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

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. [ABSTRACT FROM AUTHOR]