Poster Session

A Selective and Modular Ni(0)/Silane Catalytic System for the Isomerization of Alkenes
Kiana E. Kawamura, graduate student, Cook research group, University of Oregon
Alkenes are used ubiquitously as starting materials and synthetic targets in all areas of chemistry. Controlling their geometry and position along a chain is vital to their reactivity and properties. Alkene isomerization is an atom-economical process to synthesize targeted alkenes, and selectivity can be controlled using transition metal catalysts. Key challenges in developing isomerization catalysts are i) a lack of modularity in catalyst structure and ii) the requirement of stoichiometric additives and generation of byproducts during catalyst activation. We address both challenges with a modular (NHC)Ni(0)/silane catalytic system (NHC, N-heterocyclic carbene), demonstrating the use of triaryl silanes and readily accessible (NHC)Ni(0) complexes to form the proposed active (NHC)(silyl)Ni–H species in situ. We show that modification of the steric and electronic nature of the catalyst is easily achieved through structural changes to the ligand or silane. This creates a uniquely versatile catalytic system that is effective for the formation of internal alkenes with high yield and selectivity for the E-alkene for both 1,2-disubstituted and trisubstituted alkenes. The use of silanes as mild activators enables isomerization of substrates with a variety of functional groups, including acid-labile groups. Preliminary mechanistic studies support a Ni–H insertion-elimination pathway.

Science and Data Science for Insights: RNA examples
Anne Marie Clark and Matthew J. McBride, senior scientists, CAS IP Services, American Chemical Society
Therapeutic use of RNA is increasing as shown by the recent mRNA vaccines and siRNA drugs. Due to the inherent fragility of RNA, these substances are either chemically modified or encapsulated in lipid nanoparticles to protect them. This presentation will demonstrate techniques using CAS information and KNIME to analyze siRNA chemical modification patterns, and demonstrate combining CAS information with other sources in KNIME for insights into mRNA delivery vectors.

Synthesis and Catalytic Evaluation of Black Phosphorus / Metal Chalcogenide Heterostructures
Michael Riehs, graduate student, Velian research group, University of Washington
Heterostructures based upon two-dimensional black phosphorus and atomically precise metal chalcogenide nanoclusters (M₃Co₆Se₈ where M=Co, Cr, Fe, Mn, and Sn) have been prepared by thermolysis and their catalytic activity for the hydrogen evolution reaction (HER) has been evaluated. Both bulk and exfoliated black phosphorus were treated with a variety of clusters and thermolyzed to remove the organic ligands associated with the clusters. Through this decomposition, transition metal species are left on the surface of black phosphorus. Initial studies by XRD and SEM/EDS show these to be a mixture of cobalt selenide species and M/Co or M/Se species although further analysis is needed to determine the exact nature of them (i.e., crystallinity, interaction with phosphorus atoms, stoichiometry). Preliminary electrocatalytic studies for the hydrogen evolution reaction in organic solvent using trifluoracetic acid (TFA) as a proton source have shown an increase in activity for these heterostructures as compared to pristine black phosphorus.

Atomically precise clusters as nanomaterial building blocks and single atom catalysts
Sebastian Krajewski and Daniel Zhou, graduate students, Velian research group, University of Washington
Atomically defined nanoclusters provide a compelling platform for the exploration of deterministic nanomaterials and the study of the metal-support interaction. Here we report some applications of the Co₆Se₈ system. Hierarchical nanosheets based on the trimetalated nanoclusters M₃Co₆Se₈L₆ (M = Co, Zn, L = Ph₂PNHTol) and a variety of ditopic linkers were found to exhibit single crystal-to-single crystal redox intercalation and quasi-chiral phase separation. Further studies revealed that control of the oxidation state of the initial building block could fundamentally alter the dimensionality of the resulting material. We also demonstrate a scheme for the attachment of a single transition metal atom to the Co₆Se₈ cluster, enabling precise catalytic studies of metals bound to the cluster surface. The series MCo₆Se₈L₂(PEt₃)₄ (M = Cr, Mn, Fe, Co, Ni, Zn) was synthesized, and the relative catalytic activity of each complex determined.

