New organometallic Schiff-base copper complexes as efficient "click" reaction precatalysts

A new ferrocenyl-containing unsymmetrical Cu^II-Schiff-base complex, 2, and its covalently poly(methyl) (methacrylate) (PMMA)-grafted counterpart 3 were synthesized and characterized using elemental analysis, electrospray ionisation (ESI) mass spectrometry for 2, and FT-IR spectroscopy. New complex 3 was employed as a precatalyst in the copper-catalyzed [3+2] cycloaddition of organic azides to alkynes (CuAAC, "click" reaction). The active Cu^I species generated from only 0.2 mol% of Cu^II precatalyst 2 and sodium ascorbate displayed high activity at room temperature in ethanol for 24 hours allowing the synthesis of a wide variety of 1,4-disubstituted 1,2,3-triazoles in high isolated yields. The PMMA-supported catalyst 3 is also efficient and has been reused at least three times in these "click" reactions without any loss of activity or copper leaching.