Metal-ligand cooperation (MLC) is currently receiving much attention as a novel synthetic methodology to expand the role of transition metals in organometallic reactions. The ligand in MLC delivers necessary electron, proton and/or a functional group to assist metal. Although non-innocent phosphine ligands are relatively rare, our group reported a new type of metal-ligand cooperation with an anionic PPP ligand (PPP– = –P[2-PiPr2-C6H4]2). In this system, the reversible phosphide/phosphinite interconversion of a PPP ligand is coupled with a 2-electron redox change of nickel (II and 0). To study the reversible formation of a P-N bond, divalent nickel amide species (PPP)Ni-NHR with two different amido groups (–NHMes and –NTol2) were prepared. A 2-electron reduction of a nickel(II) ion coupled with a P-N bond generation was successfully achieved by adding CO(g) to the solution of (PPP)Ni-NTol2 (Figure 1, left). In the case of (PPP)Ni-NHMes, the formation of a dimeric nickel(0) species, {(PPP)NiCO}2 was, however, observed from the carbonylation of (PPP)Ni(NHMes) (Figure 1, right). By coordination of CO(g), the P-P bond formation occurs with the reduction of a nickel(II) ion revealing a PPP ligand is responsible for a 1-electron transfer process. Details of reaction pathways and reactivity of {(PPP)NiCO}2 will be discussed in this presentation.

P-P bond employed in metal-ligand cooperation as an active 1-electron reservoir

256th National Meeting (2018)

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