New Frontiers in Porous Materials Chemistry
Austin Kamin, Kathleen Snook, Jack Geary, and Leo Porter-Zasada, graduate students, Xiao research group, University of Washington
Traditional metal–organic frameworks (MOFs) lack the desirable physicochemical properties found in conjugated carbon nanostructures (e.g. charge transport), the complex structure and catalytic activity of enzymes, and the advantageous mechanical properties observed in soft materials like polymers and liquid crystals (e.g. solution processability and stimuli-responsiveness). Work in the Xiao lab seeks to address these shortcomings through innovative organic and inorganic synthesis. This poster describes work in three distinct areas: (1) the synthesis of conjugated metal–organic nanostructures, (2) the development of bioinspired heterogeneous catalysts, and (3) the self-assembly of soft nanoporous materials.

Probing the Metal-Support Interface in an Atomically Precise Cr/Co/Se Nanocluster
Jonathan Kephart, doctoral candidate, Velian research group, University of Washington
Earth abundant and compositionally diverse, nanostructured transition metal-chalcogenides exhibit excellent activity for a range of catalytic transformations, empowering breakthrough discoveries in clean energy and chemical manufacturing. Yet due to the limitations of surface analysis techniques, the interfacial processes governing their reactivity are often poorly understood. We prepared a family of atomically defined M₃Co₆Se₈L₆ (L = Ph₂PNTol; M = 3d metal) nanoclusters, in which a miniaturized transition metal-chalcogenide surface binds three catalytically competent active sites. This molecular construct enables an unprecedented atom-level inspection of the solid state catalytic interface, revealing a dynamic coordinative and electronic interplay between substrate (e.g. organic azide, isocyanide), active site (M), and support (Co­₆Se₈). The catalytic functionality of this platform was first showcased using the triiron nanocluster, Fe₃Co₆Se₈L₆, which we found to be an exceptional catalyst for the conversion of TsN­₃ and CN^tBu to the asymmetric carbodiimide TsN=C=N^tBu. This transformation ostensibly proceeds through the intermediacy of an iron-nitrenoid, yet the identity of this species has remained elusive.
Here, we demonstrate that the trichromium variant, Cr₃(py)₃Co₆Se₈L₆, exhibits analogous reactivity toward carbodiimide formation while also taming the reactivity of metal-nitrenoid intermediates. A detailed investigation of stoichiometric azide activation and nitrene transfer was performed, ultimately enabling the isolation of a series of key mono-, bis- and tris(imido) intermediates. In addition to structural determination via single crystal X-ray analysis, the nature of the metal-nitrenoid bond was interrogated using a suite of characterization techniques including solid-state magnetometry, cyclic voltammetry, and quantum chemical calculations. Remarkably, the catalytic edge metals are site-differentiated on the Co₆Se₈ surface, as dynamic Cr–Se bonds adopt a low-symmetry (⍺,⍺,β) configuration. Owing to their structural differentiation, the reactivity of the active edge metals appears to be correlated and we observe a step-wise and site-specific substrate activation and transfer mechanism.

Surface Functionalization of Black Phosphorus with Discrete Organometallic Fragments
Kendahl Walz Mitra, doctoral candidate, Velian research group, University of Washington
Precise structural assignment and controlled manipulation of single-atom active sites on solid state catalytic materials is critical to the development of next-generation energy conversion materials. Black phosphorus (bP), a layered 2D allotrope of phosphorus, is a particularly promising support as the lone pairs on each P atom are available to interact with metal centers.
While decoration of bP with metal nanoparticles has previously been explored for catalysis, there are few reports of functionalization with mononuclear organometallic complexes. This work demonstrates the successful covalent functionalization of bP with catalytically relevant organometallic Re and Mo complexes and probes the structure of the resulting surface sites. The modified nanosheets feature discrete mononuclear organometallic fragments on the bP surface with no signs of nanoparticle formation or metal leaching. Ligands on the metal centers contain functional groups with spectroscopic tags (e.g. CO, BF4) to allow for characterization with a multitude of techniques including vibrational and X-ray photoelectron spectroscopies as well as powder X-ray diffraction. Carbonyl ligands on the functional groups coupled with infrared spectroscopy, Gaussian fitting, and DFT calculations allow the dominant M–bP binding mode of each material to be identified.
As a proof-of-concept that the modified nanosheets are stable to transformations at the metal center, anion exchanges of Re(CO)3Cl-functionalized bP were performed. There are few reports of similar transformations on other materials, and no previous reports of these transformations on bP. Remarkably, new vibrational modes post-exchange clearly show successful transformation of the Re center, suggesting that the functionalized metal centers are available for traditional organometallic manipulation.

