Nickel(II) and nickel(0) complexes of bis(diisopropylphosphino)amine: Synthesis, structure, and electrochemical activity

• Preparation of Ni complexes containing neutral HN(PiPr)2 (HL) ligands.
• Crystal structures of Ni-HL complexes.
• Electrochemical reduction of CO2 using [(HL)2Ni]X2 (X = BF4, NO3, ClO4).

In its neutral state, bis(diisopropylphosphino)amine HL reacts in equimolar amounts with the nickel halides NiCl2·6H2O, NiBr2, and NiI2 in ethanol solutions to give the air- and moisture-stable P,P-chelated complexes (HL)NiX2 (X = Cl, Br, I). Under similar conditions, complexes of the form [(HL)2Ni]X2 (X = BF4, NO3, ClO4) were prepared from 2:1 ligand-metal ratios of Ni(BF4)2·6H2O, Ni(NO3)2·6H2O, or Ni(ClO4)2·6H2O. Deprotonation of the ligand with NaNH2 followed by reaction with NiI2 gives L2Ni when performed in Et2O, but leads to the co-crystal L2Ni·2[NCCHC(Me)NH2] when the solvent is acetonitrile. In addition to these Ni2+ compounds, the Ni0 complex (HL)2Ni can be prepared from a toluene solution of Ni(cod)2. Each complex has been characterized by a combination of IR and multi-nuclear NMR spectroscopies, as well as single-crystal X-ray diffraction. Electrochemical studies of the complexes revealed irreversible decomposition of the (HL)NiX2 (X = Cl, Br, I) series, but electrocatalytic CO2 reduction by the [(HL)2Ni]X2 (X = BF4, NO3, ClO4) compounds.

Bis(diisopropylphosphino)amine (HL) reacts with NiX2 (X = Br, I) and NiX2·6H2O (X = Cl, BF4, NO3, ClO4) to form P,P-chelated complexes (HL)NiX2 (X = Cl, Br, I) and [(HL)2Ni]X2 (X = BF4, NO3, ClO4), each of which was crystallographically characterized. Electrocatalytic reduction of CO2 was observed for each of the latter set of compounds.Figure optionsDownload as PowerPoint slide