摘要：

In this study, two iridium complexes competent for non-radical C-H activation are studied computationally to determine how alterations to their structure can extend their lifetime and activity. Both catalysts are pincer complexes, so modular changes to the structure are feasible, making these systems ideal for study.21 (NNC)IrIII(TFA)(C2H4)Et (Figure 2.1a, NNC = h3-6- phenyl--4,4'-di-tert-butyl-2,2'-bipyridine) catalyzes H/D exchange between 35 atm CH4 and solvent trifluoroacetic acid (HTFA) at 180 ˚C with a TOF of 2.12 x 10-2 s-1. In the presence of 0.4207 mmol oxidant at 180˚C, methane is converted to methyltrifluoroacetate, but the catalyst decomposes on a similar timescale so that a low TON (6.3) is achieved.15 The NNC framework resulted from a quantum-mechanical rapid prototyping process14 that screened putative catalysts by activation barriers for H3C-H activation, redox and M-CH3 functionalization reactions followed by synthetic elaboration to aid synthesis of the h3 complex.15 The second iridium complex, bis(oxazolinyl)phenyl iridium (NCN or Phebox, Figure 2.1b), was shown to dehydrogenate octane22 and catalytically activate benzene and various alkanes in benzene and alkane solvent23 and has been investigated previously in methane activation.24 These catalysts are named NNC and NCN due to the order in which the terdentate pincer binds to the metal. First, we will investigate experimental results and mechanisms using two monodentate ligands, acetate (OAc) and trifluoroacetate (TFA), in conjunction with the NCN catalyst. In these studies, mesitylene is used as a liquid-phase methane surrogate, as it provides three alkyl sp3 methyl groups for reaction. This study is followed by the comparison between NNC and NCN ligands for C-H activation in methane, as well as predictions for future iterations on this catalyst.

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