From a Phosphaketenyl-Functionalized Germylene to 1,3-Digerma-2,4-diphosphacyclobutadiene.

The first 4π-electron resonance-stabilized 1,3-digerma-2,4-diphosphacyclobutadiene [L(H)2Ge2P2] 4 (L(H)=CH[CHNDipp]2 Dipp=2,6-(i)Pr2C6H3) with four-coordinate germanium supported by a β-diketiminate ligand and two-coordinate phosphorus atoms has been synthesized from the unprecedented phosphaketenyl-functionalized N-heterocyclic germylene [L(H)Ge-P=C=O] 2 a prepared by salt-metathesis reaction of sodium phosphaethynolate (P≡C-ONa) with the corresponding chlorogermylene [L(H)GeCl] 1 a. Under UV/Vis light irradiation at ambient temperature, release of CO from the P=C=O group of 2 a leads to the elusive germanium-phosphorus triply bonded species [L(H)Ge≡P] 3 a, which dimerizes spontaneously to yield black crystals of 4 as isolable product in 67% yield. Notably, release of CO from the bulkier substituted [L(tBu)Ge-P=C=O] 2 b (L(tBu)=CH[C((t)Bu)N-Dipp]2 ) furnishes, under concomitant extrusion of the diimine [Dipp-NC((t)Bu)]2, the bis-N,P-heterocyclic germylene [DippNC((t)Bu)C(H)PGe]2 5.