V(iv), Fe(ii), Ni(ii) and Cu(ii) complexes bearing 2,2,2-tris(pyrazol-1-yl)ethyl methanesulfonate: application as catalysts for the cyclooctane oxidation

Abstract

Water-soluble compounds [VOCl₂{CH₃SO₂OCH₂C(pz)₃}] (pz = pyrazol-1-yl) 1, [FeCl₂{CH₃SO₂OCH₂C(pz)₃}] 2, [NiCl₂{CH₃SO₂OCH₂C(pz)₃}] 3 and [Cu{CH₃SO₂OCH₂C(pz)₃}₂](OTf)₂4 were obtained by reactions between the corresponding metal salts and 2,2,2-tris(pyrazol-1-yl)ethyl methanesulfonate, CH₃SO₂OCH₂C(pz)₃. They were isolated as air-stable solids and fully characterized by IR, FTIR, NMR (for 2), EPR (for 1), ESI-MS(+/−), elemental analysis and (for 4) single-crystal X-ray diffraction. In all, half- (1–3) or full-sandwich (4), compounds the C-scorpionate ligand shows the N,N,N-coordination mode. 3 and 4 appear to provide the first examples of a Ni(II) and a full-sandwich Cu(II) compound respectively, bearing that scorpionate ligand. Compound 3 is the first Ni(II) tris(pyrazol-1-yl)methane type complex to be applied as catalyst for the oxidation of alkanes. Compounds 1–4 exhibit catalytic activity for the peroxidative (with aq. H₂O₂) oxidation, in water/acetonitrile medium and under mild homogeneous conditions, of cyclooctane to the corresponding alcohol and ketone (yields up to ca. 27%). The effect of the presence of additives, such as nitric acid or pyridine, was studied.