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Bonding and Diels–Alder reactions of substituted 2‑borabicyclo(1.1.0)

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Vol.:(0123456789)13TheoreticalChemistryAccounts(2019)138:106https://doi.org/10.1007/s00214-019-2491-5REGULARARTICLEBondingand Diels–Alderreactionsof substituted2‑borabicyclo(1.1.0)but‑1(3)‑enes:a theoreticalstudyCongjie Zhang1 ·Zhimin Wang1 ·Jinshuai Song2 ·Chunsen Li2 ·Yirong Mo3Received:16May2019/Accepted:31July2019/Publishedonline:24August2019©Springer-VerlagGmbHGermany,partofSpringerNature2019AbstractSubstituted2-borabicyclo(1.1.0)but-1(3)-enes(2BB’s)areakindofnovelmoleculeswithinvertedcarbon–carbonbondswhoseordersrangebetweenoneandtwo.ConsideringthesignificantinterestintheDiels–Alder(D–A)reactionsofsubsti-tutedcyclopropenes,herewestudiedthebondingandD–Areactionsof24substituted2BBmoleculesattheB3LYP-D3/6-311G**theoreticallevel.ComputationsshowedthattheinvertedC=Cbondlengthsfallintherangeof1.46–1.50 Åand2BBisofsignificantcharacteristicofasingletbiradicalwithtwoσsingleelectronsandπaromaticconjugationoverthethree-memberedrings.Yetab initiovalencebondcomputationsshowedthattheinvertedbondsarecharge-shifted,andtheionicresonancestructuresarisingfromcharge-shiftingareofcarbenecharacteristicsaswell.Thus,substituted2BB’scanalsobeconsideredasB-heterocycliccarbenes.SincetheLUMOsofthe2BBderivativesaresimilartothoseofetheneandcyclopropene,westudiedtheirD–Areactionswithbutadiene.Allcycloadditionreactionskineticallyandthermodynamicallyfavortheformationofthederivativesof7-bora-oct-3-ene[4.1.1]propellaneundergoingendotransitionstates.Notably,thereisagoodcorrelationbetweenthereactionbarrie

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