towards meso - meso -linked porphyrin arrays...

Towards meso–meso-LinkedPorphyrin Arrays and meso-ArylExpanded Porphyrins

Atsuhiro OsukaDepartment of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto606-8502 (Japan)E-mail: [email protected]

Received: May 30, 2014Published online: ■■

ABSTRACT: meso–meso-Linked porphyrin arrays and meso-aryl-substituted expanded porphyrinshave continuously fueled my imagination for many years. In this account, my expertise in chemicalresearch is retrospectively summarized with a particular focus on how these two novel categories ofporphyrinoids were found by our group. As part of our photosynthetic model studies in collabo-ration with Prof. N. Mataga, the energy-gap dependence of intramolecular charge separation wasexamined by exploring the photoexcited dynamics of 1,4-phenylene-bridged hybrid porphyrindimers. This study required electron-deficient porphyrins in the dimers that could serve as anelectron-accepting unit towards an octaalkyl-substituted Zn(II) porphyrin donor. To this end, weemployed meso-nitrated porphyrins and meso-pentafluorophenyl porphyrins. Efforts to preparethese electron-deficient porphyrins allowed us to serendipitously find both a meso–meso-linkedporphyrin dimer and a series of meso-pentafluorophenyl-substituted expanded porphyrins. Themeso–meso-linked Zn(II) porphyrin dimer was found as a byproduct in the nitration of 5,10-diarylZn(II) porphyrin with AgNO2 but became a major product in the reaction with AgPF6. Thisfinding opened up a new path to directly linked porphyrin oligomers. The series of meso-pentafluorophenyl-substituted expanded porphyrins were prepared via BF3·OEt2-catalyzed con-densation of pyrrole and pentafluorobenzaldehyde when the reaction was run at tenfold-highersubstrate concentrations, as compared to the optimal conditions for the synthesis of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin. These expanded porphyrins have been shown to have attrac-tive attributes such as flexible structures, versatile electronic states, multi-metal coordination, anionsensing, and large nonlinear optical properties. While these studies were mostly curiosity-driven,some of our work covers rather more general interests: how linearly connected molecules can berationally synthesized and isolated in a pure and discrete form, how large π-conjugation can berealized to allow for very low energy electronic transitions, and how easily Möbius aromatic andantiaromatic molecules can be prepared.

Keywords: aromaticity, expanded porphyrins, macrocycles, nanostructures, porphyrinoids

1. Introduction

It is my pleasure to write this Personal Account tracing myjourney in organic chemistry, with a particular focus on howI entered into the field of novel porphyrinoids and how we

found meso–meso-linked porphyrin arrays and meso-arylexpanded porphyrins. In the second year of my doctoralcourse at Kyoto University (1979), I was offered a position as

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Personal Account

Chem. Rec. 2014, ••, ••–•• Wiley Online Library© 2014 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI: 10.1002/tcr.201402050

mailto:[email protected]

Assistant Professor in the group of Prof. H. Suzuki in theDepartment of Chemistry, the Faculty of Science, EhimeUniversity. Prof. Suzuki was kind to allow me to continuemy research on the photochemical reactions ofepoxynaphthoquinones, which had been assigned as thetheme of my doctoral degree by Prof. K. Maruyama of Kyoto

University. Before joining Prof. Suzuki’s laboratory, I hadreported that irradiation of 2,3-dimethyl-2,3-epoxy-1,4-naphthoquinone (1) led to cleavage of the oxirane ring togenerate carbonyl ylide 2 or 1,3-diradical intermediate 3,which was trapped by the carbonyl group of aldehydes orketones to give 1,3-cycloaddition adducts 4 (Eq. 1).[1,2]

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As an extension of these studies, I examined thephotoirradiation of 2-methyl-3-(2-methyl)propyl-2,3-epoxy-1,4-naphthoquinone (5). Photoirradiation of 5 in a benzenesolution gave rise to a preferential intramolecular hydrogen-abstraction reaction (Norrish type II photoreaction) over theoxirane cleavage, affording cyclobutanol product 7 as a cycli-

