Bidentate guanidine ligands with ethylene spacer in copper-dioxygen chemistry: Structural characterization of bis(μ-hydroxo) dicopper complexes

The syntheses of the aliphatic bidentate guanidine–amine-hybrid ligands DMEGdmae (L1), TMGdmae (L2), TMGdeae (L3) and DPipGdmae (L4) as well as the reaction of their Cu(I) complexes with molecular oxygen (monitored by UV–Vis spectroscopy) are reported. The molecular structures of 10 bis(μ-hydroxo) dicopper complexes based on these ligands are described. The solid state structures of [Cu2(μ-OH)2(DMEGdmae)2]X2 (X− = I− (1), CF3SO3− (2), SbF6− (3), PF6− (4)), [Cu2(μ-OH)2(TMGdmae)2]X2 (X− = I− (5), CF3SO3− (6)), [Cu2(μ-OH)2(TMGdeae)2]Cu2I4 (7) and [Cu2(μ-OH)2(DPipGdmae)2]X2 (X− = CF3SO3− (8), SbF6− (9), PF6− (10)) show a square-planar distorted coordination of the copper(II) ion. The bis(μ-hydroxo) dicopper complex 1 exhibits a Cu···Cu distance of 2.860(1) Å, which is one of the smallest observed for hydroxo-bridged copper compounds so far. The influence of the anion on the structure of the bis(μ-hydroxo) dicopper(II) unit is analyzed for the reported complexes and a literature overview with emphasis on the structural characteristics of the Cu2O2 moiety of bis(μ-hydroxo) dicopper(II) and bis(μ-oxo) dicopper(III) is given.