Reductive demetallation of Cu-corroles—a new protective strategy towards functional free-base corroles

Ngo, Thien H.; Rossom, Wim Van; Dehaen, Wim; Maes, Wouter

doi:10.1039/b819185a

Cited by 86 publications

(61 citation statements)

References 57 publications

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“…Slight modification of the product yield (22%) was observed in reductive demetalation of 9 by SnCl 2 . 15 In the 1 H NMR spectrum of 16 in CDCl 3 , the sharp signal due to inner-CH moieties appeared at ¤ ¹4.80 (2H), and the broad signal due to inner-NH moieties appeared at ¤ ¹2.05 (4H), which indicated successful isolation of the free-base NCP dimer. 16 In summary, the 3,3¤-acetylene-bridged NCP dimers were readily synthesized by one-step three-component Stille coupling reactions.…”

Section: ¹1mentioning

confidence: 91%

Synthesis and Properties of Acetylene-bridged N-Confused Porphyrin Dimers

Toganoh¹,

Takayama²,

Nandy³

et al. 2011

Chemistry Letters

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Acetylene-bridged N-confused porphyrin (NCP) dimers were synthesized by Stille coupling reactions. Moderate electronic interaction between the NCP chromophores was observed in the inner-3H tautomers while strong interaction was observed in the inner-2H tautomers.Cross-coupling reactions are one of the most powerful methods to construct large ³-conjugated molecules.1 Among such molecules, porphyrin dimers as well as oligomers are a particularly important class of compounds, which often show fascinating electronic properties and functions, such as twophoton absorption, light-harvesting, and electron transport. One intrinsic characteristic of NCP is NH-tautomerization, which allows change of the electronic state significantly (Figure 1).5 Thus, the inner-3H tautomer (NCP3H) has an [18]annulenic substructure and is strongly aromatic, while the inner-2H tautomer (NCP2H) loses the [18]annulenic substructure and is moderately aromatic.6 Accordingly, NCP3H is thermodynamically more stable than NCP2H and much difference is found in their photophysical properties.7 Previously, we have demonstrated that intramolecular energy transfer could be controlled by NH-tautomerization in the porphyrinNCP dyad system. 8 Additionally, substitution effect at the 3-position would be much different between NCP3H and NCP2H.9 Along the lines of these findings, we can expect interesting electronic structures in 3,3¤-acetylene-bridged NCP dimers. In this paper, the synthesis and properties of 3,3¤-acetylene-bridged NCP dimers by the Stille coupling are reported.First, the reactions of 3-bromo-NCPs with tributyl(phenylethynyl)tin were studied to prepare 3-alkynyl-NCPs (Scheme 1). The alkynylated NCPs were previously prepared by the Sonogashira coupling 9 or inversion of alkynylated N-fused porphyrins. 10 The reaction of N-confused 3-bromotetraphenylporphyrinatosilver(III) complex 1 proceeded smoothly with Pd(OAc) 2 /AsPh 3 catalyst to give Ag III (NCP3H)CCPh 2 in 63% yield. Transmetalated product, Pd II (NCP2H)CCPh 3, was also obtained in 19% yield. This unique reductive transmetalation from Ag(III) to Pd(II) inside the NCP core was also observed in the Sonogashira coupling reaction. 9 The reaction of N-confused 3-bromotetrakis[4-(trifluoromethyl)phenyl]porphyrinatocopper(II) complex 4 proceeded in a similar manner to give Cu II (NCP2H)CCPh 5 in 48% yield. Transmetalated product 6 was also isolated in 10% yield. The AsPh 3 ligand so far afforded the better yields than the phosphine ligands such as PPh 3 and diphenylphosphinoethane.Then, syntheses of acetylene-bridged NCP dimers were examined by the reactions with bis(tributylstannyl)acetylene (Scheme 2). The Pd-catalyzed reaction of 1 successfully gave Ag III (NCP3H)CCAg III (NCP3H) 7 in 20% yield together with Ag III (NCP3H)CCPd II (NCP2H) 8 in 7% yield. In the 1 H NMR spectrum of 7 in CDCl 3 , the signals due to ¢-pyrrolic protons (12H) were observed in the region of ¤ 8.58.9, suggesting its strong aromatic character. Additionally, the number of proton signals indicated the symmetric stru...

