Chapter Four · failure evidence
What Transition Metal Catalysis got wrong, from 110 dissertations
The records document various operational difficulties and performance limitations encountered when developing transition metal catalytic systems across organic synthesis, polymerization, and electrochemistry. Researchers frequently observed that catalysts underperformed simpler alternatives, suffered active site poisoning and physical degradation, or induced unwanted side reactions and substrate decomposition. These records come from PhD theses at 30 institutions, 2021 to 2026. Each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Catalytic systems underperformed alternative catalysts or simpler baseline conditions
Transition metal complexes and modified nanomaterials frequently delivered lower yields, conversions, or selectivity compared to standard benchmark catalysts or simpler catalyst-free protocols. In several cases, multi-metal mixtures, alloy nanoparticles, or immobilised systems failed to match the activity of mononuclear or homogeneous baselines.
Lost to a baseline
Addition of HSiPh3 to [(μ-dcpe)Pd]2 (forming silyl palladium hydride 6b in situ) impeded the catalytic isomerization of 4-allylanisole compared to [(μ-dcpe)Pd]2 alone.
The Oxidative Addition of Palladium(0) to Hydro- and Halo- Silanes: Mechanisms and Applications · Scholars' Bank
Lost to a baseline
Mononuclear PdII complex C22 exhibited notably lower catalytic activity in Heck coupling compared to heterometallic polymers C24-C26
Kompleksy metalosupramolekularne z metalami d-elektronowymi jako wysoce efektywne i selektywne systemy katalityczne Metallosupramolecular complexes with d-block metals as highly effective and selective catalytic systems · AMUR - Repozytorium Uniwersytetu im. Adama Mickiewicza w Poz
Lost to a baseline
Grafted heterogeneous catalyst 4 gave only 10% yield for allylbenzene isomerization compared to 45% yield from homogeneous Pd(0) dimer 1.
The Oxidative Addition of Palladium(0) to Hydro- and Halo- Silanes: Mechanisms and Applications · Scholars' Bank
Lost to a baseline
DDQ/chiral phosphoric acid catalyst method by Reddy group surpassed vanadium-catalyzed asymmetric coupling using simpler starting materials
Aerobic Oxidation Of Phenols And Other Arenes By Transition Metal Catalysis · Penn
Lost to a baseline
Monometallic Pt octahedral nanocrystals exhibited significantly lower catalytic activity toward competitive acetylene hydrogenation even at 180 °C compared to Pd octahedra, which achieved complete conversion at 160 °C.
Palladium-Based Nanocrystals with Controlled Surfaces for Catalytic Applications · Georgia Tech
Lost to a baseline
Pd(TFA)2 (26%), PdCl2 (16%), CpPd(allyl) (20%), and Pd2(dba)3 (20%) precatalysts all gave lower yields than Pd(OAc)2 (38%) in desulfinamidative coupling.
Lost to a baseline
In the cross-coupling of 1-chloronaphthalene with 2-propanol at 110 °C, pre-catalysts 2-C1, 3-C1, and 3-C2 gave <5% yield of 3-3a compared to 45% for 2-C3
Lost to a baseline
In the cross-coupling of naphthalimide 4-9 with tert-butylamine at 80 °C, pre-catalyst 4-C1 gave only 13% yield compared to >95% for Ni(cod)2/IPr
Considered and rejected
Considered and rejected: Rejected cross-coupling catalysts RuPhos Pd G4 and rac-BINAP+Pd(OAc)2 in Dad intermediate synthesis due to lower yields compared to BrettPhos Pd G1.
Tried and failed
equimolar physical mixtures of homometallic catalyst constituents applied to multicomponent catalytic reaction networks. Outcome: worse than baseline. Reason: individual or mixed mononuclear components lacked the cooperative synergistic reactivity of the integrated heterometallic complex
Multi‐Stimuli‐Responsive Network of Multicatalytic Reactions using a Single Palladium/Platinum Catalyst · Cambridge
Tried and failed
physical mixture of homometallic catalysts applied to multicatalytic reaction network cascade. Outcome: worse than baseline. Reason: isolated mononuclear catalyst centers lacked synergistic effects present in the heterometallic complex
Multi-Stimuli-Responsive Network of Multicatalytic Reactions using a Single Palladium/Platinum Catalyst. · Cambridge
Lost to a baseline
Monometallic Pt/C showed higher overall catalytic activity (W/F = 0.01-0.3) than bimetallic Pt-M alloys (W/F = 1) for 2-acetylfuran conversion, despite having lower target selectivity.
