Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles.

The replacement of one or more pyrrolic building block(s) of a porphyrin by a nonpyrrolic heterocycle leads to the formation of so-called pyrrole-modified porphyrins (PMPs), porphyrinoids of broad structural variability. The wide range of coordination environments (type, number, charge, and architecture of the donor atoms) that the pyrrole-modified frameworks provide to the central metal ions, the frequent presence of donor atoms at their periphery, and their often observed nonplanarity or conformational flexibility distinguish the complexes of the PMPs clearly from those of the traditional square-planar, dianionic, N4-coordinating (hydro)porphyrins. Their different coordination properties suggest their utilization in areas beyond which regular metalloporphyrins are suitable. Following a general introduction to the synthetic methodologies available to generate pyrrole-modified porphyrins, their general structure, history, coordination chemistry, and optical properties, this Review highlights the chemical, electronic (optical), and structural differences of specific classes of metalloporphyrinoids containing nonpyrrolic heterocycles. The focus is on macrocycles with similar "tetrapyrrolic" architectures as porphyrins, thusly excluding the majority of expanded porphyrins. We highlight the relevance and application of these metal complexes in biological and technical fields as chemosensors, catalysts, photochemotherapeutics, or imaging agents. This Review provides an introduction to the field of metallo-PMPs as well as a comprehensive snapshot of the current state of the art of their synthesis, structures, and properties. It also aims to provide encouragement for the further study of these intriguing and structurally versatile metalloporphyrinoids.

Oxazolochlorins 21. Most Efficient Access to meso-Tetraphenyl- and meso-Tetrakis(pentafluorophenyl)porpholactones, and Their Zinc(II) and Platinum(II) Complexes.

meso-Phenyl- and meso-pentafluorophenyl-porpholactones, their metal complexes, as well as porphyrinoids directly derived from them are useful in a number of technical and biomedical applications, and more uses are expected to be discovered. About a dozen competing and complementary pathways toward their synthesis were reported. The suitability of the methods changes with the meso-aryl group and whether the free base or metal derivatives are sought. These circumstances make it hard for anyone outside of the field of synthetic porphyrin chemistry to ascertain which pathway is the best to produce which specific derivative. We report here on what we experimentally evaluated to be the most efficient pathways to generate the six key compounds from the commercially available porphyrins, meso-tetraphenylporphyrin (TPP) and meso-tetrakis(pentafluorophenyl)porphyrin (TFPP): free base meso-tetraphenylporpholactone (TPL) and meso-tetrakis(pentafluorophenyl)porpholactone (TFPL), and their platinum(II) and zinc(II) complexes TPLPt, TFPLPt, TPLZn, and TFPLZn, respectively. Detailed procedures are provided to make these intriguing molecules more readily available for their further study.

An Alternate Route of Transforming meso-Tetraarylporphyrins to Porpholactams, and Their Conversion to Amine-Functionalized Imidazoloporphyrins.

A novel and efficient synthetic pathway toward known meso-tetraphenylporpholactams, also applicable to the synthesis of hitherto unknown and inaccessible meso-C6F5-substituted porpholactam, is detailed (dioxochlorin → dioxochlorin urea adduct → porpholactam). meso-Tetraphenylporpholactam was converted to an imidazoloporphyrin-α-triflate derivative that was demonstrated to be of utility for the generation of functionalized imidazoloporphyrins with a substituted amine adjacent to the outside N atom of the imidazole moiety (using pyridine, Et2NH, diethyliminodiacetic acetate, dipicolylamine (DPA), and cyclen). The DPA- and iminodiacetate-imidazoloporphyrin conjugates were structurally characterized. The chemosensing potential of the metal chelate-imidazoloporphyrin conjugates was evaluated, though their constrained metric parameters led to muted chemosensing responses to various divalent metal ions. The accessibility of the meso-arylporpholactams and the meso-tetraphenylimidazoloporphyrin triflate enables the continued exploration of porphyrin-like pyrrole-modified porphyrins that incorporate a nitrogen atom in place of a ß-carbon atom in their macrocycles.