Occurrence of Double Bond in π-Aromatic Rings: An Easy Way to Design Doubly Aromatic Carbon-Metal Structures.

Nikolay V Tkachenko,Alvaro Muñoz-Castro,Alexander I Boldyrev

doi:10.3390/molecules26237232

Abstract

A chemical bonding of several metallabenzenes and metallabenzynes was studied via an adaptive natural density partitioning (AdNDP) algorithm and the induced magnetic field analysis. A unique chemical bonding pattern was discovered where the M=C (M: Os, Re) double bond coexists with the delocalized 6c-2e π-bonding elements responsible for aromatic properties of the investigated complexes. In opposition to the previous description where 8 delocalized π-electrons were reported in metallabenzenes and metallabenzynes, we showed that only six delocalized π-electrons are present in those molecules. Thus, there is no deviation from Hückel’s aromaticity rule for metallabenzynes/metallabenzenes complexes. Based on the discovered bonding pattern, we propose two thermodynamically stable novel molecules that possess not only π-delocalization but also retain six σ-delocalized electrons, rendering them as doubly aromatic species. As a result, our investigation gives a new direction for the search for carbon-metal doubly aromatic molecules.

Highlights

Occurrence of Double Bond in Keywords: aromaticity; double-aromaticity; metallabenzynes; Hückel’s aromaticity rule π-Aromatic Rings: An Easy Way to Design Doubly Aromatic
To model the synthesized rhenium and osmium complexes (Figure 1f–h), we replaced bulky Ph3 P- and PhMe2 P- groups with a PH3 - ligand, while we preserve all atoms in the aromatic rings as they are in the experimental structure
To ensure that the constructed single-determinant singlet wavefunction can be applied in those cases, we checked the stability of the wave function (WF) showing the absence of any RKS to UKS instabilities

Summary

Introduction

Occurrence of Double Bond in Keywords: aromaticity; double-aromaticity; metallabenzynes; Hückel’s aromaticity rule π-Aromatic Rings: An Easy Way to Design Doubly Aromatic. Since the pioneering work of Thorn and Hoffmann investigating the delocalization in metallocycles [1], and a consequent isolation of osmebenzene by Roper et al [2], a huge variety of metalla-aromatic structures have been discovered experimentally and studied computationally [3,4,5,6,7,8,9]. Those species can be described as usual aromatic compounds where one or several carbon atoms are replaced with a transition metal atom. Only two delocalized orbitals have the Hückel character, while another two orbitals (where the dyz orbital participates in delocalization) have the Möbius character [46] for which

Methods

Results

Conclusion