Craig-Type Möbius Aromaticity and Antiaromaticity in Dimetalla[10]annulenes: A Metal-Induced Yin-and-Yang Pair

Aromaticity, one
of the most fundamental concepts in chemistry,
can be classified as Hückel- and Möbius-type according
to the electron count and topology. In comparison with numerous Hückel
aromatics containing 4n+2 π-electrons, Möbius
aromatics with 4n π-electrons, especially the
Craig-type species are particularly limited. Herein we demonstrate
that the recently synthesized dimetalla[10]­annulenes could be Möbius
aromatic or antiaromatic although the organic prototype [10]­annulene
is nonaromatic due to the nonplanarity caused by the steric repulsion
of two CH groups, suggesting the first example of yin-and-yang pair
with Craig-type Möbius (anti)­aromaticity. Further study suggests
that the lithium atoms in dimetalla[10]­annulenes are not spectator
cations but play an important role in the aromaticity switch of these
species due to their bonding interaction with the diene moieties.
Our findings highlight the magic power of metals in the achievement
of Craig-type Möbius aromatics, thus opening an avenue to such
novel aromatics.