Defect Structure in Yb-Doped CsPbCl 3 Perovskites
Kyle Kluherz, graduate student advised by Profs. Daniel Gamelin and Jim De Yoreo, with co-workers David Sommer and Sebastian Mergelsberg
Yb3+-doped CsPbCl3 perovskites show great promise as quantum-cutters, by which a single high-energy photon is converted into two lower-energy photons emitted from the Yb3+ dopants. Optical spectroscopy and simulations have led to the hypothesis that the emissive Yb3+ ions substitute for Pb2+ with charge-compensating Pb2+ vacancies, but so far there is no direct structural evidence to support this interpretation. Our work aims to determine the structure of the Yb3+ dopant site in CsPbCl3 perovskites. Via a combination of X-ray absorption spectroscopy and X-ray total scattering measurements we have confirmed the Yb3+ oxidation state and shown Yb3+ to substitute exclusively at Pb2+ sites with a similar coordination of Cl- atoms. Via PDF analysis, we have observed decreases in Pb-Pb atom pair frequences, indicating the presence of Pb2+ vacancies. By comparing differential PDFs, we have ruled out single Yb3+ substutions and found a good fit from a dimer structure model. Using statistical analysis and fits based on linear combinations of different simulated Yb3+ dopant site structures, we aim to determine the distribution of hypothesized structures in our samples.

Regulating the Regulator: Optimizing P3HT-Based Blends for Organic Electrochemical Transistors
Duncan X. Haddock, undergraduate researcher, Waldow research group, Pacific Lutheran University
Blends of electronic and ionic conducting polymeric blends and their effect on the current production in organic electrochemical transistors (OECT) devices were studied. Different weight fraction blends of the charge conductive polymer (poly(3-hexylthiophene-2,5-diyl, P3HT) and an ion conductive ROMP based polymer with oligomeric ethylene oxide sidechains were studied at weight fractions of 1.00, 0.95, 0.85, 0.75, 0.65, 0.40, and 0.20 with respect to P3HT. A solution of 100 mM potassium hexafluorophosphate (KPF6) was used to dope the OECT. Transconductance was measured for each blend as well as a threshold voltage. Using that data, the figure of merit, µC*, was subsequently calculated for all systems using a range of device geometries. The figure of merit, µC*, was maintained at 55 +/- 5 F/(cmVs) up to a blend weight fraction of about 0.75 with KPF6. Preliminary data was also acquired for 100 mM KCl and transients for KPF6.

Oxidative Addition of Pd(0) to Si–H Bonds: Mechanistic Understanding, Catalytic Application, and Materials Development
Michael Hurst, graduate student, Cook research group, University of Oregon
The oxidative addition of Pd(0) to Si–H bonds to form (silyl)Pd(H) complexes is a commonly proposed step in catalysis, including in hydrosilylation, isomerization, and C–Si coupling reactions. However, these complexes have been only rarely observed, and very few studies have been conducted on their mechanism of formation and their stability with respect to silane identity. To shed light on this reaction, we have investigated the oxidative addition of Pd(0) complexes to tertiary silanes with substitution patterns probing the effect of steric and electronic influences. Our results show that oxidative addition is favored with silanes that are electron-poor and have less sterically bulky substituents at silicon. These trends are supported by kinetic and thermodynamic measurements, including the rate law of reaction, a R3Si–H/D kinetic isotope effect, and the energetic barrier to temperature-dependent exchange of ligand environments. Taken together, these data suggest a concerted mechanism of oxidative addition where the rate-determining step is initial silane coordination to form intermediate Pd–(η2-H–SiR3) sigma complexes. Applying this system in catalysis, the hydrosilylation of alkynes via (silyl)Pd(H) complexes shows enhanced reaction rate with electron-poor and less sterically hindered silanes, paralleling trends observed in oxidative addition. Building from this molecular understanding, we have synthesized new materials formed via oxidative addition of LTM (M = Ni, Pd, Pt) to the surface of silica. Treatment of dehydroxylated silica allows for the installation of targeted Si–H moieties on the surface. Preliminary reactions of Pd(0) complexes with these materials show successful oxidative addition by solid-state NMR and XPS. These materials hold potential as stable, tunable heterogeneous catalysts.

