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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

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journal contribution
posted on 15.06.1999 by Peter J. Alaimo, Robert G. Bergman
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 712, [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-Ph2PCH2PPh2}2IrMe2][OTf] (15). The molecular structure of 15 was determined by single-crystal X-ray structure analysis.