Veli T. Kasumov

Synthesis, spectroscopic characterization and ESR studies on electron transfer reactions of bis[N-(2,6-di-tert-butyl-1-hydroxyphenyl)salicylaldiminato]-copper(II) complexes with PbO2 and PPh3.

New bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylideneminato]copper(II) complexes bearing HO and CH3O substituents on the salicyaldehyde moiety were prepared, and their spectroscopic properties, as well as redox reactivity towards PbO2 and PPh3, examined by ESR and UV spectroscopy. In the process of synthesis of HO complexes unlike CH3O the oxidative C-C coupling of coordinated salicylaldimine ligands does not takes place. The powder ESR spectra of CH3O substituted complexes unlike of HO analogues are typical of a triplet state Cu(II) dimers with a half-field forbidden (deltaM = +/- 2) transition and the allowed transitions (AM = +/- 1) dimeric form of the complexes at 300 and 113 K. The one-electron oxidation of 3-CH3O and all of the OH complexes with PbO2 to give indophenoxyl type secondary radicals which are significantly different from those observed for analogues Cl, Br and NO2 substituted chelates. The presented complexes unlike their electron-withdrawing analogues are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give various radical intermediates as well as Cu(I) radical ligand compounds. The analysis of ESR spectra all of the complexes and radical intermediates are presented.

Synthesis, spectroscopy and redox chemistry of bis(n-aryl-3,5-di-tert-butylsalicylaldiminato)copper(II) complexes

A series of new bis(N-aryl-3,5-di-tert-butylsalicylaldiminato)copper(II) complexes (I), prepared from 3,5-di-tert-butylsalicylaldehyde and mono-substituted anilines, X-C6H4NH2(X = H, o-F, Cl, Br, CH3, CH3O; p-F, Cl, Br, CH3, CH3O, t-Bu and 5,6-benzo), and their spectroscopic properties as well as electrochemistry and reactivity toward PPh3 are described. Comparison of g ‖ (2.223–2.249), A ‖ (150–170 G) tensors and the axial symmetry parameter, g ‖/A ‖, (140–155 cm) of I with those of model Cu(II) complexes reveals that the coordination site is distorted from square planar toward tetrahedral geometry. The di-tert-butyl groups on the salicylaldehyde moiety unlike those introduced on the aniline rings do not facilitate reactivity toward PPh3. Electrochemical studies of I in acetonitrile solutions reveal highly irreversible behavior, due to chemical or stereochemical changes subsequent to electron transfer. In the oxidation of some complexes with (NH4)2Ce(NO3)6 in acetonitrile at 300 K, along with decreasing ESR signals of Cu(II), the appearance of coordinated phenoxyl radical signals centered at g = 2.004 were detected. The CV studies on acetonitrile solutions of I revealed well-resolved quasi-reversible redox waves at  = 0.61–0.99 V and  = 1.09–1.23 V (vs. Ag/AgCl) attributable to ligand-centered oxidation processes to yield corresponding coordinated phenoxyl radical species such as Cu(II)(phenoxyl)(phenolate) and Cu(II)(phenoxyl)2.

Synthesis, spectroscopic characterization and EPR studies on electron transfer reactions of bis[N-(2,5-di-tert-butylphenyl)salicylaldiminato]copper complexes with PPh3

New bidentate N-(2,5-di-tert-butylphenyl)salicylaldimines bearing X = H, HO, CH3O, Br, NO2, 3,5-di-Br, 3-NO2-5-Br and 5,6-benzo substituents on the salicylaldehyde moiety, LxH, and their mononuclear bis[N-(2,5-di-tert-butylphenyl)salicylaldiminato]copper(II) complexes, Cu(Lx)2, have been prepared and investigated by IR, UV-Visible, 1H NMR, ESR spectroscopy, magnetic measurements, as well as reactions of Cu(LX)2 with PPh3 were studied. It has been found that some complexes with X = HO and CH3O unlike their electron-withdrawing and unsubstituted analogues are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give Cu-stabilized radical intermediates. The spectra of the primary radicals interpreted in terms of couplings of unpaired electron with (63,65)Cu, 31P, 14N nuclei and aromatic protons.

Transition metal complexes with tridentate salicylaldimine derived from 3,5-di-t-butylsalicylaldehyde

Several new binuclear CuII, NiII, OVIV and MnII complexes of tridentate salicylaldimine (H2L), obtained from 3,5-di-t-butylsalicylaldehyde and o-aminophenol, have been prepared and characterized by analytical, spectroscopic (i.r., u.v.–vis., e.s.r.) techniques, magnetic and thermal measurements. The adduct formation or dissociation of these complexes in the presence of strongly coordinating solvents like pyridine and DMSO did not take place. The complexation of CoII with H2L is accompanied by intramolecular electron transfer from the metal to the coordinated ligand yielding the radical ligand CoIII complex (g = 2.003, ACo = 10 G). The e.s.r. spectra of the CuII, OVIV and MnII complexes in the solid state and in solution are very broad due to intramolecular dipolar antiferromagnetic interactions.

Synthesis, spectroscopic and redox properties of nickel(II) salicylaldimine complexes containing sterically hindered phenols

The preparation and spectroscopic characterization of a series of new bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylaldiminato]nickel(II) complexes, [Ni(LX)2], bearing one or two OH and MeO substituents on the salicylaldehyde moiety, as well as radical species generated from these compounds by the oxidation with PbO2, are reported. The [Ni(LX)2] chelates, which appear to be tetrahedral in the solid state and in dioxane solution, are converted into a square-planar configuration in non-donor solvents. The OH-substituted complexes, unlike their MeO analogues, form six-coordinate adducts in pyridine, DMF and DMSO. These new compounds, unlike their analogues with electron-withdrawing substituents (Cl, Br, NO2), are easily oxidized by PbO2 to produce NiII-stabilized phenoxy radicals in which the unpaired electrons are delocalized over the ligand and do not couple with the second radical center. No e.s.r. signals were observed that could be attributed to a ΔM = ±2 transition of the triplet state biradicals.

