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Porphyrins bearing imidazolium salts were synthesized and used as N-heterocylic carbene (NHC) precursors for the preparation of gold(I) complexes. The dark toxicity and phototoxicity of the obtained compounds were investigated in vitro on MCF-7 breast cancer cells. The obtained data showed that porphyrins equipped with imidazolium salts are non-toxic in the dark and present interesting photodynamic properties. On the contrary, corresponding NHC-gold(I) complexes are not suitable photosensitizers for photodynamic therapy (PDT) applications. Their dark toxicity strongly depends on the nature of the linker between the porphyrin core and the NHC. This work was extended to the synthesis of a pyropheophorbide a derivative with a pendant imidazolium group for PDT applications using excitation wavelengths of 450 nm, 545 nm, and importantly of 650 nm.

Porphyrins and N‐heterocyclic carbenes (NHCs) are both relevant ligands in the fields of coordination and organometallic chemistry. Despite evident structural differences, porphyrins and NHCs have a lot in common such as their ability to form strong metal‐ligand bonds and their use in catalysis, materials science and biomedicine. During the last decade, several molecular systems combining porphyrins and NHC ligands were reported in the literature. The present review gathers relevant examples where NHC ligands are either axially bonded to metalloporphyrins or covalently attached to the porphyrin cores. Structural diversity, electronic interplay between porphyrins and NHCs and some relevant applications in catalysis and biomedicine are notably described. Finally, molecular systems combining NHCs with other original porphyrinoids such as N‐confused porphyrins, subporphyrins and norcorroles are also presented. [ABSTRACT FROM AUTHOR]

Porphyrins are conjugated, stable chromophores with a central core that binds a variety of metal ions and an easily functionalized peripheral framework. By combining the catalytic, electronic or cytotoxic properties of selected transition metal complexes with the binding and electronic properties of porphyrins, enhanced characteristics of the ensemble are generated. This review article focuses on porphyrins bearing one or more peripheral transition metal complexes and discusses their potential applications in catalysis or biomedicine. Modulation of the electronic properties and intramolecular communication through coordination bond linkages in bis‐porphyrin scaffolds is also presented. See the future of porphyrin‐metal conjugates: Appending transition metal complexes to the periphery of porphyrins, renowned for their photo‐ and electro‐activity, opens new avenues for applications in electron‐ or photon‐triggered catalytic reactions, optoelectronic properties of self‐assembled materials, and therapeutic or diagnostic tools in biomedicine. [ABSTRACT FROM AUTHOR]

Porphyrins fused to imidazolium salts across two neighboring β-pyrrolic positions were used as N-heterocyclic carbene (NHC) precursors to anchor AuI-Cl complexes at their periphery. Synthesis of several thiolato-AuI complexes was then achieved by substituting chloride for thiolates. Photodynamic properties of these complexes were investigated: the data obtained show that the Au−S bonds could be cleaved upon irradiation. The proposed mechanism to explain the release of thiolate moiety involves the S atom oxidation by singlet oxygen generated in the course of irradiation. In view of photodynamic therapy (PDT) applications, these porphyrins fused to NHC-AuI complexes were tested as photosensitizers to kill MCF-7 breast cancer cells. Results show the important role played by the ancillary ligands (chloride versus thiolates) on the photodynamic effect. [ABSTRACT FROM AUTHOR]

We report herein a detailed study of the use of porphyrins fused to imidazolium salts as precursors of N-heterocyclic carbene ligands 1 M. Rhodium(I) complexes 6 M- 9 M were prepared by using 1 M ligands with different metal cations in the inner core of the porphyrin (M=NiII, ZnII, MnIII, AlIII, 2H). The electronic properties of the corresponding N-heterocyclic carbene ligands were investigated by monitoring the spectroscopic changes occurring in the cod and CO ancillary ligands of [( 1 M)Rh(cod)Cl] and [( 1 M)Rh(CO)2Cl] complexes (cod=1,5-cyclooctadiene). Porphyrin-NHC ligands 1 M with a trivalent metal cation such as MnIII and AlIII are overall poorer electron donors than porphyrin-NHC ligands with no metal cation or incorporating a divalent metal cation such as NiII and ZnII. Imidazolium salts 3 M (M=Ni, Zn, Mn, 2H) have also been used as NHC precursors to catalyze the ring-opening polymerization of L-lactide. The results clearly show that the inner metal of the porphyrin has an important effect on the reactivity of the outer carbene. [ABSTRACT FROM AUTHOR]

Porphyrin–metal conjugates: Some representative examples of peripherally metalated porphyrins are depicted in the graphic. By combining the catalytic, electronic or cytotoxic properties of selected transition‐metal complexes with the binding and electronic properties of porphyrins, enhanced characteristics of the ensemble are generated. Appending one or more transition‐metal complexes to the periphery of porphyrins opens new avenues for potential applications in electron‐ or photon‐triggered catalytic reactions, optoelectronic properties of self‐assembled materials, and therapeutic or diagnostic tools in biomedicine. For more details see the Review by S. Richeter et al. on page 15442 ff. [ABSTRACT FROM AUTHOR]