Huisgen click cycloadditions from a copper(II)-tren precatalyst without external sacrificial reductant

Abstract The copper(II) complex [Cu(C18 6 tren)](Br) 2 , 2 , is an efficient precatalyst for the Huisgen ‘click’ cycloaddtion which can be used at low loading without the requirement of an external sacrificial reductant such as sodium ascorbate. EPR studies support the in situ reduction of 2 by the alkyne to generate a reactive copper(I) catalyst.