Metal And Metal Oxide Nanocrystals For Catalysis And Magnetic Applications · Penn
Lost to a baseline
Single-metal catalysts (monometallic Rh) showed higher light enhancement and activity than bimetallic RhPt alloys due to higher plasmon Q-factors.
Understanding Active Sites in Plasmonic Enhanced Catalysis · DukeSpace
Lost to a baseline
Metal-modified catalysts (Ag-TiO2, Pt-TiO2, Au-TiO2, etc.) showed lower net C1 accumulation rates than unmodified semiconducting nanoparticles (SiC produced 29.5 nmol m^-2 hr^-1 vs Ag-TiO2 at 0.50 nmol m^-2 hr^-1) without hole scavengers.
Design and Engineering of Carbon Fixing Material Systems · MIT
Lost to a baseline
Catalyst-free hydrophosphinylation of PhN=C=O gave 64% isolated yield of 44a, whereas catalytic reaction with 5 mol% Fe(C6H3-2,6-Mes2)2 gave a lower isolated yield of 60% after ethanol washing
Addition of P-H Bonds to Heterocumulenes · University of Nottingham Repository
Lost to a baseline
Previously developed chiral-at-metal catalyst -Ru8 gave 32% yield and 38% e.e. (S) on diazoketone 129a compared to 99% yield and 93% e.e. (R) with -Ru6*
Design and Synthesis of Cyclometalated Chiral-at- Ruthenium Complexes for Asymmetric Catalysis Design und Synthese von cyclometallierten chiral-at-Ruthenium Komplexen für asymmetrische Katalyse · open_UMR Marburg DSpace 10.0
Lost to a baseline
Catalytic aerobic oxidation of Li[Phmal] using Fe(OTf)2 alone gave comparable yields of oxidized products (16% b, 41% c) relative to the biomimetic Fe/Tbim catalyst (22% b, 41% c)
Adventures in Coordination Chemistry: Biomimetic Fe(II) and Mn(III) Complexes with fac-N,N,N/O Coordination and a Brief Foray into Low Coordinate Organometallic P,N-Fe(II) Complexes · DSpace at SUNY Buffalo
Lost to a baseline
Multiatom catalyst activity is lower than industrial chromium- and platinum-based commercial catalysts.
Lost to a baseline
Mixed-metal and Fe-based catalysts (NiFe2O4, NiCoO2, Ni0.5Co0.5Fe2O4) had much higher overpotentials and degradation rates than baseline IrO2 (and Co3O4) in pure-water MEAs despite being superior in 3-electrode alkaline liquid cells
Advancing Anion-Exchange-Membrane Water Electrolyzer Devices: Catalyst Layer Interactions, Degradation Pathways, and Operational Development · Scholars' Bank
Lost to a baseline
Photocatalytic C–H trifluoromethylation of benzene using CoCl2 in place of III gave a statistically insignificant increase in yield relative to metal-free conditions (37% vs 35%).
Lost to a baseline
Hov-Grubbs 2nd generation catalyst gave worse yields than slower-initiating indenylidene catalyst M202 in ring expansion optimization.
1, 3-Diene Synthesis, Functionalization and Applications Via Ene-Yne Metathesis and Cobalt Mediated Hydrogen Atom Transfer for the Synthesis Nannocystin A · DSpace at SUNY Buffalo
Lost to a baseline
Divergent synthesis G0.5-COOMe-Au NCs had lower catalytic activity in 4-NP reduction compared to directly-synthesized G0.5-COOMe-Au NCs due to higher ligand passivation density.
Chemical functionalization and modification of Au clusters · HARVEST
Lost to a baseline
For cis-cyclooctene ROMP, free HG2 catalyst achieved 100% conversion while anchored mSiO2/SiO2-SH catalyst achieved 85% conversion.
