Reaction of O2 with [(-)-sparteine]Pd(H)Cl: evidence for an intramolecular [H-L]+ "reductive elimination" pathway.

Nattawan Decharin, Brian V Popp, Shannon S Stahl

Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.

Journal of the American Chemical Society 2011 Aug 31

filter terms:

Sp)PdCl(2) [Sp = (-)-sparteine] catalyzes a number of different aerobic oxidation reactions, and reaction of O(2) with a Pd(II)-hydride intermediate, (Sp)Pd(H)Cl (1), is a key step in the proposed catalytic mechanism. Previous computational studies suggest that O(2) inserts into the Pd(II)-H bond, initiated by abstraction of the hydrogen atom by O(2). Experimental and computational results obtained in the present study challenge this conclusion. Oxygenation of in-situ-generated (Sp)Pd(H)Cl exhibits a zero-order dependence on [O(2)]. This result is inconsistent with a bimolecular H-atom-abstraction pathway, and DFT computational studies identify a novel "reductive elimination" mechanism, in which the chelating nitrogen ligand undergoes intramolecular deprotonation of the Pd(II)-hydride. The relevance of this mechanism to other Pd(II) oxidation catalysts with chelating nitrogen ligands is evaluated.

Citation

Nattawan Decharin, Brian V Popp, Shannon S Stahl. Reaction of O2 with [(-)-sparteine]Pd(H)Cl: evidence for an intramolecular [H-L]+ "reductive elimination" pathway. Journal of the American Chemical Society. 2011 Aug 31;133(34):13268-71