Probing the mechanism of adaptive aromaticity in metallapyridiniums

Abstract

In general, compounds exhibit one-state aromaticity in either the ground or excited state according to the Hückel’s and Baird’s rules. Thus, species with two-state aromaticity in the lowest singlet and...

Adaptive Aromaticity in 18e Metallapentalenes

“…In addition, the M−C bond plays a crucial role in the aromaticity of metallapyridiniums. 28 The iridium complexes 4-S 0 and 6-S 0 exhibit relatively smaller M−C bond orders, 1.018 and 1.008, respectively. Such small bond orders could be one of the factors for their weak π aromaticity in the S 0 state.…”

“…Considering the individual bond orders, the M–C bond exhibits the lowest bond order on the 8MR. In addition, the M–C bond plays a crucial role in the aromaticity of metallapyridiniums . The iridium complexes 4-S 0 and 6-S 0 exhibit relatively smaller M–C bond orders, 1.018 and 1.008, respectively.…”

“…Based on carbolong chemistry, − our group found that 16e osmapentalene could exhibit aromaticity in both S 0 and T 1 states via density functional theory (DFT) calculations and termed such two-state aromaticity as adaptive aromaticity . The unconventional adaptive aromaticity breaks the limits of Hückel’s and Baird’s rules and enables two-state aromaticity, which could be applied to the design of singlet fission materials. − With the development of adaptive aromaticity, more species with the two-state aromaticity have been disclosed, − and most of them are 16e metallapentalenes and derivates (Figure b). In organometallic chemistry, the six-coordinated 18e compounds are thermodynamically more stable than other complexes according to the 18-electron rule .…”

NO-induced adaptive antiaromaticity in cyclobutadiene

“…In 2004, Ottosson and coworkers disclosed some "aromatic chameleons" with a tendency to show aromaticity in two states. 20 Later, our group and Baranac-Stojanović and coworkers reported a few remarkable examples of compounds i.e., metallapentalenes, 21 metallapyridiniums 22 tetraatomic boron species, 23 and substituted benzene 24 showing adaptive aromaticity through ligand or substituent regulation. Despite this major progress, compounds with adaptive antiaromaticity are particularly rare.…”