The field of organometallic catalysis has attracted considerable interest from both academia and industry due to its broad applications in synthetic transformations. Pd, Ni, Rh, and Ir catalysts are critical for many of these transformations, often giving rise to remarkable reactivities that were unthinkable in the past. Owing to the tremendous advances in computational methodology, computing power and software, computational tools are increasingly employed to study, rationalize, and predict organometallic reactivities. Computational chemistry has in particular become a powerful tool to gain insights into the mechanisms of catalytic organometallic processes where the active catalytic species or intermediates have been challenging or impractical to study via experimental approaches. However, there are also numerous challenges associated with the mechanistic studies of catalytic transformations. These are not only due to the limits in accuracy of the employed computational methodology but also due to the inherent complex nature of catalytic cycles that frequently involve numerous intermediates and mechanistic possibilities. In addition, the conformational freedom of commonly employed organometallic complexes and ligands and the precise reproduction of conditions (solvent and additive effects) constitute additional challenges. Nevertheless, when teamed up with experimental studies or if used to address specific relative trends in reactivities, the employment of computational tools will undoubtedly offer deeper insights than any other currently available approach.

Several reviews and book chapters have dealt with different aspects of computational chemistry, including the underlying theory and methodology of computational chemistry, as well as its applications in areas such as organic reactivity, selectivity, and NMR calculations. In addition, several reviews covering transition metals have been reported, including that from our own group which reviews the combined computational and experimental studies of palladium in a variety of oxidation states. However, to the best of our knowledge, computational studies of synthetically relevant transformations enabled by Ni, Ir, or Rh have so far not been reviewed extensively.

Herein, we aim to present a review on computational studies of Pd-, Ni-, Rh-, and Ir-mediated transformations that have been conducted between 2008 and 2014 and been of significance for organic synthesis.

For clarity, this review has been divided into four sections (one for each metal) in which the computational studies are arranged according to specific reaction categories. In addition, a section on commonly employed computational methodology is presented. For the latter, it was not intended to present an exhaustive theoretical background but rather to provide a statistical overview (based on all publications referenced in the Pd, Ni, Rh, and Ir sections) of commonly employed methodology (i.e., Density Functional Theory (DFT) and on reviewing benchmark studies that address the computational performance in geometry and energy calculations of Pd-, Ni-, Rh-, and Ir-mediated reactions.

Overall, this review is meant to provide the reader with a summary of (i) the recent computational studies that have been conducted in relation to synthetically relevant Pd-, Ni-, Rh-, and Ir-catalyzed transformations, (ii) the choice and performance (when possible) of computational methodology used therein, and (iii) the numerous mechanistic insights gained. We hope that this review will stimulate further implementation of computational tools in mechanistic studies and inspire innovative theoretical developments for the study of organometallic transformations.