Stoichiometric sensitivity and structural diversity in click-active copper(I) N,S-heterocyclic carbene complexes

A series of novel Cu(I) N, S-heterocyclic carbene (NSHC) complexes [Cu(mu-Br)(NSHC)](2), [Cu(mu-X)(NSHC)](4) (X = Br or I), [(NSHC)(2)Cu(mu-Br)(2)Cu(NSHC)], and [(NSHC)(2)CuBr] have been isolated from in situ generated (CuOBu)-Bu-t and N-substituted benzothiazolium halides and characterized by X-ray crystallography. Five structural motifs were observed, viz. MxLy where x : y = 2 : 2, 4 : 4, 2 : 3, 1 : 2 and 2 : 4, with Cu center dot center dot center dot Cu separation traversing over a wide range of 2.5626(7) to 3.4725(7) angstrom distances. A preliminary investigation of the catalytic activity of these compounds indicated that the unusual mononuclear complex 6[(NSHC)(2)CuBr] is an active catalyst for the Huisgen 1,3-dipolar cycloaddition of azide and alkynes while complexes 1-5 and 7 were marginally less active.