Probing the Origin of Challenge of Realizing Metallaphosphabenzenes: Unfavorable 1,2-Migration in Metallapyridines Becomes Feasible in Metallaphosphabenzenes

Metallabenzenes have attracted considerable interest of both theoretical and experimental chemists. However, metallaphosphabenzene has never been synthesized. Thus, understanding the origin of the challenge of synthesizing metallaphosphabenzene is particularly urgent for experimentalists. Now density functional theory (DFT) calculations have been carried out to examine this issue. Our results reveal that the 1,2-migration in metallapyridines is unfavorable whereas such a 1,2-migration in metallaphosphabenzenes is feasible, which can be rationalized by the reluctance of phosphorus to participate in π bonding. In addition, π-donor ligands and the 5d transition metals can stabilize metallaphosphabenzenes. Compared with hydride and methyl migration, the chloride migration has a relatively lower activation barrier due to the polarization of the M=P bond. CO ligand could further decrease the reaction barrier of the migration due to the reduction of the interaction between the metal centre and the phosphorus atom. All of these findings could help synthetic chemists to realize the first metallaphosphabenzene.