Activity-Based Screening of Homogeneous Catalysts through the Rapid Assessment of Theoretically Derived Turnover Frequencies

In homogeneous catalysis,
the turnover frequency (TOF) and turnover
number (TON) are the most commonly used quantities that experimentally
describe catalytic activity. Computational studies, on the other hand,
generally yield the ubiquitous free energy profile, which only provides
the relative heights of different intermediates and transition states
for a given reaction mechanism. This information, however, can be
converted into a theoretical TOF through use of the energy span model.
Clearly, directly computing turnover frequencies not only allows easy
comparison of the activity of different catalysts but also provides
a means of directly comparing theory and experiment. Nonetheless,
obtaining detailed free energy profiles for many catalysts is computationally
costly. To overcome this and accelerate the rate at which prospective
catalysts can be screened, here we use linear scaling relationships
in tandem with the energy span model to create volcano plots that
relate an easily and quickly computed energetic descriptor variable
with a catalyst’s turnover frequency. As a demonstration of
their ability, we use these “TOF volcanoes” to rapidly
screen prospective transition metal/pincer-ligand catalysts based
on activity in facilitating the hydrogenation of CO2 to
formate.