Depolymerization and polymerization in confined spaces · Iowa State
Lost to a baseline
Heterogeneous IrOx-SiO2 catalyzed hydrogenation of mesityl oxide to MIBK at a faster rate than supported pincer catalyst 23-SiO2.
Investigations Of Pincer Iridium Complexes For Glycerol Deoxygenation And For Alkane Dehydrogenation · Penn
Considered and rejected
Considered and rejected: Abandoned transition-metal-catalyzed directing-group C(sp2)-alkylation on ketones upon finding baseline basic conditions without catalyst promoted direct alpha-C- and O-alkylation.
Quaternary ammonium salts as alternative reagents in hydrocarbonylation reactions Direkte C-H Methylierungen mittels sicherer und fester Reagenzien · DSpace-CRIS at TU Wien
Considered and rejected
Considered and rejected: Use of second-generation Hoveyda-Grubbs catalyst for cross-metathesis of 2.18 and 2.27 was abandoned in favor of the less hindered and electronically different Nitro-Grela SI-o-tolyl catalyst.
Lost to a baseline
Freestanding pellet catalytic activity remained inferior to conventional thin-film benchmarks (reduced graphene oxide films, modified carbon fiber paper) due to mass transfer limitations in thick pellets.
Carbon electrode for the oxygen reduction reaction · Imperial
Lost to a baseline
Pt-only three-way catalyst supported on co-precipitated solid solution Ce0.9Zr0.1O2 underperformed core@shell Pt/0.9CeO2@0.1ZrO2 in both degreened (T90 of 205/248/260 °C vs 188/229/240 °C for CO/THC/NOx) and hydrothermally aged states (T90 of 220/262/263 °C vs 207/237/244 °C).
Development of Low-Temperature Oxidation Catalysts for Diesel and Gasoline Vehicles · DSpace at SUNY Buffalo
Lost to a baseline
Phosphine-containing catalysts (Au11 and biicosahedral Au25 on CeO2) achieved <30% CO conversion at 250 °C after 250 °C pretreatment, severely underperforming thiolate-only Au25/CeO2 (100% conversion).
The Ligand shapes the cluster: Influence and modification possibilities of protecting Ligands on gold nanoclusters Der Ligand bestimmt den Cluster: Einfluss und Möglichkeiten zur Modifizierung der Liganden an Goldnanoclustern · DSpace-CRIS at TU Wien
Lost to a baseline
In situ and ex situ transition metal catalysts resulted in a statistically significant bio-oil yield decrease of nearly 8% compared to the control
Catalytic Upgrading of Biofuel Pyrolysis · Cornell
Lost to a baseline
In the hydrosilative reduction of 3b (2 mol% catalyst, 75 °C, 1 h), M(N(SiMe3)2)2 (M = Mn, Fe, Co) gave <10% conversion of 3b, underperforming (PN)Co (72% conversion, 47% yield) and (PN)Ni (89% conversion, 67% yield).
N-Phosphinoamidinate Nickel Complexes · DalSpace
Lost to a baseline
CeCl3.7H2O-NaI catalyst for urethane prepolymer synthesis gave lower Mw (2400 g/mol) compared to toxic DBLT benchmark (4200 g/mol) and InCl3 (3900 g/mol).
Development of Innovative Polymer Matrix Materials: The Role of Polymer Functionalization and Additives. · IRIS - UNICAM - prod
Lost to a baseline
All thermal-diffusion (TD) prepared Sn-doped TiO2 catalysts achieved only ~3.0–3.8% As(III) oxidation, severely underperforming baseline commercial anatase TiO2 (24.7%).
Lost to a baseline
Re/Al2O3 and other Re-based catalysts showed lower steady-state CO2 methanation activity and methane selectivity compared to benchmark Ni/Al2O3 under conventional continuous feed
Development of novel catalysts for e-fuel production · IRIS - POLITO - prod
Lost to a baseline
Allylbenzene self-metathesis with Ru1 gave 85:15 E/Z ratio, failing to match Grubbs Z-selective catalyst GIII (11:89 E/Z ratio).
