Phosphagermylenylidenes
(R–PGe), as heavier analogs
of isonitriles, whether in their free state or as complexes with a
Lewis base, have not been previously identified as isolable entities.
In this study, we report the synthesis of a stable monomeric phosphagermylenylidene
within the coordination sphere of a Lewis base under ambient conditions.
This species was synthesized by Lewis base-induced dedimerization
of a cyclic phosphagermylenylidene dimer or via Me3SiCl
elimination from a phosphinochlorogermylene framework. The deliberate
integration of a bulky, electropositive N-heterocyclic boryl group
at the phosphorus site, combined with coordination stabilization by
a cyclic (alkyl)(amino)carbene at the low-valent germanium site, effectively
mitigated its natural tendency toward oligomerization. Structural
analyses and theoretical calculations have demonstrated that this
unprecedented species features a PGe double bond, characterized
by conventional electron-sharing π and σ bonds, complemented
by lone pairs at both the phosphorus and germanium atoms. Preliminary
reactivity studies show that this base-stabilized phosphagermylenylidene
demonstrates facile release of ligands at the Ge atom, coordination
to silver through the lone pair on P, and versatile reactivity including
both (cyclo)addition and cleavage of the PGe double bond.