Synthesis, characterization and catalytic application of some novel PNP-Ni(II) complexes: Regio-selective [2+2+2] cycloaddition reaction of alkyne

Some novel Ni(II) complexes of PN(H) P-Ph, PN(Me) P-iPr and PN(Me) P-tBu ligands have been synthesized and characterized using standard analytical and spectroscopic methods such as 1H NMR, P-31 NMR, elemental analysis, ESI-MS, UV-Visible spectroscopy and single-crystal X-ray crystallography. In the presence of silver triflate, complex [PN(H) (PNiBr)-Ni-Ph](2)NiBr4 (5) activated the C-Cl bond of dichloromethane at room temperature and afford complex [PN(H) PPhNiCl] OTf (6). We have also performed alkyne [2+2+2] cycloaddition reaction using Ni(II) complexes and observed high regioselectivity of the products. The observed selectivity is well correlating with the electronic feature of alkynes. The [2+2+2] cycloaddition of electron rich alkynes produced 1,3,5-substituted benzene derivatives as a major product whereas the electron deficient alkynes produced 1,2,4-substituted benzene derivatives as a major product. (C) 2017 Elsevier B. V. All rights reserved.