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

The reactions of chlorogermylene M s Fluind t Bu -GeCl 1 , supported by a sterically encumbered hydrindacene ligand M s Fluind t Bu , with NaPCO(dioxane) 2.5 and NaAsCO(18- c -6) in the presence of trimethylphosphine afforded trimethylphosphine-stabilized germylidenyl-phosphinidene 2 and -arsinidene 3 , respectively. Structural and computational investigations reveal that the Ge-E' bond (E' = P and As) features a multiple-bond character. 2 and 3 exhibit diverse reactivity toward trimethylsilylacetylene and 4-tetrabutylphenylacetylene. Specifically, 2 underwent cycloadditions with both alkynes affording the first six-membered aromatic phosphagermabenzen-1-ylidenes 4 and 5, respectively, through the heavier isocyanide intermediate M s Fluind t Bu -PGe. In contrast, 3 could serve as a synthetic equivalent of heavier isocyanides and nitriles when treated with trimethylsilylacetylene and 4-tetrabutylphenylacetylene yielding arsagermene 6 and arsolylgermylene 7 , respectively. The reaction mechanisms for the cycloadditions were investigated through density functional theory calculations. The reactivity studies highlight the potential of 2 and 3 in accessing heavy main-group element-containing heterocycles.