Nickel(II) bis(diphenylphosphino)amide: Redox-coupling of dppa ligands in coordination sphere of Ni 2+ and some other properties

Abstract

The reactions of Ni II[(PPh 2) 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(Ph 2P N PPh 2 PPh 2 NPPh 2) ( 4). The nickel atom in 4 has a tetrahedral coordination and is incorporated into the NiP 4N 2 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 (SO 2)Ni II[(PPh 2) 2N] 2. The reaction of 2 with allyl bromide runs as alkylation of dppa ligand to form All-N(PPh 2) 2NiBr 2. The reduction of 2 with metallic sodium in THF gives Ni(0) complex, HN(PPh 2) 2Ni(Ph 3P) 2 ( 7). The electrochemical reduction of 2 in CH 2Cl 2 takes place in two steps: reversible one-electron and quasi-reversible three-electron step.