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Section: ¹1mentioning

confidence: 91%

Synthesis and Properties of Acetylene-bridged N-Confused Porphyrin Dimers

Toganoh¹,

Takayama²,

Nandy³

et al. 2011

Chemistry Letters

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“…[7] However, recent breakthroughs on the (reductive) demetalation of Cu-and Mn-corroles allow the use of a metalation/demetalation sequence as a protection/deprotection strategy towards elaborated Fb-corroles. [8,9] Within one of our research groups, we have been studying the synthesis and reactivity of 4,6-dichloropyrimidines as versatile structural building blocks for meso-pyrimidinylsubstituted porphyrins, [10] heteracalix [m]arene [m]pyrimidines, [11] and pyrimidine-based (porphyrin) dendrimers. [12,13] During the course of our studies on pyrimidinylporphyrins, it was discovered that a slight modification of the reaction conditions, as optimized for porphyrins, results in the formation of either expanded (penta-and hexaphyrins) [14] or contracted [15] porphyrin analogues.…”

Section: Introductionmentioning

confidence: 99%

“…[10,14] In previous communications, specific synthetic aspects of pyrimidinylcorroles have been described. [9,[15][16][17] In this paper, we report a detailed multidisciplinary study on the synthesis and functionalization, structural elucidation and photophysical properties of meso-pyrimidinyl-substituted AB 2 -corroles (A = 4,6-dichloropyrimidin-5-yl). [18] Results and Discussion Synthesis of the AB 2 -pyrimidinylcorrole scaffold: In 2001, one of our groups contributed to the early stages of synthetic corrole chemistry by exploring the synthesis of sterically encumbered triarylcorroles starting from aromatic aldehydes and 5-aryldipyrromethanes.…”

Section: Introductionmentioning

confidence: 99%

“…[15] Cu insertion can also smoothly be achieved in THF. [9] Inspired by the success of similar modifications on pyrimidinylporphyrins, peripheral substitution of the pyrimidinylcorrole skeleton was first pursued by means of S N Ar reactions. Cu-metalated AB 2 -pyrimidinylcorroles 5 a,b were noticeably less reactive towards substitution than the analogous Fb A 2 B 2 -porphyrins.…”

Section: Introductionmentioning

confidence: 99%

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Synthetic, Structural, and Photophysical Exploration of meso‐Pyrimidinyl‐Substituted AB₂‐Corroles

Ngo

Puntoriero²,

Nastasi³

et al. 2010

Chemistry A European J

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meso-Pyrimidinyl-substituted AB(2)-corroles were efficiently synthesized starting from 5-mesityldipyrromethane and various 2-substituted 4,6-dichloropyrimidine-5-carbaldehydes. The corrole yield was significantly enhanced by optimization of the amount of Lewis acid catalyst (BF(3).OEt(2)). The main advantage of pyrimidinylcorroles over other meso-triarylcorroles is their wide range of functionalization possibilities, which has been explored by nucleophilic and electrophilic aromatic substitution, and Pd-catalyzed cross-coupling reactions. Stepwise substitution of the chlorine functions afforded asymmetrically substituted pyrimidinylcorroles. Due to the lability of the free-base corrole macrocycles, functionalization of the corrole periphery was preferentially performed on the Cu-metalated counterparts. Functionalized free-base AB(2)-pyrimidinylcorroles were, however, readily accessible by the reversible sequence Cu insertion and subsequent reductive demetalation. AB(2)-pyrimidinylcorroles can hence be regarded as highly versatile platforms towards more sophisticated corrole systems. X-ray analysis of a bis(4-tert-butylphenoxy)-substituted Cu-pyrimidinylcorrole showed the typical features of a Cu-corrole: short N-Cu distances and a saddled corrole plane. The absorption spectra and photophysical properties of some representative free-base AB(2)-pyrimidinylcorroles were examined in depth. The absorption spectra displayed typical corrole features: intense spin-allowed pi-pi* bands, which can be classified as Soret- and Q-type bands. The photophysical properties, investigated both in fluid solution at room temperature and in rigid matrix at 77 K, were governed by the lowest-lying pi-pi* singlet state; however, in most cases, a state with partial charge-transfer character (from the corrole ring to the pyrimidinyl group) was proposed to contribute to the dynamic properties of the emissive level.

