A P-P Bond as a Redox Reservoir and an Active Reaction Site

The carbonylation of a nickel(II) anilido species 2 led to the formation of a dinickel(0)-CO complex (P2P-PP2){Ni(CO)}(2) 3 with a P-P bond along with isocyanate generation. In this reaction, the central phosphide moiety of an anionic PPP ligand (PPP-=P-[2-(PPr2C6H4)-Pr-i](2)) acts as a single-electron donor to form a P radical. Alternatively, 3 can be synthesized from the reduction of (PPP)NiCl (1) in the presence of CO; thus, the reaction proceeds by radical coupling of a P-.-Ni-0-CO species. The reverse reaction occurred to generate 1 when 3 was treated with AgCl. Since the P-P bond is light-sensitive, its homolysis is possible and was explored by EPR spectroscopy and DFT analysis. Finally, various bond-activation reactions of 3 occurred under visible-light conditions, thus indicating that a P-P bond can act as an active reaction site.