Artículo
Monomeric alkoxide and alkylcarbonate complexes of nickel and palladium stabilized with the iPrPCP pincer ligand: a model for the catalytic carboxylation of alcohols to alkyl carbonates
Autor/es | Martínez Prieto, Luis Miguel
Palma Ramírez, María del Pilar Cámpora Pérez, Juan |
Departamento | Universidad de Sevilla. Departamento de Química Inorgánica |
Fecha de publicación | 2019 |
Fecha de depósito | 2022-10-07 |
Publicado en |
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Resumen | Monomeric alkoxo complexes of the type [(iPrPCP)M-OR] (M = Ni or Pd; R = Me, Et, CH2CH2OH; iPrPCP =
2,6-bis(diisopropylphosphino)phenyl) react rapidly with CO2 to afford the corresponding alkylcarbonates
[(iPrPCP)M-OCOOR]. ... Monomeric alkoxo complexes of the type [(iPrPCP)M-OR] (M = Ni or Pd; R = Me, Et, CH2CH2OH; iPrPCP = 2,6-bis(diisopropylphosphino)phenyl) react rapidly with CO2 to afford the corresponding alkylcarbonates [(iPrPCP)M-OCOOR]. We have investigated the reactions of these compounds as models for key steps of catalytic synthesis of organic carbonates from alcohols and CO2. The MOCO-OR linkage is kinetically labile, and readily exchanges the OR group with water or other alcohols (R’OH), to afford equilibrium mixtures containing ROH and [(iPrPCP)M-OCOOH] (bicarbonate) or [(iPrPCP)M-OCOOR’], respectively. However, [(iPrPCP)M-OCOOR] complexes are thermally stable and remain indefinitely stable in solution when these are kept in sealed vessels. The constants for the exchange equilibria have been interpreted, showing that CO2 insertion into M-O bonds is thermodynamically more favorable for M-OR than for M-OH. Alkylcarbonate complexes [(iPrPCP)M-OCOOR] fail to undergo nucleophilic attack by ROH to yield organic carbonates ROCOOR, either intermolecularly (using neat ROH solvent) or in intramolecular fashion (e.g., [(iPrPCP)M-OCOOCH2CH2OH]). In contrast, [(iPrPCP)M-OCOOMe] complexes react with a variety of electrophilic methylating reagents (MeX) to afford dimethylcarbonate and [(iPrPCP)M-X]. The reaction rates increase in the order X = OTs < IMe ≪ OTf and Ni < Pd. These findings suggest that a suitable catalyst design should combine basic and electrophilic alcohol activation sites in order to perform alkyl carbonate syntheses via direct alcohol carboxylation. |
Agencias financiadoras | Ministerio de Economía y Competitividad (MINECO). España European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER) |
Identificador del proyecto | CTQ2015-68978-P |
Cita | Martínez Prieto, L.M., Palma Ramírez, M.d.P. y Cámpora Pérez, J. (2019). Monomeric alkoxide and alkylcarbonate complexes of nickel and palladium stabilized with the iPrPCP pincer ligand: a model for the catalytic carboxylation of alcohols to alkyl carbonates. Dalton Transactions [English] ISSNs Print: URL http://pubs.rsc.org/en/Journals/JournalIssues/DT Publishers, 48 (4), 1351-1366. https://doi.org/10.1039/c8dt04919j. |
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