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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

2005; Wiley; Volume: 631; Issue: 13-14 Linguagem: Inglês

10.1002/zaac.200500053

1521-3749

Wolfgang Kaim, Christoph Titze, T. Schurr, Monika Sieger, Max Lawson, J. Jordanov, Darío Rojas, Ana M. García, Jorge Manzur,

Metal complexes synthesis and properties

Abstract 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 .