Nickel-Catalyzed Trifluoromethylselenolation of Aryl and Alkenyl-Triflates: Scope and Mechanism

Abstract

The nickel-catalyzed trifluoromethylselenolation of aryl and vinyl triflates is described herein, encompassing synthesis method development and an understanding of the reaction. The challenge lies in the propensity of the C(sp2)–SeCF3 product to undergo oxidative addition to nickel(0) intermediates, potentially initiating catalyst deactivation pathways. In this study, we disclose that the Xantphos/Ni(COD)2 catalytic system is efficient for the synthesis of aryl and vinyl trifluoromethylselenides. The key elementary steps that delineate the catalytic cycles have been investigated by a joint experimental and computational mechanistic investigation and support a Ni0/NiII process. The Xantphos/Ni0 system was found to react with both ArOTf and ArSeCF3 to give the corresponding (Xantphos)NiIIAr(X) intermediates (X = OTf or SeCF3), with the complex (Xantphos)NiIIAr(OTf) emerging as the most stable one. In line with experimental observations, computational studies indicate that oxidative addition of ArSeCF3 to Xantphos/Ni0 is faster than the oxidative addition of ArOTf but is thermodynamically much less stable. Thereof, the oxidative addition of ArSeCF3 is reversible and the product of the ArOTf oxidative addition is shown to be the most stable product. The relative stability of oxidative addition products is attributed to the coordination mode of the Xantphos ligand (κ2 vs κ3) at nickel(II) intermediates. Finally, we demonstrate that ArSeCF3 compounds can be prepared using an air-stable (Xantphos)NiII precatalyst.