Aluminacyclopropene–phosphine complex: a carbene-exchange reagent

Abstract

N-heterocyclic carbenes (NHCs) are extensively used as auxiliary ligands or organocatalysts thanks to their remarkable stability. However, due to their high structural stability, applications involving skeletal modifications without losing the low-valent nature (carbene exchange reactions) remain extremely rare. We report here that aluminacyclopropene–phosphine complex 1 promotes original “carbene-to-carbene” transformations of stable carbenes. Indeed, the Al(III)–phosphine Lewis pair complex 1, due to its high ring strain, is able to react with NHC 2 to produce a cyclopropenylidene (4), via atomic carbon transfer from the NHC to the η²-coordinated alkyne fragment, within the coordination sphere of the Al(III) center. Moreover, the complex 1 transforms the stable (diamino)cyclopropenylidene 7 into a more reactive acyclic (amino)carbene 8, which has been isolated in crystalline form.