Molecular Systems Combining Porphyrinoids and N‐Heterocyclic Carbenes

Abstract

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.

Porphyrins and Metalloporphyrins Combined with N-Heterocyclic Carbene (NHC) Gold(I) Complexes for Photodynamic Therapy Application: What Is the Weight of the Heavy Atom Effect?

“…Photophysical measurements showed that peripheral Au(I) complexes improve PDT efficiency [40]. The obtained Au(I) also presents moderate cytotoxicity in the dark [39,40]. Interestingly, we and others also showed that the anticancerous properties of NHC-Au(I) complexes can be significantly improved by changing the second ancillary ligand of the linear Au(I) complex [42,43].…”

“…N-heterocyclic carbenes (NHCs) are important ligands in the field of organometallic chemistry, and several molecular systems combining porphyrins and NHC-metal complexes were investigated during the last decade for different applications, including catalysis and PDT [39]. In this framework, we reported the synthesis of porphyrins with peripheral NHC-Au(I) complexes and their use as photosensitizers for PDT [39][40][41]. Photophysical measurements showed that peripheral Au(I) complexes improve PDT efficiency [40].…”

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

“…When NCP was treated with tosylmethyl isocyanide, novel imidazole-fused N-confused chlorins 177 , which could be converted into N-heterocyclic carbene precursors, were obtained in 65–76% yields (Scheme ). , Thus, silver metalation of 177 gave 178 , and subsequent methylation with MeI gave the precursor of N-heterocyclic carbene 179 . Finally, the treatment of 179 with Ag 2 O and then AuCl·SMe 2 afforded the N-heterocyclic carbene gold­(I) complex 180 .…”

“…Surprisingly, when 21-methyl-NCTPP 105 was treated with Re 2 (CO) 10 , the ring fusion reaction occurred inside the macrocycle in place of transformation from NCP to NFP, affording the N-heterocyclic carbene rhenium­(I) complexes 273 and 274 in 6% and 18% yields, respectively (Scheme ). , When the reaction of 22-methyl-NCTPP 99 was examined, only 273 was obtained in 25% yield as expected.…”

Perspectives on Ligand Properties of N-Heterocyclic Carbenes in Iron Porphyrin Complexes

“…N-Heterocyclic carbenes (NHCs), which are cyclic carbene species with at least one nitrogen atom, have attracted increasing attention because of their strong σ-donor capacity that makes them very useful ligands for various transition metals. − The first isolated iron porphyrin NHC complex [Fe III (TDCPP)­(1,3-Me 2 Imd) 2 ]I has been applied as a catalyst in the C­(sp3)–H amination of alkyl azides . However, controversies still exist concerning bonding in NHC-based transition-metal complexes, especially in the context of σ-donor/π-acceptor properties of NHC ligands and, in particular, regarding the importance of π-back-bonding. , NHC ligands were originally regarded basically as pure σ-donors .…”