title: Direct detection of key intermediates in rhodium(I)-catalyzed [2+2+2] cycloadditions of alkynes by ESI-MS.
abstract: 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.
authors.affiliation: Departament de Química, Universitat de Girona, Campus de Montilivi, s/n, 17071 Girona, Spain.
authors.forename: Magda
authors.initials: M
authors.lastname: Parera
authors.forename: Anna
authors.initials: A
authors.lastname: Dachs
authors.forename: Miquel
authors.initials: M
authors.lastname: Solà
authors.forename: Anna
authors.initials: A
authors.lastname: Pla-Quintana
authors.forename: Anna
authors.initials: A
authors.lastname: Roglans