Palladium’s C–H activation advantage

Reactions that sever typically unreactive carbon-hydrogen bonds, known as C–H activations, are a well-studied staple of organic chemistry. So it’s a well-known fact that palladium-based catalysts tend to work better than ones based on palladium’s cheaper, possibly greener first-row counterpart, nickel. But among the reams of scholarly papers about C–H activation methods and mechanisms, Demyan Prokopchuk saw something missing: a detailed comparison of nickel and palladium’s C–H bond-breaking abilities under identical conditions. “Really, nobody took a step back and asked, ‘How do we systematically even measure the C-H bond strength in this activation step?’ ” he says. He and his team at Rutgers University–Newark took it upon themselves to change that.The plan was simple, as these things go: create model complexes—one nickel based, the other palladium based, but otherwise identical—in which the metal center coordinates to a carbon-hydrogen bond in a carefully chosen alkane pincer ligand. The next step was to experimentally determine using nuclear magnetic resonance spectroscopy and acid-base equilibria how much each metal weakens, or activates, the bond.Prokopchuk and his group published their initial results on the nickel complex in 2022 (J. Am. Chem. Soc. DOI: 10.1021/jacs.2c05667). Their investigation into the palladium complex came out on Sept. 9 (J. Am. Chem. Soc. 2025, DOI: 10.1021/jacs.5c07649).Synthesizing the complexes was fairly straightforward, Prokopchuk says. By using X-ray crystallography, the researchers got a good “solid-state snapshot,” he says, of a key intermediate containing an agostic interaction, meaning the hydrogen atom is bound partly to carbon and partly to the metal center.Measuring