Synthesis of “capped porphyrins”

Almog, Joseph; Baldwin, Jack E.; Crossley, Maxwell J.; DeBernardis, John F.; Dyer, Robert; Huff, Joel R.; Peters, Mary A.

doi:10.1016/s0040-4020(01)98887-8

Cited by 67 publications

(53 citation statements)

References 22 publications

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“…Tripyrrolylborane (0.1 g) was dissolved in propionic acid (35 mL) and the solution added dropwise to a refluxing solution of benzaldehyde (ca. 0.1m) in propionic acid (35 mL) [7] over 1 h. After addition, the solution was further heated to reflux for 2 h. The solvent was removed, and the residue purified by column chromatography on silica gel and alumina and TLC with CHCl 3 /methanol as eluent, and size-exclusion HPLC with CHCl 3 . The TLC analysis indicated a moderate yield of about 15 %, but pure meso-phenylsubporphyrin 3 a was obtained only in about 5 % yield because of several tedious column-chromatography stages.…”

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confidence: 99%

meso‐Aryl Subporphyrins

2007

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Ring‐contracted porphyrins: meso‐Aryl subporphyrins were synthesized by using a method in which tripyrrolylborane acts as a template for the Adler method. This study demonstrates that, although the subporphyrins retain porphyrinic properties, ring contraction has a significant impact on the electronic structure. The picture shows the DFT‐optimized structure of the meso‐phenyl subporphyrin (B yellow, N blue, O red, C green, H white).

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confidence: 99%

meso‐Aryl Subporphyrins

2007

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“…For example, when (OEP)Mn N is treated with (TTP)MnCl, a formal two-electron transfer occurs which is attended by a reversible, double exchange of axial ligands as shown in eq 59. 90 The (59) chromium analog has also been reported by Bottomley (eq 60). 91 In addition, the irreversible transfer of nitrogen from (OEP)Mn==N to (TPP)CrCl is also known (eq 61).…”

Section: B Two-electron Processesmentioning

confidence: 69%

“…An atom-transfer pathway in this system is complicated mechanistically by the presence of two good bridging ligands, chloride and oxide. However, mechanistic studies using a pyrromellitoyl capped porphyrin, 59 or a bulky univalent axis ligand, pivalate, in place of chloride rule out !L-Cl bridged intermediates such as A and B. Furthermore, when chlorochromium(III) porphyrins are used as the…”

Section: B Complete Oxygen Atom Transfer-one-electron Processesmentioning

confidence: 99%

“…91 In addition, the irreversible transfer of nitrogen from (OEP)Mn==N to (TPP)CrCl is also known (eq 61). 92 For all three reactions (59)(60)(61), the (OEP)Cr==N + (TPP)CrCl ~ (OEP)CrCl + (TPP)Cr==N (60) (OEP)Mn==N + (TPP)CrCl-+ (OEP)MnCl + (TPP)Cr==N (61) kinetic analysis, solvent dependencies, M(III) axial ligand effects, steric factors, and Cl-inhibition studies support the mechanism shown in Scheme VI. The N/Cl exchange pathway for metalloporphyrins involves a preequilibrium dissociation of the monoanionic axial ligand on the M(lll) reductant.…”

Section: B Two-electron Processesmentioning

confidence: 99%

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Intermetal oxygen, sulfur, selenium, and nitrogen atom transfer reactions

Woo

1993

Chem. Rev.

122

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The importance of electron-transfer reactions is clearly indicated by the extensive literature describing this field and the present research emphasis devoted toward understanding these fundamental processes.1 The intricacies of electron-transfer reactions have been vigorously examined experimentally and theoretically for over 40 years.2·3 Because of continuing, intensive effort, fundamental aspects of these vital processes are still being elaborated. Disciplines Chemistry CommentsReprinted (adapted) with permission from Chemical Reviews 93 (1993): 1125,

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“…Through the attachment of diverse organic protecting groups to the distal face of model porphyrins, the size, shape, and functionality of such systems can be systematically varied so that steric and electronic factors for CO discrimination can be addressed individually. A large variety of model compounds have been prepared, including "chelated" [18,19], "strapped" [20][21][22][23][24][25][26], "picnic basket" [27], "picket fence" [28,29], "pocket" [30][31][32] and "capped" [33][34][35][36][37][38][39][40] porphyrins as well as hybrids [41][42][43] of these different classifications.…”

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confidence: 99%

Myoglobin models and steric origins of the discrimination between O2 and CO

Slebodnick

Ibers

1997

J Biol Inorg Chem

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Synthetic models of the myoglobin active site have provided much insight into factors that affect CO and O 2 binding in the proteins. "Capped" and "pocket" metal porphyrin systems have been developed to probe how steric factors affect ligand binding and ultimately to elucidate important aspects of the mechanism of CO discrimination in the proteins. These model porphyrins are among the most thoroughly characterized systems to date. From the twenty-one known crystal structures, analysis of the types of distortion that occur upon ligand binding under the cap, including porphyrin doming and ruffling, lateral and horizontal movement of the cap, and bending and tilting of the Fe-C-O bond, provides an indication of how steric interactions will affect structure in Hb and Mb. The model porphyrin systems discussed range from those that discriminate against O 2 binding compared to biological systems to those with similar CO and O 2 binding strength to myoglobin, and also to those that bind both O 2 and CO very weakly or not at all. The primary type of distortion observed upon CO binding is vertical or lateral movement of the cap and some ruffling of the porphyrin plane. Minimal bending or tilting of the M-C-O bond is observed, suggesting that the Fe-C-O bending that has been found from crystal structures of the hemoproteins is unlikely.Key words X-ray structure 7 Biomimetic porphyrin 7 Iron 7 Ruthenium 7 Carbonyl Despite the fact that the oxygen-carrying hemoproteins hemoglobin (Hb) and myoglobin (Mb) are among the most studied of the proteins, the question of how structure affects CO and O 2 binding to their heme centers remains contentious. These proteins contain a squareplanar heme [iron(II) protoporphyrin IX] that is embedded in the hydrophobic pocket of the globin; the heme and the globin are connected on the so-called proximal side by a covalent bond between the Fe center and a nitrogen atom of the imidazole group of a histidine residue. An open sixth coordination position on the distal side of the heme is the site of dioxygen binding. Other ligands, including CO, NO, and RNC bind at this site with respective affinities of approximately 10 2 , 10 5 , and 10 -2 times those of O 2 [1]. The binding of CO has been of particular interest because it is discriminated against: although Hb and Mb bind CO more strongly than O 2 , the M value [M p P 1/2 (O 2 )/P 1/2 (CO)] for Hb and Mb is much smaller than it is for unprotected model porphyrin systems [2,3]. This discrimination, which in energy terms amounts to about 4 kcal/ mol, is vital, since CO is produced endogenously in various biological processes [2,4], and approximately 3% of the heme sites in Hb are ligated by CO, even with the discrimination [5].A central question that has led to intense study of biological [6] and model systems [5,7] is how this discrimination occurs. Is O 2 binding stabilized or is CO binding destabilized in the biological systems? In fact, it is likely that both of these processes contribute to the lower value of M by very different chemical means....

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Synthesis of “capped porphyrins”

Cited by 67 publications

References 22 publications

meso‐Aryl Subporphyrins

meso‐Aryl Subporphyrins

Intermetal oxygen, sulfur, selenium, and nitrogen atom transfer reactions

Myoglobin models and steric origins of the discrimination between O2 and CO

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