Inter- and Intramolecular Hydrogen-Bonding Interaction of Hydroxo Groups and Steric Effect of Alkyl Substituents on Pyrazolyl Rings in TpR Ligands: Synthesis and Structural Characterization of Chloro-, Acetylacetonato-, and Hydroxo Complexes of VO2+ with TpPri2 and TpMe2 Ligands

Novel vanadyl (VO 2+ ) chloro and hydroxo complexes with the hindered Tp Pr i 2 (hydrotris(3,5-diisopropyl-1-pyrazolyl)borate) and Tp Me 2 (hydrotris(3,5-dimethylpyrazolyl-1-pyrazolyl)borate) ligands were prepared and structurally characterized successfully. Ligand displacement of VOCl 2 (MeCN) 2 (H 2 O) by Tp R afforded a series of octahedral chloro complexes, Tp R V(O)(Cl)(X) ( 1: R = Pr i 2, X = Pz Pr i 2 H; 2: R = Pr i 2, X = py; 6: R = Me 2, X = NCMe). Hydrolysis of the obtained chloro complexes yielded the corresponding hydroxo complexes 4, 5, and 7, but their structures were very unique and different from that of the previously reported dinuclear VO 2+ bis( μ -hydroxo) complex with the less hindered Tp H 2 (hydrotris(1-pyrazolyl)borate) ligand. For the Tp Pr i 2 complexes, the octahedral hydroxo−aqua complex, Tp Pr i 2 V(O)(OH)(OH 2 ) ( 4 ), and the trinuclear bis( μ -hydroxo)bis( μ -pyrazolato) complex, Tp Pr i 2 V(O)( μ -OH)( μ -Pz Pr i 2 )V(O)( μ -OH)( μ -Pz Pr i 2 )V(O)Tp Pr i 2 ( 5 ), were isolated. The hydroxo−aqua complex 4 was dimerized through the intermolecular hydrogen-bonding interaction between the hydroxo and aqua ligands forming the H 3 O 2 - bridging ligand. The trinuclear complex 5 consisted of two octahedral Tp Pr i 2 V(O) fragments and a distorted trigonal-bipyramidal non-Tp Pr i 2 -supported VO 2+ center, sitting on the pseudo C 2 symmetry axis, and was formed via coupling of 4 and the VO 2+ −pyrazolato species, resulting from partial decomposition of the chloro complexes during the hydrolysis. Steric repulsion of the bulky Pr i groups in Tp Pr i 2 might hinder the formation of a dinuclear bis( μ -hydroxo) complex like the Tp H 2 and Tp Me 2 derivatives. The dinuclear bis( μ -hydroxo) complex with the Tp Me 2 ligand, ( κ 3 -Tp Me 2 )V(O)( μ -OH) 2 V(O)( κ 2 -Tp Me 2 ) ( 7 ), consisted of syn -arranged V O fragments, having the different coordination geometries of the vanadium centers (octahedron with κ 3 -Tp Me 2 and trigonal bipyramid with κ 2 -Tp Me 2 ). Intramolecular hydrogen-bonding interaction between one of the two hydroxo groups and the noncoordinated pyrazolyl nitrogen atom in κ 2 -Tp Me 2 was observed.