PREPARATION OF VO3+ AND VO2+ COMPLEXES USING HYDROLYTICALLY STABLE, ASYMMETRIC LIGANDS DERIVED FROM SCHIFF-BASE PRECURSORS

The synthesis and characterization of the first water-stable monomeric monooxovanadium(V)) complexes are reported. These complexes are chelated by novel multidentate N/O donor ligands. The ligands were synthesized by reduction of the Schiff base precursors H(2)sal(2)en, N,N'-bis(salicylidene)ethylenediamine, and H(2)shed, N-salicylidene-N'-(2-hydroxyethyl)ethylenediamine, using sodium borohydride to produce H(2)sal(2)enr, N,N'-bis-((o-hydroxyphenyl)methyl) ethylenediamine, and H(2)shedr, N-((o-hydroxyphenyl)methyl)-N'-(2-hydroxyethyl)-ethylenediamine, which are stable to hydrolysis at the imine linkage. Alkylation of H(2)shed followed by reduction leads to the higher denticity, hydrolytically stable ligands H(3)heshedr, N-((o-hydroxyphenyl)methyl)-N'-bis(2-hydroxyethyl)ethylenediamine, and H(3)salshedr, N-(2-hydroxyethyl)-N,N'-bis((o-hydroxyphenyl)methyl)ethylene- diamine. Similarly, alkylation of H(2)sal(2)enr with 2-(bromomethyl)phenyl acetate produces H(2)sal(3)enr, N,N,N'-tris((o-hydroxyphenyl)methyl)ethylenediamine. These ligands have been developed in order to solve the problem of imine hydrolysis that is often associated with vanadium Schiff base complexes. Reaction with sodium vanadate or triethyl vanadate gives a series of dioxo- and monooxovanadium(V) complexes. The compound [VO2(Hshedr)](2),, 2, is a water-soluble and water-stable analogue of [VO2(Hshed)](2), 1, whose X-ray structure reveals that it is isostructural with 1. Complexation of vanadium by the higher denticity ligands leads to monooxovanadium(V) compounds with the general composition seen in the X-ray structure of VO(salshedr), 4. The complexes VO-(sal(3)enr), 5, and 4are stable in mixed organic/aqueous solution and in the presence of hydrogen peroxide. In contrast, VO(heshedr), 3, will convert to VO2(H(2)heshedr), 6, with trace water. The application of C-13 and V-51 NMR spectroscopies allows evaluation of the solution complexation behavior of both the VO2+ and VO3+ compounds. These data show that the molecules retain their integrity in solution and allow us to specify which ligand heteroatoms dissociate on metal hydrolysis or reaction with peroxide. X-ray parameters for 2: triclinic, space group P (1) over bar (No. 2), a = 7.112(1) Angstrom, b = 8.407(2) Angstrom, c = 11.280(3) Angstrom, alpha = 92.66(2)degrees, beta = 95.57(2)degrees, gamma = 97.31(2)degrees V = 664.7(2) Angstrom(3), and Z = 1. The final R indices were R = 0.0350 and R(w), = 0.0376. The complex forms a dimer in the solid state with a vanadium-vanadium separation of 3.1 Angstrom. The hydroxyl remains unbound and is hydrogen-bonded to a water molecule. The complex [VO(salshedr)], 4, has the following crystallographic parameters: monoclinic, space group P2(1)/c (No. 14), a = 6.825(2) Angstrom, b = 19.23(1) Angstrom, c = 12.901(5) Angstrom, alpha = 90.000 degrees, beta = 92.49(3)degrees, gamma = 90.000 degrees, V = 1692(1) Angstrom(3), and Z = 4. The final R indices were R = 0.0756 and R(w) = 0.0658.