Synthesis and structure of an asymmetric copper(I) dimer with two-coordinate and four-coordinate copper(I) sites

Copper(I) coordination compounds have been studied intensively due to their biological relevance, catalytic properties, and theoretical interests. Numerous mononuclear and polynuclear copper(I) complexes with different coordination numbers have been prepared and characterized. Recently the possible d10-d10 interactions in copper(I) dimers have been the subjects of many experimental and theoretical studies. Among the dimers and even polynuclear complexes, asymmetric ones are rare, especially when the compounds are synthesized from a single copper(I) source. Because of their potential of being selective catalysts and biomimetic models, asymmetric polynuclear complexes are of great interest, and several examples have been reported.3 An example is CuI 2Cl2(PPh3)3 (1), which has both three- and four-coordinate copper(I).4 Herein, we report an unusual asymmetric copper(I) dimer with both 2- and 4-coordinate copper(I) sites (2a and its most important resonance form 2b). 2 is an unusual homobimetallic complex with two isolated donor sets of different coordinate numbers,3d and more importantly it was prepared in a way to not enforce asymmetry, i.e., it self assembles. Hence, asymmetric 2 appears to be more stable than symmetric 3, while our calculations of those of others5 show that 3 is a possible stable structure.