Synthesis and characterization of nickel-N-heterocyclic carbenes linked to a calix[6]arene platform and their applications in Suzuki-Miyaura cross-coupling catalysis

Abstract

The synthesis and catalytic activity of a series of tris-half sandwich cyclopentadienyl nickel (II) N-heterocyclic carbene (NHC) complexes, that have approximate C3 symmetry, is described. The molecules consist of [Ni(NHC)BrCp] groups (Cp = η-C5H5) in which the NHC ligand is grafted on to the lower rim of a 1,3,5 trimethoxy p-tert butylcalix [6] arene via methylene spacers. These species are all synthesized from 1,3,5-trimethoxy-2,4,6 tris-substituted imidazolium tribromide salts via reactions with nickelocene. All complexes were fully characterized by 1H and 13C NMR spectroscopy and by mass spectrometry. Their catalytic activity in the Suzuki-Miyaura cross coupling reaction was probed.