Low Valent Nickel Hydrosilylation Catalyst Exhibiting Unique Markovnikov-Selectivity & Mechanistic Insights on Catalyst Behavior
Alison Chang, graduate student, Cook research group, University of Oregon
Hydrosilylation is one of the most industrially significant homogenous transition metal-catalyzed reactions, and it is important because it is used to produce durable silicone material feedstocks. Traditionally, highly active Pt complexes are most widely exploited in this field, yet they show undesired side reactivity, producing byproducts that result from catalyst degradation. Their most notable trait is their high anti-Markovnikov selectivity, and this advantage has strengthened the foundations of the silicone industry. Few examples of efficient Markovnikov-selective, Earth-abundant systems have been developed, of which the products are also of great value. We envision the development of low-valent nickel catalysts for hydrosilylation will further advance the field in several aspects: 1) Ni’s Earth-abundance will be of greater interest due to its inexpensiveness and potential for increased sustainability, 2) a Ni(0) catalyst will eradicate exogeneous activators required to initiate catalysis (e.g. base, nucleophile) and reduce byproduct production, and 3) it will enable the use of tertiary, organo-silanes, a notably difficult task. Our studies display Markovnikov-selectivity obtained with Ni(NHC) complexes for the hydrosilylation of styrene and 2° or 3° silanes. With modular control over the ligand scaffold, we show that increasing steric bulk results in a reversal of selectivity. This Ni(NHC) catalyst system can tolerate a range of electronically and sterically diverse styrene and silane substrates. Preliminary mechanistic experiments such as rate law, deuterium labelling studies, and deuterium cross-over studies have been carried out to elucidate the reaction mechanism.

Selenium Catalyzed C-H amination
Alex Dohoda, Nicole Rishwain, graduate students, Michael research group, University of Washington
The selective replacement of C−H bonds in complex molecules is a highly efficient way to introduce new functionality and/or couple fragments.The Michael lab has developed a new Selenium Catalyzed allylic amination of alkenes that allows the introduction of a wide range of nitrogen functionality at the allylic position of alkenes with unique regioselectivity and no allylic transposition. This method has been expanded to propargyl C-H amination and allylic amination of enol-derivatives, vinyl silanes, and vinyl boronic esters.

Predicting indium phosphide quantum dot properties using machine learning on synthetic procedures
Hao Nguyen, graduate student, Cossairt research group, University of Washington
Indium phosphide quantum dots (QDs) are a promising alternative to traditional Cd- and Pb- based materials for lighting, displays, and optoelectronic technology. Intensive studies in the past decades have been devoted to optimizing synthetic parameters to control the quality of InP QDs. However, it still remains challenging to obtain precise emission and absorption wavelengths of InP QDs from tuning synthetic conditions. Recently, machine learning (ML) has emerged as a useful technique in the field of chemical synthesis to optimize chemical reactions, predict synthetic outcomes, design new procedures, study underlying mechanisms, simulate processes, etc. In 2020, Santos and coworkers reported the very first application of ML on quantum dot synthesis. In the study, ML algorithms were applied to identify important variables in the synthesis and to predict the final size of CdSe, CdS, PbS, PbSe, and ZnSe QDs. Using a similar methodology, we have trained and optimized several ML models in two different ways, using single- and multi-outputs, to predict the diameter, absorption, and emission wavelength of InP QDs based on their synthetic conditions. The dataset was manually extracted from 179 publications that report the synthesis of InP QDs. A data augmentation technique was applied to complete the dataset that includes 216 syntheses. Both the single-output and multi-output models showed high accuracy with the mean absolute errors (MAE) as low as 0.33, 11.46, 20.29 nm for diameter, emission, and absorption wavelength respectively. The ML models also recognized nucleation temperature, reaction time, and addition of zinc as the most important parameters for the synthesis. Furthermore, we also deployed an accessible and interactive webapp using the best single-output models, which can be accessed through the URL https://share.streamlit.io/cossairt-lab/indium-phosphide/streamlit/st_all.py. Finally, eight ‘new’ experiments were designed based on extensions of literature procedures and ran to confirm the accuracy of the webapp. The experimental results showed MAEs around 16 nm for both absorption and emission wavelengths when compared with the predicted values from the webapp. This approach and the results from this study are believed to demonstrate the capability of ML in chemical synthesis and contribute to our understanding of InP QD synthesis.