N-Heterocyclic Carbene Containing Macrocycles: Design, Synthesis and Applications · DSpace at SUNY Buffalo
Lost to a baseline
PtPdIrRhRu nanocatalyst ORR mass activity reached only 12.2% of pure platinum catalyst baseline
Multi-Principal Element Alloys Synthesis and Their Application on Electrocatalysis · JScholarship
Unsuitable ligand or precatalyst choices prevented reaction activation and turnover
Catalytic reactions failed when the oxidation state, coordination environment, or ligand electronic properties were mismatched to the substrate. Systems stalled due to a lack of thermal activation, unfavorable metal intermediate thermodynamics, or the absence of required promoter additives.
Tried and failed
anionic palladium catalysts in cross-coupling applied to heteroaryl reductive cross-coupling. Outcome: no signal. Reason: complexes provided no catalytic improvement over standard palladium precursors
Development of catalytic carbon-carbon bond forming reactions by leveraging the iodide effect · UT Austin
Tried and failed
room-temperature palladium-catalyzed cross-coupling without external heating applied to sterically hindered heteroaryl C-N bond formation. Reason: catalytic system lacked sufficient thermal activation for oxidative addition or transmetalation/reductive elimination
Development of Deactivation-Resistant Catalysts for Pd-Catalyzed C–N Cross-Coupling Reactions · MIT
Tried and failed
transferring standard cross-coupling catalyst to alkynyl electrophiles applied to tethered palladium-catalyzed carboetherification. Outcome: did not generalise. Reason: standard catalyst ligand was unsuitable for alkynyl bromides, requiring a different phosphine ligand pre-catalyst
Stereoselective palladium-catalyzed carboetherification of cyclopropenes via a tethering strategy · EPFL
Tried and failed
electron-deficient pyridone ligands in palladium-catalysed C-H functionalisation applied to palladium norbornene relay C-H acetoxylation. Reason: electron-deficient pyridone ligands deactivated the palladium catalyst giving trace product
Tried and failed
Zero-valent palladium precatalysts applied to Directed catalytic C-H functionalisation. Outcome: worse than baseline. Reason: Lower oxidation state precatalysts failed to improve reaction efficiency compared to standard palladium(II) salts
Tertiary alkylamines as effective directing groups for palladium-catalysed C(sp3)–H activation strategies · Cambridge
Tried and failed
bidentate chiral phosphines in palladium allylic reduction applied to allylic carbonate hydrogenolysis. Reason: bidentate phosphine ligands resulted in no catalytic conversion
Tried and failed
transition metal-catalyzed alpha-alkylation with unactivated alkyl halides applied to aldehydes via enamine intermediates. Outcome: no signal. Reason: unactivated primary alkyl halides failed to couple across diverse palladium catalysts and ligand conditions
Considered and rejected
Considered and rejected: Rejected synthesis of thiophenol catalyst C17 via copper-catalysed cross-coupling of potassium thioacetate with aryl iodides due to poor conversion.
