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Synthesis, Structure, and Properties of Zirconium and Hafnium Complexes Containing η 2 ‐Pyrazolato Ligands
Author(s) -
Sebe Elena,
Guzei Ilia A.,
Heeg Mary Jane,
LiableSands Louise M.,
Rheingold Arnold L.,
Winter Charles H.
Publication year - 2005
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200500378
Subject(s) - hafnium , chemistry , tetrahydrofuran , zirconium , toluene , tetrachloride , lutetium , inorganic chemistry , crystal structure , medicinal chemistry , crystallography , organic chemistry , tin , oxide , solvent , yttrium
Treatment of tetrakis(dimethylamido)zirconium with four equiv. of 3,5‐dimethylpyrazole, 3,5‐di‐ tert ‐butylpyrazole, or 3,5‐diphenylpyrazole in refluxing toluene afforded tetrakis(η 2 ‐3,5‐dimethylpyrazolato)zirconium (86 %), tetrakis(η 2 ‐3,5‐di‐ tert ‐butylpyrazolato)zirconium (88 %), and tetrakis(η 2 ‐3,5‐diphenylpyrazolato)zirconium (85 %), respectively, as colorless crystalline solids. The analogous hafnium complexes were prepared through treatment of hafnium tetrachloride with four equiv. of the potassium salts of 3,5‐dimethylpyrazolate, 3,5‐di‐ tert ‐butylpyrazolate, or 3,5‐diphenylpyrazolate in tetrahydrofuran to afford tetrakis(η 2 ‐3,5‐dimethylpyrazolato)hafnium (75 %), tetrakis(η 2 ‐3,5‐di‐ tert ‐butylpyrazolato)hafnium (58 %), and tetrakis(η 2 ‐3,5‐diphenylpyrazolato)hafnium · toluene (38 %), respectively, as colorless crystalline solids. X‐ray crystal structures of representative members of these complexes revealed monomeric species containing four η 2 ‐pyrazolato ligands and approximate dodecahedral geometry about the metal centers. Treatment of tetrakis(η 2 ‐3,5‐dimethylpyrazolato)hafnium with 3,5‐dimethylpyrazole in a 1:1 molar ratio afforded tris(η 2 ‐3,5‐dimethylpyrazolato)(η 1 ‐3,5‐dimethylpyrazolato)(η 1 ‐3,5‐dimethylpyrazole)hafnium as colorless crystals (84 %). Tris(η 2 ‐3,5‐dimethylpyrazolato)(η 1 ‐3,5‐dimethylpyrazolato)(η 1 ‐3,5‐dimethylpyrazole)hafnium contains three η 2 ‐3,5‐dimethylpyrazolato, one η 1 ‐3,5‐dimethylpyrazolato, and one η 1 ‐3,5‐dimethylpyrazole ligands. The η 1 ‐3,5‐dimethylpyrazolato and η 1 ‐3,5‐dimethylpyrazole ligands are connected through a N–H ··· N hydrogen bond. Tetrakis(η 2 ‐3,5‐dimethylpyrazolato)hafnium did not form an adduct with pyridine or tetrahydrofuran, suggesting that the formation of a hydrogen bond is important to the stability of adducts. Attempted sublimation of all of the new pyrazolato complexes led to some decomposition, as evidenced by the formation of the free pyrazoles in the sublimates and significant amounts of nonvolatile residues. This work greatly expands the number of zirconium and hafnium complexes that contain η 2 ‐pyrazolato ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)