Copper(I) complexes with N-(2-quinolinylmethylene)-1, 5-dimethyl- 2-phenyl-1-pyrazole-3-(2H)-one and phosphine as ligands: Effective catalyst for Sonogashira cross-coupling reaction

Abstract

A new series of copper(I) complexes of the type [Cu(<strong>L</strong>)(PPh₃)₂]X (<strong>1a-c</strong>) and [Cu(<strong>L</strong>)(dppe)]X (<strong>2a-c</strong>) have been prepared by the reaction of Cu(MeCN)₄]X (where X = ClO<img src='http://www.niscair.res.in/jinfo/Subscript4.gif' border=0>, BF<img src='http://www.niscair.res.in/jinfo/Subscript4.gif' border=0> and PF<img src='http://www.niscair.res.in/jinfo/Subscript4.gif' border=0>) with N-(2-quinolinylmethylene)-1,5-dimethyl-2-phenyl-1-pyrazole-3-(2H)-one (<strong>L</strong>) in presence of triphenylphosphine (PPh₃) or 1,2-bis(diphenylphosphino)ethane (dppe) as an ancillary ligand. The UV-visible spectra indicate that, the ancillary phosphine ligands significantly perturb the MLCT state of copper(I) complexes. The thermally stable <strong>1a-c</strong> and <strong>2a-c</strong> complexes exhibit quasireversible redox behaviour corresponding to Cu(I)/Cu(II) couple. All complexes are tested as catalyst for Sonogashira cross-coupling of phenylacetylene with aryl iodide. The results show that all complexes worked as an effective catalyst at low temperature yielding substituted aryl alkynes as a product. The nature of phosphine ligands and size of counter anions shows marked effect on catalytic properties of all the complexes.