Large metal ion-centered template reactions. Chemical and spectral studies of the "superphthalocyanine" dioxocyclopentakis(1-iminoisoindolinato)uranium(VI) and its derivatives

This paper reports on chemical and spectral studies of the macrocyclic uranyl complexes dioxocyclopentakis(1-iminoisoindolinato)uranium(VI), SPcUO₂, and dioxocyclopentakis(1-imino-5-methylisoindolinato)uranium(VI), Me₅SPcUO₂. These expanded, five-subunit analogues of phthalocyanines were synthesized in template reactions from uranyl salts and the corresponding phthalonitriles. The conditions for a high-yield synthesis are critical and include a polar solvent (e.g., dimethyl-formamide), high temperatures, and strict exclusion of water. Phthalocyanine, PcH₂, is a side product of the reaction with the source of protons being the solvent. Attempts to displace the uranyl ion from SPcUO₂ with acids or other metal ions (Mⁿ⁺) invariably result in macrocycle contraction to produce PcH₂ or PcM^n-2 and phthalonitrile. ¹H NMR studies reveal the five-subunit macrocycle to be stereochemically dynamic. The analysis of ring current induced ¹H NMR shifts indicates considerably reduced π electron delocalization in SPcUO₂ compared to PcM derivatives. The electronic spectrum of SPcUO₂ exhibits strong absorption maxima at 4240 and 9140 Å. With the aid of Pariser-Parr-Pople SCFLCAOCl π electron molecular orbital calculations, the electronic structure of the macrocycle and the origin of the spectral transitions can be shown to be closely analogous to phthalocyanine systems. Many of the chemical and spectral properties of SPcUO₂ and Me₅SPcUO₂ reflect the severe buckling and strain within the macrocyclic ligand.