes, natural 'tripyrrolic' alkaloids with interesting antibacterial and antifungal properties, 33 which are also capable of binding a variety of metal ions. 16,33 In methanolic solution, the diamagnetic Cd(II)-and Zn(II)-complexes of 1 exhibited strong red luminescence, whereas the paramagnetic Cu(II)-complex Cu-1 and the Ni(II)-complex Ni-1 showed negligible emission, as expected (see Fig.…”