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Título: | Palladium(II) carboxylates and palladium(I) carbonyl carboxylate complexes as catalysts for olefin cyclopropanation with ethyl diazoacetate |
Autor: | Shishilov, Oleg N.; Stromnova, Tatiana A.; Cámpora, Juan CSIC ORCID; Palma, Pilar CSIC ORCID; Cartes, M. Ángeles CSIC; Martínez-Prieto, Luis Miguel CSIC ORCID | Palabras clave: | Palladium carbonyl carboxylate complexes Catalist Olefin Cyclopropane Diazo compounds H NMR |
Fecha de publicación: | 8-jul-2009 | Editor: | Royal Society of Chemistry (UK) | Citación: | Dalton Transactions (33) : 6626-6633 (2009) | Resumen: | Palladium(I) carbonyl carboxylate complexes [Pd(μ-CO)(μ-RCO2)]n (R = Me, n = 4; R = CMe3, n = 6) and the corresponding palladium(II) carboxylates (acetate and pivalate) catalyze the cyclopropanation of olefins with ethyl diazoacetate. The performance of these catalysts is similar in terms of selectivity and cyclopropane yields, regardless of the oxidation state of the metal center. However the rates of the cyclopropanation reactions are significantly higher for the acetate based catalysts than for the pivalate derivatives, which suggests that the main catalytic species are carboxylate containing palladium complexes. Kinetic measurements show that reaction rates are independent of the olefin concentration when these are 1-hexene or styrene, but norbornene exerts an inhibitory effect. In spite of this, competition experiments indicate that the cyclopropanation of styrene is 2.2 times as favorable as that of 1-hexene for any of the four catalysts. These observations indicate that while the rate-determining formation of the intermediate palladium carbenoid species is controlled by the catalyst structure, this is followed by a rapid and less specific cyclopropanation step that is not affected by the nature of the carboxylategroups present in the catalyst. An independent test using a 1:1 benzene/cyclohexane mixture of solvents showed that the transfer of ethoxycarbonylcarbene (:C(CO2Et)H) to these molecules is unselective (relative rate of benzene/cyclohexane functionalization ≈1.8, independent of the catalyst). This result can be interpreted as an indication of the involvement of free ethoxycarbonylcarbene in the carbene transfer step. | Descripción: | 8 páginas, 2 figuras, 3 tablas, 4 esquemas. | Versión del editor: | http://dx.doi.org/10.1039/b904891j | URI: | http://hdl.handle.net/10261/37091 | DOI: | 10.1039/B904891J | ISSN: | 1477-9226 |
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