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46329-B3
The 'Helmet Phthalocyanines': Synthetic and Catalytic Studies on a New Class of Chiral Phthalocyaninato-Metal Complexes

Robert W. McGaff, University of Wisconsin (La Crosse)

One aim of our PRF-supported research over the course of the past 15 months has been the search for improved synthesis, purification, and isolation techniques for so-called “helmet” metallophthalocyanine complexes containing the 14,28-[1,3-diiminoisoindolinato]phthalocyaninato (diiPc) ligand.  Specifically, we have sought to improve upon procedures that have been employed in our laboratory for obtaining complexes L(diiPc)Fe(III) and L(diiPc)Co(III), where L is either a labile methanol or methanol and water combination.  Expanding our efforts in this area beyond the work originally proposed, we have also sought to improve our methods for isolating related Ni complexes of general formula[14, 28-(RO)₂Pc]Ni(II), where R represents Me, Et or <b-hydroxyethoxy. While we have observed no significant improvement in purity or yield of materials isolated via simply harvesting crystals from the reaction vessels in which they are formed, we have been encouraged by recent experiments in which we have studied the behavior of L(diiPc)Co(III) and the nickel complexes under normal phase HPLC conditions on a cyano column.  Specifically, we have observed that the mother liquor in these cases holds a significant amount of the desired metallophthalocyanine products beyond what may be isolated by simply collecting crystals from the reactors and washing.  We have found that evaporating the alcohol solvent from the reactors, followed by re-dissolving in dichloromethane and HPLC employing a dichloromethane/isopropanol gradient affords baseline separation of fractions,  The identities of these fractions have been confirmed as the desired products by comparison of their retention times to those of authentic samples.  We are currently in the process of scaling up these separations.

Another major focus of our efforts has been the search for methods for isolation of the (chiral) metallophthalocyanines described above in enantiopure or enantiomerically-enriched form.  Our initial experiments in this arena involved attempted preparation of diastereomers Y* (diiPc)Fe(III) and Y*(diiPc)Co(III), where Y* represents an enantiomerically pure chiral ligand to be introduced either by ligand replacement on L(diiPc)Fe(III) and L(diiPc)Co(III) or by formation of the diastereomeric metallophthalocyanines via syntheses carried out in the presence of excess chiral ligand.  These experiments have thus far proved unsuccessful, either due to chiral ligand loss upon purification, decomposition of the complexes in the presence of chiral ligands (especially for (diiPc)Fe(III) in the presence of chiral amines and phosphines), or complete failure of the chiral ligand Y* to bind to the metal.  However, we have had much more encouraging results by a second strategy involving liquid chromatography and chiral stationary phases (CSPs).  Preliminary experiments using standard flash columns and (chiral) microcrystalline cellulose showed small but measurable (by polarimetry) enantiomeric enrichment of L(diiPc)Co(III).  We then moved on to HPLC with a variety of CSPs on analytical scale.  Very recently, we found that a racemic mixture of [14, 28-(RO)₂Pc]Ni(II) can be resolved to baseline on a carbohydrate-based  column.  We are highly confident that the method we have optimized for this separation on analytical scale can be extended to the other chiral metallophthalocyanines described above, and also scaled up to provide experimentally useful amounts of enantiopure material.

The ultimate goal of our PRF-supported work continues to be the discovery of enantioselective oxidation catalysts among the chiral metallophthalocyanines described above.  To this end, we have begun to screen on-hand racemic mixtures of chiral metallophthalocyanines for catalytic activity.  The bulk of our initial work in this area has involved L(diiPc)Co(III), due to its superior stability as compared to other known chiral metallophthalocyanines.  We have employed indan as a test substrate, due to its well-known oxidation chemistry and the formation of (chiral) 1-indanol as a major product.  We have found that L(diiPc)Co(III) does in fact catalyze the oxidation of indan to 1-indanol and 1-indanone.  The best oxidant seems to be TBHP, but O₂ in the presence of benzaldehyde produces similar products.  When we have developed preparative-scale enantiomeric separations of L(diiPc)Co(III) and other chiral metallophthalocyanines, we will begin the process of screening for enantioselective catalysis.

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