Yilin Cao

In this work, we demonstrate that directing group flexibility plays a decisive role in overcoming reactivity barriers in PdII-catalyzed alkene functionalization. Kinetic, organometallic, and DFT studies reveal that employing the rigid 8-aminoquinoline (AQ) auxiliary in α,α-disubstituted substrates leads to high activation barriers for a turnover-limiting product dissociation step arising from geometric distortion. Guided by these insights, we show that judicious tuning of the directing group can minimize energetic penalties with the use of a flexible 2-pyridylmethylamine (PM) auxiliary. This mechanistically informed approach led to a 115-fold rate increase for the model α,α-dimethyl substrate and broadens the scope to sterically encumbered alkenes, including α-spiro(hetero)cyclic systems, with tolerance for diverse N–H and C–H nucleophiles. Furthermore, we demonstrate that the mechanistic framework developed for hydroamination extends to other difunctionalization reactions such as carboamination and cyclopropanation. This work expands access to structurally complex and lipophilic scaffolds from readily available alkenes.

Here we present the ambiphilic reactivity of alkyl sulfonyl fluorides in the stereoselective synthesis of diverse cyclopropanes from olefins, under palladium(II) catalysis. The sulfonyl fluoride functionality serves as both an acidifying group and an internal oxidant within the ambiphile, enabling successive carbopalladation and oxidative addition steps in the catalytic cycle, respectively. The transformation grants access to cis -substituted cyclopropanes and exhibits broad compatibility with various alkyl sulfonyl fluorides, including those bearing –CN, –CO ₂ R, isoxazolyl, pyrazolyl and aryl groups. With internal alkene substrates, 1,2,3-trisubstituted cyclopropanes that are otherwise challenging to synthesize are formed in good-to-moderate yields and predictable diastereoselectivity. Detailed mechanistic insights from reaction progress kinetic analysis and density functional theory calculations reveal that the S _N 2-type C–SO ₂ F oxidative addition is the turnover-limiting and diastereoselectivity-determining step.

Disclosed herein is the invention of a method for facile C–H alkylation of a range of (hetero)arenes under Ni-catalysis. This reaction takes place at 50 °C, is scalable, tolerates heterocyclic substrates, and can be applied to both primary and complex secondary alkyl donors. Success hinges on the use of sulfonylhydrazide-based alkyl donors that mildly generate alkyl radicals thereby obviating the need for alkyl halide precursors that require more harsh conditions to activate. The demonstrated substrate scope is broad (>70 examples), and the reaction was also applied to natural product synthesis. Mechanistic studies (both computational and experimental) suggest that an asynchronous, amine-assisted C–H activation pathway is operative which may have larger implications for the field.

The ambiphilic reactivity of alkyl sulfonyl fluorides in the stereoselective synthesis of diverse cyclopropanes from ole-fins under palladium(II) catalysis is presented. The sulfonyl fluoride functionality serves as both an acidifying group and an internal oxidant within the ambiphile, enabling the successive carbopalladation and oxidative addition steps in the catalytic cycle, respectively. The transformation grants access to cis-substituted cyclopropanes and exhibits broad compatibility with various alkyl sulfonyl fluorides, including those bearing –CN, –CO2R, isoxazolyl, pyrazolyl, and aryl groups. With internal alkene substrates, 1,2-3-trisubstituted cyclopropanes that are otherwise challenging to synthesize are formed in good to moderate yield and predictable diastereoselectivity. Detailed mechanistic insights from reaction progress kinetic analysis (RPKA) and density functional theory (DFT) calculations reveal that the SN2-type C–SO2F oxidative addition is the turnover-limiting and diastereoselectivity-determining step.

A three‐component coupling approach toward structurally complex dialkylsulfides is described via the nickel‐catalyzed 1,2‐carbosulfenylation of unactivated alkenes with organoboron nucleophiles and alkylsulfenamide (N−S) electrophiles. Efficient catalytic turnover is facilitated using a tailored N−S electrophile containing an N ‐methyl methanesulfonamide leaving group, allowing catalyst loadings as low as 1 mol %. Regioselectivity is controlled by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, amides, sulfinamides, phosphoramides, and carbamates. Key to the development of this transformation is the identification of quinones as a family of hemilabile and redox‐active ligands that tune the steric and electronic properties of the metal throughout the catalytic cycle. Density functional theory (DFT) results show that the duroquinone (DQ) ligand adopts different coordination modes in different stages of the Ni‐catalyzed 1,2‐carbosulfenylation‐binding as an η ⁶ capping ligand to stabilize the precatalyst/resting state and prevent catalyst decomposition, binding as an X‐type redox‐active durosemiquinone radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, and binding as an L‐type ligand to promote N−S oxidative addition at a relatively more electron‐rich Ni(I) center.

