(Aza)Acenes Share the C2 Bridge with (Anti)Aromatic Macrocycles: Local vs. Global Delocalization Paths

Abstract

Astrong conjugation present in fused systems plays acrucial role in tuning of the properties that would be showing adependence on the efficiency of p-electrons coupling.The pcloud available in the final structure can be drastically influenced by as ide-or al inear fusion of unsaturated and conjugated hydrocarbons.T he linear welding of naphthalene/ anthracene or quinoxaline/benzo[g]quinoxaline with triphyrin(2.1.1) gives structures where the competition between local and global delocalization is distinguished. The aromatic character observed in skeletons strongly depends on the oxidation state of the macrocyclic flanking and is either extended over the whole system or kept as ac omposition of local currents (diatropic and paratropic) of incorporated units. The hybrid systems showt he properties derived from the pconjugations that interlace one another but also showasignificant independence of (aza)acene subunits reflected in the observed spectroscopic properties.

Reductive Dimerization of Macrocycles Activated by BBr3

“…As documented in the 1 H NMR analysis (Figure A), 3 remains locally aromatic according to the magnetic criterion, with a downfield-shifted line of H­(3,20) at δ 8.18. The recorded spectroscopic properties are consistent with rather negligible macrocyclic delocalization compared with other structures of similar size − but also containing pyridine and carbazole . The lack of macrocyclic delocalization is consistent with the presence of the carbonyl linker documented in the 13 C NMR (δ 187.1) that efficiently blocks the delocalization.…”

“…The lack of macrocyclic delocalization is consistent with the presence of the carbonyl linker documented in the 13 C NMR (δ 187.1) that efficiently blocks the delocalization. The final structure shows a strongly downfield-shifted internal proton of the NH group (δ 18.48), proving the proximity of three nitrogen centers and a strong hydrogen bond responsible for the significant deshielding of hydrogen. , The presence of three nitrogen donors in a confined macrocyclic construction similar to triphyrins creates a perfect environment for small cations such as boron­(III). , The reaction of 3 with boron­(III) tribromide (BBr 3 ) in the presence of triethyl amine (Et 3 N), applied as a neutralizing medium, showed the internal variant of reactivity (Scheme , path b ). The LC-MS analysis of the reaction mixture showed an m / z peak at 486.2330, consistent with that of monomeric skeleton 4a with a hydroxy axial ligand isolated in 28% yield.…”

“…The linking of two monomeric macrocycles into covalently bound skeletons was realized via a transition-metal catalyst or with a standard condensation approach . As reported to date, the triheterocyclic/carbocyclic systems linked with carbon bridges form a perfect environment for binding boron­(III), which effectively interacts with carbon or nitrogen but also stabilizes a global effect of antiaromatic delocalization . However, the triangular shape of the macrocyclic environment that is predefined for binding boron­(III) can create different sets of donors very efficiently, utilizing the electron deficiency of the central ion and leading to the intriguing modulation of the final skeleton, while the global delocalization is disturbed and the local influences are crucial. , Following these observations, here we report the studies of the precisely designed and synthesized macrocycle constructed of heterocyclic subunits linked with a carbonyl (CO) unit, showing two reactivities distinguished as internal and peripheral .…”

“…In our approach, we applied Suzuki–Miyaura coupling as a versatile tool for the formation of π-extended molecules, − and it is also applicable for the synthesis of macrocycles . Both required reagents 1 and 2 were obtained as previously described , and subjected to palladium-catalyzed coupling (Scheme , path a ), eventually giving macrocycle 3 in 20% yield.…”

Tropo(thio)ne-embedded homoHPHACs: does the tropylium cation induce global antiaromaticity in expanded hexapyrrolohexaazacoronene?

“…The negative NICS(0) values at points A, F, G, and H of 2 2+ and 3 2+ become larger in their absolute values, which indicates a switch from local to global aromaticity upon oxidation (Table S11 in ESI‡). 10,20…”