Copper Complexes with Guanidine‐Based Tripodal Ligands and their Reactivity Toward Dioxygen

The copper(I) TMG 3 tren complex (TMG 3 tren = a tris(2‐aminoethyl)amine ligand modified with guanidine groups) reacts with dioxygen exclusively to form a relatively stable end‐on superoxido complex. In contrast, the related copper(I) tmpa complex (tmpa = tris[(2‐pyridyl)methyl]amine) reacts further to generate a dinuclear trans peroxido copper complex. Substitution of one pyridine group in tmpa with a guanidine moiety yields the ligand TMGuns‐penp. The copper(I) complex of this ligand reacts with dioxygen to form a dinuclear trans peroxido copper complex as well; however, in this case, rapid decomposition was observed, unlike the more stable copper tmpa complex. In contrast, substitution of the ethyl‐guanidine group (in TMGuns‐penp) with a propyl‐guanidine group (thus increasing one chelate ring size from 5 to 6) only showed the formation of the end‐on superoxido copper complex (less stable than the copper TMG 3 tren complex) without reacting further to the dinuclear peroxido complex. The ligand TMG 2 apme, in which two of the pyridyl groups of tmpa are replaced by guanidine groups, also supports the formation of only the corresponding end‐on superoxide copper complex. Yet here, too, the stability of this species was significantly lower compared to the parent copper TMG 3 tren complex.