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 CH 2 Cl 2 solutions of Cp*IrMe 4 (Cp* = η 5 -C 5 Me 5 ) at low temperature provided Cp*Ir(Me) 3 X (X = Cl, 5; X = OSO 2 CF 3 = 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)IrMe 3 ][OTf] (L = PMe 3, 7; L = PEt 3, 8; L = PPh 3, 9; L = AsEt 3, 10; L = AsPh 3, 11; L = SbPh 3, 12 ). Metathesis of the triflate anion of antimony complex 12 for the tetraphenylborate anion afforded [Cp*(SbPh 3 )IrMe 3 ][BPh 4 ] ( 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*(PMe 3 )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 -{PMe 3 } 4 IrMe 2 ][OTf] ( 14 ) as an impure mixture. Reaction of 6 with excess dppm (dppm = Ph 2 PCH 2 PPh 2 ) afforded [ cis -{η 2 -Ph 2 PCH 2 PPh 2 } 2 IrMe 2 ][OTf] ( 15) . The molecular structure of 15 was determined by single-crystal X-ray structure analysis.