STRUCTURAL AND SPECTROSCOPIC CHARACTERIZATION OF DIOXOVANADIUM(V) COMPLEXES WITH ASYMMETRIC SCHIFF-BASE LIGANDS

A wide range of asymmetric Schiff base ligands containing primary amine functions can be prepared in one step and in high yield by the reaction of VO(OEt)3 with salicylaldehyde and the appropriate diamine. The resulting VO2L complexes contain tridentate ligands with phenolate, imine, and amine coordination to the dioxovanadium(V) complex ion. An X-ray structure of one compound ([VO2(1,2-pnSAL)], 5A, where 1,2-pnSAL = 1(N-salicylideneamino)-2-aminopropane) demonstrates that it is a dimer in the solid state with a V2O4 core. However, when dissolved in DMSO, this material dissociates into monomers. Proton NMR spectroscopy reveals that the second isomer, 5B [VO2(1-amino-2(salicylideneamino)propane], is prepared in the process, but to a much lesser extent than 5A (85:15). The reactivity of VO2(enSAL) [enSAL = 1-(N-salicylideneamino)-2-aminoethane] with peroxides in neutral, basic, and acidic media is discussed. Significantly, the reported synthetic methodology does not yield successful VO2(1-(N-salicylideneamino)-3-aminopropane) [VO2(1,3-pnSAL)]. Instead, the V(IV) complex VO(SALPN)DMSO (8) is isolated and has been characterized structurally (SALPN = 1,3-bis-(N-salicylideneamino)propane). Although VO(SALPN)DMSO and VO(SALEN) have markedly different solution spectra, their reactivity with coordinating and noncoordinating acids are very similar. X-ray parameters: [VO2(1,2-pnSAL)] (5A), C10H13N203V, 260.1 g/mol, triclinic crystal system, P1BAR, (No. 2), a = 7.270(2) angstrom, b = 7.686(2) angstrom, c = 11.082(4) angstrom, alpha = 72.16(2)-degrees, beta = 73.23(2)-degrees, gamma = 85.95(2)-degrees, V = 564.2(3) angstrom3, Z = 2, 2244 data collected with 5-degrees < 2theta < 50-degrees, 1786 data with (F(o)) +/- 0.6sigma(F), R = 0.072, R(w) = 0.097; [VO(SALPN).DMSO] (8), C19H22N204VS, 425.4 g/mol, monoclinic crystal system, P2(1), (No. 14), a = 11.436(3) angstrom, b = 7.775(2) angstrom, c = 11.661(2) angstrom, beta = 109.47(2)-degrees, V = 977.5(3) angstrom3, Z = 2, 6224 data collected in the range 5-degrees < 2theta < 55-degrees, with 4240 data with (F(o)) +/- 0.6sigma(F), R = 0.054, R(w) = 0.062.