Synthesis, Characterisation and Reactions of Truly Cationic NiI–Phosphine Complexes

: The recently published purely metallo-organic NiI salt [Ni(cod)2 ][Al(ORF )4 ] (1, cod=1,5-cyclooctadiene, RF =C(CF3 )3 ) provides a starting point for a new synthesis strategy leading to NiI phosphine complexes, replacing cod ligands by phosphines. Clearly visible colour changes indicate reactions within minutes, while quantum chemical calculations (PBE0-D3(BJ)/def2-TZVPP) approve exergonic reaction enthalpies in all performed ligand exchange reactions. Hence, [Ni(dppp)2 ][Al(ORF )4 ] (2, dppp=1,3-bis(diphenylphosphino)propane), [Ni(dppe)2 ][Al(ORF )4 ] (3, dppe=1,3-bis(diphenyl-phosphino)ethane), three-coordinate [Ni(PPh3 )3 ][Al(ORF )4 ] (4) and a remarkable two-coordinate NiI phosphine complex [Ni(PtBu3 )2 ][Al(ORF )4 ] (5) were characterised by single crystal X-ray structure analysis. EPR studies were performed, confirming a nickel d9 -configuration in complexes 2, 4 and 5. This result is supported by additional magnetization measurements of 4 and 5. Further investigations by cyclic voltammetry indicate relatively high oxidation potentials for these NiI compounds between 0.7 and 1.7 V versus Fc/Fc+ . Screening reactions with O2 and CO gave first insights on the reaction behaviour of the NiI phosphine complexes towards small molecules with formation of mixed phosphine-CO-NiI complexes and oxidation processes yielding new NiI and/or NiII derivatives. Moreover, 4 reacted with CH2 Cl2 at RT to give a dimeric NiII ylide complex (4 c). As CH2 Cl2 is a rather stable alkyl halide with relatively high C-Cl bond energies, 4 appears to be a suitable reagent for more general C-Cl bond activation reactions.