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

The first 4π‐electron resonance‐stabilized 1,3‐digerma‐2,4‐diphosphacyclobutadiene [LH2Ge2P2] 4 (LH=CH[CHNDipp]2 Dipp=2,6‐iPr2C6H3) 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 [LHGe‐P=C=O] 2 a prepared by salt‐metathesis reaction of sodium phosphaethynolate (P≡C−ONa) with the corresponding chlorogermylene [LHGeCl] 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 [LHGe≡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 [LtBuGe‐P=C=O] 2 b (LtBu=CH[C(tBu)N‐Dipp]2) furnishes, under concomitant extrusion of the diimine [Dipp‐NC(tBu)]2, the bis‐N,P‐heterocyclic germylene [DippNC(tBu)C(H)PGe]2 5. Elusive Ge≡P: A 4π‐electron resonance‐stabilized 1,3‐digerma‐2,4‐diphosphacyclobutadiene derivative [LH2Ge2P2] (3; LH=CH[CHN(2,6‐iPr2C6H3]2), could be synthesized, isolated, and structurally characterized. This compound resulted from the phosphaketenyl‐functionalized germylene [LHGe(P=C=O)] (1) through photolytic release of CO and subsequent head‐to‐tail dimerization of the presumed phosphagermyne intermediate, [LHGe≡P] (2).