New directions in the Mitsunobu reaction · University of Nottingham Repository
Tried and failed
catalytic hydrogen auto-transfer without acidic alcohol additive applied to enantioselective carbonyl allylation. Outcome: worse than baseline. Reason: inefficient protolytic cleavage of the metal alkoxide intermediate led to very low yield
Development of catalytic carbon-carbon bond forming reactions by leveraging the iodide effect · UT Austin
Tried and failed
increasing metal dopant loading in zeolite catalysts applied to methane catalytic oxidation. Outcome: worse than baseline. Reason: excessive metal loading formed inactive oxide clusters instead of active isolated sites, lowering turnover frequency
Design and Engineering of Carbon Fixing Material Systems · MIT
Tried and failed
unpyrolyzed metal-organic frameworks as heterogeneous catalysts applied to alcohol oxidation and arene hydrogenation. Outcome: no signal. Reason: active metal sites remained coordination-saturated by organic linkers without thermal decomposition
Tried and failed
transition metal substitution in porous framework catalysts applied to nitrous oxide activation catalysts. Reason: metal-oxo intermediate formation is thermodynamically unfavorable for late and alkaline earth transition metal centers
Tried and failed
dual transition metal catalyzed enantioselective hydroalkenylation applied to unactivated vinyl halides. Reason: gave moderate yields but poor enantioselectivity compared to pseudohalide coupling partners
Tried and failed
extraframework metal oxide cluster catalysis applied to Lewis acid transfer hydrogenation reactions. Outcome: worse than baseline. Reason: Metal oxide clusters lacked accessible Lewis acidic coordination and exhibited negligible catalytic activity compared to framework sites
Catalytic implications of confined solvent ensembles within Lewis acid zeolites · MIT
Tried and failed
reducing base loading or adding water additive applied to transition metal catalyzed allylic alkylation. Reason: failed to improve reaction conversion
Tried and failed
transition metal additive catalytic co-milling applied to mechanochemical polymer depolymerization. Outcome: worse than baseline. Reason: metal and metal oxide powders suppressed monomer yield rather than catalyzing chain scission
The kinetics of ball mill mechanochemistry in its application to the depolymerization of poly(styrene) · Georgia Tech
Tried and failed
chemical reduction without Lewis acid additive applied to transition metal catalyst activation. Reason: reductant failed to reduce the metal complex without Lewis acid activation
New Radical Approaches to C–C Bond Formation in Small Molecules · Cornell
Tried and failed
Strong reducing agents and non-aqueous solvents during synthesis applied to metal nanocluster catalytic activity. Outcome: worse than baseline. Reason: harsh reduction and organic solvents produced clusters with markedly reduced catalytic activity compared to mild aqueous conditions
Engineering catalytic gold nanoclusters and nanovesicles for detection of disease · Imperial
Tried and failed
unsupported metal oxide electrocatalyst applied to electrochemical nitrogen reduction. Outcome: worse than baseline. Reason: exhibited much higher cell resistance, leading to lower Faradaic efficiency and yield compared to supported catalysts
REALIZING SELECTIVE ELECTROCHEMICAL CO2 AND N2 REDUCTION BY INTERFACIAL ENGINEERING AND RATIONAL CATALYST DESIGN · JScholarship
Tried and failed
reducing precursor feed ratio in epitaxy applied to ternary nitride thin film growth. Reason: lower ratio reduced catalytic surface coverage, counterintuitively increasing metal accumulation and precipitating secondary metallic phases
Controlling Adatom Kinetics to Overcome Traditional Limitations for III-Nitride Ternary Alloys · Georgia Tech
Tried and failed
incorporating multi-element dopants in liquid metal catalysts applied to electrochemical nitrate reduction. Reason: active site dopant causes premature intermediate desorption instead of complete multi-step reduction
Configuring a Liquid State High-entropy Metal Alloy Electrocatalyst · EPFL
Tried and failed
transition metal impregnation on zeolite catalyst applied to olefin skeletal isomerization. Outcome: worse than baseline. Reason: metal modification degraded catalytic performance and alkali exchange eliminated active acid sites needed for conversion
Promoting And Deactivating Effects of Carbonaceous Deposits During Skeletal 1-Butene Isomerization Over Ferrierite · Georgia Tech
Active catalytic sites were poisoned or inhibited by coordinating species and impurities
Competitive coordination from substrates, coordinating solvents, or functional groups such as thiols, amines, and phosphines caused catalytic deactivation. External contaminants, halides, sulfur compounds, and reaction byproducts similarly bound to metal centers and halted turnover.
Tried and failed
Suzuki cross-coupling with free thiol functionalised reagents applied to conjugated polymer end-group functionalisation. Outcome: too slow. Reason: Free thiol groups poisoned the palladium catalyst, preventing the cross-coupling reaction from completing
Tried and failed
cationic palladium catalyzed insertion polymerization applied to norbornene derivatives in coordinating ethereal solvents. Outcome: no signal. Reason: coordinating ethereal solvents inhibit or poison the cationic palladium catalyst, preventing polymerization
Chemical Sensing of N-Nitrosodimethylamine and Methane · MIT
Tried and failed
Late transition metal catalyzed addition polymerization applied to norbornenes with coordinating functional groups. Outcome: no signal. Reason: Coordinating substituents poison or bind competitively to the cationic palladium catalyst, inhibiting polymerization
Chemical Sensing of N-Nitrosodimethylamine and Methane · MIT
Considered and rejected
Considered and rejected: Rejected synthesis of amide-linked triphenylphosphonium oleanolic acid conjugate via Pd/C hydrogenation of azido intermediate 118 because phosphonium prevented catalyst turnover.