zed product and phthiocol 9 as an elimination product via1,4-biradical 6 (Scheme 1). The cyclobutanol 7 underwentsecondary photoreactions to give rearranged products 11and 12, probably via biradical 10 formed by Norrishtype I α-cleavage.[3,4] Under similar photoirradiationconditions, 2-methyl-3-(2-methyl)propyl-2,3-methano-1,4-naphthoquinone (13) gave cyclobutanol product 15 as amajor product via a Norrish type II 1,4-biradical 14(Scheme 2). It was found that 15 underwent a secondaryphotoinduced cleavage to give the same 1,4-biradical 14. Pro-longed irradiation of a mixture of 13 and 15 led to formationof γ,δ-unsaturated alcohol 16 as a rare photoproduct, possiblyvia slow disproportionation of the 1,4-biradical 14.[5,6] Iobtained my doctoral degree on the basis of thesestudies on the photochemistry of epoxynaphthoquinonesin 1982.

Alongside these studies, I started synthetic organic chem-istry using tellurium compounds, which was one of the mainresearch themes in the research group of Prof. Suzuki.Sodium hydrogentelluride (NaTeH) was used fordehalogenation of α-halo carbonyl compounds (Eq. 2),[7]

chemoselective reduction of α,β-epoxy ketones to β-hydroxyketones (Eq. 3),[8] and reductive removal of aliphatic nitrogroups (Eq. 4).[9] Reactions of telluronium ylides with car-bonyl compounds gave olefination products or epoxidationproducts depending upon the stability ofthe telluronium ylide. Namely, the reactions ofdialkyltelluronium carbethoxymethylide with aldehydes and

Atsuhiro Osuka was born in Gamagori,Aichi, Japan, in 1954. He received hisPh.D. degree on the photochemistry ofepoxyquinones from Kyoto Universityin 1982. In 1979, he started his aca-demic career at the Department ofChemistry of Ehime University as anAssistant Professor. In 1984, he movedto the Department of Chemistry of Kyoto University, wherehe became a Professor of Chemistry in 1996. He was awardedthe CSJS Award for Young Chemists in 1988, the JapanesePhotochemistry Association Award in 1999, the NOZOEMemorial Lectureship Award at the 13th ISNA conference in2009, and the Chemical Society of Japan Award in 2010. Hewas selected as a project leader of Core Research forEvolutional Science and Technology (CREST) of JST during2001–2006. His research interests cover many aspects ofsynthetic approaches toward artificial photosynthesis and thedevelopment of porphyrin-related compounds with novelstructures, electronic systems, and functions.

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P e r s o n a l A c c o u n t T H E C H E M I C A L R E C O R D

ketones gave α,β-unsaturated esters with trans stereoselectivity(Eq. 5),[10] but the reactions of dialkyltelluronium allylidewith aldehydes provided vinyl epoxides with cis selectivity(Eq. 6).[11] These reactivities are different from the establishedfeatures of the corresponding reactions of sulfonium andselenonium ylides with aldehydes.[12] These are, to the best ofmy knowledge, the first reports on the use of telluroniumspecies for C–C bond-forming reactions.

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Scheme 1. Norrish type-II photoreaction of en epoxynaphthoquinone.

Scheme 2. Norrish type-II photoreaction of a methanonaphthoquinone.



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In 1984, I moved to the Department of Chemistry in theFaculty of Science at Kyoto University as an Assistant Professorin the group of Prof. Maruyama. At that time, Prof. Maruyamawas interested in a chemical approach to photosynthetic reac-tion centers and naturally he requested me to pursue a researchproject along such a direction. I was forced to abandon thechemistries pursued at Ehime University and started researchrelated to artificial photosynthesis by preparing a series ofoctaalkyl-substituted mesoporphyrins bearing amino acidsthrough an ester or an amide linkage. Disappointingly,however, such appended amino acid side chains did not displayany meaningful interactions with the porphyrin chromophorein the ground state. Fluorescence emissions of these porphyrinsare not quenched, indicating almost no interaction in thesinglet excited states of porphyrins with the amino acid resi-dues. However, in the meantime, we noticed strong chemicallyinduced dynamic nuclear polarization (CIDNP) signals duringirradiation (λ > 590 nm) of a benzene solution of tyrosine-linked porphyrin 29[13–16] and tryptophan-linked porphyrin30[17] in the presence of 1,4-benzoquinone (Figure 1).

