Controlled Core‐Modification of a Porphyrin into an Antiaromatic Isophlorin

Abstract

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.

Status of Inorganic Chemistry Research in India

“…R N Mukherjee and his group at Kanpur, have contributed significantly to the development of broadbased synthetic coordination chemistry of transition metal ions with designed organic ligands to address shown that a monopyrrole porphyrin exhibits antiaromatic characteristics (Panchal et al, 2016).…”

“…Recently, a selenabenzoporphyrin and its Pd(II) complex were synthesized and characterized . Anand and co-workers have been involved in the synthesis of large porphyrin-like macrocycles with a view to studying concepts such as aromaticity and anti-aromaticity (Panchal et al, 2016), (Gopalakrishna et al, 2014). Panda and co-workers have been working on various porphyrin-based macrocycles including isomeric porphyrins (Sarma et al, 2015).…”

Redox Assisted Reversible Aromaticity Transition Between 30π Hückel and 28π Möbius Dication of a Core‐Modified Isophlorinoid

“…Air‐stable macrocycles with an isophlorin like conjugation bearing 20π electrons have been synthesized with heterocycles such as furan and thiophene [21] . A 20π core‐modified porphyrin, 5 a , and a few expanded porphyrins, 7 a , are known to adopt an isophlorin‐like conjugation [22,23] . Significantly, isophlorinoids are susceptible to either reversible two‐electron ring oxidation or proton‐coupled electron transfer (PCET) involving more than two electrons (Figure 2).…”

“…Significantly, isophlorinoids are susceptible to either reversible two‐electron ring oxidation or proton‐coupled electron transfer (PCET) involving more than two electrons (Figure 2). For example, a 20π antiaromatic mono‐pyrrole isophlorin 5 a resists PCET and is more susceptible to ring oxidation to yield the 18π dicationic aromatic species 5 b [22] . A non‐pyrrolic expanded 32π hexaoxa non‐antiaromatic isophlorinoid 6 a undergoes reversible ring oxidation to yield a planar 30π dicationic aromatic species 6 b [24] .…”

Tetra S-confused porphyrinoids

“…Furthermore, these macrocycles do not exhibit typical reversible oxidations in cyclic voltammetry (ESI†) as expected for 4 n π porphyrinoids. 27 This can be attributed to the cross conjugation arising due to the successive α, β links of thiophene units in the macrocycle.…”