Probing Hyperconjugative Aromaticity of Monosubstituted CyclopentadienesSubmitted by Jun Zhu on Fri, 01/11/2019 - 20:13
Hyperconjugation and aromaticity are two of the most important concepts in chemistry. Mulliken and co‐workers combined both terms to explain the stability of cyclopentadiene. Here, we carried out DFT calculations on a series of mono‐ and disubstituted cyclopentadiene derivatives to investigate their hyperconjugative aromaticity. Our results revealed that one electropositive substituent can induce aromaticity, whereas one electronegative substituent prompts nonaromaticity rather than antiaromaticity.
σ‐Aromaticity in a Fully Unsaturated RingSubmitted by Jun Zhu on Tue, 11/06/2018 - 21:55
Aromaticity is one of the most fundamental and fascinating chemical topics, attracting both experimental and theoretical chemists owing to its many manifestations. Both σ‐ and π‐aromaticity can be classified depending on the character of the cyclic electron delocalization. In general, σ‐aromaticity stabilizes fully saturated rings with σ‐electron delocalization whereas the traditional π‐aromaticity describes the π‐conjugation in fully unsaturated rings.
Nickel Complexes with Non‐innocent Ligands as Highly Active Electrocatalysts for Hydrogen EvolutionSubmitted by Jun Zhu on Tue, 11/06/2018 - 08:51
Rational design of a molecular catalyst for a hydrogen evolution reaction (HER) with both high rates and low overpotential remains a challenge. Here we report a series of Ni‐based catalysts incorporating non‐innocent ligands and aimed at reduction of the overpotential by reserving electrons in the ligand, which could decouple the correlation between metal center reduction and metal hydride formation.
Probing the Strongest Aromatic Cyclopentadiene Ring by HyperconjugationSubmitted by Jun Zhu on Wed, 09/12/2018 - 07:51
Hyperconjugation, an interaction of electrons in a σ orbital or lone pair with an adjacent π or even σ antibonding orbital, can have a strong effect on aromaticity. However, most work on hyperconjugative aromaticity has been limited to main-group substituents. Here, we report a thorough density functional theory study to evaluate the aromaticity in various cyclopentadienes that contain both main-group and transition-metal substituents.
An isolable catenane consisting of two Möbius conjugated nanohoopsSubmitted by Jun Zhu on Sat, 09/01/2018 - 16:57
Besides its mathematical importance, the Möbius topology (twisted, single-sided strip) is intriguing at the molecular level, as it features structural elegance and distinct properties; however, it carries synthetic challenges. Although some Möbius-type molecules have been isolated by synthetic chemists accompanied by extensive computational studies, the design, preparation, and characterization of stable Möbius-conjugated molecules remain a nontrivial task to date, let alone that of molecular Möbius strips assembling into more complex topologies.
Probing the Most Aromatic and Antiaromatic Pyrrolium Rings by Maximizing Hyperconjugation and Push–Pull EffectSubmitted by Jun Zhu on Sat, 09/01/2018 - 16:45
Hyperconjugation, a weak interaction in organic chemistry, can have a strong effect on aromaticity, leading to the concept of hyperconjugative aromaticity, which was first proposed by Mulliken in 1939. However, most studies are limited to main group chemistry. Here we report the most aromatic and antiaromatic pyrrolium ring by maximizing the hyperconjugation caused by transition metal fragments and the push–pull effect.
Predicting an unconventional facile route to metallaanthracenesSubmitted by Jun Zhu on Sat, 09/01/2018 - 16:34
Metallaaromatics have attracted considerable interest from both experimentalists and theoreticians since the first prediction of metallabenzenes, in which a CH group is replaced by a transition metal fragment. In comparison with monocyclic metallabenzenes and bicyclic metallanaphthalenes, tricyclic metallaanthracenes are quite less developed. Thus, it is urgent to explore synthetic methods for this rare system. Here we report a thorough investigation on the formation of metallaanthracenes from transition metal fluorenyl complexes via density functional theory calculations.
Isolation of an Eleven‐Atom Polydentate Carbon‐Chain Chelate Obtained by Cycloaddition of a Cyclic Osmium Carbyne with an AlkyneSubmitted by Jun Zhu on Sat, 09/01/2018 - 16:20
Carbon ligands have long played an important role in organometallic chemistry. However, previous examples of all‐carbon chelating ligands are limited. Herein, we present a novel complex with an eleven‐atom carbon chain as a polydentate chelating ligand. This species was formed by the [2+2+2] cycloaddition reaction of two equivalents of an alkyne with an osmapentalyne that contains the smallest carbyne bond angle (127.9°) ever observed. Density functional calculations revealed that electron‐donating groups play a key role in the stabilization of this polydentate carbon‐chain chelate.
Rational Design and Synthesis of Unsaturated Se‐Containing Osmacycles with σ‐AromaticitySubmitted by Jun Zhu on Sat, 09/01/2018 - 16:05
Isolation of the simplest 4π three‐membered heterocycles (1H‐azirine, oxirene, thiirene, and selenirene) remains a big challenge due to their π‐antiaromaticity and significant ring strain. Here we demonstrate that the incorporation of a transition‐metal fragment could stabilize the antiaromatic selenirene and pentalene frameworks simultaneously by density functional theory (DFT) calculations. Experimental verification leads to the Se‐containing metallapolycycles, osmapentaloselenirenes, with remarkable thermal stability.
Adaptive aromaticity in S0 and T1 states of pentalene incorporating 16 valence electron osmiumSubmitted by Jun Zhu on Sat, 09/01/2018 - 15:55
Aromaticity is a fundamental chemical concept of ever-increasing diversity. According to Hückel’s and Baird’s rules, cyclic conjugated species with 4n+2 π-electrons are aromatic in the singlet electronic ground state (S0) and antiaromatic in the lowest triplet state (T1), and vice-versa. Thus, species with aromaticity in both states have not yet been reported.