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.

The application of electrospray ionization mass spectrometry to homogeneous catalysis

“…In 2012 an ESI-MS investigation of Rh-catalyzed [2+2+2] cycloaddition reaction was reported [55]. In this DFT-supported study, several key intermediates were observed and characterized by MS/MS tandem spectrometry.…”

“…Rhodim-catalyzed [2+2+2] cycloaddition mechanism for of diynes and monoynes based on detected species by ESI-MS and CID characterization[55].…”

Indenyl Effect Due to Metal Slippage? Computational Exploration of Rhodium‐Catalyzed Acetylene [2+2+2] Cyclotrimerization

“…The former is a coordinatively saturated intermediate due to the presence of CO. [38] CO-5-Cp is converted by reductive elimination into CO-6-Cp, from which benzene is cleaved by stepwise addition of two acetylene molecules. The conversion of CO-1-Cp into CO-2-Cp is accompanied by the slippage change h 1 !h 3 + h 2 and the release of 65.8 kcal mol À1 .…”

Practical approaches to the ESI-MS analysis of catalytic reactions

“…For reactive organometallics, this is especially probable since many metals are strongly oxophilic. Such reactions are usually not problematic, as understanding the source of such ions is typically sufficient for correct interpretation, and the promiscuity of ions towards reaction offers an entirely new opportunity to push the instrument beyond a simple means of analysis, and instead using it as a reaction chamber. Details of such reactions are beyond the scope of this perspective (and have been well reviewed elsewhere), but an example from our group is illustrative of the kind of experiment that can be conducted.…”