Tracking Reaction Pathways by a Modular Flow Reactor Coupled to Electrospray Ionization Mass Spectrometry

Abstract

Reaction monitoring by electrospray ionization mass spectrometry (ESI-MS) is a popular method for investigation of reaction mechanisms. Here, we present a new approach based on a coupling between a modular capillary flow reactor and ESI-MS. The flow reactor allows a sequential adding of the reactants. We demonstrate the approach for oxidation of Ph2S by ArIO catalyzed by [(TPA)Fe(TfO)2] (ArIO=2-(tBuSO2)C6H4IO, TPA=tris(2-pyridylmethyl)amine, TfO−=triflate). In steps, we could follow the formation of the reactive iron(IV)oxo complexes, then the oxygen transfer reaction from the iron(IV)oxo to the sulfide, and finally the reoxidation of the iron complexes. The flow reactor also allows kinetic experiments by changing relative concentrations of the reactants. We could analyze in detail the formation of various [(TPA)FeIVO(X)]2+/+ complexes (X=MeCN, ArI, ArIO, TfO−) and compare their relative reactivity with Ph2S. The [(TPA)FeIVO(MeCN)]2+ complex is the most reactive complex for the oxygen atom transfer reaction whilst [(TPA)FeIVO(ArIO)]2+ prevails in solution under catalytic conditions.