Planar <i>Meso</i> Pentafluorophenyl Core Modified Isophlorins

Reddy, J. Sreedhar; Anand, Venkataramanarao G.

doi:10.1021/ja710664y

Cited by 79 publications

(85 citation statements)

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“…By contrast, Setsune's N 21 ,N 22 -bridged N 4 -isophlorins are not highly deviated from planarity and exhibit paratropic ring current effects in the 1 H NMR spectra [17]. Anand's core-modified O 4 -and O 2 ,S 2 -isophlorins bearing meso-pentafluorophenyl groups have a completely planar structure and display antiaromatic character [18]. In addition to these isophlorin free bases, a few TPP-type metal-N 4 -isophlorin complexes have recently been characterized by spectroscopy and/or X-ray crystallography [19,20].…”

Section: Crystal Structuresmentioning

confidence: 96%

Synthesis, structures, and aromaticity of phosphole-containing porphyrins and their metal complexes

Matano

Nakabuchi

Imahori

2010

Pure and Applied Chemistry

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Our recent studies on the synthesis, structures, and aromaticity of phosphole-containing porphyrins and their metal complexes are summarized. Core-modified P,X,N 2 -porphyrins (X = S, N) are accessible from a σ 4 -phosphatripyrrane and the corresponding 2,5-difunctionalized heteroles in a few steps. X-ray structural analysis of the σ 3 -P,N 3 porphyrin revealed that it possesses a slightly distorted 18π plane. The phosphorus atom incorporated at the core plays an important role in producing unprecedented reactivity and coordinating ability for the porphyrin ring. The P,N 3 free base reacts with [RhCl(CO) 2 ] 2 in dichloromethane, ultimately yielding an 18π P,N 3 -rhodium(III) complex, whereas the P,S,N 2 free base undergoes redox-coupled complexation with zero valent group 10 metals to afford the corresponding P,S,N 2 -isophlorin-metal(II) complexes. The aromaticity of the free-base porphyrins and the metal complexes was uncovered based on both experimental and theoretical results. It is of particular interest that the P,S,N 2 -isophlorin -metal complexes exhibit only a weak antiaromaticity in terms of the magnetic criterion.Our studies concerning the synthesis and coordination chemistry of the phosphole-containing porphyrin family were overviewed in a recent account [1j]. Herein we particularly focus on the phosphaporphyrins and their metal complexes, and describe their structures and aromaticity in detail. SYNTHESIS OF PHOSPHAPORPHYRINSThe phosphole-containing hybrid porphyrins (denoted hereafter as P,X,N 2 -porphyrins) 4X (X = N, S) were successfully synthesized from P-masked phosphatripyrrane 1 and 2,5-difunctionalized heteroles 2X (X = N, S) [9,10] by three-step sequential reactions (Scheme 1) [6]: (i) BF 3 -promoted dehydrative condensation of 1 with 2X, (ii) desulfurization at the phosphorus center of 3X-S (X = N, S) with P(NMe 2 ) 3 , and (iii) ring oxidation of σ 3 -porphyrinogens 3X (X = N, S) with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). During the ring oxidation from 3X to 4X side reactions took place probably via P-oxidation (vide infra). The target P,X,N 2 -porphyrins 4N and 4S were isolated as reddish purple solids after column chromatography on alumina, and their structures were fully characterized by spectroscopy and X-ray crystallography (vide infra). In an attempt to synthesize a TPP-type phosphaporphyrin (TPP = 5,10,15,20-tetraphenylporphyrin) based on a different [3+1] approach, Mathey and co-workers isolated a small amount of "P-confused" carbaporphyrinoid instead of normal phosphaporphyrin [4]. These results indicate that a suitable choice of precursors is of utmost importance in promoting the desired porphyrin-ring formation.The P,X,N 2 -porphyrins 4X exhibit unique reactivities depending on the heteroatom (X) (Scheme 2). On treatment with H 2 O 2 , the 18π σ 3 -P,X,N 2 -porphyrins 4N and 4S were gradually transformed into 22π σ 4 -P,N 3 -porphyrin 6 and 20π σ 4 -P,S,N 2 -porphyrin 7, respectively, as major isolable products [6b,c]. These reactions are probably initiated by oxygenation ...

