Reactivity of Copper(I) Complexes with Tripodal Ligands towards O2: Structures of a Precursor [L3CuI(NCCH3)](BF4), L3 = Tris(3‐isopropyl‐4,5‐trimethylenepyrazolyl)methane and of its Oxidation Product [L3CuII(μ‐OH)2CuIIL3](BF4)2 with Strong Antiferromagnetic Spin‐Spin Coupling

Abstract

AbstractThe molecular structure of the highly oxygen‐sensitive complex [L3CuI(NCCH3)](BF4) (1) reveals approximately symmetrical coordination by the fac‐tridentate (tripodal) ligand L3 = tris(3‐isopropyl‐4,5‐trimethylenepyrazolyl)methane and a rather short CuI‐N(acetonitrile) distance of 1.865(5) Å. In CH2Cl2 at −78 °C the colourless compound reacts with O2 to yield a labile purple intermediate (λmax 517 nm) – presumably a peroxodicopper(II) complex – which decomposes at −30 °C. No such intermediate was observed on reaction of the CuI complex of bis(2‐pyridylmethyl)benzylamine with O2 at −80 °C. However, an EPR spectrum with g‖ = 2.17 and g⊥ = 2.03 without 63,65Cu hyperfine splitting was observed at low temperatures. Exposure of the precursor 1 to air under ambient conditions yields dinuclear [L3CuII(μ‐OH)2CuIIL3](BF4)2 (2) which exhibits an EPR detectable dissociation into monomers in CH2Cl2 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 CuII 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 L3.