(L)₂ C₂ P₂ : Dicarbondiphosphide Stabilized by N-Heterocyclic Carbenes or Cyclic Diamido Carbenes

Carbon phosphides, C_n P_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)₂ C₂ P₂ with diverse structures. The use of imidazolylidenes as ligands L give complexes with a central four-membered ring C₂ P₂ , while more electrophilic cyclic diamidocarbenes (DAC) give a compound with an acyclic π-conjugated CP-PC unit. Cyclic C₂ P₂ compounds are best described as non-Kekulé molecules that are stabilized by coordination to the NHC ligands NHC→(C₂ P₂ )←NHC. These species can be easily oxidized to give stable radical cations [(NHC)₂ C₂ P₂ ]^+. . The remarkably stable molecules with an acylic C₂ P₂ core are best described with electron-sharing bonds (DAC)=C=P-P=C=(DAC).