Abstract

Metallabenzynes are derived from formal substitution of one of the carbyne carbons in o-benzyne by an isolobal 14-electron transition metal complex fragment. These complexes have attracted considerable attention because of their unexpectedly higher stability comparing with organic benzyne. In the past two decades, a number of metallabenzynes have been reported, and their reactivity has been investigated. However, all reported examples of metallabenzynes contain substituent group(s), and the unsubstituted (or parent) metallabenzyne is still unknown. We herein report the synthesis of the first example of unsubstituted osmabenzyne OsCl2(PPh3)2(C5H4), from the reaction between OsCl2(PPh3)3 and an alkyne-functionalized phosphorous ylide. This osmabenzyne was found to be active towards electrophilic substitution and nucleophilic addition reactions, with regioselectivity determined by the molecular orbital composition of its frontier orbitals.