Prolonged irradiation of a solution of 29 and 1,4-benzoquinone gave quinone-linked porphyrin 32 via oxidationof hydroquinone-linked porphyrin 31 with an excess amountof the quinone (Scheme 3). On the basis of extensive anddetailed studies, the formation of 32 has been determined tooccur by the mechanism shown in Scheme 4. Electron-transferquenching of the triplet excited state of the porphyrin by1,4-benzoquinone gives a porphyrin cation radical and aquinone anion radical. Subsequent proton transfer from thetyrosine residue to the quinone anion radical generates a phe-nolate anion and a neutral semiquinone radical, which areconverted to a neutral radical pair of a semiquinone radical anda phenoxy radical via intramolecular electron transfer from thephenolate to the porphyrin cation radical. Coupling of thisradical pair results in the formation of hydroquinone-linkedporphyrin, which is finally oxidized to form quinone-linkedporphyrin upon photoirradiation in the presence of an excessamount of quinone. The observed strong CIDNP signals werethus ascribed to competitive disproportionation of the neutralradical pair to regenerate the starting state and recombination

Fig. 1. Tyrosine-linked and tryptophan-linked porphyrins.



to give the hydroquinone-linked porphyrin with concomitantspin polarization. This photoinduced coupling of quinones tophenol-linked porphyrin has been extended to the synthesis ofvarious quinone-linked and quinone-capped porphyrins.[15,16]

During these studies, we recognized the appearance of thecrystal structure of a bacterial photosynthetic reaction center asan epoch-making event.[18] The structure of the reaction centerstrongly suggested that the spatial arrangements of the chro-mophores, such as the special pair, bacteriochlorophylls,

bacteriopheophytins, and quinones, are critically important forthe photoinduced events such as excitation-energy transfer andelectron transfer. We thus prepared quinone-capped porphy-rins 33, 34, and 35 with different orientations by this photo-induced coupling reaction with the intention to examine theorientation dependence of intramolecular electron transferfrom the porphyrin to the quinone (Figure 2).[15] Unfortu-nately, these quinone-capped porphyrins were conformation-ally very flexible and unsuitable for detailed investigation of the

Scheme 3. Photo-induced coupling reaction of 1,4-benzoquione to tyrosine-lined porphyrin.

Scheme 4. Reaction mechanism of photo-induced coupling reaction of 1,4-benzoquinone to tyrosine-linkedporphyrin.



orientation dependence of the intramolecular electron-transferreactions. In addition, the electron-transfer reactions of thequinone-capped porphyrins were too fast to allow determina-tion of the precise rates in those days.

We then turned our attention to the synthesis of cova-lently linked porphyrin dimers that are conformationallyrestricted at varying orientations. As a structural motif, wechose a peripherally octaalkyl-substituted porphyrin that islinked directly at its meso positions to a naphthalene bridge(36, 37, and 38, Figure 3). In these diporphyrins, the naph-thalene bridge is held nearly perpendicularly to the porphyrin

plane due to the steric congestion of the flanking alkylgroups. This conformationally restricted feature is suitable forstudies on the geometry dependence of excitation-transferand energy-transfer reactions. Zn(II) complexes of thesedimers exhibit remarkable exciton coupling in their Soretbands, reflecting the respective orientation.[19] The observedsplit Soret bands of these dimers were analyzed on the basisof the exciton coupling theory developed by Kasha.[20] Theseporphyrin dimers were used to examine the geometry depen-dencies of intramolecular excitation-energy transfer andelectron-transfer reactions.[21,22] As an extension of these

Fig. 2. Quinone-capped porphyrins.

Fig. 3. Naphthalene-bridged porphyrin dimers.



studies, we developed an efficient method that allowed thesynthesis of conformationally restricted porphyrin oligomerssuch as 39 and 40 (Figure 4).[23] With this synthetic methodin hand, we explored covalently linked donor–acceptor por-phyrin compounds as models of the photosynthetic reactioncenter, with the ultimate goal of mimicking the whole eventsof the excitation-energy transfer and electron transfer in thephotosynthetic reaction centers within a single molecularentity.[24–31]

As part of these studies, we were interested in the energy-gap dependence of intramolecular electron-transfer reactions in1,4-phenylene-bridged diporphyrins that bear an octaalkyl-substituted Zn(II) porphyrin as an electron donor and variouselectron-deficient porphyrins as an electron acceptor. Usingdiporphyrins 41–48 (Figure 5), we revealed a bell-shapedenergy-gap dependence for the rates of charge separation andcharge recombination.[32] More importantly, this study allowedus to find two important reactions. In the course of our studyto prepare meso-nitrated diporphyrins 46 and 48, we found adirect meso–meso coupling reaction of 5,15-diaryl-substitutedZn(II) porphyrins, and our attempt to prepare meso-pentafluorophenyl-substituted diporphyrin 45 led to thediscovery of an effective synthesis for a series of meso-aryl-substituted expanded porphyrins.