Nuevos sistemas de reconocimiento molecular basados en organocalcógenos. Agentes antiparasitarios y antiproliferativos · Repositorio Institucional BUAP
Considered and rejected
Considered and rejected: Rejected PdCl2(PPh3)2 as catalyst due to strong phosphine ligand coordination completely halting the etherification reaction.
Développement de nouveaux groupes protecteurs et de nouvelles conditions de protections-déprotection pour la synthèse organique Application en synthèse · DSpace at the University of Batna 1
Considered and rejected
Considered and rejected: Rejected Pd2(dba)3 / P(o-tolyl)3 catalyst system in favor of Pd(PPh3)4 because the former was poisoned/inhibited by the pincer ligand side chains.
Dynamic Metal-Ligand Interactions in Semiconducting π-Conjugated Materials · Scholarship at UWindsor Institutional Repository
Tried and failed
Lewis acid catalyzed epoxide ring opening applied to heterocycle-containing nucleophiles. Reason: Unhindered electron-rich nitrogen heterocycles coordinate competitively to the metal catalyst, causing catalyst poisoning and inhibition
Addressing the Extremes of Reactivity in Small-Molecule-Catalyzed Stereoselective Glycosylation · Harvard
Tried and failed
catalytic low-temperature supercritical water gasification applied to sulfur-rich biomass waste. Reason: sulfur compounds rapidly poisoned and deactivated the catalysts
Decision support for the design of integrated biorefineries · EPFL
Tried and failed
increasing metal catalyst loading applied to olefin metathesis reactions. Outcome: worse than baseline. Reason: active site poisoning by stable carboxylic species and side-product oligomers from acid-catalyzed dimerization
Propylene Metathesis over Molybdenum Silicate Microspheres with Dispersed Active Sites · MIT
Tried and failed
electrochemical decomposition on noble metal catalysts applied to ammonium formate decomposition. Outcome: unstable. Reason: catalyst poisoning and voltage instability over time
Kinetic and Thermodynamic Aspects of Voltage as a Driving Force for Ammonia Activation · MIT
Tried and failed
ring-opening metathesis polymerisation with ruthenium catalyst applied to functionalised cyclic diketone monomers. Reason: diketone coordination to the ruthenium catalyst poisoned or deactivated the catalyst
Development of additives for the controlled degradation of polyethylene · Imperial
Tried and failed
one-pot catalytic functionalization using in situ reagents applied to diazo compound alkynylation. Reason: catalyst deactivation caused by metal coordination poisoning from reaction components
Tried and failed
anhydrous catalytic oxidation over metal oxide applied to room temperature volatile organic compound oxidation. Reason: absence of water causes catalyst poisoning through intermediate accumulation of formates and carbonates
Trends in C-H bond dehydrogenation energetics for small molecule conversion · MIT
Lost to a baseline
[As7] cluster catalyst 7 gave 49% conversion for acetophenone hydroboration, significantly lower than the 91% conversion achieved by [P7] parent catalyst 1 (caused by product coordination poisoning).
Zintl Clusters as a Platform for Lewis Acid Catalysis · Oxford
Considered and rejected
Considered and rejected: Rejected phosphate buffer electrolytes for bicarbonate dependence studies due to catalyst surface poisoning.
Overcoming challenges of fundamental electrochemical kinetic studies under dilute-reagent conditions · MIT
Considered and rejected
Considered and rejected: Rejected final-step 18F-fluorination on unprotected secondary amine precursors due to catalyst poisoning/inhibition
Copper-mediated radiosynthesis of 18F- and 123I-radiolabelled PARP inhibitors · Oxford
Considered and rejected
Considered and rejected: Direct debenzylation of secondary amine/conjugate 35 using catalytic transfer hydrogenation or standard Pd/C failed due to amine poisoning of the catalyst, requiring BCl3 with pentamethylbenzene scavenger.
