Synthesis of the Electron-Poor Dicationic Arene Complex [Cp*Ir(η<sup>6</sup>-<i>p</i>-bis(difluoromethyl)benzene)][BF<sub>4</sub>]<sub>2</sub> and Ring Attack by Hydroxide in Attempted Deprotonation: Synthesis, Structures, and C−H···F Hydrogen Bonding
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Treatment of p-bis(difluoromethyl)benzene, p-CF2H-C6H4-CF2H, with [Cp*Ir(acetone)3][OTf]2 (prepared in situ) along with BF3·2H2O provided the target compound [Cp*Ir(η6-p-CF2H-C6H4-CF2H)][BF4]2 (3) in good yield, which was fully characterized, and its X-ray molecular structure was determined. Interestingly the usual π-complexation procedure in the absence of BF3·2H2O did not lead to complex 3; instead, the hydroxypentadienyl complex [Cp*Ir(η5-CH2C(Me)CHC(OH)CH2)][OTf] (2) was formed. The latter was also identified by X-ray analysis. Reaction of 3 with a base such as LiOH or Ag2CO3 did not yield the neutral tetrafluoro-p-xylylene complex [Cp*Ir(η4-p-CF2-C6H4-CF2)] (4), in which the reactive intermediate tetrafluoro-p-xylylene (1) would be stabilized by Cp*Ir coordination. Instead the dinuclear iridium complex [{Cp*Ir(η5-p-CF2H-C6H4-CF2H)}2O][BF4]2 (5) was obtained. Complex 5, with two η5-cyclohexadienyl moieties bridged by an oxygen atom, is the net result of water or hydroxide attacking two molecules of the arene complex 3. A mechanism for this transformation is discussed.
