Modeling the proposed intermediate in alkane carbon-hydrogen bond activation by Cp*(PMe3)Ir(Me)OTf: Synthesis and stability of novel organometallic iridium(V) complexes

Article abstract of DOI:10.1021/om990255p

Addition of HX to CH₂Cl₂ solutions of Cp*IrMe₄ (Cp* = η⁵-C₅Me₅) at low temperature provided Cp*Ir(Me)₃X (X = Cl, 5; X = OSO₂CF₃ = OTf, 6). Both complexes are very thermally sensitive yet proved to be useful precursors for novel cationic iridium(V) complexes. Treatment of 6 with a variety of trisubstituted phosphines, arsines, and stibines (L) afforded compounds 7-12, [Cp*(L)IrMe₃][OTf] (L = PMe₃, 7; L = PEt₃, 8; L = PPh₃, 9; L = AsEt₃, 10; L = AsPh₃, 11; L = SbPh₃, 12). Metathesis of the triflate anion of antimony complex 12 for the tetraphenylborate anion afforded [Cp*(SbPh₃)IrMe₃][BPh₄] (13). The molecular structure of 13 was determined by single-crystal X-ray diffraction analysis. Complex 7 is a potential model for the proposed intermediate on the methane carbon-hydrogen bond activation reaction pathway by Cp*(PMe₃)Ir(Me)OTf, and its relevance to this reaction is discussed. Complex 7 decomposed by reductive elimination of MeCp*. The remaining iridium fragment was trapped by added phosphine to form [cis-{PMe₃}₄IrMe₂][OTf] (14) as an impure mixture. Reaction of 6 with excess dppm (dppm = Ph₂PCH₂PPh₂) afforded [cis-{η²-Ph₂PCH₂-PPh₂} ₂IrMe₂][OTf] (15). The molecular structure of 15 was determined by single-crystal X-ray structure analysis.