Diphosphagermylene information

Diphosphagermylenes are a class of compounds containing a divalent germanium atom bound to two phosphorus atoms. While these compounds resemble diamidocarbenes, such as N-heterocyclic carbenes (NHC), diphosphagermylenes display bonding characteristics distinct from those of diamidocarbenes.^[1] In contrast to NHC compounds, in which there is effective N-C p(π)-p(π) overlap between the lone pairs of planar nitrogens and an empty p-orbital of a carbene, systems containing P-Ge p(π)-p(π) overlap are rare. Until 2014, the geometry of phosphorus atoms in all previously reported diphosphatetrylenes are pyramidal, with minimal P-Ge p(π)-p(π) interaction.^[1] It has been suggested that the lack of p(π)-p(π) in Ge-P bonds is due to the high energetic barrier associated with achieving a planar configuration at phosphorus, which would allow for efficient p(π)-p(π) overlap between the phosphorus lone pair and the empty P orbital of Ge.^[1] The resulting lack of π stabilization contributes to the difficulty associated with isolating diphosphagermylene^[2] and the Ge-P double bonds.^[3] However, utilization of sterically encumbering phosphorus centers has allowed for the isolation of diphosphagermylenes with a planar phosphorus center with a significant P-Ge p(π)-p(π) interaction.^[1]