Cp*Ir Complexes Relevant to C-H Activation and Oxidation Reactions.

摘要

This dissertation focuses on the synthesis and reactivity of Cp*Ir complexes towards C-H bond activation and oxidation. Transition metal complexes incorporating the Cp*IrIII framework are known to be some of the best activators of C-H bonds. For this reason a variety of these complexes were synthesized and their reactivity was studied.;In Chapter 2, the reactivity and mechanism of C-H bonds activation was explored through hydrogen/deuterium exchange between benzene and a variety of deuterated solvents. Cp*IrIII catalysts were used for this study with different strongly and weakly electron donating ligands. From these studies, it was shown that the mechanism of C-H activation varied dramatically based on the nature of the ancillary ligand as well as the solvent/deuterium source. When reactions were run in strongly acidic solvents, such as trifluoroacetate, a nucleophilic aromatic substitution mechanism was operative and did not show a strong dependence on the ancillary ligand. The reactivity in acetic acid also showed no dependence on the nature of the ancillary ligand. Acetate containing catalysts were synthesized and shown to have similar reactivity regardless of the electron donating ability of the ancillary ligand. For this reason a well know acetate assisted sigma bond metathesis mechanism is proposed for C-H activation in this solvent. However, when methanol was used as the deuterium source, strongly electron donating groups afforded the highest reactivity. This reactivity was attributed to the ability of these complexes to form iridium-hydride intermediates.;In Chapter 3, the reactivity of Cp*Ir(NHC)Me(L)+ complexes were synthesized and studied for oxyfunctionalization towards methanol production under dioxygen pressure. Methanol production was achieved with these complexes in D2O solvent when heated to 100 °C. Isotope labeling studies confirmed the oxygen atom in the methanol product originated from the O 2 atmosphere. A strong dependence of the ability to dissociate a ligand from the coordination sphere was determined through kinetic studies. Based on this result, in Chapter 4, a Cp*Ir(NHC)Me complex was synthesized in situ in the absence of a coordinating ligand. This complex produced methanol in quantitative yields at ambient temperature and pressure. A bimetallic IrIV complex with a bridging oxo was identified and characterized as a kinetically competent intermediate. In both systems the Ir-Me bond is being oxidized and an iridium product containing the Cp* and NHC ligands was observed and quantified.;In Chapter 5, catalytic aerobic oxidations of alcohols were studied. The best conditions found for this reaction were with Cp*IrIII complexes incorporating a NHC ligand in basic conditions. Dioxygen was needed for catalytic turnovers. Iridium-hydride complexes were identified as possible reaction intermediate.