Process of Elimination

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Science  14 Mar 2014:
Vol. 343, Issue 6176, pp. 1179
DOI: 10.1126/science.343.6176.1179-a

Transition metals such as rhodium and palladium (Pd) often catalyze reactions through a pair of processes termed oxidative addition and reductive elimination. Effectively, the metal inserts itself between two bonded atoms, and then after some rearrangements or substitutions in the coordination sphere, a different bond forms via the reverse process. Pérez-Temprano et al. explored the factors underlying which bonds form most readily by reductive elimination from Pd(IV). They prepared a complex with fluoride, tosyl-substituted nitrogen (NHTs), and aryl as well as alkyl carbon ligands, and then measured a ratio of alkyl C-F, C-C, and alkyl C-N bonded products of roughly 5:3:1. By adding an (NHTs) salt to the reaction mixture, the authors could shift the ratio almost completely in favor of the C-N elimination pathway. Kinetic studies implicated a mechanism in which dissociation of (NHTs) from Pd leads to a transient five-coordinate intermediate common to all three product channels, with the C-N pathway proceeding stepwise via subsequent attack by the nitrogen anion at carbon. The results could help to optimize synthetic protocols for C-N bond formation.

J. Am. Chem. Soc. 136, 10.1021/ja411433f (2014).

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