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Catechol derivatives of Group 4 and 5 compounds

2005; Elsevier BV; Volume: 24; Issue: 10 Linguagem: Inglês

10.1016/j.poly.2005.03.055

1873-3719

Timothy J. Boyle, L.J. Tribby, Todd M. Alam, S.D. Bunge, Gregory P. Holland,

Lanthanide and Transition Metal Complexes

The structural modifications of Group 4 and 5 metal alkoxides using the bidentate catechol (C6H3(OH)2-1,3 = cat-H2) have been investigated. From the reaction of [Ti(μ-ONep)(ONep)3]2 (ONep = OCH2CMe3), [Zr(μ-OPri)(ONep)3 · HONep]2(OPri = OCHMe2), Hf(OEt)4 (OEt = OCH2Me) with 2 equivalents, and M(OEt)5 (M = Nb or Ta) with 3 equiv. of cat-H2 in pyridine (py), the complete removal of alkoxide ligands and isolation of the first neutral catechol derivatives of the Group 4 and 5 species were observed. The corresponding catechol derivatives were structurally characterized as: Ti3(μ3-O)(μ-cat)3(cat)(cat-H)2 (1), Zr4(μ4-O)(μ-cat)6(μ-cat-H)2(py)4 (2), Hf4(μ4-O)(μ-cat)6(μ-cat-H)2(py)4 (3), M(cat)2(cat-H)(py) (M = Nb (4); Ta (5)). Compound 1 is trinuclear with each octahedrally bound metal center having three chelating and three chelating bridging cat ligands, along with a μ3-O ligand, to form a corner-missing cube arrangement. Based on charge balance, two of the cat ligands must retain a hydrogen atom (cat-H). The congeners 2 and 3 adopt similar structures wherein each of the metal centers is eight coordinated, adopting a dodecahedral-like geometry. The metals are joined by a μ4-O ligand and each cation uses two chelating cat ligands to bridge to two other metal centers as well as coordinating a single py ligand. Again, based on charge balance, two of the ligands must be cat-H ligands. Compounds 1–3 are insoluble at room temperature in their parent solvent. Compounds 4 and 5 are mononuclear wherein each metal center formally adopts a seven coordination capped-trigonal prism involving three chelating catechol ligands, with one being cat-H, along with a coordinated pyridine ligand. Multinuclear NMR data indicate that the structures of 4 and 5 are retained in solution. TGA/DTA data indicated that compound 1 is a reasonable precursor for nanoparticles. 1 was used to generate nanoparticles of TiO2 from benzylalcohol.