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 oneelectron reduction to yield compounds of the type (L) 2 C 2 P 2 with diverse structures. The use of imidazolylidenes as ligands L give complexes with a central four-membered ring C 2 P 2 , while more electrophilic cyclic diamidocarbenes (DAC) give a compound with an acyclic p-conjugated CPÀPC unit. Cyclic C 2 P 2 compounds are best described as non-KekulØ molecules that are stabilized by coordination to the NHC ligands NHC! (C 2 P 2 ) ! NHC. These species can be easily oxidized to give stable radical cations [(NHC) 2 C 2 P 2 ] + C. The remarkably stable molecules with an acylic C 2 P 2 core are best described with electron-sharing bonds (DAC)=C=PÀP=C=(DAC).Carbonnitridewasmentionedas"melon"byLiebigasearly as 1834, [1] and graphitic carbon nitride, g-C 3 N 4 , in particular was found in recent years to be a material with outstanding properties for catalytic, optical, electronic, and mechanical applications.[2] Relatively little is known about related carbon phosphides, C n P m . Calculations predict that these materials are highly promising high-performance materials for electronics and optoelectronics.[3] Physical doping of the diamond lattice with phosphorus [4] or chemical vapor deposition methods from the gas phase using CH 4 /PH 3 mixtures [5] have been used to produce amorphous films of C n P m with variable composition n and m. Molecules of the composition CP, C 2 P, and C 2 P 2 have been generated in the diluted gas-phase and were spectroscopically characterized [6a-c] and investigated by quantum-chemical methods.[6d,e] Among the calculated fifteen stable isomers, which have linear, bent, cyclic, or bicyclic structures, the isomers A and B are the most stable (Scheme 1). Interestingly, other "classical" linear isomers, known for molecules of composition C 2 N 2 , are highly unstable and do not represent minima on the energy hypersurface.To the best of our knowledge, molecules of composition C 2 P 2 have never been isolated as pure materials and are also unknown as ligands in metal complexes. All attempts failed to synthesize cubic C 24 P 8 and C 54 P 8 with P À C C À P and P À C C À CCÀP units, which should show a high degree of cyclic electron delocalization.[7a] Only some precursor molecules such as metal CP complexes were obtained. [7b,c] N-heterocyclic carbenes (NHCs) can be used to stabilize small molecules that are too reactive to be isolated.[8] Herein we report the synthesis of dicarbondiphosphides, (L) 2 C 2 P 2 , which are stabilized by two L = NHC or cyclic diamidocarbene (L = DAC) units. The cyclic isomers can easily be oxidized to their stable radical cations. Furthermore we report on the complex, (DAC)CP-CP(DAC), which contains the elusive bis(isophosphanitrile), DC = P À P = CD, in the core. Scheme 1. Selected isomers of neutral C 2 P 2 species. The i...
