scholarly journals Disulfonated Xantphos for Mass Spectrometric Mechanistic Analysis

2020 ◽  
Author(s):  
Mathias Paul ◽  
Katarina Lana Laketic ◽  
J. Scott McIndoe
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Ionization Mass ◽  
Real Time Analysis ◽  
Bite Angle ◽  
Anionic Ligand ◽  
Low Concentrations ◽  
Mechanistic Analysis ◽  
Binding Event ◽  
Initial Binding

Xantphos is a wide bite angle bisphosphine ligand that finds wide application in catalysis. Tracking its behavior during reactions under realistic reaction conditions can be difficult at low concentrations, and while electrospray ionization mass spectrometry (ESI-MS) is effective at real-time monitoring of catalytic reactions, it can only observe ions. Accordingly, we experimented with the dianionic disulfonated version of xantphos as a charged tag for mechanistic analysis. It proved to behave exactly as hoped, providing good intensity and enabled the direct study of both an initial binding event (to copper, very fast) and a subsequent transfer to another metal (palladium). Its dianionic nature makes it especially promising for the study of reactions in which metals change charge state, because a cationic metal complex with an anionic ligand is an invisible zwitterion, whereas a dianionic ligand would instead make the same cationic complex appear due to the overall charge of −1. As such, disulfonated xantphos holds genuine promise as a mechanistic probe in real time analysis using mass spectrometry.

scholarly journals Disulfonated Xantphos for Mass Spectrometric Mechanistic Analysis

2020 ◽  
Author(s):  
Mathias Paul ◽  
Katarina Laketic ◽  
J Scott McIndoe
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Ionization Mass ◽  
Real Time Analysis ◽  
Bite Angle ◽  
Anionic Ligand ◽  
Low Concentrations ◽  
Mechanistic Analysis ◽  
Binding Event ◽  
Initial Binding

Xantphos is a wide bite angle bisphosphine ligand that finds wide application in catalysis. Tracking its behavior during reactions under realistic reaction conditions can be difficult at low concentrations, and while electrospray ionization mass spectrometry (ESI-MS) is effective at real-time monitoring of catalytic reactions, it can only observe ions. Accordingly, we experimented with the dianionic disulfonated version of xantphos as a charged tag for mechanistic analysis. It proved to behave exactly as hoped, providing good intensity and enabled the direct study of both an initial binding event (to copper, very fast) and a subsequent transfer to another metal (palladium). Its dianionic nature makes it especially promising for the study of reactions in which metals change charge state, because a cationic metal complex with an anionic ligand is an invisible zwitterion, whereas a dianionic ligand would instead make the same cationic complex appear due to the overall charge of −1. As such, disulfonated xantphos holds genuine promise as a mechanistic probe in real time analysis using mass spectrometry.

scholarly journals Disulfonated Xantphos for Mass Spectrometric Mechanistic Analysis

2020 ◽  
Author(s):  
Mathias Paul ◽  
Katarina Laketic ◽  
J Scott McIndoe
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Ionization Mass ◽  
Real Time Analysis ◽  
Bite Angle ◽  
Anionic Ligand ◽  
Low Concentrations ◽  
Mechanistic Analysis ◽  
Binding Event ◽  
Initial Binding

Xantphos is a wide bite angle bisphosphine ligand that finds wide application in catalysis. Tracking its behavior during reactions under realistic reaction conditions can be difficult at low concentrations, and while electrospray ionization mass spectrometry (ESI-MS) is effective at real-time monitoring of catalytic reactions, it can only observe ions. Accordingly, we experimented with the dianionic disulfonated version of xantphos as a charged tag for mechanistic analysis. It proved to behave exactly as hoped, providing good intensity and enabled the direct study of both an initial binding event (to copper, very fast) and a subsequent transfer to another metal (palladium). Its dianionic nature makes it especially promising for the study of reactions in which metals change charge state, because a cationic metal complex with an anionic ligand is an invisible zwitterion, whereas a dianionic ligand would instead make the same cationic complex appear due to the overall charge of −1. As such, disulfonated xantphos holds genuine promise as a mechanistic probe in real time analysis using mass spectrometry.

scholarly journals Real-Time Analysis of Methylalumoxane Formation

2020 ◽  
Author(s):  
Anuj Joshi ◽  
Harmen S. Zijlstra ◽  
Elena Liles ◽  
Carina Concepcion ◽  
Mikko Linnolahti ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Complex Mixture ◽  
Activation Process ◽  
Ionization Mass ◽  
Time Analysis ◽  
Real Time Analysis ◽  
Sheet Structure ◽  
Industrial Samples ◽  
Hydrolysis Of

<p>Methylalumoxane (MAO), a perennially useful activator for olefin polymerization precatalysts, is famously intractable to structural elucidation, consisting as it does of a complex mixture of oligomers generated from hydrolysis of pyrophoric trimethylaluminum (TMA). Electrospray ionization mass spectrometry (ESI-MS) is capable of studying those oligomers that become charged during the activation process. We’ve exploited that ability to probe the synthesis of MAO in real time, starting less than a minute after the mixing of H<sub>2</sub>O and TMA and tracking the first half hour of reactivity. We find that the process does not involve an incremental build-up of oligomers; instead, oligomerization to species containing 12-15 aluminum atoms happens within a minute, with slower aggregation to higher molecular weight ions. The principal activated product of the benchtop synthesis is the same as that observed in industrial samples, namely [(MeAlO)<sub>16</sub>(Me<sub>3</sub>Al)<sub>6</sub>Me]<sup>–</sup>, and we have computationally located a new sheet structure for this ion 94 kJ mol<sup>-1</sup> lower in Gibbs energy than any previously calculated.</p>

scholarly journals Real-Time Analysis of Methylalumoxane Formation

2020 ◽  
Author(s):  
Anuj Joshi ◽  
Harmen S. Zijlstra ◽  
Elena Liles ◽  
Carina Concepcion ◽  
Mikko Linnolahti ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Complex Mixture ◽  
Activation Process ◽  
Ionization Mass ◽  
Time Analysis ◽  
Real Time Analysis ◽  
Sheet Structure ◽  
Industrial Samples ◽  
Hydrolysis Of

<p>Methylalumoxane (MAO), a perennially useful activator for olefin polymerization precatalysts, is famously intractable to structural elucidation, consisting as it does of a complex mixture of oligomers generated from hydrolysis of pyrophoric trimethylaluminum (TMA). Electrospray ionization mass spectrometry (ESI-MS) is capable of studying those oligomers that become charged during the activation process. We’ve exploited that ability to probe the synthesis of MAO in real time, starting less than a minute after the mixing of H<sub>2</sub>O and TMA and tracking the first half hour of reactivity. We find that the process does not involve an incremental build-up of oligomers; instead, oligomerization to species containing 12-15 aluminum atoms happens within a minute, with slower aggregation to higher molecular weight ions. The principal activated product of the benchtop synthesis is the same as that observed in industrial samples, namely [(MeAlO)<sub>16</sub>(Me<sub>3</sub>Al)<sub>6</sub>Me]<sup>–</sup>, and we have computationally located a new sheet structure for this ion 94 kJ mol<sup>-1</sup> lower in Gibbs energy than any previously calculated.</p>

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