DUGi

Direct detection of key intermediates in rhodium(I)-catalyzed [2+2+2] cycloadditions of alkynes by ESI-MS

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@2072@@296588

The mechanism of the Rh-catalysed [2+2+2] cycloaddition reaction of diynes with monoynes has been examined using ESI-MS and ESI-CID-MS analysis. The catalytic system used consisted of the combination of a cationic rhodium(I) complex with bisphosphine ligands, which generates highly active complexes that can be detected by ESI(+) experiments. ESI-MS on-line monitoring has allowed the detection for the first time of all of the intermediates in the catalytic cycle, supporting the mechanistic proposal based mainly on theoretical calculations. For all ESI-MS experiments, the structural assignments of ions are supported by tandem mass spectrometry analyses. Computer model studies based on density functional theory (DFT) support the structural proposal made for the monoyne insertion intermediate. The collective studies provide new insight into the reactivity of cationic rhodacyclopentadienes, which should facilitate the design of related rhodium-catalysed C-C couplings. Detecting intermediates: The mechanism of the Rh I-catalyzed [2+2+2] cycloaddition reaction was examined using ESI-MS (see scheme). All of the intermediates in the catalytic cycle were detected by ESI-MS for the first time and characterized by ESI-MS/MS. DFT was used to support the structural proposal made for the monoyne insertion intermediate

Financial support from the Spanish Ministry of Education and Science (MEC) (Projects Nos.: CTQ2011-23121/BQU and CTQ2011-23156/BQU) and the DIUE of the Generalitat de Catalunya (Project No.: 2009SGR637) is gratefully acknowledged. M. P. thanks the Generalitat de Catalunya for a predoctoral grant. We would also like to thank Anna Costa for her technical assistance with the ESI mass spectrometer and Jesus Orduna for helpful discussions. Excellent service by the Centre de Serveis Cientifics i Academics de Catalunya (CESCA) is gratefully acknowledged. Support for the research of M. S. was received through the ICREA Academia 2009 prize for excellence in research funded by the DIUE of the Generalitat de Catalunya

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