Double Ligands Enabled Ruthenium Catalyzed ortho ‐C−H Arylation of Dialkyl Biarylphosphines: Straight and Economic Synthesis of Highly Steric and Electron‐Rich Aryl‐Substituted Buchwald‐Type Phosphines

Late-Stage Diversification of Phosphines by C-H Activation: A Robust Strategy for Ligand Design and Preparation

ConspectusThe advent of the twenty-first century marked a golden era in the realm of synthetic chemistry, exemplified by groundbreaking advancements in the field of C-H activation, which is a concept that quickly transitioned from mere academic fascination to an essential element within the synthetic chemist's toolkit. This methodological breakthrough has given rise to a wealth of opportunities spanning a wide range of chemical disciplines. It has facilitated the late-stage diversification of elaborate organic frameworks, encompassing the spectrum from simple methane to complex polymers, thus refining the lead optimization process and easing the production of diverse molecular analogues. Among these strides forward, the development of phosphorus(III)-directed C-H activation stands out as an increasingly significant and inventive approach for the design and synthesis of ligands, substantially redefining the contours of synthetic methodology.Phosphines, renowned for their roles as ligands and organocatalysts, have become fundamentally important in modern organic chemistry. Their efficiency as ligands is significantly affected by coordination with transition metals, which is essential for their involvement in catalytic processes, influencing both the catalytic activity and the selectivity. Historically, the fabrication of phosphines predominantly relied on synthesis employing complex, multistep procedures. Addressing this limitation, our research has delved into ligand design and synthesis through innovative catalytic P(III)-directed C-H activation strategies. In this Account, we have explored a spectrum of procedures, including direct arylation using metal catalysis, and ventured further into domains such as C-H alkylation, alkenylation, aminocarbonylation, alkynylation, borylation, and silylation. These advances have enriched the field by providing efficient methods for the late-stage diversification of biaryl-type monophosphines as well as enabled the C-H activation of triphenylphosphine and its derivatives. Moreover, we have successfully constructed libraries of diverse axially chiral binaphthyl phosphine ligands, showcasing their potency in asymmetric catalysis. Through this Account, we aim to illuminate the exciting possibilities presented by P(III)-directed C-H activation in propelling the boundaries of organic synthesis. By highlighting our pioneering work, we hope to inspire further developments in this promising field of chemistry.

Rhodium(i)-catalyzed cascade C(sp2)-H bond alkylation - amidation of anilines: phosphorus as traceless directing group

We introduce a versatile Rh(i)-catalyzed cascade reaction, combining C(sp2)-H bond functionalization and amidation between N-arylphosphanamines and acrylates. This innovative approach enables the rapid synthesis of dihydroquinolinone scaffolds, a common heterocycle found in various pharmaceuticals. Notably, the presence of the phosphorus atom facilitates the aniline ortho-C(sp2)-H bond activation prior to N-P bond hydrolysis, streamlining one-pot intramolecular amidation. Moreover, we demonstrate the applicability of this reaction by synthesizing an antipsychotic drug. Detailed mechanistic investigations revealed the involvement of a Rh-H intermediate, with substrate inhibition through catalyst saturation.

Sterically Controlled Late‐Stage Functionalization of Bulky Phosphines

The fine‐tuning of metal‐phosphine‐catalyzed reactions relies largely on accessing ever more precisely tuned phosphine ligands by de‐novo synthesis. Late‐stage C−H functionalization and diversification of commercial phosphines offers rapid access to entire libraries of derivatives based on privileged scaffolds. But existing routes, relying on phosphorus‐directed transformations, only yield functionalization of Csp2 −H bonds in a specific position relative to phosphorus. In contrast to phosphorus‐directed strategies, herein we disclose an orthogonal functionalization strategy capable of introducing a range of substituents into previously inaccessible positions on arylphosphines. The strongly coordinating phosphine group acts solely as a bystander in the sterically controlled borylation of bulky phosphines, and the resulting borylated phosphines serve as the supporting ligands for palladium during diversification through phosphine self‐assisted Suzuki‐Miyaura reactions.

Upgrading Carbazolyl-Derived Phosphine Ligands Using RhI-Catalyzed PIII-Directed C-H Bond Alkylation for Catalytic CO2-Fixation Reactions

We report an Rh(I)-catalyzed C-H bond alkylation of PhenCarPhos [N-(2-(diphenylphosphaneyl)phenyl)carbazole] and some congener phosphine ligands with alkenes. The C-H bond functionalization occurred exclusively at the C1 position of the carbazolyl unit because the trivalent phosphine acts as a directing group. This protocol provides straightforward access to a large library of C1-alkyl substituted PhenCarPhos, which outperformed common commercial or unfunctionalized phosphines and their precursors in the Pd-catalyzed carbon dioxide-fixation reactions with propargylic amines.

Rhodium-catalyzed selective direct arylation of phosphines with aryl bromides

The widespread use of phosphine ligand libraries is frequently hampered by the challenges associated with their modular preparation. Here, we report a protocol that appends arenes to arylphosphines to access a series of biaryl monophosphines via rhodium-catalyzed P(III)-directed ortho C-H activation, enabling unprecedented one-fold, two-fold, and three-fold direct arylation. Our experimental and theoretical findings reveal a mechanism involving oxidative addition of aryl bromides to the Rh catalyst, further ortho C-H metalation via a four-membered cyclometalated ring. Given the ready availability of substrates, our approach opens the door to developing more general methods for the construction of phosphine ligands.