INVESTIGATION OF THE SCOPE OF HETEROGENEOUS AND HOMOGENEOUS PROCEDURES FOR PREPARING MAGNESIUM CHELATES OF PORPHYRINS, HYDROPORPHYRINS, ANDPHTHALOCYANINES

A simple method has been developed for metalation of porphyrinic compo unds under homogeneous conditions at room temperature using a stable e thereal solution of MgI2 and N,N-diisopropylethylamine. A previously d eveloped heterogeneous procedure employs a mixture of a magnesium hali de and a nonnucleophilic amine in a noncoordinating solvent at room te mperature. The scope of the heterogeneous and homogeneous magnesium in sertion procedures has been investigated across a family of 19 porphyr inic 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 pht halocyanines have the smallest core size, the magnesium phthalocyanine s were far more stable than magnesium porphyrins to acid-induced demet alation. The heterogeneous method is broadly applicable to porphyrins, chlorins, and phthalocyanines. The homogeneous method is generally sl ower than the heterogeneous method, though both afford rapid metalatio n of most porphyrins, including electron-deficient, peripherally coord inating, or facially encumbered meso-substituted tetraarylporphyrins, and the beta-substituted octaethylporphyrin. Chlorin e(6) trimethyl es ter and methyl pyropheophorbide a were metalated cleanly under homogen eous but not heterogeneous conditions, while pheophytin a failed with both methods. The homogeneous method failed altogether with phthalocya nines. Several methods in magnesium chemistry have been developed that augment these procedures, including a mild synthesis of tetraphenylch lorin and a streamlined separation of porphyrin, chlorin, and bacterio chlorins based on selective formation of the magnesium chelates. Colle ctively, these methods should broaden the scope of model systems based on magnesium chelates of porphyrinic compounds.