Oligosaccharides based antibacterial drug conjugates · Leibniz Universität Hannover Repository
Considered and rejected
Considered and rejected: Rejected Pt and Pd catalysts as primary study catalysts because they are too active for ORR (reducing methane activation sites) and suffer CO poisoning upon overoxidation.
ELECTROCHEMICAL CONVERSION OF METHANE TO LIQUID PRODUCTS MEDIATED BY REACTIVE OXYGEN SPECIES · JScholarship
Considered and rejected
Considered and rejected: DioRASSP Cbz/tBu catalytic hydrogenation strategy: rejected due to palladium expense/toxicity and susceptibility to sulfur poisoning from Met/Cys.
New synthetic methodology for chiral amines and peptides via gap technology · Texas Tech
Considered and rejected
Considered and rejected: Platinum group metal catalysts in desalination fuel cells deprioritized due to catalyst poisoning by halide ions in the brine.
Considered and rejected
Considered and rejected: Rejected Karstedt's platinum catalyst for polar bottlebrush polymers containing cyano groups due to catalytic poisoning by nitrogen compounds
Bottlebrush Dielectric Elastomers with Improved Properties for Actuation · EPFL
Competing reaction pathways led to bond cleavage and substrate degradation
Catalysts promoted undesirable side transformations including beta-hydride elimination, excessive hydrogenolysis, and retro-aldol cleavages rather than the targeted couplings. In other instances, unselective catalyst insertion into sensitive bonds triggered extensive substrate decomposition and coking.
Tried and failed
Suzuki-Miyaura cross-coupling applied to substrates containing N-O bonds. Reason: Palladium catalyst inserted into the weak N-O bond rather than the aryl-halide bond
Chain Scissionable Resists Based on Poly(acetal) Motif for Extreme Ultraviolet Lithography · Cornell
Tried and failed
macrocyclization via Stille cross-coupling applied to polyketide macrolactone synthesis. Outcome: unstable. Reason: various palladium catalysts led exclusively to substrate degradation instead of ring closure
Synthesis of the Phormidolide A Macrocycle Supports the Proposed Configurational Reassignment. · Cambridge
Considered and rejected
Considered and rejected: Direct cross-coupling of secondary benzylic alcohols/ethers bearing β-hydrogens using dppf ligand rejected because dppf caused exclusive β-hydride elimination whose product inhibited catalytic turnover
TRANSITION METAL CATALYZED CROSS-COUPLINGS OF ALKYL SULFONE ELECTROPHILES · Queens University Institutional Repository
Considered and rejected
Considered and rejected: Pd(II) catalysts (e.g. Pd(dppf)Cl2, Pd(PhCN)2Cl2) rejected due to low conversion and promoting electrophilic C1-C3 bond cleavage/isomerization to cyclobutenes
Synthesis of 1,3-disubstituted bicyclo[1.1.0]butanes via directed bridgehead functionalization · Oxford
Considered and rejected
Considered and rejected: Rejected non-preformed Pd(OAc)2/BINAP catalyst system for Buchwald-Hartwig cyclization of 2-pyridylmethyl substrates due to competitive Csp3-Csp3 retro-aldol cleavage
Considered and rejected
Considered and rejected: Rejected precious/noble metal catalysts (Ru, Pd, Pt) due to high cost and preferential selectivity for undesirable decarboxylation/decarbonylation pathways over dehydration.
Novel Catalysts Development for Production of Jet Fuel Range Hydrocarbons from Vegetable Oils · HARVEST
Considered and rejected
Considered and rejected: Rejected gold(III) and gold(I) catalysts due to poor enantioselectivity despite significantly faster reaction turnover compared to palladium(II)
Considered and rejected
Considered and rejected: Rejected using 1,2-dichloroethane or toluene with single Au(I) catalysts due to poor mass balance and partial cyclization diene byproduct formation, pivoting to dual Au(I)/In(III) catalysis.
