Alkoxo Bound Monooxo- and Dioxovanadium(V) Complexes:  Synthesis, Characterization, X-ray Crystal Structures, and Solution Reactivity Studies

Abstract

A large variety of oxovanadium(V) complexes, mononuclear VO(2)(+) and VO(3+) in addition to the dinuclear VO(3+), of the structural type (VOL)(2), (VOHL)(2), VOLHQ, K(VO(2)HL), K(VO(2)H(2)L), or (salampr) (VO(2)L) {where L = Schiff base ligand possessing alkoxo group(s); HQ = 8-hydroxyquinoline; salampr = cation of reduced Schiff base derived from salicylaldehyde and 2-amino-2-methylpropan-1-ol}, bound to alkoxo, phenolate and imine groups have been synthesized in high yields and characterized by several spectral and analytical methods, including single crystal X-ray studies. While the mononuclear VO(2)(+) complexes have been synthesized at alkaline pH, the dinuclear VO(3+) complexes have been synthesized under neutral conditions using alkoxo rich Schiff base ligands. The X-ray structures indicate that the cis-dioxo complexes showed longer V-O(alkoxo) bond lengths compared to the monooxo counterparts. The plot of V-O(phen) bond distances of several VO(3+) complexes vs the lmct showed a near linear correlation with a negative slope. The cyclic voltammograms revealed a reversible V(V)/V(IV) couple with the reduction potentials increasing to more negative ones as the number of alkoxo groups bound to V increases from 1 to 2. Moreover, the cis-dioxo VO(2)(+) complexes are easier to reduce than their monooxo counterparts. The solution stability of these complexes was studied in the presence of added water (1:4, water:solvent), where no decomposition was observed, unlike other Schiff base complexes of V. The conversion of the dioxo complexes to their monooxo counterparts in the presence of catalytic amounts of acid is also demonstrated. The reactivity of alkoxo bound V(V) complexes is also reported. X-ray parameters are as follows. H(4)L(3): monoclinic space group, P2(1)/c; a = 10.480(3), b = 8.719(6), c = 12.954(8) Å; beta = 101.67(4) degrees; V = 1126(1) Å(3); Z = 4; R = 0.060, R(w) = 0.058. Complex 1: monoclinic space group, P2(1)/n; a = 12.988(1), b = 9.306(2), c = 19.730(3) Å; beta = 99.94(1) degrees; V = 2348.9(7) Å(3); Z = 4; R = 0.031, R(w) = 0.027. Complex 2: monoclinic space group, P2(1)/n; a = 12.282(3), b = 11.664(2), c = 12.971(4) Å; beta = 97.89(2) degrees; V = 1840.5(8) Å; Z = 4; R = 0.035, R(w) = 0.038. Complex 5: monoclinic space group, P2(1)/c; a = 17.274(2), b = 6.384(2), c = 16.122(2) Å; beta = 116.67(1) degrees; V = 1588.7(7) Å(3); Z = 4; R = 0.039, R(w) = 0.043. Complex 8: monoclinic space group, P2(1)/c; a = 11.991(1), b = 11.696(4), c = 12.564(3) Å; beta = 110.47(1) degrees; V = 1650.8(8) Å(3); Z = 2; R = 0.045, R(w) = 0.049.

Synthesis, spectral and structural studies of oxovanadium(IV/V) complexes derived from 2-hydroxyacetophenone-3-hydroxy-2-naphthoylhydrazone: polymorphs of oxovanadium(V) complex [VOL(OCH3)]

“…The richness and importance of vanadate chemistry have emerged for quite some time [5][6][7]. In continuation of our work on the synthesis and characterization of aroyl hydrazones and their coordination compounds [8][9][10][11][12], we report here the synthesis and characterization of oxovanadium (IV/V) complexes of 2-hydroxyacetophenone-3-hydroxy-2-naphthoylhydrazone (H 2 L) along with the crystal structure of an oxovanadium(V) complex existing in two polymorphic forms.…”

Fifteen Years of Dancing with Vanadium

“…Many different classes of vanadium(V) alkoxides now exist, and the reader is referred to the Cambridge Crystallographic Data Centre [1,[3][4][5][10][11][12][13][14]16,17,[86][87][88][89][90]. The Rosenthal group [91,92] has recently reported an interesting example of this type of chemistry.…”

“…11 [44,54,60,80]. 1 H and 13 C NMR spectroscopy have been very useful techniques for studying the solution structure of vanadium(V) complexes [12,14,16,17,41,44,60,72,74,75,80,88,90,95,114]. Both 1D [54] and 2D NMR methods have been very informative with regard to the formation of reaction intermediates [44,120].…”

Synthesis, characterization and biological studies of diorganotin(IV) complexes with tris[(hydroxymethyl)aminomethane] Schiff bases

“…Some metal complexes with TRIS Schiff base have been reported. For example, TRIS Schiff bases with dioxomolydenum(VI) complexes have been investigated and used as catalysts in epoxidation of alkenes while its dioxovanadium(IV) complexes have been studied as potential biomimetics [20,21].…”