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Title: Reactivity of Rh(III) acyl complexes and their roles in catalytic mechanisms
Author: Griffin, David
ISNI:       0000 0004 7658 5711
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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Chapter 1: This chapter introduces catalysis and fundamental aspects of organometallic chemistry, including ligand effects in catalysis. The mechanism of methanol carbonylation is discussed including a recent proposal for an alternate mechanism of product formation. The intermediate proposed for this alternative product formation mechanism is also a proposed intermediate for decarbonylative dehydration. Chapter 2: Chapter two provides full experimental details for all procedures described in this thesis. Chapter 3: Chapter three investigates the reactions of a range of Rh(III) acetyl diphosphine species with carboxylates. Most complexes reacted readily with acetate or benzoate to give a rhodium acetyl carboxylate complex, observed in situ and subsequently eliminated an anhydride. In the presence of carbon monoxide, a known Rh(I) species was formed upon reductive elimination. The coordination of carboxylate to rhodium was determined to be bidentate by ATR IR spectroscopy and DFT. The reaction of these complexes with silver trifluoroacetate produced a mixture of mono- and di-trifluoroacetate complexes. Reductive elimination of anhydride from rhodium trifluoroacetate acetyl complexes was slow. Chapter 4: Chapter four extends the investigation of the reactions of Rh(III) acetyl complexes with carboxylates, utilising unsymmetrical heterodifunctional ligands. Reactions of these Rh(III) acetyl complexes with acetate and benzoate proceeded via substitution of an iodide ligand and subsequent reductive elimination of an anhydride. Anhydride elimination from these complexes was much slower than for complexes in Chapter three as such several rhodium acetyl carboxylate complexes were isolated and crystal structures obtained by X-ray crystallography. The reaction of these rhodium acetyl complexes with silver trifluoroacetate proceeded by abstraction of an iodide ligand by silver and coordination of trifluoroacetate, these complexes did not eliminate an anhydride as such several species were isolated and characterised. Chapter 5: Chapter five investigates the reactivity of Rh(III) acetyl diphosphine complexes with nitrogen containing nucleophiles. N-methyl aniline did not react with these complexes. Diethylamine reacted rapidly with Rh(III) acetyl diphosphine complexes to form N,N-diethyl acetamide. The formation of N,N-diethyl acetamide was tracked kinetically via IR spectroscopy. Activation parameters for these reactions were determined, the entropy of activation was large and negative indicating an associative mechanism. Chapter 6: Chapter six gives an introduction to decarbonylative dehydration as a method of accessing linear alpha olefins from long chain fatty acids. A range of Rh(I) complexes were tested as catalysts for decarbonylative dehydration, which were generally high yielding but gave poor selectivity for terminal alkenes. Deuterium was found in the alkene product when using deuterated acetic anhydride, this was quantified to determine percentage incorporation. Following on from a previous observation of acetylation of an iminophosphine ligand when used for decarbonylative dehydration the mechanism of acetylation was probed. Chapter 7: Chapter seven consists of suggestions for future work and conclusions. Chapter 8: Chapter eight gives supplementary spectroscopic and additional details.
Supervisor: Haynes, Anthony Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available