Four Criteria for Evaluating Pure Component Spectral Estimates and the Subsequent Identification of Intermediates in Homogeneous Catalysis

In situ spectroscopic studies are increasingly used to better understand mechanistic aspects of homogeneous catalytic systems. In many cases, the raw measured spectra are simply inspected to identify new bands that appear under catalytic conditions. However, various types of advanced signal processing techniques can often provide considerably more detail and can even provide the underlying pure component spectra. Since intermediates are rarely isolatable, the availability of new pure component spectral estimates suggests a need for internal consistency checks and other forms of validation. The present contribution surveys four recently developed criteria for assessing the accuracy of pure component spectral estimates and then their subsequent usefulness in confirming the identity of newly discovered and nonisolatable intermediates in complex metal-mediated syntheses. Criteria I and II address the consistency of spectral estimates within an experimental study and between different experimental studies, and criteria III and IV deal with establishing the stoichiometry and geometry of the nonisolatable complexes and their potential role as intermediates, respectively.