(L)₂C₂P₂: Dicarbondiphosphide Stabilized by N-Heterocyclic Carbenes or Cyclic Diamido Carbenes

Carbon phosphides, C_nP_m, may have highly promising electronic, optical, and mechanical properties, but they are experimentally almost unexplored materials. Phosphaheteroallenes stabilized by N-heterocyclic carbenes undergo a one-electron reduction to yield compounds of the type (L)₂C₂P₂ with diverse structures. The use of imidazolylidenes as ligands L give complexes with a central four-membered ring C₂P₂, while more electrophilic cyclic diamidocarbenes (DAC) give a compound with an acyclic π-conjugated CP−PC unit. Cyclic C₂P₂ compounds are best described as non-Kekulé molecules that are stabilized by coordination to the NHC ligands NHC→(C₂P₂)←NHC. These species can be easily oxidized to give stable radical cations [(NHC)₂C₂P₂]^+.. The remarkably stable molecules with an acylic C₂P₂ core are best described with electron-sharing bonds (DAC)=C=P−P=C=(DAC).