Nickel(II) bis(diphenylphosphino)amide: Redox-coupling of dppa ligands in coordination sphere of Ni2+ and some other properties

The reactions of NiII[(PPh2)2N]2 (2) with various reagents are described. Addition of two moles of carbon monoxide to 2, at 20 °C and atmospheric pressure leads to the redox coupling of dppa ligands and formation of zero-valent nickel complex (CO)2Ni(Ph2Psingle bondNdouble bond; length as m-dashPPh2single bondPPh2double bond; length as m-dashNPPh2) (4). The nickel atom in 4 has a tetrahedral coordination and is incorporated into the NiP4N2 ring adopting a distorted chair conformation with phosphorus–phosphorus bond length 2.2777(5) Å. Contrary to CO, sulphur dioxide reacts with 2 to form simple adduct (SO2)NiII[(PPh2)2N]2. The reaction of 2 with allyl bromide runs as alkylation of dppa ligand to form All-N(PPh2)2NiBr2. The reduction of 2 with metallic sodium in THF gives Ni(0) complex, HN(PPh2)2Ni(Ph3P)2 (7). The electrochemical reduction of 2 in CH2Cl2 takes place in two steps: reversible one-electron and quasi-reversible three-electron step.