Chiral Cu(II) salen complexes catalyzed aerobic oxidative biaryl coupling-probing the reaction by EPR

Sabarinathan, Subbaramanian; Vasuki, G.; Rao, P. Sambasiva

doi:10.5155/eurjchem.1.4.360-367.221

Cited by 9 publications

(4 citation statements)

References 29 publications

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“…Some unidentifiable products could also have been formed and held on the surface. This along with chelate formation ,, accounts for the mass imbalance that occurs during catalytic conversion of 2-napthol to BINOL.…”

Section: Catalytic Activitymentioning

confidence: 99%

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Enhanced Catalytic Activity of Zeolite Encapsulated Fe(III)-Schiff-Base Complexes for Oxidative Coupling of 2-Napthol

et al. 2012

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Iron(III) Schiff-base complexes of general formula [Fe(L)(2)Cl]·2H(2)O, where L = N,Ń-bis(salicylidene)ethylenediamine and N,Ń-disalicylidene-1,2-phenylenediamine have been encapsulated within various alkali exchanged zeolites viz. LiY, NaY, and KY by flexible ligand method. The encapsulated complexes are characterized by EDX, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), FT-IR, UV-vis, diffuse reflectance spectroscopy (DRS), electron spin resonance spectroscopy (ESR) and cyclic voltammetry studies. The diffuse reflectance UV-vis spectra of encapsulated complexes show a dramatic red shift of the charge transfer band with increasing electropositivity of the exchangeable cations. The electrochemical analysis predicts the shifting of the reduction potential toward negative values with increasing size of the alkali exchanged cations. The zeolite encapsulated Schiff-base complexes of iron are found to be catalytically active toward the oxidative coupling of 2-napthol. Metal complexes incorporated in potassium exchanged zeolite-Y are found to be more effective for catalytic conversion of 2-naphthol to binaphthol and induces higher selectivity toward the R-conformation. The catalytic conversion of 2-napthol to BINOL is found to depend on the reduction potential of the catalyst, with a more negative reduction potential being better for the catalytic conversion. Density functional calculation is being carried out on both the neat Fe-Salen and Fe-Salophen complexes and those encapsulated in NaY zeolite to investigate change in structural parameters, energies of the HOMO and LUMO, and global hardness and softness. Fukui functions, as local descriptors, are used to analyze the hard-hard interaction at a particular site of the complexes.

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Section: Catalytic Activitymentioning

confidence: 99%

“…Some unidentifiable products could also have been formed and held on the surface. This along with chelate formation 27,70,71 accounts for the mass imbalance that occurs during catalytic conversion of 2-napthol to BINOL. The turnover number (TON) increases on encapsulation of the iron-Schiff-base complexes into different cation exchanged zeolites.…”

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confidence: 99%

Enhanced Catalytic Activity of Zeolite Encapsulated Fe(III)-Schiff-Base Complexes for Oxidative Coupling of 2-Napthol

et al. 2012

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“…Cu(II) complexes synthesized using salen-type ligands are known to acquire nonplanar geometry around the Cu(II) center, while noninnocent ligands upon coordination with the Cu(II) ion under air provide π-radical-coordinated Cu(II) complexes. Hence, a combination of both the salen unit and the noninnocent unit in a single ligand will provide a π-radical-containing Cu(II) complex with a distorted coordination environment around the Cu(II) center.…”

Section: Introductionmentioning

confidence: 99%

Effect of Geometrical Distortion on the Electronic Structure: Synthesis and Characterization of Monoradical-Coordinated Mononuclear Cu(II) Complexes

et al. 2016

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Ligand H3Sami(Mixed(tBu)) was composed of two different compartments, a redox-active 2-aminophenol and a salen salicylidene. Both compartments were linked via a benzyl linker. The ligand reacted with CuCl2·2H2O under air in the presence of Et3N and provided the corresponding monoradical-coordinated mononuclear Cu(II) complex (1). Complex 1, in solution, reacted with air and provided complex 2 via ligand-centered oxygenation at the benzyl-CH2 position. Both complexes were characterized via IR, mass spectrometry, X-ray single-crystal diffraction, variable-temperature magnetic susceptibility, cyclic voltammograms (CVs), and UV-vis/NIR spectroscopic techniques. X-ray crystallographic analyses clearly showed almost equally distorted square planar geometry around the Cu(II) atom in both complexes. However, the bending of the radical-containing C6 ring compared to the N1-Cu1-O1 plane was different in both complexes. While complex 1 was paramagnetic and showed a ferromagnetic coupling between the d(x(2)-y(2)) magnetic orbital of Cu(II) ion and the p(z) orbital of coordinated π-radical, complex 2 was diamagnetic by experiencing a strong antiferromagnetic coupling between the two magnetic orbitals. UV-vis/NIR spectra of the complexes were dominated by charge-transfer transitions. CVs of the complexes showed two reversible one-electron oxidations and one reversible one-electron reduction. E(1/2)(ox2) and E(1/2)(red1) potentials were different in both complexes, while E(1/2)(ox1) values were almost the same and the process corresponded to the formation of phenoxyl radical. Theoretical studies were also performed to understand the magnetic coupling phenomena, and TD-DFT calculations were employed for the assignment of charge-transfer absorption bands.

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“…CBS catalysts (Me-CBS and Ph-CBS) were purchased from Strem Chemicals Inc. The following catalysts for the chiral Lewis acid plate (See Figure 2) were made following known procedures: Salen complexes AlCl 16 , Co(OAc) 17 , CrCl 18 , MnCl 19 , TiCl 2 20 , Zn 21 , Cu 22 , Pd, Ni 23 ; PYBOX complexes AlCl 3 , In(OTf) 3 , Sc(OTf) 3 , Yb(OTf) 3 24 , CuCl 2 , PdCl 2 , NiCl 2 , ZnCl 2 25 ; STEIN complexes AlMe, TiCl 2 26 ; TADDOL complexes AlMe, TiCl 2 27 .…”

Section: Methodsmentioning

confidence: 99%

Lewis Acid-Promoted Enantioselective Dearomative Spirocyclizations of Allenes

et al. 2018

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A chiral oxazaborolidine combined with SnCl has been found to promote the dearomative spirocyclization of electron-rich benzyl allenyl ketones. The reaction outcome is sensitive to the nature of activating acid, which was rationalized using hard-soft acid-base (HSAB) theory. The spirocyclic product was obtained with up to 72% ee, which is the best result reported to date for these substrates. The formation of cross-conjugated or conjugated products is readily controlled by changing the oxygen-protecting groups.

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Chiral Cu(II) salen complexes catalyzed aerobic oxidative biaryl coupling-probing the reaction by EPR

Cited by 9 publications

References 29 publications

Enhanced Catalytic Activity of Zeolite Encapsulated Fe(III)-Schiff-Base Complexes for Oxidative Coupling of 2-Napthol

Enhanced Catalytic Activity of Zeolite Encapsulated Fe(III)-Schiff-Base Complexes for Oxidative Coupling of 2-Napthol

Effect of Geometrical Distortion on the Electronic Structure: Synthesis and Characterization of Monoradical-Coordinated Mononuclear Cu(II) Complexes

Lewis Acid-Promoted Enantioselective Dearomative Spirocyclizations of Allenes

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