Stabilization of a Diphosphagermylene through pπ-pπ Interactions with a Trigonal-Planar Phosphorus Center

N-Heterocyclic carbenes and their heavier homologues are, in part, stabilized by delocalization of the N lone pairs into the vacant p-orbital at carbon (or a heavier Group 14 element center). These interactions are usually absent in the corresponding P-substituted species, owing to the large barrier to planarization of phosphorus. However, judicious selection of the substituents at phosphorus has enabled the synthesis of a diphosphagermylene, [(Dipp)2P]2 Ge, in which one of the P centers is planar (Dipp=2,6-diisopropylphenyl). The planar nature of this P center and the correspondingly short P-Ge distance suggest a significant degree of P-Ge multiple bond character that is due to delocalization of the phosphorus lone pair into the vacant p-orbital at germanium. DFT calculations support this proposition and NBO and AIM analyses are consistent with a Ge-P bond order greater than unity.