Hand in Hand: Experimental and Theoretical Investigations into the Reactions of Copper(I) Mono‐ and Bis(guanidine) Complexes with Dioxygen

Abstract

Mono‐ and bis(guanidine) ligands stabilise bis‐µ‐oxido dicopper(III) complexes. Here, the formation of these complexes has been investigated in detail by means of low‐temperature stopped‐flow techniques for the monoguanidine 2‐[3‐(dimethylamino)propyl]‐1,1,3,3‐tetramethylguanidine (TMGdmap) and the related bis(guanidine) 1,3‐bis(N,N,N′,N′‐tetramethylguanidino)propane (btmgp). Low‐temperature IR studies in solution support the formation of bis‐µ‐oxido complexes. For both systems, no intermediates on the pathways to the bis‐µ‐oxido complexes could be detected; this has been explained through extensive DFT calculations. In the first step, the oxygen reduction during the binding to the copper(I) complex to form a superoxido species was studied. In the second step, the full path from superoxido through trans‐µ‐peroxido to side‐on peroxido and finally bis‐µ‐oxido was modelled for singlet and triplet states. Hereby, a clear picture of the detailed reaction mechanism, which directly correlates with the observed activation enthalpies and reaction orders, was gained. The superoxido formation is rate‐determining as pseudo‐first order in copper(I) although the bis‐µ‐oxido formation is observed. The results illustrate the strength of density functional theory for the prediction of the reactivity of real‐life systems.