Striking reactivity of ylide-like germylene toward terminal alkynes: [4+2] cycloaddition versus C-H bond activation.

The isolable ylide-like N-heterocyclic germylene LGe: (2) {L = CH[(C=CH(2))CMe][N(aryl)](2), aryl = 2,6-(i)Pr(2)C(6)H(3)} shows an unprecedented dual reactivity toward terminal alkynes: its reaction with acetylene leads via [4+2] cycloaddition to the novel intramolecular donor stabilised germylene 3, while conversion of phenylacetylene furnishes the analogous cycloadduct 4 along with a C-H bond activation product, the novel N-donor stabilised alkynyl germylene 5.