2. meso–meso-Linked Porphyrin Arrays

In the above-mentioned study on the energy-gap dependenceof the intramolecular electron-transfer reaction of 1,4-phenylene-bridged diporphyrins, we chose meso-nitrated por-phyrins as the electron-deficient porphyrin part. By followingBaldwin’s protocol,[33] 5,15-diaryl Zn(II) porphyrin 49 wasnitrated with AgNO2 and I2 in CHCl3 (Scheme 5). The

Fig. 4. Conformationally restricted porphyrin oligomers.

Fig. 5. 1,4-Phenylene-bridged porphyrin dimers.



nitration proceeded nicely to give meso-nitrated porphyrin 50in 90% yield, but my student did not miss a side product thateluted on a silica gel TLC plate essentially in the same manneras 49. This side product was soon identified as meso–meso-linked Zn(II) diporphyrin 51. The formation of 51 wasthought to be initiated by one-electron oxidation of 49 withAg(I) ion to generate the cation radical of 49, followed bynucleophilic attack by another neutral molecule of 49. We thuschose AgPF6 as an oxidant, since it has a non-nucleophilicanion that has no chance to react with the cation radical of 49.The reaction of 49 with AgPF6 in CHCl3 gave 51 and 52 in27% and 4% yields, respectively, along with recovery of 49(47%) (Scheme 5).[34] Synthesis of an extremely long discretemolecule was indeed a challenge. We decided to synthesize longmeso–meso-linked Zn(II) porphyrin arrays, since such mol-ecules would be promising as photonic wires and the orthogo-nal arrangement of neighboring porphyrins is favorable for ahigh degree of solubility. However, we soon faced a serioussolubility problem at the stage of the octamer. Thus, wedesigned a more soluble substrate, Z1, which bears two 3,5-dioctyloxyphenyl substituents. The established standard cou-pling protocol is very simple and involves treatment of Z1 or itsoligomers Zn with AgPF6 in CHCl3 at room temperature forseveral hours (Scheme 6).[35] It is important to monitor theprogress of the coupling reaction by gel permeation chroma-tography (GPC) HPLC or 1H NMR spectroscopy, and toquench the reaction at 30–40% conversion, since further reac-tion leads to production of larger porphyrin arrays, whichmakes separation of the products more tedious. Usually thecoupling products were separated from the starting substratethrough GPC-HPLC columns. In each iterative coupling reac-tion, the rigorous purification of coupled products is critically

important for the separation of their further coupled products.This coupling reaction has proved very effective, particularlyfor large porphyrin substrates.[35] It is amazing that extremelylong porphyrin arrays (even Z128 and Z256) smoothlyundergo the coupling reaction to provide Z1024,[36] despite theextremely long molecular shapes with only two edge free mesopositions available for the coupling. This meso–meso couplingreaction of porphyrins allowed us to prepare three-dimensionally extending windmill porphyrin arrays,[37–39]

dihedral-angle-controlled meso–meso-linked diporphyrins,[40,41]

large porphyrin wheels,[42–44] helical porphyrin arrays held byintermolecular hydrogen-bonding interactions,[45] and directlylinked porphyrin rings (Figure 6).[46] The meso–meso-linkeddiporphyrin motifs are suitable for supramolecular assembly.By this strategy, three-dimensional porphyrin boxes and otherinteresting architectures have been constructed through rigor-ous self-sorting assembly of pyridine-appended orcinchomeronimide-appended meso–meso-linked Zn(II)diporphyrins (Scheme 7).[47–50]

In the meantime, we explored an effective oxidative fusion–dimerization reaction of Ni(II) porphyrins to give meso, βdoubly linked porphyrin dimers (Eq. 7) and a ring-closurereaction of meso–meso-linked diporphyrins to β, meso, βtriply linked diporphyrins, initially with tris(4-bromophenyl)aminium hexachloroantimonate (BAHA) (Eq.8)[51–53] and later with the combined use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and Sc(OTf)3 (Eq. 9).[54]

