Inter- and intramolecular hydrogen-bonding interaction of hydroxo groups and steric effect of alkyl substituents on pyrazolyl rings in Tp(R) ligands:Synthesis and structural characterization of chloro-, acetylacetonato-, and hydroxo complexes of VO2+ with Tp(Pri2) and Tp(Me2) ligands

Novel vanadyl (VO2+) chloro and hydroxo complexes with the hindered Tp(Pri2 ) (hydrotris(3,5-diisopropyl-1-pyrazolyl)borate) and Tp(Me2) (hydrotris(3,5 -dimethylpyrazolyl-1-pyrazolyl)borate) ligands were prepared and structural ly characterized successfully. Ligand displacement of VOCl2(MeCN)(2)(H2O) b y Tp(R) afforded a series of octahedral chloro complexes, Tp(R)V(O)(Cl)(X) (1: R = Pr-2(i), X = Pz(Pri2)H; 2: R = Pri(2), X = py; 6: R = Me-2, X = NCM e). Hydrolysis of the obtained chloro complexes yielded the corresponding h ydroxo complexes 4, 5, and 7, but their structures were very unique and dif ferent from that of the previously reported dinuclear VO2+ bis(mu-hydroxo) complex with the less hindered Tp(H2) (hydrotris(1-pyrazolyl)borate) ligand . For the Tp(Pri2) complexes, the octahedral hydroxo-aqua complex, Tp(Pri2) V(O)(OH)(OH2) (4), and the trinuclear bis(mu u-hydroxo)bis(mu-pyrazolato) c omplex, Tp(Pri2)V(O)(mu-OH)(mu-Pz(Pri2))V(O)(mu-OH)(mu-Pz(Pri2))V(O)Tp(Pri2 ) (5), were isolated. The hydroxo-aqua complex 4 was dimerized through the intermolecular hydrogen-bonding interaction between the hydroxo and aqua li gands forming the H3O2- bridging ligand. The trinuclear complex 5 consisted of two octahedral Tp(Pri2)V(O) fragments and a distorted trigonal-bipyrami dal non-Tp(Pri2)-supported VO2+ center, sitting on the pseudo C-2 symmetry axis, and was formed via coupling of 4 and the VO2+-pyrazolato species, res ulting from partial decomposition of the chloro complexes during the hydrol ysis. Steric repulsion of the bulky Pr-i groups in Tp(Pri2) might hinder th e formation of a dinuclear bis(mu u-hydroxo) complex like the Tp(H2) and Tp (Me2) derivatives. The dinuclear bis(mu-hydroxo) complex with the Tp(Me2) l igand, (kappa(3)-Tp(Me2))V(O)(mu-OH)(2)V(O)(kappa(2)-Tp(Me2)) (7), consiste d of syn-arranged V=O fragments, having the different coordination geometri es of the vanadium centers (octahedron with kappa(3)-Tp(Me2) and trigonal b ipyramid with kappa(2)-Tp(Me2)). Intramolecular hydrogen-bending interactio n between one of the two hydroxo groups and the noncoordinated pyrazolyl ni trogen atom in kappa(2)-Tp(Me2) was observed.