The study of the mechanism of a reaction is always a complicated task that usually starts with a draft on paper. You apply your knowledge in chemistry to make a hypothesis that you then need to prove with experimental facts. Even when the analyses performed in the lab strongly support your proposals you will never have complete certainty if you don’t have “the photo” of your “intermediate suspects”. A common strategy for the study of reaction mechanisms involving organometallic species is the synthesis of the proposed intermediates (your suspects) and then try to capture “the photo” with the use of X-Ray crystallography techniques. I mean, you have to pray for your compounds to crystallise…
Because I have suffered all these problems in the lab is why I consider so remarkable the mechanistic study of a Palladium-mediated aromatic bromination published by Fujita and co-workers in 2014 in JACS. The strategy carried out by the authors consists of the use of a crystalline flask of ZnI2 and tris(4-pyridyl)triazine in which the Palladium complex object of the study is embedded. The reaction is performed in the crystalline flask and the intermediates captured in-situ by time dependent X-Ray diffraction. The authors literally take “photos” of the catalytic cycle of the reaction and show in-situ cristallography as a great tool for the elucidation of reaction mechanisms.
Do you want to know more? Then go directly to the source.
Ikemoto, Y. Inokuma, K. Rissanen and M. Fujita. X‑ray Snapshot Observation of Palladium-Mediated Aromatic Bromination in a Porous Complex. J. Am. Chem. Soc. 2014, 136, 6982-6985