Design and synthesis of rhodium and iridium bis-η2 diolefin catalysts: : Applications in C–C bond formation and asymmetric catalysis

Abstract

This thesis deals with the design and synthesis of rhodium and iridium bis-η2 diolefin catalysts and their applications in C–C bond formation and asymmetric catalysis.
More specifically, the second chapter describes the development of inter- and intramolecular (5+2) cycloadditions catalyzed by cationic iridium(I) complexes that lead to the formation of seven-membered rings in a single step. DFT was applied to investigate the mechanism of this reaction.
Based on the findings described in Chapter 2, Chapter 3 discusses the relationship between the structure and the reactivity of a set of iridium and rhodium based bis–η2 diolefin complexes with respect to their application in four selected reactions.
Chapters 4-6 discuss the design and development of chiral bis–η2 diolefin ligands and their application in asymmetric catalysis. The knowledge gained from the first chapters is applied to the development of C2-symmetric bis–η2 diolefin ligands and their complexation to transition metals. More specifically, Chapters 4 and 6 focus on the design, synthesis, and resolution of such chiral complexes, while their application and reactivity are discussed in chapter 5 and partly in chapter 6.

Abstract (Swedish)

Catalysis is one of the few scientific concepts that has entered common parlance. To laymen catalysts simply speed up processes, but to a chemist they are much more interesting and complex. Catalysis offers the possibility to accomplish chemical reactions in a targeted manner with the least expenditure of energy and material. Given the increasing scarcity of resources, catalysts have become relevant to science, but also to economy, ecology, and politics. Catalysts render chemicals and materials more accessible. Without maybe even realizing it, we are confronted with catalysis and catalysts almost every day. Catalysts break down paper pulp to produce the smooth paper used in magazines, they clean contact lenses, they turn milk into yogurt, petroleum into plastic milk jugs, CDs or plastic bags, and they maintain food production in pace with the augmented rate of our population. Due to growing demand and diminishing resources there is an increasing need to enhance current technologies with more selective and efficient catalysts.
The design and development of efficient and selective catalysts is often not an easy task. On one hand, the catalytic performance of a catalyst has to be precisely measurable, analyzable, and reproducible. On the other hand, it has to be designed and engineered into practical processes to be useful. Traditionally, a trial-and-error approach was pursued to develop novel catalyst, but with the advancement of modern technologies the experimentalist is often aided by in silico techniques such as computational modeling.
This thesis discusses the design and development of rhodium and iridium based catalysts and their application in synthesis. More specifically, the synthesized catalysts were applied in several key reactions. Two of which were of particular importance: a (5+2) cycloaddition and an asymmetric 1,4-addition. The first reaction is used to construct seven-membered rings in a single step. Medium-sized rings are frequently found in bioactive natural products and their synthesis still represents a challenge to the synthetic chemist. The latter reaction introduces chirality to the target molecule. The property of chirality – non-superimposable forms that are mirror images of one another, so-called enantiomers from a chemist’s perspective – is present in both molecular and macroscopic objects. For centuries, scientists as well as artists, mathematicians, laymen, children, and writers were intriguied by asymmetric concepts; even Alice in ‘Through the Looking glass’ wondered if looking-glass milk were good to drink… Although enantiomers are identical in their chemical and physical composition and only stand apart in their ability to rotate plane-polarized light, the manner in which they interact with other chiral molecules often differs significantly. L-dopa, for example, reduces Parkinson’s symptoms, while its mirror image, D-dopa, is toxic. Therefore, it is of outmost importance to develop new methods that allow for the efficient and selective synthesis of such optically active substances in their enantiomerically pure form, especially in fields such as medicine and pharmacy, nutrition, or materials with optical properties. Asymmetric catalysis, in which each molecule of chiral catalyst, by virtue of being continually regenerated, can yield many molecules of chiral products, provides an efficient and step-economic tool to synthesizing optically active organic compounds in both, industry and academia. An easy way to optimize such catalysts is by designing and developing efficient chiral ligands, with strong metal affinity and a suitable chiral backbone. To this end, we designed and synthesized a series of novel all-carbon C2-symmetric ligands and complexed them to Rh to generate efficient chiral catalysts.

• author: Melcher, Michaela
• supervisor: Daniel Strand; Charlotta Turner
• opponent: Professor Öhrström, Lars, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden
• organization: Centre for Analysis and Synthesis
• publishing date: 2018-01
• type: Thesis
• publication status: published
• subject: Natural Sciences
• keywords: catalysis, transition metal, ligand design, enantioselectivity, cycloadditions
• pages: 241 pages
• defense location: Lecture hall F, Center for chemistry and chemical engineering, Naturvetarvägen 14, Lund
• defense date: 2018-02-09 09:15:00
• ISBN: 978-91-7422-562-4
• language: English
• LU publication?: yes
• id: 9565a7db-588b-4dc8-bb23-e108d4c30b80
• date added to LUP: 2018-01-15 12:42:52
• date last changed: 2018-11-21 21:37:21