| dc.description.abstract | Pincer ligands are commonly utilized in the design of transition metal catalysts. Our group recently reported the synthesis of diarylboryl-based Ir and Rh complexes, which feature an X-type boryl ligand that is Lewis acidic. Herein, we explored the properties and reactivity of Ag, Ir and Rh metal complexes that feature boryl or borane ligand.
In Chapter II, silver halide complexes of a borane/bis(phosphine) ligand were prepared and characterized. With AgF, the borane abstracts fluoride, resulting in a zwitterionic complex. With AgCl, AgBr, and AgI, the halide stays coordinated to Ag, with little to no Ag–B interaction.
In Chapter III, H–X bond addition across the Ir–B unit of the previously reported (PBP)Ir(CO)₂ were examined. Water, methanol, ethanol, cyclohexanol, phenols, benzoic acid, and triethylamine trihydrofluoride added the O–H and F–H units across the Ir–B bond, resulting in dicarbonyl complexes with Ir–H and B–O/F bonds. Thermolysis of (PBP)Ir(CO)₂ with n-butylamine resulted in a monocarbonyl product of N-H addition. Two possible mechanisms were proposed, and mechanistic experiments were conducted to study this system.
In Chapter IV, reactions of (PBP)Ir complexes with ethylene were examined. (PBP)IrH₄, (PBP)IrH₂(CO), and (PBP)Ir(CO)₂ activated the C–H bond in ethylene to form unique products that have the elements of ethylene incorporated into the molecules and resulted in B–C bonds. These reactions demonstrate that the boryl donor is not merely an electronically unique central donor with Lewis acidic properties. It also participates in the activation of C–H bonds by the metal center and forms B–C bond in the product.
In Chapter V, we examined selective C–H activation of pyridines with (PBP)Rh and (PBP)Ir complexes. We observed the isomerism derived from the 2-pyridyl fragment connecting either via B-N/C-M bonds or via B-C/N-M bonds. This M-C/M-N isomerism was systematically examined for four structural Types, totaling 16 compounds. Several of these compounds were isolated or observed in solution by experimental methods, in addition to a few 2-quinolyl variants. The DFT predictions concerning the thermodynamic preference within each M-C/M-N isomeric match the experimental findings very well.
In Chapter VI, we utilized (PBP)Rh complexes synthesized in Chapter V to catalyze norbornylation of substrates containing pyridyl groups. For substrates such as pyridine, quinoline, 4-tert-butylpyridine, 4-dimethylaminopyridine, and 3-ethylpyridine, the norbornylation happened at the pyridine ortho position. However, for 2-tolylpyridine, the norbornylation happened on the tolyl group. | |