The latter method is superior to the former because of theabsence of serious halogenation side products, and allow theconversion of long meso–meso-linked Zn(II) porphyrin arrays tothe corresponding meso–meso, β–β, β–β triply linked porphyrinarrays that are called porphyrin tapes. On the basis of this

Scheme 5. Formation of meso-meso linked porphyrin dimer and trimer.



oxidation, we have succeeded in the synthesis of π-conjugatedporphyrin tapes that display remarkably red-shifted andenhanced absorptions reaching deep into the infrared region(Scheme 8).[54–57] We have also explored an antiaromatic tetra-meric porphyrin sheet, which exhibits a strong paratropic ringcurrent above the central plane of the cyclooctatetraene core,[58–

60] and two-dimensionally extending porphyrin tapes.[61] Thebay-area selective cycloaddition reactions of porphyrin tapesproceeded nicely with an o-xylylene[62] and an azomethineylide.[63] The chemistry of meso–meso-linked porphyrin arraysand porphyrin tapes has been reviewed elsewhere.[64–70]

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Scheme 6. Iterative doubling elongation of meso-meso linked porphyrin oligomers.



Fig. 6. Various meso-meso linked porphyrin oligomers.



Scheme 7. Self-assembled formation of porphyrin boxes.

Scheme 8. Synthesis of porphyrin tape 12-mer.



(9)3. meso-Aryl-Substituted Expanded Porphyrins

In recent years, the chemistry of expanded porphyrins has beenactively explored in light of their favorable attributes, such asrich coordination chemistry, anion sensing, large two-photonabsorption cross-sections, and extended π-electronic systems.[71–

79] Sessler, an important pioneer of this field, developed thesynthesis of a pentadentate texaphyrin in 1988[80] and a rationalsynthesis of sapphyrins in 1990,[81] improvisation that led to anexciting boom of novel expanded porphyrins. meso-Arylexpanded porphyrins can be regarded as legitimate expandedporphyrins in terms of their regular and alternating arrange-ments of pyrroles and aryl-substituted meso carbons. Weserendipitously found the formation of these meso-arylexpanded porphyrins during the synthesis of tetrakis(pentafluorophenyl)porphyrin by the Lindsey method[82] usingpentafluorobenzaldehyde and pyrrole. We made the fortunatemistake to run the reaction at a substrate concentration of 67

mM, which is approximately tenfold higher than the optimizedconcentration for porphyrin synthesis. Under these conditions,a series of meso-aryl expanded porphyrins including N-fusedpentaphyrins, hexaphyrin, heptaphyrin, octaphyrin,nonaphyrin, decaphyrin, undecaphyrin, and dodecaphyrinwere formed in a surprisingly effective manner (Scheme 9).[83,84]

At this time, we knew that a communication by Cavaleiro et al.had appeared, which reported the isolation of [26]hexaphyrinand [28]hexaphyrin in low yields.[85] We were very shocked bythis paper but soon realized that our synthetic protocol wassuperior to Cavaleiro’s method in regard to the formation of aseries of expanded porphyrins and better yields. Initially, theseparation of meso-aryl expanded porphyrins was not easy andneeded repeated chromatographic separation, but this separa-tion difficulty has been somewhat mitigated by size-selectivesynthesis of the expanded porphyrins using a dipyrromethaneand a tripyrromethane as precursors.[86,87] Use of high concen-trations of the substrates led to better yields of larger expanded

Scheme 9. Synthesis of meso-aryl substituted expanded porphyrins.



porphyrins.[88] These meso-aryl expanded porphyrins haveproved to be attractive platforms for rich coordinationchemistry,[89–95] versatile aromatic compounds such as stronglyHückel aromatic[90,91,96] and antiaromatic molecules,[90,91] andstable organic radical species.[96–98] Unprecedented rearrange-ments are triggered by transannular electronic interactions aidedby the conformational flexibility of expanded porphyrins.[99,100]

Besides these, the meso-aryl expanded porphyrins are quiteinteresting from the viewpoint of mutual chemicalinterconversions (metamorphosis).[101,102] The most remarkableexample of this is the efficient and quantitative splitting reac-tion of bis-Cu(II) [36]octaphyrin complex 66 into two mol-ecules of Cu(II) porphyrins 67 upon heating (Eq. 10).[103] Thissplitting reaction also proceeded quantitatively in a Co(II)–

