New Computational Collaboration – Online Today in J. Am. Chem. Soc.

Today we are pleased to announce publication of a collaborative study with Prof. Yu Lan’s group at Zhengzhou University elucidating the mechanism of nickel-catalyzed conjunctive cross-coupling reactions of alkenes, aryl iodides, and organozinc reagents, which reveals a previously under-appreciated role of the organozinc reagent as a Z-type ligand that facilitates reductive elimination. This revised mechanistic model explains how this type of conjunctive cross-coupling can proceed under such mild conditions without specialized ligand, despite involving a typically challenging C(sp3)–C(sp3) reductive elimination event. Congrats to the entire project team!

For a link to the paper in J. Am. Chem. Soc., click here: https://pubs.acs.org/doi/full/10.1021/jacs.2c09739

Kinetic Alkene Isomerization via Tungsten Catalysis – Pre-Print Online

In our newest pre-print posted online today, we continue our explorations of reactions enabled by the W0/WII redox manifold and report the discovery of a mild method for selectively isomerizing γ,δ-unsaturated amides into their β,γ-unsaturated counterparts without “over-isomerization” into conjugation. By controlling the ligand environment around the metal center, stereoselectivity can be controlled to favor either the (Z)- or the (E)-isomer. Though organometallic synthesis, we were able to shed light on some details of the reaction mechanism, highlighted by synthesis of a stable WII(π-Allyl)(OAc) complex that can converted in situ to a WII(π-allyl)(H) species, thereby intercepting a proposed intermediate in the catalytic cycle. Congrats to Tanner, Camile, and Raul!

For a link to the pre-print in ChemRxiv, click here: https://chemrxiv.org/engage/chemrxiv/article-details/63bfba1c741025af42ec927c

Anna Liu is recognized as a 2023 Regeneron STS Scholar

Congrats to Rancho Bernardo High School senior and Engle lab member, Anna Liu, who was selected today as a 2023 Regeneron Science Talent Search Scholars. Anna is one of only 300 awardees selected from a pool of nearly 2,000 applicants from across the United States. Anna has been a member of the Engle lab since November 2022 and has worked under the mentorship of Taeho Kang. Anna recently earned her first publication in the group (Organometallics 2023, 42, 11). We are so proud of you Anna! Congrats on your achievement!

For more information about the Regeneron STS program and a link the announcement, click here: https://www.societyforscience.org/regeneron-sts/2023-scholars/

Redox-Paired Alkene Functionalization – Pre-Print Now Online

Today we report a new strategy for alkene functionalization that can deliver two valuable products in a single step by partnering a mutually enabling oxidative difunctionalization and reductive difunctionalization, a process we term redox-paired alkene functionalization. In the reported reaction system, a single palladium(II) catalyst switches between PdIIX and PdIIAr forms during the catalytic cycle, each of which is active in the respective half-reactions. Specifically, the catalytic cycle achieves oxidative [3+2] annulation with 2-naphthols and reductive 1,2-diarylation with aryl iodides, expanding the scope and utility of both of these transformations. Congrats to all of the co-workers in this collaborative project: Hui-Qi, Tian (May), Shenghua, and Zhen; as well as Malkanthi, who performed computational studies under the joint guidance of Profs. Ken Houk (UCLA) and Peng Liu (Pittsburgh).

For a link to the pre-print in ChemRxiv, click here: https://chemrxiv.org/engage/chemrxiv/article-details/63ad635fff4651a6983afddf

Stereodivergent Nickel-Catalyzed Isomerization of Terminal Alkenes – Pre-Print Now Online

This week, in collaboration with the group of Prof. Julien Vantourout of ICBMS Lyon, we report complementary methods for E– and Z-selective kinetic isomerization of terminal alkenes under nickel catalysis. The two protocols are operationally simple to perform, employ commercially available reagents, and tolerate numerous synthetically useful functional groups. Congrats to all of the co-authors: Camille, Anne, Shenghua, and Zi-Qi. The project was initiated during Camille’s stint as a visiting student in Lyon earlier this year and was then wrapped up over the past few weeks to close out 2022 on a high note.

For a link to the pre-print in ChemRxiv, click here: https://chemrxiv.org/engage/chemrxiv/article-details/63aa9d68a53ea689e3590038

Beta-Carbon Elimination Paper – Now In Press

The peer-reviewed version of our paper describing the synthesis and characterization of elusive post-β-C-elimination organopalladium complexes is online today in Organometallics. In this paper, we find that the combination of chelation stabilization from the 8-aminoquinoline directing auxiliary and strain-release from ring-opening of the nopol framework allows for facile β-C-elimination to yield a series of N,N,π-C palladacycle products. Congrats to Taeho, Rei, Anna, and Tanner from our group at Scripps; Yue from Prof. Peng Liu’s group at University of Pittsburgh; and Arnie, Jake, and Milan from the crystallography core at UCSD.

For a link to the manuscript in Organometallics, click here: https://pubs.acs.org/doi/10.1021/acs.organomet.2c00530

As a reminder, a pre-print describing this work appeared at the end of October: https://chemrxiv.org/engage/chemrxiv/article-details/635875afca86b8d57fc36848

2022 Engle Lab Holiday Party

As per tradition, we celebrated the end of the year in style with tasty food, a fun white elephant gift exchange, and great company. Johny stole the show fashion-wise with his llama-themed sweater, and the burrito blanket was the hottest gift of the lot. Wishing everyone a magical holiday seasons, and looking forward to another great year to come in 2023!

Nickel(0) precatalyst toolkit paper – Now in press in Angewandte Chemie

The final version of our manuscript describing the development of a toolkit of bench-stable Ni(0) precatalysts for diverse organic transformations is now in press in Angewandte Chemie. This toolkit enables reactions reliant on air-stable Ni(0) sources such as Ni(COD)2 to be performed without an inert atmosphere glovebox using standard Schleck techniques, offering a path forward for commercial scale-up of such catalytic methods. This work was made possible through a large network of collaborators at Scripps Research, USCD, Cornell, and Bristol Myers Squibb.

For coverage of this work in C&E News, see: https://cen.acs.org/acs-news/acs-meeting-news/Nickel-tamed-reagent-toolkit/100/i11

For a link to the paper in Angewandte Chemie, click here: https://onlinelibrary.wiley.com/doi/10.1002/anie.202211794

As a reminder, a pre-print of this work was uploaded to ChemRxiv back in February: https://onlinelibrary.wiley.com/doi/10.1002/anie.202214153

Elusive Intermediates Captured in Latest Pre-Print

During the past few years, numerous synthetic methods have been developed that take advantage of catalytic C–C bond cleavage via β-C elimination from an alkylmetal intermediate to furnish a new PdII(olefin)(R) (R = Alkyl, Aryl, etc.) species. Nevertheless, igorous characterization of said post-β-C-elimination organometallic species has proven elusive. In collaboration with the Liu group at the University of Pittsburgh and the X-ray crystallography facility at UCSD, we have successfully synthesized well-defined post-β-C-elimination organopalladium complexes, enabled by a combination of strain-release to provide thermodynamic driving force and chelation stabilization to suppress potential side reactions. The complexes were characterized by single-crystal X-ray diffraction, and the potential energy surface of the β-C elimination step and other relevant processes was computed using density functional theory. Congrats to Taeho, Rei, Anna, and Tanner from Scripps Research; Yue from Pitt; and Arnie, Jake, and Milan from UCSD.

For a link to the pre-print in ChemRxiv, click here: https://chemrxiv.org/engage/chemrxiv/article-details/635875afca86b8d57fc36848