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

Addition of HX to CH2Cl2 solutions of Cp*IrMe4 (Cp* = eta(5)-C5Me5) at low temperature provided Cp*Ir(Me)(3)X (X = Cl, 5; X = OSO2CF3 = OTf, 6). Both complexes are very thermally sensitive yet proved to be useful precursors f or novel cationic iridium(V) complexes. Treatment of 6 with a variety of tr isubstituted 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 = AsPhs(3) 11; L = SbPh3, 12). Metathesis of the triflate anion of antimo ny complex 12 for the tetraphenylborate anion afforded [Cp*(SbPh3)IrMe3][BP h4] (13). The molecular structure of 13 was determined by single-crystal X- ray diffraction analysis. Complex 7 is a potential model for the proposed i ntermediate on themethane carbon-hydrogen bond activation reaction pathway by Cp*(PMe3)Ir(Me)OTf, and its relevance to this reaction is discussed. Com plex 7 decomposed by reductive elimination of MeCp*. The remaining iridium fragment was trapped by added phosphine to form [cis-{PMe3}(4)IrMe2][OTf] ( 14) as an impure mixture. Reaction of 6 with excess dppm (dppm =Ph2PCH2PPh2 ) afforded [cis-{eta(2)-Ph2PCH2-PPh2}(2)IrMe2][OTf] (15). The molecular str ucture of 15 was determined by single-crystal X-ray structure analysis.