Periodic Reporting for period 1 - Cross-Bit (Bismuth Redox Catalysis for C–C Coupling Reactions)
Berichtszeitraum: 2022-06-01 bis 2024-05-31
The formation of C‒C and C‒heteroatom bonds through transition metal-catalyzed cross-coupling reactions represents the cornerstone strategy to build chemical complexity in a myriad of contexts, spanning from academic laboratories to industrial settings. These remarkable reactions generally proceed through three elementary steps—oxidative addition, transmetallation and reductive elimination—which couple two organic fragments together using transition-metal complexes as redox-active catalysts. Recently, bismuth—a main-group element—has been found to take part in this type of redox events, resulting in the formation of C–F and C–O bonds, or in H-transfer processes. However, at the outset of these investigations, the use of bismuth redox catalysis to forge the highly coveted and synthetically relevant C–C and C–N bonds remained elusive. In this project, we aimed at two main objectives:
1) The discovery and study of new fundamental organometallic steps in bismuth redox chemistry, with a focus on oxidative additions and formal reductive-elimination processes.
2) Harnessing this new redox behavior to unlock unprecedented bismuth-catalyzed cross-coupling catalytic cycles to forge new C–N and C–C bonds.
Thus, we proposed the design of low-valent Bi(I/III) or Bi(I/II/III) redox platforms, cycling through key steps of classical transition metal-catalyzed couplings. We developed new types of oxidative-addition reactions, which were often found to follow unprecedented radical mechanisms. The study of these and other challenging steps, such as novel formal reductive-elimination processes from Bi(III), allowed forging new C–N and C–C bonds upon regeneration of Bi(I). Furthermore, all these processes could be aided by the introduction of photochemical steps, generating highly reactive excited-state bismuth complexes.
All these findings converged in the development of novel bismuth catalyzed cross-coupling reactions that take place through a combination of radical and polar mechanisms. Besides the conceptual breakthrough derived from these discoveries, these ideas represent a proof-of-concept to implement bismuth-catalyzed cross-coupling reactions as competent, cheaper, and less toxic alternatives to traditional methods based on transition-metal catalysis.
1) The discovery and study of new fundamental organometallic steps in bismuth redox chemistry, with a focus on oxidative additions and formal reductive-elimination processes.
2) Harnessing this new redox behavior to unlock unprecedented bismuth-catalyzed cross-coupling catalytic cycles to forge new C–N and C–C bonds.
Thus, we proposed the design of low-valent Bi(I/III) or Bi(I/II/III) redox platforms, cycling through key steps of classical transition metal-catalyzed couplings. We developed new types of oxidative-addition reactions, which were often found to follow unprecedented radical mechanisms. The study of these and other challenging steps, such as novel formal reductive-elimination processes from Bi(III), allowed forging new C–N and C–C bonds upon regeneration of Bi(I). Furthermore, all these processes could be aided by the introduction of photochemical steps, generating highly reactive excited-state bismuth complexes.
All these findings converged in the development of novel bismuth catalyzed cross-coupling reactions that take place through a combination of radical and polar mechanisms. Besides the conceptual breakthrough derived from these discoveries, these ideas represent a proof-of-concept to implement bismuth-catalyzed cross-coupling reactions as competent, cheaper, and less toxic alternatives to traditional methods based on transition-metal catalysis.
Over the course of this action, we have worked on the development of fundamentally new elementary redox steps that occur at low-valent bismuth centers, which would potentially enable the discovery of new catalytic coupling reactions. This led us to unveiling a wide variety of radical and polar oxidative-addition reactions, as well as formal reductive-elimination processes that allow the completion of full catalytic redox cycles. Some of these processes occur under thermal control, whereas some others take place on photo-excited bismuth complexes upon visible light irradiation. All this has established N,C,N-ligated bismuth complexes both as a catalytically competent and photoactive family of compounds, which has unlocked a variety of lines of research.
Throughout this action, we have established the foundations for the development of bismuth radical cross couplings and photochemical reactions. This was achieved by merging the discovery of fundamentally new elementary steps at bismuth complexes (such as unprecedented radical oxidative additions or formal reductive eliminations) with the development of new catalytic approaches to forge highly coveted C–N and C–C bonds.