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C–H Insertion Catalyzed by Tetratolylporphyrinato Methyliridium via a Metal–Carbene Intermediate
  • Bernie Anding, Iowa State University
  • Jakoah Brgoch, Iowa State University
  • Gordon J. Miller, Iowa State University
  • L. Keith Woo, Iowa State University
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C–H insertion reactions between different substrates and diazo reagents were catalyzed by tetratolylporphyrinato methyliridium (Ir(TTP)CH3). The highest yields were achieved for reactions between the bulky diazo reagent methyl 2-phenyldiazoacetate (MPDA) and substrates containing electron-rich C–H bonds. An intermediate metalloporphyrin complex was identified as a metal–carbene complex, Ir(TTP)(═C[Ph]CO2CH3)(CH3) (4), using 1H NMR and UV/vis absorption spectroscopy. The presence of 4 was further supported by computationally modeling the absorption spectra with time-dependent DFT (6-31G(d,p)/SBKJC basis set, PBE0 functional). Kinetic studies for C–H insertion reactions using different substrates showed substantial differences in the rate of MPDA consumption, suggesting that carbene transfer is rate-limiting. Furthermore, primary kinetic isotope effects of 3.7 ± 0.3 and 2.7 ± 0.4 were measured using toluene and cyclohexane, respectively. These data are consistent with a mechanism that involves direct C–H insertion rather than a radical rebound pathway.

Reprinted (adapted) with permission from Organometallics, 2012, 31 (15), pp 5586–5590. Copyright 2012 American Chemical Society.

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Bernie Anding, Jakoah Brgoch, Gordon J. Miller and L. Keith Woo. "C–H Insertion Catalyzed by Tetratolylporphyrinato Methyliridium via a Metal–Carbene Intermediate" Organometallics Vol. 31 Iss. 15 (2012) p. 5586 - 5590
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