Cu(II) hybrid octaphyrin complex.[104] In a heptaphyrinsystem, treatment of heptaphyrin Cu(II) complex 68 with BBr3

in the presence of a sterically hindered amine led to the for-mation of subporphyrin 69 and Cu(II) porphyrin 70 in 36%and 13% yields, respectively (Eq. 11).[105] Similar treatment ofmeso-trifluoromethyl-substituted heptaphyrin Cu(II) complex71 with BBr3 gave meso-trifluoromethyl subporphyrin 72 andCu(II) porphyrin 73 (Eq. 12).[106] Subporphyrins are my otherfavorite porphyrinoids, which were first synthesized in mygroup in 2006.[107] The chemistry of subporphyrins arereviewed elsewhere.[108,109] It is worthwhile to note thatsubporphyrins 69 and 72 cannot be synthesized by the usualcondensation methods and thus these splitting reactions areimportant from a synthetic viewpoint.

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These splitting reactions require the rapture and formationof two carbon–carbon double bonds in a metathesis manner. Wethought that the transannular electronic interaction would beenhanced at the hinge position of the figure-eight conformationof the expanded porphyrins upon metalation and, thus, thistrend would be more general. In order to examine the scope ofthis unique metal-induced splitting reaction, we examined thecomplexation of expanded porphyrins with various transitionmetal ions such as Rh(I), Ni(II), Pd(II), and Pt(II). In 2006, wereported [28]hexaphyrin Ni(II), Pd(II), and Pt(II) complexes(74, 75, and 76, Figure 7).[110] Although we collected all the datafor these complexes including their crystal structures and noted

that the inner β-protons appeared at high field, we did not noticethat the high-field shifts were caused by the diatropic ringcurrents of 74–76, which are all Möbius aromatic molecules.We also reported the formation of Rh(I) complexes 77 and 78from N-fused pentaphyrin 60 (Scheme 10).[111] The 1H NMRspectrum of 78 shows a signal due to the inner β-proton in thehigh-field region at 0.10 ppm. At the time of publication, wecould not explain this particular high-field shift. In 2008, wereported that meso-aryl expanded porphyrins such asoctaphyrin, heptaphyrin, and hexaphyrin can form Möbiusaromatic complexes almost spontaneously upon metalationwith Pd(II) ions.[112] In this paper, we revealed that the com-



plexes 79 and 80 (Figure 8) along with 74–76 are all Möbiusaromatic molecules. Soon after, we reported that the complex 78is also a Möbius aromatic molecule.[113] Following these studies,we have explored many expanded porphyrins, which displayversatile electronic states such as Hückel aromatic, Hückelantiaromatic, Möbius aromatic, Möbius antiaromatic,[114,115]

and stable radical states.[96,98] Such molecules are outside thescope of this account and are reviewed elsewhere.[116,117]

4. Summary

As described above, my research career has been guided by nomeans by my idea but simply led by many fortunate unex-

pected encounters with the assistance of many students andpostdocs. Throughout my career in the Department of Chem-istry, the Faculty of Science, Ehime University, and in theDepartment of Chemistry, the Graduate School of Science,Kyoto University, I have been very fortunate to have had theopportunity to serve as a mentor for many talented students.To be honest, my laboratory has not been well organized. Inother words, I have tried to keep my students and postdocs asfree as possible. They have to think and explore novel chemistryby themselves. Most of them have demonstrated themselves tobe quite motivated in synthesizing new porphyrinoids andexploring new chemistry of such molecules and have nowbecome eligible staff members of universities, institutes, andcompanies. They are indeed my pride. Therefore, it is obvious

Fig. 7. Structures of Möbius aromatic hexaphyrin Ni(II)-, Pd(II)-, and Pt(II) complexes.

Scheme 10. Rh(I) metalation of N-fused [22]pentaphyrin.



that I should thank them for their outstanding devotion to thechemistry of novel porphyrinoids.

Acknowledgements

This work was partly supported by Grants-in-Aid (No.25220802 (S)) from MEXT. The author thanks Dr. T. Tanakafor making the schemes, equations, and figures.

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Fig. 8. Structures of Möbius aromatic heptaphyrin Pd(II) complex and octaphyrin bis-Pd(II) complex.



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