Catalyst selection: survival of the weakest
ADF calculations support a new mass spectrometric method to select the best catalysts from a combinatorial library in a combined experimental-theoretical study.
The turnover frequency determining step for the Pd-catalyzed allylic alkylation is the nucleophilic attack on the Pd-allyl intermediate. Destabilizing this intermediate decreases the activation energy, thus improving the catalyst. Consequently, the least abundant Pd-allyl complex in the ESI-MS spectrum is the most active catalyst: ‘survival of the weakest’. The DFT calculations are in agreement with the experiments: larger bite angles increase the steric congestion and thus strain at Pd, destabilizing the diphosphino-Pd-allyl complex, leading to lower MS abundance and a higher TOF.
Destabilizing the Pd-allyl intermediate enhances catalytic allylic alkylation.
J. Wassenaar, E. Jansen, W.-J. van Zeist, F. M. Bickelhaupt, M. A. Siegler, A. L. Spek, and J. N. H. Reek Catalyst selection based on intermediate stability measured by mass spectrometry. Nature Chem. 2, 417 (2010)
