Syntheses And Characterizations Of Fused Rhena-2-Benzopyrylium

As the new type of aromatic system,fused heterometallaaromatics have unique optical and electrical properties.Therefore they have potential application value in the fields of biomedicine,optoelectronic materials,etc,with attracting the attention of researchers for many years.Fused heterometallaaromatics can be generally divided into two categories:metallabenzenes and metallapentalynes.Experimental results and theoretical studies have shown that both metallabenzenes and metallapentalynes have good aromatic properties.The metallaoxabenzene is an important part of the metallabenzenes,while there are only few studies on it.After successfully constructing the first metallaoxabenzene,iridapyrylium complex in1997,other metallaoxabenzene complexes have not been reported.In this paper,we herein repored the constructions of metallapyryliums with the rhenium atom as the metal center.Rhenium and iridium are in the same period of the periodic table.The synthetic route is as follows:first,ReCl₃(PPh₂Me)₃(compound 2-1)and organic substrates:o-ethynyl aromatic ketone(compounds 2-3)and o-ethynyl aromatic aldehydes(compounds 2-5,2-7,2-9)were prepared according to previous reports.Then,products 2-10,2-11 2-12 and 2-13 were prepared from simple one-pot reactions of ReCl₃(PPh₂Me)₃ with organic substrates,using tetrahydrofuran as the reaction solvent,heating at 60^oC for 1 hour.The products were characterized by nuclear magnetic resonance,x-ray diffraction of single crystal etc,and structures of the products were proved to contain rhenapyrylium and rhenacyclopropene units.On the base of the successful construction of fused rhenapyrylium,this work further explored its aromaticity.The structure and reactivity of the products were studied experimentally first,the results showed that the atoms in the rhenapyrylium unit are closed to coplanar and the bond lengths tend to be equal.The bond distance of C–O is between single bond and double bond.The bond distance of Re–C is much shorter than Re=C bonds in rhenabenzene complexes,and is slightly shorter than those in rhenacyclopropene complexes.In addition,the products have a good stability with a poor activity of electrophilic substitution reactions and cycloaddition reactions.In terms of theoretical calculations,the nuclear independent chemical shift(NICS),aromatic stabilization energy(ASE)and anisotropy of the induced current density(AICD)of the product model were calculated,the results show that rhenacyclopropene unit has?-aromaticity,while rhenapyrylium unit has?-aromaticity.Finally,this work also tested the ultraviolet-visible absorption spectrums of the products,and achieved a preliminary understanding of the optical properties of these.