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submitted on 27.02.2020 and posted on 28.02.2020by Anuj Joshi, Sofia Donnecke, Ori Granot, Dongju Shin, Scott Collins, Irina Paci, J Scott McIndoe
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 [Cp2Ti(NCMe)2]+[ZnCl3]–
and the olefin polymerization precatalyst [Cp2Zr(µ-Me)2AlMe2]+
[B(C6F5)4]–, 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.