Reactivity of Copper(I) Complexes with Tripodal Ligands towards O 2 : Structures of a Precursor [L 3 Cu I (NCCH 3 )](BF 4 ), L 3 = Tris(3‐isopropyl‐4,5‐trimethylenepyrazolyl)methane and of its Oxidation Product [L 3 Cu II (μ‐OH) 2 Cu II L 3 ](BF 4 ) 2 with Strong Antiferromagnetic Spin‐Spin Coupling

The molecular structure of the highly oxygen‐sensitive complex [L 3 Cu I (NCCH 3 )](BF 4 ) ( 1 ) reveals approximately symmetrical coordination by the fac ‐tridentate (tripodal) ligand L 3 = tris(3‐isopropyl‐4,5‐trimethylenepyrazolyl)methane and a rather short Cu I ‐N(acetonitrile) distance of 1.865(5) Å. In CH 2 Cl 2 at −78 °C the colourless compound reacts with O 2 to yield a labile purple intermediate (λ max 517 nm) – presumably a peroxodicopper(II) complex – which decomposes at −30 °C. No such intermediate was observed on reaction of the Cu I complex of bis(2‐pyridylmethyl)benzylamine with O 2 at −80 °C. However, an EPR spectrum with g ‖ = 2.17 and g ⊥ = 2.03 without 63,65 Cu hyperfine splitting was observed at low temperatures. Exposure of the precursor 1 to air under ambient conditions yields dinuclear [L 3 Cu II (μ‐OH) 2 Cu II L 3 ](BF 4 ) 2 ( 2 ) which exhibits an EPR detectable dissociation into monomers in CH 2 Cl 2 solution. The structure of the hexakis(dichloromethane) solvate of 2 with Cu–Cu and Cu‐O distances of 3.055 and 1.94Å, respectively, is typical for dihydroxo‐bridged dicopper compounds with square‐pyramidal Cu II configuration (τ = 0.03), adopting an anti arrangement. In agreement with the relatively wide Cu‐O‐Cu angles of 103.5° an analysis of the temperature dependence of the magnetic susceptibility revealed a rather strong ( J = −633 cm −1 ) antiparallel spin‐spin coupling. The effect is ascribed to the steric bulk of the ligand L 3 .