Mass spectrometry allows for the detection and manipulation of low-concentration species extracted from complex reactive mixtures, and therefore, it is a powerful tool for studying reaction intermediates in homogeneous catalysis. However, only limited chemical structure information can be obtained from conventional MS experiments. The recent addition of cryogenic ion vibrational predissociation spectroscopy to the MS toolkit allows for detailed structural characterization of mass-selected ions. This talk will highlight the capabilities of this approach with recent results on the reaction intermediates in the [Ru(tpy)(bpy)(H2O)]2+ catalyzed water oxidation. Three central capabilities will be illustrated: 1) Characterization of long-lived intermediates using electrochemical electrospray ionization (EC-ESI) allowing access to products of the first two oxidation steps: [Ru-OH]2+and [Ru=O]2+ intermediates. 2) Controlled formation of unstable or inaccessible intermediates using ion-molecule reactions allowing for production of the [Ru-O2]2+ and [Ru=O]2+ intermediates. These species are formed by collisional activation of [Ru-H2O]2+ complex resulting in an activated [Ru]2+ which is subsequently reacted with O2 or O3 in a temperature-controlled ion trap. Vibrational spectroscopy is then used to clarify the structure and spin multiplicity of these intermediates. 3) Elucidation of the role of the hydrogen-bonded water solvation network around the active site. Using low-temperature condensation in ion trap allows the clustering of water molecules at the active site. Vibrational spectroscopy then reveals how water network can influence the reactivity.

Spectroscopic characterization of mass-selected catalytic reaction intermediates

ACS Fall 2020 Virtual Meeting

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