Pd-Catalyzed Cross-Couplings: On the Importance of the Catalyst Quantity Descriptors, mol % and ppm

ABSTRACT: This Review examines parts per million (ppm) palladium concentrations in catalytic cross-coupling reactions and their relationship with mole percentage (mol %). Most studies in catalytic cross-coupling chemistry have historically focused on the concentration ratio between (pre)catalyst and the limiting reagent (substrate), expressed as mol %. Several recent papers have outlined the use of ppm level palladium as an alternative means of describing catalytic cross-coupling reaction systems. This led us to delve deeper into the literature to assess whether ppm level palladium is a practically useful descriptor of catalyst quantities in palladium-catalyzed cross-coupling reactions. Indeed, we conjectured that many reactions could, unknowingly, have employed low ppm levels of palladium (pre)catalyst, and generally, what would the spread of ppm palladium look like across a selection of studies reported across the vast array of the cross-coupling chemistry literature. In a few selected examples, we have examined other metal catalyst systems for comparison with palladium.

Automated summary

This review analyzes the use of ppm level palladium concentrations in catalytic cross-coupling reactions and their relationship to mole percentage. It suggests that ppm level palladium could be a practical descriptor of catalyst quantities in palladium-catalyzed cross-coupling reactions. The study also compares palladium with other metal catalyst systems, providing insights into the spread of ppm palladium across various studies in cross-coupling chemistry literature.