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“…3,4,5,6,7 A notable success of this 'reductive demetalation' approach has been the synthesis of free-base -octabromocorroles 5,4,7,8 and their subsequent use as ligands. 9,10 Here we report that copper undecaarylcorroles 11,12,13 demetalate with unusual ease, in a matter of minutes, on exposure to acid, under both reductive and nonreductive conditions.…”

mentioning

confidence: 99%

Demetalation of copper undecaarylcorroles: Molecular structures of a free-base undecaarylisocorrole and a gold undecaarylcorrole

Capar

Zonneveld

Berg

et al. 2016

Journal of Inorganic Biochemistry

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Abstract. Copper undecaarylcorroles were found to undergo acid-induced demetalation with unusual ease under both reductive and nonreductive conditions. The resulting free-base undecaarylcorroles were found to be rather reactive, readily photooxygenating to yield 5/10-hydroxyisocorroles and biliverdines. The use of nonreductive conditions led to fairly good yields of undecaarylisocorroles, a new class of sterically hindered ligands, of which one proved amenable to single-crystal X-ray structural analysis. In one case, interaction of an undecaarylisocorrole with gold(III) acetate resulted in aromatization of the macrocycle and a gold undecaarylcorrole. The Au complex exhibited Au-N distances of 1.941(3)-1.965(3) Å, and no significant nonbonded interactions involving the gold. The significant solubility of this complex in organic solvents, compared with the relative insolubility of gold -octabromo-mesotriarylcorroles, appears to be related to the lack of aurophilic and metallophilic interactions.2

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Reductive demetallation of Cu-corroles—a new protective strategy towards functional free-base corroles

Abstract: A novel procedure for the reductive demetallation of Cu-meso-triarylcorroles has been disclosed. The reversible sequence copper metallation/demetallation was proven to be an effective protection/deprotection strategy towards sophisticated functionalized free-base corroles.

Cited by 86 publications

References 57 publications

Synthesis and Properties of Acetylene-bridged N-Confused Porphyrin Dimers

Synthesis and Properties of Acetylene-bridged N-Confused Porphyrin Dimers

Synthetic, Structural, and Photophysical Exploration of meso‐Pyrimidinyl‐Substituted AB₂‐Corroles

Demetalation of copper undecaarylcorroles: Molecular structures of a free-base undecaarylisocorrole and a gold undecaarylcorrole

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Reductive demetallation of Cu-corroles—a new protective strategy towards functional free-base corroles

Abstract: A novel procedure for the reductive demetallation of Cu-meso-triarylcorroles has been disclosed. The reversible sequence copper metallation/demetallation was proven to be an effective protection/deprotection strategy towards sophisticated functionalized free-base corroles.

Cited by 86 publications

References 57 publications

Synthesis and Properties of Acetylene-bridged N-Confused Porphyrin Dimers

Synthesis and Properties of Acetylene-bridged N-Confused Porphyrin Dimers

Synthetic, Structural, and Photophysical Exploration of meso‐Pyrimidinyl‐Substituted AB2‐Corroles

Demetalation of copper undecaarylcorroles: Molecular structures of a free-base undecaarylisocorrole and a gold undecaarylcorrole

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Synthetic, Structural, and Photophysical Exploration of meso‐Pyrimidinyl‐Substituted AB₂‐Corroles