Phosphine-Stabilized Germylidenylpnictinidenes as Synthetic Equivalents of Heavier Nitrile and Isocyanide in Cycloaddition Reactions with Alkynes.

The reactions of chlorogermylene MFluind-GeCl , supported by a sterically encumbered hydrindacene ligand MFluind, with NaPCO(dioxane) and NaAsCO(18--6) in the presence of trimethylphosphine afforded trimethylphosphine-stabilized germylidenyl-phosphinidene and -arsinidene , respectively. Structural and computational investigations reveal that the Ge-E' bond (E' = P and As) features a multiple-bond character. and exhibit diverse reactivity toward trimethylsilylacetylene and 4-tetrabutylphenylacetylene. Specifically, underwent cycloadditions with both alkynes affording the first six-membered aromatic phosphagermabenzen-1-ylidenes and respectively, through the heavier isocyanide intermediate MFluind-PGe. In contrast, could serve as a synthetic equivalent of heavier isocyanides and nitriles when treated with trimethylsilylacetylene and 4-tetrabutylphenylacetylene yielding arsagermene and arsolylgermylene , respectively. The reaction mechanisms for the cycloadditions were investigated through density functional theory calculations. The reactivity studies highlight the potential of and in accessing heavy main-group element-containing heterocycles.