Controlling Carbenes: Stories of Diruthenium, Dirhodium, and Photoinduced Carbene Transformations Pubblico
Sailer, Joshua (Spring 2025)
Abstract
Carbene intermediates are a valuable synthetic tool in organic chemistry. These highly reactive species are capable of a wide variety of transformations, most notably via metallo-carbene intermediates. Dirhodium tetracarboxylate catalysts are capable of rendering cyclopropanation and C–H insertion reactions in a highly selective manner, enabling the synthesis of valuable scaffolds. However, while this is a powerful catalytic system, using rhodium offers a sustainability issue due to the high price. Herein, the development of an alternative metal for carbene transfer reactions has been developed and optimized. Additionally, two novel methodologies for synthesis of strained rings have been developed using carbenes, showcasing the powerful capabilities of these reactive intermediates.
Chapter 1: This chapter will give an overview of carbenes as reactive intermediates. Singlet and triplet carbenes are discussed, along with dirhodium tetracarboxylate complexes, with a brief survey of reactions that these complexes catalyzed. Then, some drawbacks and limitations of the dirhodium systems will be discussed along with the introduction to the solutions developed in later chapters of this dissertation.
Chapter 2: This chapter will discuss the optimization of alternative metals in the tetracarboxylate bimetallic core for cyclopropanation using aryldiazoacetate compounds. Ruthenium is shown to be the optimal metal, and a large scope of olefin cyclopropanation is disclosed. Computational studies help elucidate some of the key differences between the two metal centers.
Chapter 3: This section elaborates on the diruthenium catalysts for C–H functionalization of a variety of alkanes using aryldiazoacetates as carbene precursors. General reactivity trends for the ruthenium complexes are developed by testing substrates with differing sites of C–H insertion. A direct comparison is made with the dirhodium analogues highlighting the similarities and differences between the two catalyst systems.
Chapter 4: The chapter will explore the development of a cyclopropanation reaction of exocyclic olefins to afford chiral spiro[2.n]cyclopropanes using dirhodium catalysts. Several classes of exocyclic olefins are explored, with high levels of diastereoselectivity and enantioselectivity achieved.
Chapter 5: The final chapter will discuss a novel synthesis of 2-substituted bicyclo[1.1.1]pentanes via triplet carbene addition to the strained C–C bond of bicyclo[1.1.0]butane. This methodology affords rapid access to a challenging synthetic scaffold to reach, highlighting the power of carbene intermediates to afford privaliged motifs.
Table of Contents
Chapter 1. An Introduction to Carbenes and Dirhodium Tetracarboxylate Catalysis 1
1.1 Introduction 1
1.2 Electronic Structure of Carbenes 3
1.3 Generation of Carbenes 4
1.4 Reactions of Carbenes 6
1.5 Dirhodium metallo-carbene complexes 7
1.6 Dirhodium tetracarboxylate catalyzed Carbene Transfer Reactions 8
1.7 Drawbacks and Solutions to Dirhodium Tetracarboxylate Chemistry 11
1.8 Conclusion 12
1.9 References 14
Chapter 2. Development of Diruthenium (II,III) Tetracarboxylate Catalysts for Cyclopropanation using Aryldiazoacetates as Carbene Precursors 18
2.1 Introduction 18
2.2 Results and Discussion 26
2.3 Conclusion 37
2.4 Distribution of Credit 37
2.5 References 38
Chapter 3. Comparison of Diruthenium and Dirhodium Tetracarboxylate Catalyzed C–H Functionalization with Aryldiazoaceate compounds 40
3.1 Introduction 40
3.2 Results and Discussion 42
3.3 Conclusion 53
3.4 References 55
Chapter 4. Dirhodium Catalyzed Spiro[2.n]cyclopropanation of Exocyclic Olefins 57
4.1 Introduction 57
4.2 Results and Discussion 62
4.3 Conclusion 71
4.4 Distribution of Credit 72
4.5 References 73
Chapter 5. Synthesis of 2-Substituted Bicyclo[1.1.1]pentanes via Triplet Carbene insertion into Bicyclo[1.1.0]butanes 76
5.1 Introduction 76
5.2 Results and discussion 84
5.3 Conclusion 89
5.4 References 91
Appendix A. Chapter 2 Supporting Information 94
Appendix B. Chapter 3 Supporting Information 219
Appendix C. Chapter 4 Supporting Information 331
Appendix D. Chapter 5 Supporting Information 439
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