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

摘要

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 (pathwayA) and without a Ti-F interaction (pathwayB), are possible. PathwayA leads to a sigma-bond metathesis transition state, whereas pathwayB 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.