ESI-MS Detection of Proposed Reaction Intermediates in the Air-Promoted and Ligand-Modulated Oxidative Heck Reaction

Abstract

Electrospray ionization mass spectrometry (ESI-MS) and subsequent MS/MS analyses were used to directly detect palladium-containing cationic reaction intermediates in a ligand controlled palladium(II)-catalyzed oxidative Heck arylation. All potential intermediates were observed as dmphen-ligated palladium(II) species, suggesting that the dmphen bidentate ligand is attached to the metal center during the entire catalytic cycle. The study supports previous mechanistic propositions and provides new information regarding the composition of aryl-containing Pd(II) complexes in an ongoing oxidative Heck reaction. In addition, sodium acetate was found to be a useful base alternative to previously used tertiary amines.

The application of electrospray ionization mass spectrometry to homogeneous catalysis

“…While ESI-MS analysis of this type can reveal the presence of any low-concentration potential intermediates, simple detection of a low concentration species does not clarify its role in the overall solution phase reaction. In order to understand the role of observed species it would be highly desirable to monitor the reaction profile of key species continuously over the course of the reaction in such a way that kinetic data can be obtained [8,18,89,92]. A few groups, including our own, have worked to develop such methodology.…”

“…Since then, the primary use of ESI-MS in the area of solution-phase organometallic chemistry has been in the identification of short-lived, low concentration intermediates from catalytic mixtures. Toward this end, ESI-MS has been used to study catalytic oxidations [5][6][7][8], hydrogenations [9][10][11], hydrosilylations [12] and carbon-carbon bond-forming [13][14][15] reactions with the most attention given to palladium-catalyzed carbon-carbon bond-forming reactions [14,[16][17][18][19][20][21]. A number of book chapters have been written on the subject of ESI-MS analysis of organometallic reaction intermediates [22][23][24] and this review aims to highlight more recent advances and new directions in the field.…”

“…Cationic intermediates in the oxidative Heck arylation of 1-vinyl-2-pyrrolidinone by ptolylboronic acid observed by ESI(+)-MS[18].Reaction monitoring by ESI-MS is not limited to monitoring catalytic intermediates, valuable information can also be obtained by monitoring the interplay of the various reactants in solution. In 2007, a manganese-catalyzed oxygen-evolving system that acts as a model for the oxygen-evolving complex of photosystem II was also studied by periodic sampling and analysis by ESI-MS (as well as EPR, UV/Vis, and XAS).…”

Palladium Intermediates in Solution

“…The same authors also used ESI-MS/MS to study an air-promoted oxidative Heck reaction between arylboronic acids and enamides as electron-rich olefins (Scheme 7.13) [29]. In addition to the conventional Mizoroki-Heck reaction of unsaturated compounds with organic halides or triflates as electrophiles, the use of nucleophilic organometallic reagents, such as organoboron compounds, has also been studied [30].…”

Catalytic Amide‐Mediated Methyl Transfer from Silanes to Alkenes in Fujiwara–Moritani Oxidative Coupling

“…[14] It may be understood in the context of a catalytic cycle (Scheme 3, step f), based on previous postulates for Heck reactions under oxidative conditions. [15] [a] 1 equiv of monosilyl reagents, 0.5 equiv of disilyl reagents (see The synthetic scope of the methyl-transfer method.…”