Oxidorhenium(V) Complexes with Oxazolinylmethoxido Ligands – Structure and Catalytic Epoxidation

Terfassa, Belina; Traar, Pedro; Volpe, Manuel; Mösch‐Zanetti, Nadia C.; Raju, V.S.; Megersa, Negussie; Retta, Negussie

doi:10.1002/ejic.201100538

Cited by 15 publications

(5 citation statements)

References 46 publications

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“…Prolonged reaction times did not lead to a significant increase in the epoxide yield. Conversions between 50 and 70%, as reported herein, were observed for the vast majority of oxidorhenium(V) complexes. ,,,− This limitation in the catalytic activity can be attributed to two main effects: oxidation to unreactive perrhenate(VII) species by the oxidant TBHP as well as inhibition by accumulating t BuOH, the follow-up product after TBHP oxidation. ,,, …”

Section: Resultssupporting

confidence: 51%

“…20,22,25,44−46 This limitation in the catalytic activity can be attributed to two main effects: oxidation to unreactive perrhenate(VII) species by the oxidant TBHP as well as inhibition by accumulating tBuOH, the follow-up product after TBHP oxidation. 21,22,45,46 However, by a direct comparison of the performance of complexes 1−3 and 2a in catalysis, interesting trends regarding the influence of the isomeric form could be observed. Compound 1 was previously used in the same epoxidation reaction in chloroform.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Oxidorhenium(V) Complexes with Tetradentate Iminophenolate Ligands: Influence of Ligand Flexibility on the Coordination Motif and Oxygen-Atom-Transfer Activity

et al. 2016

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The synthesis of oxidorhenium(V) complexes 1-3 coordinated by tetradentate iminophenolate ligands H2L1-H2L3 bearing backbones of different rigidity (alkyl, cycloalkyl, and phenyl bridges) allows for the formation of distinct geometric isomers, including a symmetric trans-oxidochlorido coordination motif in complex 3. The complex employing a cycloalkyl-bridged ligand (2) of intermediate rigidity exhibits an interesting solvent- and temperature-dependent equilibrium between a symmetric (trans) isomer and an asymmetric (cis) isomer in solution. The occurrence of a symmetric isomer for 2 and 3 is confirmed by single-crystal X-ray diffraction analysis. Chlorido abstraction from 2 with AgOTf yields the corresponding cationic complex 2a, which does not exhibit an isomeric equilibrium in solution but adopts the isomeric form predominant for 2 in a given solvent. All complexes were, furthermore, employed in three benchmark oxygen-atom-transfer (OAT) reactions, namely, the reduction of perchlorate, the epoxidation of cyclooctene, and OAT from dimethyl sulfoxide (DMSO) to triphenylphosphane (PPh3), to assess the influence of the isomeric structure on the reactivity in these reactions. In perchlorate reduction, a clear structural influence was observed, where the trans arrangement in 3 led to the complete absence of activity. In the epoxidation reaction, all complexes led to comparable epoxide yields, albeit higher catalytic activity but lower overall stability of the catalysts with a trans arrangement was observed. In OAT from DMSO to PPh3, also a clear structural dependence was observed, where the trans complex 3 led to full phosphane conversion with an excess of oxidant, while the cis compound 1 was completely inactive.

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Section: Resultssupporting

confidence: 51%

Section: ■ Results and Discussionmentioning

confidence: 99%

Oxidorhenium(V) Complexes with Tetradentate Iminophenolate Ligands: Influence of Ligand Flexibility on the Coordination Motif and Oxygen-Atom-Transfer Activity

et al. 2016

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“…All compounds give bond lengths for RevO within the expected range for six-coordinate monooxorhenium(V) complexes. [8][9][10][11][12][13][14][15][16][17][18][19][20] The longest RevO distance (1.735(7) Å) has been reported for complex 4. Elongation of the RevO bond length in 4 is accompanied by significant shortening of the Re-OCH 3 distance (1.731(11) Å), which is a consequence of the competition of methoxide with the oxo group in the interaction with the dπ orbitals of the metal and is frequently…”

Section: Molecular Structuresmentioning

confidence: 99%

“…These features make Re(V) compounds attractive options as catalysts and justify the further investigations in order to obtain more efficient catalysts. [8][9][10][11][12] Our recent studies on oxorhenium(V) complexes [ReOX-(N-O) 2 ] with phenolate-and carboxylate-based ligands showed high initial activity for one of the examined complexes, namely [ReO(OMe)(quin) 2 ] (where quinH = quinaldic acid). This was highly interesting because [ReO(OMe)(quin) 2 ] was the only complex showing a rare ligand arrangement, with two chelating quinoline-2-carboxylate ligands in the equatorial plane and a linear axial [OvRe-OMe] unit.…”

