Cryogenic Ion Spectroscopy of Reactive Organometallic Intermediates and Non-covalent Complexes.

摘要

The analysis of transient chemical intermediates present during a catalytic reaction cycle offers a direct means for physical chemists to contribute to ongoing synthetic efforts in organic and organometallic synthesis. Cryogenic ion vibrational predissociation (CIVP) spectroscopy, a recently developed laser spectroscopic technique, is an ideal means to isolate and freeze electrosprayed ions along their reaction profile, and enables subsequent characterization with infrared spectroscopy. The studies presented here utilize CIVP spectroscopy to track the spectral signatures of structural reorganization in a collection of supramolecular and catalytic organometallic systems. With a limited conformational landscape, the diphenyactylene molecular switch is shown to change between three distinct conformations depending on the complexing counterion, giving a clear means by which to identify the spectral signatures of functionalities found in reactive organometallic complexes. With these spectral signatures identified, CIVP is utilized to quench the internal energy of a variety of large macromolecules. First, the infrared characterization of a manganese-based organometallic intermediate extracted directly from solution is presented, and the binding motif of the activated oxo-ligand is identified. Next, species created in the initial oxidative activation of an organometallic iridium water oxidation precursor are identified, and their multiple conformations are characterized using a two-laser isomer sorting technique. Additionally, to address technical demands in future studies on heavy, isotopically complex organometallic compounds, the implementation of a high performance Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometer is described. Finally, a review of recent progress in CIVP is presented, with an outlook on the cryogenic processing of very large molecules and the activation of species directly in the gas phase.