Mechanism of C−H Bond Activation of Alkyl-Substituted Benzenes by Cationic Platinum(II) Complexes
While all methyl- and ethyl-substituted benzenes react with diimine Pt(II) methyl cations to give η^3-benzyl products, they do not all get there by the same pathway. For toluene and p-xylene, isotopic labeling shows that initial activation occurs at aryl positions with subsequent intermolecular conversion to the benzyl product. For ethylbenzene and 1,4-diethylbenzene, initial activation takes place exclusively at aryl C−H bonds, and conversion to the η^3-benzyl product takes place via intramolecular isomerization. Only in the most extreme case of steric crowding the reaction of a bulky diimine platinum methyl cation (Ar = Mes) with triethylbenzene does direct activation of the ethyl group become preferred to aryl activation.
Additional Information© 2005 American Chemical Society. Received April 4, 2005. Publication Date (Web): June 22, 2005. Funding for this work was provided by the bp MC2 program and the NIH in the form of a NRSA fellowship to T.G.D. (GM070272-02). We thank Jonathan S. Owen for insightful discussions, Dr. Scott Ross for assistance with NMR spectrometry, Dr. Mona Shahgholi for mass spectrometry data, and Mr. Larry M. Henling for crystallographic analysis.
Supplemental Material - om050251msi20050404_055926.cif
Supplemental Material - om050251msi20050509_053711.pdf