Activation of Epoxides by a Cooperative Iron Thiolate Catalyst: Intermediacy of Ferrous Alkoxides in Catalytic Hydroboration

作者：Song Heng; Ye Ke; Geng Peiyu; Han Xiao; Liao Rongzhen^*; Tung Chen Ho; Wang Wenguang^*

来源：ACS Catalysis, 2017, 7(11): 7709-7717.

DOI：10.1021/acs.catal.7b02527

• iron catalysis
• metal-ligand cooperation
• epoxide hydroboration
• ferrous-borane adduct
• ferrous-alkoxide

This paper describes a cooperative iron thiolate catalyst Cp*Fe(1,2-Ph2PC6H4S)(NCMe) (Cp*(-) = CsMes-, [1(NCMe)]) for regioselective hydroboration of aryl epoxide by pinacolborane (HBpin). The critical catalytic step involves the direct addition of epoxide to the catalyst rather than activation of the B H bond of HBpin. Through iron thiolate cooperation, [1(NCMe)] opens the aryl epoxide rings affording ferrous alkoxide compounds. Notably, the ferrous alkoxide intermediate (4) was structurally characterized after its isolation from the reaction of [1(NCMe)] with trans-2,3-diphenyloxirane. The more Lewis acidic hydroboranes such as H3B THF and 9-BBN (BBN = borabicyclononane) can also be captured by [1(NCMe)]. The resulting iron borane adducts [1H(BH2)] and [1H(BBN)] feature an agnostic Fe center dot center dot center dot B-H interaction. DFT calculations indicate that the addition of HBpin across the iron-thiolate sites is endergonic by 12.9 kcal/mol, whereas it is exergonic by 20.2 kcal/mol with BH3 and 4.6 kcal/mol with 9-BBN. Combining the experimental data with theoretical studies, a mechanism of the substrate activation by [1(NCMe)], followed by HBpin addition, is proposed for the catalysis.

• 出版日期2017-11
• 单位山东大学