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Section: Crystal Structuresmentioning

confidence: 96%

Synthesis, structures, and aromaticity of phosphole-containing porphyrins and their metal complexes

Matano

Nakabuchi

Imahori

2010

Pure and Applied Chemistry

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“…It was also observed that 7 exhibited significant emission at l = 410 and 434 nm when excited either at l = 360 or 370 nm, with aq uantum yield (F)o f2 .2 %i nd ichloromethane,a nd 10 displayed aweak (F = 1.2) but strong red-shifted emission at l = 650 nm, which is very much similar to that observed for tetraphenyl porphyrins.C yclic voltammetry studies revealed two reversible reductions and oxidations,w ith a D redox of 1.18 V. More significantly, 7 displayed ar elatively lower oxidation potential compared to that of the tetraphenyl porphyrin and meso-tetra(pentafluorophenyl)teraoxaisophlorin. [3] These lower oxidation values were found to be quasireversible in nature.Inanattempt to reduce the dication to the 20p antiaromatic isophlorin, 10 was treated with reducing agents such as FeCl 2 and sodium. Neither of them yielded 7.However,itcould be reduced to 7 by the addition of zinc dust.…”

Section: Angewandte Chemiementioning

confidence: 92%

“…[1] Donor atoms such as OorS or Se in core-modified porphyrins alter the ligating properties while sustaining the structural features and electronic properties of the parent macrocycle.H owever,r eplacement of all four pyrroles by other heterocyclic units in aporphyrin yields antiaromatic 20p isophlorins (4 and 5)with similar structural characteristics but altered electronic properties. [2,3] As ignificant difference between porphyrin and isophlorin is observed in their reactivity towards protic acids.2 0 p isophlorins are characteristic organic molecules with pseudometal properties. [4] Thec ompounds 4 and 5 undergo two-electron ring oxidation to yield the 18p aromatic dication.…”

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confidence: 99%

“…[9] As observed earlier, [1] thepyrrole NH is prone to oxidation so as to accommodate the nitrogen atom of the pyrrole in the conjugation (Scheme 2). It can be envisaged that the oxidation of 7 can yield either the 18p radical dication 12 or the 19p radical cation 11.F rom our earlier reports,w eh ave observed that salts such as [Et 3 O] + [SbCl 6 ] À [10] and [NO] + -[BF 4 ] À are excellent oxidizing agents for antiaromatic systems. [9a] [NO] + [BF 4 ] À was added to as olution of 7 in dichloromethane and stirred for ten minutes under nitrogen atmosphere.T he solution displayed as ubtle change from ayellowish-green to pink color upon oxidation.…”

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Controlled Core‐Modification of a Porphyrin into an Antiaromatic Isophlorin

2016

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Partial core-modification of ap orphyrin can be employed to synthesize the 20p antiaromatic isophlorin. Unlike the tetra-, tri-, and dipyrrole derivatives of aporphyrin, amonopyrrole porphyrin exhibits antiaromatic characteristics. It undergoes at wo-electron reversible ring oxidation to yield the 18p aromatic dication. 1 HNMR analysis provides distinct evidence of the altered electronic characteristics through typical paratropic and diatropic ring current effects for the 4n and the (4n + 2) p-electron systems,respectively.

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“…1 H NMR (500 MHz, (CD 3 ) 2 CO, 175 K): d = 12.83(d, 2 H, 16 Hz), 5.98 (d, 2 H, 4 Hz), 6 H), 5.51 (d, 2 H, 4 Hz), 5.42 (d, 2 H, 4 Hz), 5.37 ppm 1 H NMR (500 MHz, (CD 3 ) 2 CO, 175 K): d = 12.83(d, 2 H, 16 Hz), 5.98 (d, 2 H, 4 Hz), 6 H), 5.51 (d, 2 H, 4 Hz), 5.42 (d, 2 H, 4 Hz), 5.37 ppm…”

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