A three‐component coupling approach toward structurally complex dialkylsulfides is described via the nickel‐catalyzed 1,2‐carbosulfenylation of unactivated alkenes with organoboron nucleophiles and alkylsulfenamide (N−S) electrophiles. Efficient catalytic turnover is facilitated using a tailored N−S electrophile containing an N‐methyl methanesulfonamide leaving group, allowing catalyst loadings as low as 1 mol %. Regioselectivity is controlled by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, amides, sulfinamides, phosphoramides, and carbamates. Key to the development of this transformation is the identification of quinones as a family of hemilabile and redox‐active ligands that tune the steric and electronic properties of the metal throughout the catalytic cycle. Density functional theory (DFT) results show that the duroquinone (DQ) ligand adopts different coordination modes in different stages of the Ni‐catalyzed 1,2‐carbosulfenylation‐binding as an η⁶ capping ligand to stabilize the precatalyst/resting state and prevent catalyst decomposition, binding as an X‐type redox‐active durosemiquinone radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, and binding as an L‐type ligand to promote N−S oxidative addition at a relatively more electron‐rich Ni(I) center.

Over the last fifty years, the use of nickel catalysts for facilitating organic transformations has skyrocketed. Nickel(0) sources act as useful precatalysts because they can enter a catalytic cycle through ligand exchange, without needing to undergo additional elementary steps. However, most Ni(0) precatalysts are synthesized with stoichiometric aluminum–hydride reductants, pyrophoric reagents that are not atom‐economical and must be used at cryogenic temperatures. Here, we demonstrate that Ni(II) salts can be reduced on preparative scale using electrolysis to yield a variety of Ni(0) and Ni(II) complexes that are widely used as precatalysts in organic synthesis, including bis(1,5‐cyclooctadiene)nickel(0) [Ni(COD)₂]. This method overcomes the reproducibility issues of previously reported methods by standardizing the procedure, such that it can be performed anywhere in a robust manner. It can be transitioned to large scale through an electrochemical recirculating flow process and extended to an in situ reduction protocol to generate catalytic amounts of Ni(0) for organic transformations. We anticipate that this work will accelerate adoption of preparative electrochemistry for the synthesis of low‐valent organometallic complexes in academia and industry.

Over the last fifty years, the use of nickel catalysts for facilitating organic transformations has skyrocketed. Nickel(0) sources act as useful precatalysts because they can enter a catalytic cycle through ligand exchange, without needing to undergo additional elementary steps. However, most Ni(0) precatalysts are synthesized with stoichiometric aluminum–hydride reductants, pyrophoric reagents that are not atom‐economical and must be used at cryogenic temperatures. Here, we demonstrate that Ni(II) salts can be reduced on preparative scale using electrolysis to yield a variety of Ni(0) and Ni(II) complexes that are widely used as precatalysts in organic synthesis, including bis(1,5‐cyclooctadiene)nickel(0) [Ni(COD)₂]. This method overcomes the reproducibility issues of previously reported methods by standardizing the procedure, such that it can be performed anywhere in a robust manner. It can be transitioned to large scale through an electrochemical recirculating flow process and extended to an in situ reduction protocol to generate catalytic amounts of Ni(0) for organic transformations. We anticipate that this work will accelerate adoption of preparative electrochemistry for the synthesis of low‐valent organometallic complexes in academia and industry.

Over the last fifty years, the use of nickel catalysts for facilitating organic transformations has skyrocketed. Ni(0) sources act as useful precatalysts because they can enter a catalytic cycle through ligand exchange, without needing to undergo additional elementary steps. However, most Ni(0) precatalysts are synthesized with stoichiometric aluminum–hydride reductants, pyrophoric reagents that are not atom-economical and must be used at cryogenic temperatures. Here, we demonstrate that Ni(II) salts can be reduced on preparative scale using electrolysis to yield a variety of Ni(0) and Ni(II) complexes that are widely used as precatalysts in organic synthesis, including bis(1,5-cyclooctadiene)nickel(0) [Ni(COD)2]. This method overcomes the reproducibility issues of previously reported methods by standardizing the procedure, such that it can be performed anywhere in a robust manner. It can be easily transitioned to large scale through an electrochemical recirculating flow process. We anticipate that this work will accelerate adoption of preparative electrochemistry for the synthesis of low-valent organometallic complexes in academia and industry.