London dispersion forces (LDFs) are weak interactions arising from instantaneous induced dipoles between closely neighboring atoms and are the weakest component of Van der Waals interactions. However, in large molecules featuring high numbers of C–H moieties which produce many LDFs such as those found in multicyclic scaffolds, collectively amount to a significant energy contribution which can aid in the stabilization of otherwise non-isolable organometallic complexes.<br/><br/>Using these design principles, a series of homoleptic tris-substituted borane complexes formed via the anti-Markovnikov hydroboration of multicyclic terpenoid derivatives and borane have been isolated and characterized. The isolated boranes were found to exhibit highly unusual and crowded geometries. Their Lewis acidities were probed by the formation adducts with various Lewis bases. The bonding in the borane complexes has been interrogated by computational methods. Density Functional Theory (DFT) analysis showed that LDF effects arising from the many C–H moieties within the multicyclic components of the borane complexes were considerable, and the collective energy contribution resulted in attractive forces between the molecular frameworks of the natural product ligands. Adducts of the boranes were synthesized to probe the relationship between Lewis acidity and dispersion. We further report on the coordination chemistry and geometry of these complexes as a consequence of the LDF interactions present, and how this tunes the reactivity of the organometallic complexes with small molecules.These observations provide key insights into the significance and relevance that accumulative LDF effects can play in both organic and inorganic chemical systems.

Boranes as probes for London dispersion force effects in multicyclic natural products

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.