Stable Expanded Porphycene‐Based Diradicaloid and Tetraradicaloid

Rana, Anup; Hong, Yongseok; Gopalakrishna, Tullimilli Y.; Phan, Hoa; Herng, Tun Seng; Yadav, Priya; Ding, Jun; Kim, Dongho; Wu, Jishan

doi:10.1002/ange.201807411

Cited by 9 publications

(6 citation statements)

References 36 publications

(9 reference statements)

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“…Therefore, a bithiophene bridged expanded porphycene 24 and a cyclopentabithiophene bridged expanded porphycene 25 (Figure 6a) were synthesized by McMurry coupling of the respective aldehyde precursor, followed by oxidative dehydrogenation (Scheme 1d). 63 Compounds 24 and 25 have intrinsic tendency to become open-shell diradicals/tetradicals by recovery of two/four aromatic thiophene rings (Figure 6a). Magnetic measurements and theoretical calculations reveal that both 24 and 25 exhibit open-shell singlet ground state with significant radical character (y 0 = 0.63 for 24; y 0 = 0.68, y 1 = 0.18 for 25) and small singlet−triplet energy gap (ΔE S−T = −3.25 kcal/mol for 24 and ΔE S−T = −0.92 kcal/mol for 25).…”

Section: Accounts Of Chemical Researchmentioning

confidence: 99%

Global Aromaticity in Macrocyclic Polyradicaloids: Hückel’s Rule or Baird’s Rule?

et al. 2019

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CONSPECTUS: Aromaticity is one of the most important concepts in organic chemistry to understand the electronic properties of cyclic πconjugated molecules. Over a century, different aromaticity rules have been developed and validated. For planar monocyclic conjugated polyenes (also known as [n]annulenes), they will be aromatic if they contain [4N + 2] π electrons according to Huckel's rule, or antiaromatic if they have [4N] π electrons. Topological change from a planar to a half-twisted Mobius strip will lead to [4N] ([4N + 2]) aromaticity (antiaromaticity), which is just inverse to Huckel's rule. When the molecules are excited into the first triplet excited state, the Huckel (anti)aromaticity observed in the ground state will become reversed according to Baird's rule. Strictly speaking, these basic rules are only applicable for monocyclic conjugated systems, but some polycyclic systems such as porphyrinoids may also follow these rules if there is a dominant [n]annulene-like conjugation pathway. On the other hand, all-benzenoid polycyclic aromatic hydrocarbons usually display local aromaticity with π electrons predominantly localized at certain benzene rings according to Clar's aromatic sextet rule. In recent years, some proaromatic and antiaromatic molecules with even number of paired electrons have been found to exhibit open-shell diradical character and unique optical, electronic, and magnetic activities. One of the major driving forces is their intrinsic tendency to become aromatic in the open-shell diradical/polyradical forms. A number of stable diradicaloids and linear polyradicaloids have been successfully synthesized by using thermodynamic and kinetic stabilizing strategies. Herein, our particular interest is a type of macrocyclic polyradicaloid in which multiple frontier π-electrons are antiferromagnetically coupled with each other in a cyclic mode. Formally, these free electrons may behave like normal π-electrons in the [n]annulenes, and thus, it raises questions about their possible global aromaticity and which rule they will follow. In the past 5 years, our group has synthesized a series of macrocyclic polyradicaloids and systematically investigated their global aromaticity and electronic properties. Some important findings include: (1) global (anti)aromaticity is generally observed, but there is a balance between local aromaticity and global aromaticity; (2) most of these molecules follow Huckel's rule in the singlet state and display respective (anti)aromatic characteristics; (3) in some special cases, both Huckel's rule and Baird's rule can be applicable, and a unique annulene-within-an-annulene super-ring structure was demonstrated for the first time; (4) global antiaromaticity in the transition state is also important and a slow valence tautomerization process was observed in a supercyclobutadiene tetraradicaloid. These studies demonstrate how these open-shell macrocyclic polyradicaloids adapt their geometry and spin state to reach the lowest-energy state (aromatic). In this Account, we will main...

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Section: Accounts Of Chemical Researchmentioning

confidence: 99%

Global Aromaticity in Macrocyclic Polyradicaloids: Hückel’s Rule or Baird’s Rule?

et al. 2019

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“… 96 Another experiment related to porphycene is the synthesis of expanded porphycene containing 34 π-electrons, 172. 97 The molecule is stable in ambient air and light due to a highly effective cyclic π-conjugation. The large conjugated pi-electron system also plays a role in stabilizing highly reactive organic radical compounds.…”

Section: Applications Of the Mcmurry Reactionmentioning

confidence: 99%

Recent advances of carbonyl olefination via McMurry coupling reaction

2022

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“…The recent literature on the diradicaloid topic is replete with a large diversity of examples [9–12] wherein, however, more detailed explanations of the origin of the mosaic of diradicaloid properties would be desirable. To attempt this, we review the basic concepts that give rise to the emergence of the diradical character in the important area of polycyclic hydrocarbon compounds based on [4 n ]annulene peripheries, with particular emphasis in those which are internally “functionalized” or “hybridized” by covalent structures.…”

Section: Introductionmentioning

confidence: 99%

Polycyclic Hydrocarbons from [4n]Annulenes: Correlation versus Hybridization Forces in the Formation of Diradicaloids

et al. 2022

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The conceptual connections between [4n] Hückel antiaromaticity, disjoint orbitals, correlation energy, proaromaticity and diradical character for a variety of extended π-conjugated systems, including some salient recent examples of nanographenes and polycyclic aromatic radicals, are provided based on their [4n]annulene peripheries. The realization of such structure-property relationships has led to a beneficial pedagogic exercise establishing design guidelines for diradicaloids. The antiaromatic fingerprint of the [4n]annulene peripheries upon orbital interactions due to internal covalent connectors gives insights into the diradicaloid property of a diversity of π-conjugated molecules that have fascinated chemists recently.

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Stable Expanded Porphycene‐Based Diradicaloid and Tetraradicaloid

Cited by 9 publications

References 36 publications

Global Aromaticity in Macrocyclic Polyradicaloids: Hückel’s Rule or Baird’s Rule?

Global Aromaticity in Macrocyclic Polyradicaloids: Hückel’s Rule or Baird’s Rule?

Recent advances of carbonyl olefination via McMurry coupling reaction

Polycyclic Hydrocarbons from [4n]Annulenes: Correlation versus Hybridization Forces in the Formation of Diradicaloids

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