The application of aromaticity and antiaromaticity to reaction mechanisms

Aromaticity,in general,can promote a given reaction by stabilizing a transition state or a product via a mobility ofπelectrons in a cyclic structure.Similarly,such a promotion could be also achieved by destabilizing an antiaromatic reactant.However,both aromaticity and transition states cannot be directly measured in experiment.Thus,computational chemistry has been becoming a key tool to understand the aromaticity-driven reaction mechanisms.In this review,we will analyze the relationship between aromaticity and reaction mechanism to highlight the importance of density functional theory calculations and present it according to an approach via either aromatizing a transition state/product or destabilizing a reactant by antiaromaticity.Specifically,we will start with a particularly challenging example of dinitrogen activation followed by other small-molecule activation,Csingle bondF bond activation,rearrangement,as well as metathesis reactions.In addition,antiaromaticity-promoted dihydrogen activation,CO_(2)capture,and oxygen reduction reactions will be also briefly discussed.Finally,caution must be cast as the magnitude of the aromaticity in the transition states is not particularly high in most cases.Thus,a proof of an adequate electron delocalization rather than a complete ring current is recommended to support the relatively weak aromaticity in these transition states.

Synthesis,Structure and Chemical Bonding of Polyantimony Clusters Containing Coinage Metals[M_(2)Sb_(14)]^(4-)(M=Cu,Ag)

Binary polyantimony clusters,namely[Cu_(2)Sb_(14)]^(4–) and [Ag_(2)Sb_(14)]^(4–),containing coinage metals,were successfully synthesized and characterized,in which two homoatomic Sb73–subunits are bridged by two coinage metals in η^(4):η^(1) and η^(1):η^(1) coordination modes,respectively.In[M_(2)Sb_(14)]^(4-),two bridging Cu ions and two Sb atoms form a planar rhombic unit,which was revealed to have antiaromatic properties by theoretical calculations.Further electron structure and bonding analysis confirmed the presence of delocalized bonds in the rhombic unit and the metallophilic interaction between two formal M^(+) ions.

Progress of Indeno-type Organic Diradicaloids

Organic diradicaloids have unusual open-shell nature and properties and are promising materials for organic electronics,spintronics,energy storage and nonlinear optics.In this review,we focus on indeno-type organic diradicaloids and summarize their molecular design and synthesis,as well as topological structures,open-shell characters and diradical properties.The molecular systems are classified into indenofluorenes and diindenoacenes,indeno-based molecules with one-dimensional,two-dimensional and unique topological structures,and heterocyclic indeno-based molecules.By constructing these various topologicalπ-skeletons with tunable conjugation modes and variation of atomic composition,their key open-shell parameters,such as diradical characters and singlet-triplet energy gaps,along with the optical,electronic and magnetic properties,as well as stabilities are efficiently modulated.More attention may be paid to accurate computational analysis,rational design and synthesis,and novel functions of indeno-type diradicaloids,which will promote the development of radical chemistry and materials.

Recent Advances in Aromatic Antimony Clusters

This paper highlights the compounds containing Sb cluster fragments, either synthesized in the solid-state, discovered from the gas phase, or only theoretically predicted. These Sbn clusters feature unique chemical bonding, fascinating structures, and special stabilities that can be well rational- ized by aromaticity or antiaromaticity. A deep understanding to their electronic structures is essential and will greatly facilitate the experimental synthesis of new Sbn cluster-based materials.