Geminal dianionic complexes and their corresponding carbenoids for small molecule activation
The thesis describes the synthesis of metal carbenoids and their application towards small molecule activation and the catalytic reduction of CO2 with borane. Chapter 1 describes the synthesis of a novel unsymmetric phosphonium-stabilized methane ligand, the monoanionic and dianionic lithium and ma...
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| Format: | Theses and Dissertations |
| Language: | English |
| Published: |
2016
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| Online Access: | http://hdl.handle.net/10356/68863 |
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| Institution: | Nanyang Technological University |
| Language: | English |
| Summary: | The thesis describes the synthesis of metal carbenoids and their application towards small molecule activation and the catalytic reduction of CO2 with borane.
Chapter 1 describes the synthesis of a novel unsymmetric phosphonium-stabilized methane ligand, the monoanionic and dianionic lithium and magnesium derivatives. Their electronic structures were elucidated by X-ray crystallography and DFT calculations.
Chapter 2 reports the mild oxidation of the dianionic complexes, which underwent an unprecedented intramolecular B-H insertion with BH3 into the central carbon via a carbenoid species. In addition, the carbenoid Ph2P(S)C(Cl)P(S)Ph2Li, underwent a similar intermolecular B-H insertion with BH3. The mechanism of the B-H bond insertion was studied by NMR spectroscopy and DFT calculations, which shows the concerted bond breaking of a B-H and C-Cl bond and the bond forming of a Li-Cl and C-H bond. This accounts for the low energy required for the B-H insertion reaction. Moreover, the attempted isolation of the magnesium carbenoid intermediate was described.
The synthesis and reactivity of bis(iminophosphoranyl)carbenoid Ph2P(NMes)C(Cl)P(NMes)Ph2Li (Mes = 1,3,5-Me3C6H2 ) was presented in Chapter 3 and reacted with BH3 yielding the boronium species. ClC(PPh2NMes)2BH2, and LiBH4.
Chapter 4 describes the application of the boronium as one of the best catalyst for CO2 reduction by BH3. An intermediate ClC{PPh2NMes}2BH{OC(O)H} was isolated and a mechanism of this transformation was proposed.
Lastly, in chapter 5, the step wise synthesis of a novel unsymmetric carbenoid and its reactivity with BH3 was probed and showed a B-H insertion reaction. |
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