Competition of Nucleophilic Aromatic Substitution, σ‐Bond Metathesis,and syn Hydrometalation in Titanium(III)‐Catalyzed Hydrodefluorination of Arenes

Several functionalized and non‐functionalized perfluoroarenes were catalytically transformed into their para‐hydrodefluorinated products by using catalytic amounts of titanocene difluoride and stoichiometric amounts diphenylsilane. Turnover numbers of up to 93 were observed. Solution density functional theory calculations at the M06‐2X/TZ(PCM)//M06‐2X/TZ(PCM) level of theory provided insight into the mechanism of Ti^III‐catalyzed aromatic hydrodefluorination. Two different substrate approaches, with a Ti–F interaction (pathway A) and without a Ti–F interaction (pathway B), are possible. Pathway A leads to a σ‐bond metathesis transition state, whereas pathway B proceeds by means of a two‐step mechanism through a syn‐hydrometalation intermediate or through a Meisenheimer intermediate. Both pathways are competitive over a broad range of substrates.