Gas-Phase Oxidation of Reactive Organometallic Ions

Abstract

Analysis of highly reactive compounds at very low concentration in solution using electrospray ionization mass spectrometry requires the use of exhaustively purified solvents. It has generally been assumed that desolvation gas purity needs to be similarly high, and so most chemists working in this space have relied upon high purity gas. However, the increasingly competitiveness of nitrogen generators, which provide gas purity levels that vary inversely with flow rate, prompted an investigation of the effect of gas-phase oxygen on the speciation of ions. For moderately oxygen sensitive species such as phosphines, no gas-phase oxidation was observed. Even the most reactive species studied, the reduced titanium complex [Cp<sub>2</sub>Ti(NCMe)<sub>2</sub>]<sup>+</sup>[ZnCl<sub>3</sub>]<sup>–</sup> and the olefin polymerization precatalyst [Cp<sub>2</sub>Zr(µ-Me)<sub>2</sub>AlMe<sub>2</sub>]<sup>+</sup> [B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]<sup>–</sup>, only exhibited detectable oxidation when they were rendered coordinatively unsaturated through in-source fragmentation. Computational chemistry allowed us to find the most plausible pathways for the observed chemistry in the absence of observed intermediates. The results provide insight into the gas-phase oxidation of reactive species and should assure experimentalists that evidence of significant oxidation is likely a solution rather than a gas-phase process, even when relatively low-purity nitrogen is used for desolvation.

Catalyst Deactivation Processes during 1-Hexene Polymerization

“…Similar effects have been noted before in the case of ion 1, which generates ion 2 via CID within the source compartment of the mass spectrometer. 26,46 Indeed in those experiments where ion 6 was prominent, the same was true of ion 2 -prior to the introduction of hexene.…”

“…The relative intensities of m/z 363 and 279 were highly variable in this work, and experiments at different cone voltages established that the loss of hexene from 363 occurs at low collision energies, during transit of ions from the source compartment to the high vacuum region of the spectrometer. Even subtle changes in the pressure (and presumably atmospheric composition 46 ) within the source compartment had noticeable effects on the ratio of these two ions. Similar effects have been noted before in the case of ion 1, which generates ion 2 via CID within the source compartment of the mass spectrometer.…”