Study of the Transient Reactive Pd(IV) Intermediate in the Pd(OAc)₂‐Catalyzed Oxidative Coupling Reaction System by Electrospray Ionization Tandem Mass Spectrometry

Abstract

Pd‐catalyzed oxidative coupling reaction was of great importance in the aromatic CH activation and the formation of new CO and CC bonds. Sanford has pioneered practical, directed CH activation reactions employing Pd(OAc)2 as catalyst since 2004. However, until now, the speculated reactive Pd(IV) transient intermediates in these reactions have not been isolated or directly detected from reaction solution. Electrospray ionization tandem mass spectrometry (ESI‐MS/MS) was used to intercept and characterize the reactive Pd(IV) transient intermediates in the solutions of Pd(OAc)2‐catalyzed oxidative coupling reactions. In this study, the Pd(IV) transient intermediates were detected from the solution of Pd(OAc)2‐catalyzed oxidative coupling reactions by ESI‐MS and the MS/MS of the intercepted Pd(IV) transient intermediate in reaction system was the same with the synthesized authentic Pd(IV) complex. Our ESI‐MS(/MS) studies confirmed the presence of Pd(IV) reaction transient intermediates. Most interestingly, the MS/MS of Pd(IV) transient intermediates showed the reductive elimination reactivity to Pd(II) complexes with new CO bond formation into product in gas phase, which was consistent with the proposed reactivity of the Pd(IV) transient intermediates in solution.

The application of electrospray ionization mass spectrometry to homogeneous catalysis

“…Dependence of intermediates and products to the type of solvents were clearly observed. (B)Observed fragmentation pathways by loss of the product (left) and loss of phenyl pyridine which is followed by dissociation of PdH (right)[54].While ESI-MS studies of systems catalyzed by other metals are less common, one report investigated a ruthenium-catalyzed reaction with naturally charged Ru-cluster intermediates. The cubane structure [Ru 4 (η 6 -C 6 H 6 ) 4 (OH) 4 ] 4+ was shown to exist in solution by direct observation of [Ru 4 (η 6 -C 6 H 6 ) 4 (O) 3 (OH)] + [9].…”

Two competing ionization processes in electrospray mass spectrometry of indolyl benzo[b ]carbazoles: formation of M+• versus [M + H]+

“…Electrospray ionization mass spectrometry (ESI‐MS) has emerged as a particularly useful tool for the analysis of various compounds, including the transient reactive intermediates . The ionization process in ESI‐MS has been viewed as a result of acid‐base reactions and/or a coordination with metal cations, involving formation of protonated molecules ([M + H] + ), deprotonated molecules ([M − H] − ), and/or cationized molecules (i.e., [M + Na] + ) .…”

Processed eggshell as sample carrier for rapid analysis of organometallic compounds by desorption electrospray ionization mass spectrometry

“…The frequently used ionization technique for organometallic compounds characterization is electrospray ionization (ESI), which plays an important role in connecting gas-phase and solution chemistries [1] by providing information of the analyte structure [2] and reaction mechanism. [3,4] However, it consumes much time and solvents to clean the ion source and might cause cross-talk and sample carryover effect when analyzing organometallic compounds by ESI-(MS). [5] The analyses of organometallic compounds by matrix-assisted laser desorption/ionization (MALDI)-MS with particular matrix were reported in some literatures.…”