Investigation of the Scope of Heterogeneous and Homogeneous Procedures for Preparing Magnesium Chelates of Porphyrins, Hydroporphyrins, and Phthalocyanines

Abstract

A simple method has been developed for metalation of porphyrinic compounds under homogeneous conditions at room temperature using a stable ethereal solution of MgI(2) and N,N-diisopropylethylamine. A previously developed heterogeneous procedure employs a mixture of a magnesium halide and a nonnucleophilic amine in a noncoordinating solvent at room temperature. The scope of the heterogeneous and homogeneous magnesium insertion procedures has been investigated across a family of 19 porphyrinic compounds, including synthetic porphyrins, synthetic or naturally occurring chlorins, and organic-soluble phthalocyanines. The rate of magnesium insertion increased in the series phthalocyanines < chlorins < porphyrins, which parallels the basicity of the ligands. Though phthalocyanines have the smallest core size, the magnesium phthalocyanines were far more stable than magnesium porphyrins to acid-induced demetalation. The heterogeneous method is broadly applicable to porphyrins, chlorins, and phthalocyanines. The homogeneous method is generally slower than the heterogeneous method, though both afford rapid metalation of most porphyrins, including electron-deficient, peripherally coordinating, or facially encumbered meso-substituted tetraarylporphyrins, and the beta-substituted octaethylporphyrin. Chlorin e(6) trimethyl ester and methyl pyropheophorbide a were metalated cleanly under homogeneous but not heterogeneous conditions, while pheophytin a failed with both methods. The homogeneous method failed altogether with phthalocyanines. Several methods in magnesium chemistry have been developed that augment these procedures, including a mild synthesis of tetraphenylchlorin and a streamlined separation of porphyrin, chlorin, and bacteriochlorins based on selective formation of the magnesium chelates. Collectively, these methods should broaden the scope of model systems based on magnesium chelates of porphyrinic compounds.

Synthesis and Characterization of Mono-, Di-, and Tri-Poly(ethylene glycol) Chlorin e6 Conjugates for the Photokilling of Human Ovarian Cancer Cells

“…A number of contributions have been made to understanding chlorin sensitizers in photodynamic therapy 1 and ovarian cancer killing reactions, 2 where substitution on the chlorin is done to overcome poor sensitization efficiency from aggregate formation 3 and low aqueous solubility. A pegylated polymer (PEG 8000) chlorin e 6 was studied, where the large PEG served as a solubilizing agent, inverting philicity from hydrophobic to hydrophilic.…”

Multiporphyrin coordination arrays based on complexation of magnesium(ii) porphyrins with porphyrinylphosphine oxides

“…This obstacle has been removed by the heterogeneous and homogeneous Mg(II) insertion methods of Lindsey and co-workers. 5, 11 However, suitable ligands that show a high affinity towards magnesium porphyrins have not been reported so far. There is only one example of triphenylphosphine oxide as a ligand for chlorophyll a and b.…”

Ground and Excited State Electronic Properties of Halogenated Tetraarylporphyrins: Tuning the Building Blocks for Porphyrin-based Photonic Devices

“…The Mg porphyrins were prepared via the heterogeneous magnesium insertion method [26,27]. This procedure involves a slurry of MgI 2 in a CH 2 Cl 2 solution of the Fb porphyrin and diisopropylethylamine (DIEA) and affords efficient metalation with a wide variety of porphyrins, including those with bulky o-substituents [27].…”