Synthesis and structural features of a series of Cu(i) furan-2-thiocarboxylate complexes: efficient “click” catalysts for the synthesis of glycoconjugates and glycocluster

Abstract

Cu(I) furan-2-thiocarboxylate complexes [(PPh₃)₂Cu(fCOS)₂] (1), [(PPh₃)₂Cu(fCOS)₂·H₂O] (2), [(dppf)Cu(fCOS)·CH₃CN] (3), [(PPh₃)₃Cu₂(μ-fCOS)(μ-Cl)] (4), and [(dppee)Cu(μ-fCOS)]₂ (5) (where dppee = 1,1′-bis(diphenylphosphinoethene), dppf = 1,1′-bis(diphenylphosphinoferrocene), fCOS⁻ = furan-2-thiocarboxylate ion) have been synthesized. The complexes have been structurally characterized by single-crystal X-ray diffraction analysis and spectroscopic techniques. In the solid state, the coordination geometry around the Cu(I) center is distorted trigonal pyramidal in cases 1 and 2, whereas, the Cu(I) center has trigonal planar geometry in case 3. However, in case 4, the complex forms an unsymmetrical dimer in which one copper center has tetrahedral geometry and the other copper has trigonal planar coordination geometry. Complex 5 is an approximately symmetrical dimer possessing two Cu(I) centers, both of which are in an tetrahedral environment. The catalytic activities of all the complexes have been studied. It was found that complex 1 is a good catalyst in azide–alkyne cycloaddition “click” reactions and could be magnificently utilized for the synthesis of a glycocluster (7j). The general applicability of complex 1 as a catalyst for the regioselective synthesis of a series of glycoconjugate triazoles (7a–7i) has also been evaluated. It has been found that complex 1 is an excellent catalyst that does not require a base and efficiently works at room temperature in a short time.