Signet-Ring-Shaped Octaphosphorus-Cobalt Complexes: Synthesis, Structure, and Functionalization Reactions with Carbene Analogs.

White phosphorus activation with low-valent metal species has proved to be very effective in converting P into small P-containing molecules with ≤ 4. Much less developed are metal-mediated P-coupling reactions that can yield selectively large polyphosphorus clusters. Herein, we report P-activation reactions with three-coordinate -heterocyclic carbene(NHC)-cobalt(0)-alkene complexes, which produce the P complexes of cobalt [(NHC)Co(μ-η:η-P)] (NHC = 1,3-dimesitylimidazol-2-ylidene (IMes), ; 1,3-bis(2,6-diethylphenyl)imidazol-2-ylidene (IDep), ) in high yields. The P ligand in and exhibits a signet-ring type structure that was predicted by theoretical study but has never been obtained in synthetic molecules. Theoretical studies suggest that [(NHC)Co(μ-η:η-P)] is best described as a Co-[P]-Co complex featuring a Co-Co σ-bond and discernible Co-to-P back-donation. By treating with -heterocyclic silylene, phosphinidene precursor, organic azides, and NHCs, complex was transformed into [(IMes)Co(μ-η:η-PX)] (X = 1,3-bis(-butyl)-1,3-diaza-2-silacyclopent-4-en-2-ylidene, ; PNMe, ), [(IMes)Co(σ:(μ-η:η)-RNPPP)] (R = SO-CH--Me, ; C(CF)Ph, ), and [(IMes)Co(μ-η:η-PP(IPr))(μ-η:η-P)] (), respectively. Complexes - can be viewed as the adducts of with the corresponding carbene analogous SiR, PR, NR, and CR, but their core structures are distinct. Under similar conditions, white phosphorus is inert toward these reagents. These cage functionalization reactions showcase the enhanced reactivity of the P ligand in [(NHC)Co(μ-η:η-P)] over that of P, and indicate the amphiphilicity of the P ligand toward electrophiles and nucleophiles.