Synthesis of New Porphyrins with Peripheral Conjugated Chelates and Their Use for the Preparation of Porphyrin Dimers Linked by Metal Ions

Abstract

This article describes the preparation of several new porphyrins bearing chelating peripheral groups fully conjugated with the macrocyclic pi-system. Treatment of a 2-nitro-meso-tetraarylporphyrin with phosphite gave a cyclic enamine, whose formylation gave an enaminoaldehyde. The thio analogue was obtained on treatment with Lawesson's reagent. The same reagent was also used to obtain the isomeric thioenaminoketone chelates. A enaminoketone ligand was prepared from a porphyrinic pyrrolone. All these ligands, as internal nickel complexes, could be metalated with palladium to yield porphyrinic dimers. The dimers obtained from enaminoketones and thioketones show a trans geometry, while in the enaminoaldehyde and -thioaldehyde series the cis isomer is thermodynamically favored. The bathochromic shifts of the electronic spectra of the aldehyde-derived dimers illustrate the strong electronic effect of peripheral metalation and dimerization. However, in the case of the pyrrolone-derived ligand, opposite effects were observed, due to partial reconstitution of the porphyrin chromophore on complexation. As with the dimers derived from enaminoketones, the dimers derived from the new ligands show typical splitting (up to 190 mV) of the electrochemical waves confirming large porphyrin-porphyrin interactions.

β-Pyrazino-fused tetrarylporphyrins

“…Following the common acid catalyzed route to condense aromatic o -diamines with vicinal diketones [13], the zinc α-dione porphyrin derivative 3 [14] was reacted with the 2,3-diaminoporphyrin zinc complex 2 . Porphyrin 1 (Scheme 1) was synthesized and isolated according to literature procedures [11,12] and subsequently reduced with NaBH 4 , in the presence of Pd/C 10% wt, under nitrogen in a CH 2 Cl 2 /MeOH (10:1) solution. Complete reduction was verified by UV–Vis spectroscopy and TLC and, after 2 h, the resulting solution of 2 was passed through a pad of Celite to remove the catalyst and hydride excess.…”

“…Porphyrin 1 has been prepared following the reaction pathway reported in Scheme 1, according to literature methods [11,12]. …”

Meso-aryl-ß-pyrrolic positions interactions in meso-tetraarylporphyrins: Flat arylporphyrins and building blocks for oligoporphyrins

“…The reaction is shown in Scheme 9. Last but not least, an aza analog of the cyclization reaction was developed (Scheme 10) and resulted in the "umpolung" of the pyrrole ßß double-bond, changing a nitroolefin 35 into an enamine 36 [21]. In turn, this enamine proved to be a choice starting material for electrophilic reactions later used to build chelating porphyrins 37 and oligoporphyrins (see below).…”

A 1,10‐Phenanthroline‐Containing Ring Connected to a Porphyrin by a Rigid Aromatic Spacer and Its Copper‐Complexed Pseudorotaxane

“…[7] Then, adapted from Burn's methodology, [8] this porphyrin was demetallated with H 2 SO 4 and the NO 2 function was reduced to an NH 2 group by SnCl 2 and HCl in CH 2 Cl 2 . The subsequent oxidation reaction leading to 1 was carried out by using Dess-Martin periodinane.…”