Synthesis, spectroscopic characterization and redox reactivity of some transition metal complexes with salicylaldimines bearing 2,6-di-phenylphenol.

New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X=H and 3,5-di-t-butyl substituents on the salicylaldehyde ring, L(x)H, and their copper(II) complexes, M(Lx)2, (M=Cu(II), Co(II), Pd(II), Ni(II) and Zn(II)) have been synthesized and characterized by IR, UV/vis, 1H NMR, 13C NMR, ESR spectroscopy, magnetic susceptibility measurements, as well as their oxidation with PbO(2) and reduction (for Cu(Lx)2) with PPh(3) were investigated. ESR studies indicate that oxidation of M(Lx)2 produces ligand-centered M(II)-phenoxyl radical species. The Cu(Lx)2 complexes, unlike others M(Lx)2, are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give unstable radical intermediates which are converted to another stable secondary radical species. The analysis of ESR spectra of Cu(Lx)(2), Co(L1)(2) and generated phenoxyl radicals are presented.

Synthesis and ESR studies of redox reactivity of bis (3,5-di-tert-butyl-1,2-benzoquinone-2-monooximato)Cu(II)

Complexing of 3,5-di-tert-butyl-1,2-benzoquinone-2-monooxime with Cu(II) in air and under N2 gave Cu(qo)2 and Cu(qo)2 x H2O (where qo is 3,5-di-tert-butyl-1,2-benzoquinone-2-monooximato-anion) complexes, respectively. The ESR spectroscopy showed that the reduction of these complexes with P(PhX)3 (X = H, m-Cl, m-CH3, p-Et2N-) and 1,4-bis(diphenyldiphosphino) butane (dppb) proceeds via the radical formation (phenoxazine, amino phenoxy and nitrene type radical intermediates) and pathways of reduction depend on the structure of these complexes. The reaction of Cu(qo), with dppb and P(PhX)3 phosphines gave essentially identical ESR spectra. At the same time, reduction of Cu(qo)2 x H2O with PPh3 result in entirely different unstable radical spectrum (g = 2.0046) which is further converted to another relatively stable Cu-containing radical signal (g = 2.0052). The unstable radical species attributed to nitrene type radicals. The initial complexes and all radical products were characterized by their ESR and optical spectra.

Synthesis, Spectroscopic Characterization and Redox Reactivity of Some New N-(2,6-Di-Tert-Butyl-L-Hydroxyphenyl) Salicylaldimines

Abstract New substituted N- (2,6-Di-tert-butyl-l-hydroxyphenyl) Salicylaldimines (LxH) were prepared by the condensation of various hydroxy and methoxy salicylaldehyde derivatives and 2,6-Di-tert-butyl-4-aminophenol and characterized by elemental analysis, IR, UV-Vis, 1H NMR spectroscopy, as well as ESR studies of the oxidation products of LxH. It was found that LxH, unlike analogous electron-withdrawing C1, Br, NO2 bearing derivatives, in the solid state exist both in associated and non-associated forms. UV-Vis and 1H, NMR studies show that LxH in solutions exists both in phenolimine and ketoamine tautomer forms. In addition, alcohol solutions of LxH exhibited a new band in the region of 630-675 run. The ESR studies of one -electron oxidation of LxH, in the condition of THF, CHC13 and toluene solutions at 300 K, indicate the formation of corresponding primary or secondary phenoxyl radicals. It was found that the stability and conversion pathway of the primary phenoxyl radicals are dependent upon both kin...

Bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylideneaminato]palladium(II) complexes and their radical intermediates generated by PbO2 and PPh3

New bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylideneminato]palladium(II) [Pd(Lx)2] complexes bearing HO and MeO substituents on the salicyaldehyde moiety were prepared, and their spectroscopic properties, as well as redox reactivity towards PbO2 and PPh3, examined by e.s.r. and u.v. spectroscopy. The complexes display charge-transfer bands in the 670–692 nm range in polar solvents, which are assigned to the d(Pd) → π* (chelated quinoid) transition. One-electron oxidation of Pd(Lx)2 produces PdII-stabilized radicals in which the unpaired electrons are localized on the phenoxy fragments and do not couple with the two radical centers. The complexes are easily reduced with PPh3via intramolecular electron-transfer from ligand to metal to give various radical intermediates and Pd. All detected radical species have been characterized by e.s.r. spectroscopy.

Preparation, spectral behaviour and oxidation of some new zinc(II) salicylaldimines containing sterically hindered phenol

A series of new bis[N-(2,6-di-tert-butyl-1-hyxyphenyl)salicylideneminato]zinc(II) complexes bearing one or two HO- and CH3O-substituents on the salicylaldehyde moiety were prepared, and their spectroscopic properties (IR, electronic, 1H NMR) as well as the ESR spectra of the one-electron oxidation products were examined. The 1H NMR examination of Zn(Lx)2 indicates that, contrary to expectations, the proton resonances of the complexes are shifted to the high-field side compared with those of the free ligands. Oxidation of these compounds with PbO2 results in the formation of mono- and biradical types Zn(II)-stabilized phenoxyls in which there are both anisotropic and alternating line-width trends. Some spectral patterns are typical for weak interacting (J << A) or the case of J approximately A biradicals, in which ESR signal appeared as superimposition of two non-interacting monoradical centers with S = 1/2. ESR studies on biradicals type of Zn(L*x)2 at 300 and 77 K did not show any evidence of strong exchange coupling in these systems. All radical species were characterized by the ESR parameters.