Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles

Abstract

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, N 4 -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.

TEtraQuinolines: A Missing Link in the Family of Porphyrinoid Macrocycles

“…The formation of 7 appeared to be kinetically irreversible, which was empirically supported by an unsuccessful attempt to transform 7 into 8a upon exposure to the optimized reaction conditions using alkyne 6 and Py (Figure a; more detailed data are summarized in Supporting Information Section 3). On the other hand, using the more electron-rich pyridines Py and Py favors the formation of pyridine adducts INT-III′ , III from dinitrilium intermediate INT-II , which likely suppresses the undesired formation of ddc dication 7 . Py, which bears three methoxy substituents, is better suited to temporarily protect the intermediate as pyridine adducts and more easily accepts the addition of alkyne 6 from INT-III′ to INT-Alk , which is consistent with the experimental observation that Py outperforms Py and Py in terms of the yield of TEQ 8a .…”

“…On the other hand, using the more electron-rich pyridines Py and Py favors the formation of pyridine adducts INT-III′ , III from dinitrilium intermediate INT-II , which likely suppresses the undesired formation of ddc dication 7 . Py, which bears three methoxy substituents, is better suited to temporarily protect the intermediate as pyridine adducts and more easily accepts the addition of alkyne 6 from INT-III′ to INT-Alk , which is consistent with the experimental observation that Py outperforms Py and Py in terms of the yield of TEQ 8a .…”

Lanthanide porphyrinoids as molecular theranostics

“…89 Porphodilactone is a porphyrinoid product in which two 3,4-pyrrolic CQC bonds are replaced by two lactone moieties with cis-or trans-carbonyl groups. [159][160][161] To date, Zhang and co-workers have reported that the resulting configurational difference may be used to tune photophysical properties, 162 affect the self-assembly morphology, 163 modulate the extent of aromaticity, 164 and modify the efficacy of photon upconversion. 165 In the case of Zhang and co-worker's porphodilactone, regioisomerism modulated the T 1 energy state of cis/trans-F 20 TPPDL, in loose analogy to ChI b, d, and f (Fig.…”

TEtraQuinolines (TEQs): A missing link in the family of porphyrinoid macrocycles

“…Porphyrin, a nitrogen-functionalized pseudo-D4h-symmetric 18π aromatic macrocycle, is arguably one of the most important naturally occurring small cyclic molecules, whose metal complexes enable a myriad of enzymatic chemical transformations as essential cofactors and serve as key signalling and transportation substances in a vast array of living organisms 1,2 . Thus, porphyrins have inspired decades of intense research on their structural modification, which has led to a variety of porphyrinoids and their metal complexes in order to explore new molecular functions [3][4][5][6][7] . Among the related macrocycles that feature four inwardly oriented nitrogen atoms, structures are usually characterized according to the number of protonated and positively charged nitrogen atoms and the overall architecture (Fig.…”