Preparation of Se(IV) Aryltrifluoromethylselenide Dichlorides

Trifluoromethylselenide dichlorides are rare selenium(IV) derivatives that have received limited attention despite their potential in organoselenium chemistry. We report a straightforward and efficient synthesis of dichloro(aryl)(trifluoromethyl)‐λ 4 ‐selanes (ArSeCl 2 CF 3 ) via chlorination of aryl trifluoromethylselenides in acetonitrile as the solvent of choice. After evaluating various chlorinating agents, sulfuryl chloride (SO 2 Cl 2 ) revealed to be very efficient in a broad scope of substrates. Complementary density functional theory calculations provided mechanistic insight, indicating that chlorination proceeds via an asynchronous concerted mechanism with an accessible activation barrier and is exergonic, readily leading to the formation of Se(IV) fluorinated compounds. In contrast, the formation of the Se(VI) tetra‐chlorinated derivative via oxidative addition of Cl 2 to the Se(IV) derivative was found to be both kinetically and thermodynamically infeasible.