Mechanistic insights from mass spectrometry: examination of the elementary steps of catalytic reactions in the gas phase

Abstract

Real-time mass spectrometric monitoring of speciation in a catalytic reaction while it is occurring provides powerful insights into mechanistic aspects of the reaction, but cannot be expected to elucidate all details. However, mass spectrometers are not limited just to analysis: they can serve as reaction vessels in their own right, and given their powers of separation and activation in the gas phase, they are also capable of generating and isolating reactive intermediates. We can use these capabilities to help fill in our overall understanding of the catalytic cycle by examining the elementary steps that make it up. This article provides examples of how these simple reactions have been examined in the gas phase.

Gas‐Phase Dehydrogenation of Alkanes: C−H Activation by a Graphene‐Supported Nickel Single‐Atom Catalyst Model

“…A strong understanding of the underlying catalytic mechanisms is crucial to the advancement of this field. Surface analysis tools can become less effective at the atomic level, but robust single molecule techniques, such as mass spectrometry, are capable of studying catalytic organometallic mechanisms in detail at the single molecule level . In the past, bare metals and metal clusters have been generated in the gas phase as model systems for heterogeneous catalysts .…”

“…Surface analysis tools can become less effective at the atomic level, but robust single molecule techniques,s uch as mass spectrometry,a re capable of studying catalytic organometallic mechanisms in detail at the single molecule level. [8][9][10][11][12] In the past, bare metals and metal clusters have been generated in the gas phase as model systems for heterogeneous catalysts. [13][14][15][16][17] Using established gas-phase synthetic techniques, [18,19] we have generated the first example of ag as-phase zero-valent Ni complex, I,t hat can act as amodel for apristine graphene-supported SAC.…”

A Mechanistic Investigation of the Suzuki Polycondensation Reaction Using MS/MS Methods

“…PPh3 (an L-type ligand) is readily lost from palladium through a simple ligand dissociation, hence the lower voltage required compared to decomposition of the triphenylphosphonium tag. L-type ligands tend to dissociate first because they are stable as free entities, while X-type ligands take more energy for homolytic dissociation due to the requirement of radical formation.. 26,28,39,40 The product ion spectra of the 2n ions were especially interesting because there is some structural ambiguity in all 2n ions except 20. 20 must be [(Ph3P)2Pd(C6H4CH2PPh3)I] + , the product of oxidative addition of 10 to Pd(PPh3)n. In contrast 21 could be analogous to 20 i.e.…”

“…[18][19][20][21][22] We have previously used real-time mass spectrometric methods to study the Suzuki-Miyaura cross-coupling (SMC) reaction and various other transformations. [23][24][25][26][27][28][29] Our standard method of real-time reaction analysis involves transporting a solution from the reaction flask to an electrospray ionization (ESI) mass spectrometer using pressurized sample infusion (PSI). 30,31 ESI-MS provides powerful real-time information, but the technique can observe only ions, not neutrals, so the entities of interest need to carry a charge (inherent, or appended synthetically in a location that does not affect the chemistry under investigation).…”

Ionization methods for the mass spectrometry of organometallic compounds

“…Most often, mild CID causes organometallic ions to dissociate L‐type ligands, but other common unimolecular reactions can also occur, such as beta elimination or reductive elimination. The combination of CID, m/z , isotope pattern, chemical intuition, and molecular formula finders is a powerful means of identifying unknown compounds …”