Regiodivergent Synthesis of Allylic Alcohols from Terminal Alkynes
James E. Baumann, Austin Shaff, graduate students, Lalic research group, University of Washington
Our group focuses on developing methods that take advantage of the transition metal-catalyzed hydrofunctionalization of alkynes. Recently we have discovered two such transformations that allow the convergent synthesis of allylic alcohols through reductive cross coupling of terminal alkynes. The first transformation utilizes differential dihydrofunctionalization followed by palladium catalyzed cross coupling with an alkenyl electrophile. The second transformation affords allylic alcohols by coupling an alkyne with an a-chloro boronate ester via a catalytically generated alkenyl boronate intermediate. Together these two methods provide a regiodivergent strategy for the synthesis of allylic alcohols from terminal alkynes.

Synthetic Organic Materials in the Golder Research Lab
Meredith Pomfret, Sarah Zeitler, Ray Huang, graduate students and undergraduate researcher, Golder research group, University of Washington
This poster will highlight an overview of recent work in the Golder laboratory spanning synthetic organic materials across a variety of scale. Some representative examples include (1) modulating the properties of rigid-rod polymers through pericyclic reactions in the polymer backbone, (2) novel initiators to access cyclic macromolecules, (3) the use of mechanical force for free radical polymerization reactions, and (4) upcycling of commodity polymers to alter physical properties.

The chemistry of indigenous peoples
Marcos Aurélio Gomes da Silva, master’s student, Universidade Federal de Juiz de Fora

Remarkably Stable [FeII(SMe2N3(Et,Et))(CO)2]Cl Illustrates the Impact of Alkyl Thiolates on Stability of Fe hydrogenase enzymes
Paige Gannon, Douglas Baumgardner, Maria Greiner, graduate students, Kovacs research group, University of Washington
Hydrogenase enzymes are highly efficient at generating hydrogen as an energy source in nature, and all share the common architecture of an iron center with an alkyl thiolate and carbonyl ligands in the coordination sphere. It is hypothesized that the role of the alkyl thiolate is to stabilize the coordination of CO while the Fe center is in the +2 oxidation state via electron donation. We have synthesized [FeII(SMe2N3(Et,Et))(CO)2]Cl as a model compound for the active site of hydrogenases and found it to be stable in solution at room temperature for several days. DFT studies of the electronic structure support the role of electron delocalization in the unusual stability of this complex.

Model Systems for Isopenicillin N Synthase and Cysteine Dioxygenase
Paige Gannon, Alexandra Downing, Dylan Rogers, Maria Greiner, Bennet Karel, Christopher Lowe, graduate students, Kovacs research group, University of Washington
Non-heme thiolate-ligated iron enzymes, cysteine dioxygenase (CDO) and Isopenicillin N Synthase (IPNS) use dioxygen as an oxidant to facilitate specific chemical transformations. We report a variety of model systems relevant to these enzymes, including [FeII(S2Me2N3(Pr,Pr))] which forms a reactive iron superoxo intermediate capable of abstracting H atoms with a bond dissociation energy of at least 92 kcal/mol. A related complex, FeII(S2H2N3(Pr,Pr))] is investigated for intramolecular H atom abstraction via an analogous superoxo intermediate. We also examine how variations in ligand backbone length constrain coordination geometry and impact the reactivity of iron sulfur compounds with oxygen and oxo atom donors.

Poster Submission Form – To present your work, please submit your title and abstract by October 5, 2021. If you would like to participate, but missed the deadline, please submit the form and then email Diana Knight. You are welcome to bring your poster, but we likely won’t be able to add your abstract to this page before the event.

For the event schedule and location, visit the Award Symposium page.

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