Catechol derivatives of Group 4 and 5 compounds

Abstract

The structural modifications of Group 4 and 5 metal alkoxides using the bidentate catechol (C 6H 3(OH) 2-1,3 = cat-H 2) have been investigated. From the reaction of [Ti(μ-ONep)(ONep) 3] 2 (ONep = OCH 2CMe 3), [Zr(μ-OPr i )(ONep) 3 · HONep] 2(OPr i = OCHMe 2), Hf(OEt) 4 (OEt = OCH 2Me) with 2 equivalents, and M(OEt) 5 (M = Nb or Ta) with 3 equiv. of cat-H 2 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: Ti 3(μ 3-O)(μ-cat) 3(cat)(cat-H) 2 ( 1), Zr 4(μ 4-O)(μ-cat) 6(μ-cat-H) 2(py) 4 ( 2), Hf 4(μ 4-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 μ 3-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 μ 4-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 TiO 2 from benzylalcohol.