This thesis focuses on the syntheses and reactivity of low-valent rhenium carbyne and rhenacyclobutadiene complexes. We have synthesised a series of Re(I) complexes, including [Re(dppm)
3]I, [Re(dppm)
3]BPh
4, [Re(dppm)
2(MeCN)
2]I and [Re(dppm)
2(MeCN)
2]BPh
4; and the Re(III) complex ReH(dppm)
2I
2. They are all reactive towards terminal alkynols and internal alkynes to give a variety of complexes, including hydroxyvinylidene complexes, η
2-alkyne complexes and P–C bond cleaved complexes, depending on supporting ligands of the rhenium complexes. We have prepared a series of alkoxy-rhenacyclobutadienes (RCBDs), and investigated their reactivity with electron-rich terminal alkynes. Reactions with 4-ethynylanisole gave exclusively η
5-cyclopentadienyl complexes, while reactions with 4-ethynyl-N,N-dimethylaniline gave a mixture of η
5-cyclopentadienyl complexes and vinyl-substituted rhenacyclobutadienes. We have prepared a series of alkoxy-, thio- and amino-RCBDs, and studied their reactions with electron-rich internal alkynes. Reactions of these RCBDs with amino-alkynes gave a series of η
5-oxocyclohexadienyl complexes. Upon hydrolysis with water, poly-substituted phenols could be obtained. The synthetic strategy implemented is different from and complementary to Dötz and Danheiser benzannulations. Reactions of RCBDs with terminal and internal alkynes can give several different types of rhenium complexes. The reaction mechanisms leading to these complexes have been studied computationally. It was found that the thermodynamics and kinetics were sensitively affected by the electronic and steric properties of the substituents on the rhenacyclobutadienes and alkynes. We have computationally studied the alkyne metathesis activity of a series of low-valent rhenium carbyne complexes bearing bidentate phopshino-phenolate ligands, pincer-type [PNP] and [PNO] ligands, and the related bidentate PN, PS, P(SO
2) and acetylacetate ligands, as well as the tridentate PO
2, SO
2, Cp* and Tp* ligands. The metathesis activity of these carbyne complexes were found to be greatly affected by the electronic and steric properties of the ligands. The overall barrier is determined by ligand dissociation to generate coordinatively unsaturated species, and coordination of alkynes. The most active system was found to be the system supported by bidentate phopshino-phenolate ligands.
| Date of Award | 2024 |
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| Original language | English |
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| Awarding Institution | - The Hong Kong University of Science and Technology
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| Supervisor | Guocheng JIA (Supervisor) |
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