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Published October 10, 2011 | Supplemental Material
Journal Article Open

Synthesis and Characterization of the k^2-acac-O,O Complex Os_(IV)(acac)_2PhCl and Study of CH Activation with Benzene

Abstract

We have synthesized and fully characterized the air-stable complex (κ^2-acac-O,O)2Os^(IV)(Ph)Cl (Cl-1-Ph; acac-O,O = acetylacetonate), which reacts with C_6D_6 to generate Cl-1-Ph-d_5 in high yield and catalyzes the H/D exchange reaction between benzene and toluene-d_8 upon heating to 140 °C. To our knowledge, this is the first example of stoichiometric and catalytic, homogeneous, intermolecular CH activation of arenes by a discrete Os complex. The reactions show extended induction periods. DFT studies of Cl-1-Ph and cis-(κ^2-acac-O,O)_2Os^(III)(C_6H_5)(C_6D_6) (cis-(C_6D_6)-2-Ph) found a mechanism involving CH activation by traces of Os(III) and Cl atom transfer between Cl-1-Ph and cis-(C_6D_6)-2-Ph. Experimental data showing that addition of reductants eliminates the induction periods suggest that CH activation occurs from an oxidation state lower than Os^(IV), consistent with the DFT predictions. Consistent with a Cl atom transfer mechanism, the triflate analogue of Cl-1-Ph, OTf-1-Ph, does not undergo a stoichiometric or catalytic reaction with C_6D_6.

Additional Information

© 2011 American Chemical Society. Received: November 08, 2010. Article Published September 15, 2011. Published In Issue October 10, 2011. We thank Prof. William C. Kaska, Prof. W. Dean Harman, and William Tenn III for helpful discussions. We acknowledge the National Science Foundation (No. CHE-0328121), Chevron Energy Technology Co., and the Center for Catalytic Hydrocarbon Functionalization, an Energy Frontier Research Center (DOE DE-SC000-1298), for financial support for this research.

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