Mechanistic studies on the selective oxidative carbonylation of MeOH to dimethyl oxalate catalyzed by [Pd(COOMe)n(TsO)2−n(PPh3)2] (n = 0, 1, 2) using p-benzoquinone as a stoichiometric oxidant
| Autor: | Luigi Toniolo, Emanuele Amadio |
|---|---|
| Rok vydání: | 2014 |
| Předmět: |
chemistry.chemical_classification
Base (chemistry) Organic Chemistry Nuclear magnetic resonance spectroscopy Biochemistry Benzoquinone Medicinal chemistry Catalysis Inorganic Chemistry chemistry.chemical_compound chemistry Catalytic cycle Materials Chemistry Organic chemistry Reactivity (chemistry) Physical and Theoretical Chemistry Dimethyl carbonate Dimethyl oxalate |
| Zdroj: | Journal of Organometallic Chemistry. 750:74-79 |
| ISSN: | 0022-328X |
| DOI: | 10.1016/j.jorganchem.2013.11.009 |
| Popis: | The reactivity of the complexes cis -[Pd(OTs) 2 (PPh 3 ) 2 ] ( I ), trans -[Pd(COOMe)(OTs)(PPh 3 ) 2 ] ( II ) and trans -[(COOMe) 2 (PPh 3 ) 2 ] ( III ), regarding the catalytic oxidative carbonylation of MeOH to dimethyl oxalate (DMO) using benzoquinone (BQ) as a stoichiometric oxidant, has been studied in CD 2 Cl 2 /MeOH (10/1, v/v) by 1 H and 31 P{ 1 H} NMR spectroscopy. I reacts with CO and MeOH at 193 K giving II , which is transformed into III upon addition of a base. The same occurs in the presence of BQ. Instead, if the base is added before admission of CO, [Pd(BQ)(PPh 3 ) 2 ] is formed. Starting also from II , complex III is formed only after addition of a base. The base neutralizes TsOH which is formed in the transformation of I to II and III . III is unstable in the presence of 1 equivalent of TsOH and it is transformed into II . At 333 K, under 0.4 MPa of CO, III decomposes with formation of DMO and dimethyl carbonate (DMC) (15%) each), whereas, in the presence of BQ, III is unstable already at 298 K, with formation of only DMO (10%). Catalysis to DMO is observed at 333 K. Thus BQ enhances the reactivity of III and directs the catalysis selectively to DMO. I , II and III have also been used in catalytic experiments in pure MeOH at 298 K, under 0.3 MPa of CO. II and III are active even in the absence of a base (TOF ca . 30 h −1 ). I is active only after addition of a base. A catalytic cycle is proposed. |
| Databáze: | OpenAIRE |
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