Section: Introductionmentioning

confidence: 99%

Oxorhenium(v) complexes of quinoline and isoquinoline carboxylic acids – synthesis, structural characterization and catalytic application in epoxidation reactions

et al. 2013

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Six novel oxorhenium(V) complexes incorporating quinoline and isoquinoline carboxylic acid derivatives were prepared in good yields. Relying on the experimental conditions, compounds with two chelate ligands [ReOCl(iqc)2]·MeOH (1), [ReO(OMe)(iqc)2] (2), [ReO(OMe)(mqc)2] (3) and [ReO(OMe)(8-qc)2] (4) and compounds incorporating one bidentate ligand [ReOCl2(iqc)(PPh3)] (5) and [ReOCl2(mqc)(PPh3)] (6) were synthesized (iqcH = isoquinoline-1-carboxylic acid, mqcH = 4-methoxy-2-quinolinecarboxylic acid and 8-qcH = 8-quinolinecarboxylic acid). The reported compounds were characterized by spectroscopic methods and single crystal X-ray diffraction analysis. In compounds 1 and 2, one chelate ligand occupies an axial and an equatorial position, while the other one occupies two equatorial positions, forming a cis-(N,N) isomer. In turn, complexes 3 and 4 show a rare ligand arrangement with two trans-N, trans-O chelate ligands in the equatorial plane and a linear axial [O=Re-OMe] unit. The complexes with one chelate ligand 5 and 6 are cis-(Cl,Cl)-isomers. All compounds were tested as potential catalysts in the epoxidation of cyclooctene with 3 equiv. of tert-butylhydroperoxide. The yield of cyclooctane oxide varies between 16 and 68% (50 °C, 24 h), and the catalytic competency of compounds 1-6 was discussed with regard to the structure of each complex.

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“…Rhenium(V) complexes, initially investigated for their role in oxygen-atom transfer reactions, have found use as moisture-stable catalysts in some epoxidation reactions. − In early investigations, such compounds coordinated by bidentate or tetradentate Schiff base ligands were found to catalyze the epoxidation of cyclooctene with tert -butylhydroperoxide (TBHP) and gave yields of up to 66%. Also, oxorhenium(V) complexes with pyridylalkoxide ligands showed catalytic activity in olefin oxidation but only up to 30% conversion .…”

Section: Introductionmentioning

confidence: 99%

Oxorhenium(V) Complexes with Phenolate–Pyrazole Ligands for Olefin Epoxidation Using Hydrogen Peroxide

et al. 2014

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Oxorhenium(V) complexes of the general formula [ReOCl2(PPh3)(L)] (2a-c) and [ReOCl(L)2] (3a-c) with L being monoanionic, bidentate phenolate-pyrazole ligands 1a-c that bear substituents with various electronic features on the phenol ring (1a Br, 1b NO2, 1c OMe) were prepared. The compounds are stable toward moisture and air, allowing them to be handled in a normal lab atmosphere. All complexes were fully characterized by spectroscopic means and, in the case of 2b, 2c, 3b, and 3c, also by single-crystal X-ray diffraction analyses. Electrochemical investigations by cyclic voltammetry of complexes 3a-c showed a shift to more positive potentials for the Re(V)/Re(VI) redox couple in the order of 3b > 3a > 3c (R = NO2 > Br > OMe), reflecting the higher electrophilic character of the Re atom caused by the ligands 1a-c. Complexes 2a-c and 3a-c display excellent catalytic activity in the epoxidation of cyclooctene, where all six complexes give quantitative conversions to the epoxide within 3 h if tert-butylhydroperoxide (TBHP) is employed as oxidant. Moreover, they represent rare examples of oxorhenium(V) catalysts capable of using the green oxidant hydrogen peroxide, leading to high yields up to 74%. Also, green solvents such as diethylcarbonate can be used successfully in epoxidation reactions, albeit resulting in lower yields (up to 30%).

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Oxidorhenium(V) Complexes with Oxazolinylmethoxido Ligands – Structure and Catalytic Epoxidation

Cited by 15 publications

References 46 publications

Oxidorhenium(V) Complexes with Tetradentate Iminophenolate Ligands: Influence of Ligand Flexibility on the Coordination Motif and Oxygen-Atom-Transfer Activity

Oxidorhenium(V) Complexes with Tetradentate Iminophenolate Ligands: Influence of Ligand Flexibility on the Coordination Motif and Oxygen-Atom-Transfer Activity

Oxorhenium(v) complexes of quinoline and isoquinoline carboxylic acids – synthesis, structural characterization and catalytic application in epoxidation reactions

Oxorhenium(V) Complexes with Phenolate–Pyrazole Ligands for Olefin Epoxidation Using Hydrogen Peroxide

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