Chlorination of a Pyrazole Ligand in Vanadium(V)alkoxo Complexes¹

Abstract

VOCl3 reacts with pyrazolylpyridines in the presence of tBuOH to give new six-coordinate vanadium oxoalkoxo complexes. Changing from tBuOH to tBuOOH does not lead to the corresponding tbutylperoxo complexes but to oxidation of Cl-, which finally results in chlorination of the pyrazole fragment of the chelate ligand. These new V(V) complexes catalyze the epoxidation of allylic alcohols and unfunctionalized olefins in the presence of tBuOOH.

Two new scorpionates vanadium haloperoxidases model complexes: Synthesis and structure of VO(O2)(pzH)(HB(pz)3) and VO(O2)(pzH)(B(pz)4) (pzH=pyrazole(C3H4N2))

“…The distances of V-N in axial plane (V-N2, 2.240(2) Å ), is longer than those in the equatorial plane (V-N8 (2.151(2) Å , V-N4 (2.167(3) Å ) and V-N6 (2.131(2) Å ), which can be attributed to the trans effect exerted by the oxo group (V@O). And the average distance of V-N (N atoms contained in the equatorial plane) is longer than that of those reported vanadium(V) complexes containing poly(pyrazolyl)borate ligands [42][43][44][45][46]. The average distance of V-Op is similar to those reported oxo-monoperoxo vanadium (V) complexes [47][48][49][50], and the distance of V-O2 (1.890(2) Å ) is longer than that of V-O1 (1.866(2) Å ), due to O2 involving in the hydrogen-bond network.…”

Pyrazolylcyclohexanol Complexes of Vanadium − A Temperature- and Solvent-Dependent Monomer−Dimer Equilibrium

“…Owing to the tridentate ligand, the position of the oxo ligand is fixed trans to pyrazole, which is confirmed by a single 51 V NMR resonance and one set of resonances in the 1 H NMR spectrum. This is in contrast to the behavior of oxoalkoxo V V complexes of bidentate pyrazolylpyridines, [5] which exist as mixtures of two isomers differing in the orientation of the oxo and alkoxo ligands relative to the N,NЈ-donor. Scheme 2 As expected, the tridentate ligand enhances the stability of the V V complex relative to the V V complexes of bidentate pyrazolylpyridines.…”

“…Despite the crystallographic disordering in the individual crystal that was used for the structure determination, a satisfactory solution of the structure could be performed. While the VϭO [1.597(2) Å ] and VϪO distances [1.762(2) Å ] in 2 are only a few pm longer than the distances found in the isostructural oxoalkoxo vanadium(V) complexes bearing bidentate pyrazolylpyridine ligands [VϭO ϭ 1.575(3) and 1.579(2) Å ; VϪO ϭ 1.740(2) and 1.735(2) Å ], [5] the VϪN distances in 2 are drastically shortened due to the tridentate ligand system. Usually, the MϪN bonds (N ϭ N-donor ligand) in the trans position to strong σ-donor ligands (e.g.…”

“…[4] In a project on vanadium-catalyzed olefin epoxidation, our group has investigated structurally well-defined vanadium(V) complexes bearing bidentate pyrazolylpyridine ligands equipped with alkyl and ester side chains. [5] Owing to this feature, these ligands increase the solubility of the derived metal complexes in nonpolar organic solvents and therefore should allow detailed mechanistic investigations on the oxygen-transfer processes. They are active catalysts for the epoxidation of olefins as well as for the oxidation of aromatic alcohols, giving the corresponding aldehydes in high yield.…”

Vanadium(IV) and -(V) Complexes with O,N-Chelating Aminophenolate and Pyridylalkoxide Ligands

“…The V-O distance (1.763(3) Å) falls in the range reported for other vanadium(V) alkoxo compounds (1.74-1.99 Å). [28][29][30] However, the V-Cl and the VdO distances (av 2.23 and 1.578-(3) Å, respectively) are among the shortest ever reported. Also in view of the small bite angle of the η 2 -O,N-chelate bonded pyridylalkoxide ligand of 75.39(12)°, this structure is probably best described starting from a tetrahedral geometry.…”