Bimetallic rhodium complexes for promoting C-X Bond formation: Structure and mechanism

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Copyright: Choy, Sandra
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Abstract
A series of novel bimetallic Rh(I) complexes were prepared, containing bidentate imidazolyl-imine ligand motifs attached to rigid scaffolds including phenylene or anthracene, or flexible scaffolds including cyclohexane, ethylene or hexane. The three dimensional structure and conformational flexibility of the dirhodium complexes containing diimine ligands with a phenylene scaffold were investigated using X-Ray crystallography and DFT calculations. These dirhodium complexes were tested as catalysts for C-X (where X= O, N, Si, or B) and N-Si bond formation reactions, and their catalytic activities were compared to those of the monometallic analogue. Cooperative enhancements in reaction efficiencies or selectivities were observed on using the bimetallic complexes as catalysts for C-O and C-Si bond formation reactions compared to those using the monometallic analogue. Kinetic studies of the C-O and C-N bond formation reactions catalysed by mono- and bi-metallic Rh(I) complexes were also conducted. Empirical rate laws and activation parameters for these Rh(I) catalysed dihydroalkoxylation and hydroamination reactions were determined. Computational modelling of the mechanistic pathways using DFT indicated that the dihydroalkoxylation reaction catalysed by the dirhodium complex, containing the ortho-substituted phenylene scaffold, accessed significantly more efficient mechanistic pathways than those of the monometallic catalysed reaction. The computational modelling of the mechanism for the bimetallic catalysed dihydroalkoxylation reaction of oct-4-yn-1,8-diol demonstrated that the proximal second rhodium centre promoted cooperative interactions via either direct Rh-Rh interactions, or carbonyl or hydrido bridging between the two rhodium centres.
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Author(s)
Choy, Sandra
Supervisor(s)
Messerle, Barbara
Gooding, Justin
Macgregor, Stuart
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Publication Year
2016
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Thesis
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PhD Doctorate
UNSW Faculty
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