Tried and failed
mechanocatalytic hydrogenolysis with supported precious metal catalysts applied to lignin model compounds. Reason: catalysts induced extensive over-hydrogenolysis to methane, degrading carbon balance without yielding monomeric aromatics
The Mechanocatalytic Depolymerization of Lignin and Lignin Model Compounds · Georgia Tech
Lost to a baseline
SD-1:6-Ag:Pd/carbon catalyst lost all semi-hydrogenation selectivity (0% MBE vs 84.7% for monometallic Ag) due to over-hydrogenation to MBA.
Lost to a baseline
Catalytic hydrocracking of plastic mixture yielded only 59.28% BTX at 450 °C vaporization, performing worse than pure HDPE (72.86%), LDPE (70.51%), and PS (83.15%) feeds due to PP presence and severe coke accumulation
CHEMICAL ENGINEERING FOR SUSTAINABILITY: REACTIVE AND REVERSIBLE SORPTION OF NITROGEN OXIDES AND CATALYTIC UPCYCLING OF WASTE PLASTICS · JScholarship
Considered and rejected
Considered and rejected: Rejected AuCl as a catalyst due to elevated redox potential causing substantial substrate decomposition.
Catalytic Activation of Strained C–C Bonds · Publikationssystem UB Tuebingen
Considered and rejected
Considered and rejected: Rejected DTT and TCEP as chemical reductants for disulfide-containing metal catalysts due to preferential metal abstraction over selective disulfide reduction
The development of switchable initiators for rac-Lactide ring-opening polymerisation · Imperial
Catalysts suffered from physical degradation, leaching, sintering, and precipitation
Transition metal centers frequently degraded into inactive precipitates, sintered into bulk metallic phases, or leached from their supports during reaction or purification. Exposure to reducing impurities, harsh thermal calcination, or reactive byproducts also caused severe coking and structural support collapse.
Tried and failed
heterogeneous palladium black catalyst applied to biaryl cross-coupling reactions. Outcome: unstable. Reason: gave poor reproducibility and inconsistent product yields across runs
Tried and failed
silica-supported palladium catalyzed continuous-flow cross-coupling applied to fluorinated heteroaryl coupling reactions. Outcome: unstable. Reason: In situ generated fluoride byproducts chemically etched and degraded the silica catalyst support
Considered and rejected
Considered and rejected: Rejected the palladium-catalysed vinylation route to ene-carbamates via catalyst 4.6 due to poor synthetic reproducibility (biphasic precipitation and decomplexation)
Photochemical Alkynylations with Hypervalent Iodine Reagents · EPFL
Tried and failed
pulsed co-electrodeposition without coordinating ligands applied to bimetallic catalyst synthesis. Outcome: unstable. Reason: loss of active transition metal ions due to insoluble precipitate formation and uncontrolled oxidation
Selective Electrochemical Nitrate Reduction to Ammonia over Cobalt-based Catalysts · Queens University Institutional Repository
Tried and failed
Supported nickel catalyst in flow-through reductive fractionation applied to lignocellulosic biomass upgrading. Outcome: unstable. Reason: Rapid catalyst deactivation caused by metal sintering, leaching, and surface poisoning from soluble biomass components
Tried and failed
using commercial solvent directly without scavenging pretreatment applied to homogeneous palladium catalysis reactions. Outcome: unstable. Reason: trace reducing impurities caused premature reduction and precipitation of active catalyst as metal black
Electrochemical Mechanisms in Thermochemical Catalysis · MIT
Tried and failed
transition metal dual catalyzed oxidative olefin functionalization applied to unprotected and basic aminoalkenes. Outcome: unstable. Reason: catalyst deactivation and substrate decomposition under oxidative catalytic conditions
Tried and failed
transition metal doping in perovskite catalyst applied to solid oxide fuel cell anodes. Outcome: unstable. Reason: Dopants reduced to metallic phase under hydrocarbons, causing rapid coking and cell degradation
Development of Novel Electrode and Catalyst Materials for Solid Oxide Electrochemical Cells · Georgia Tech
Tried and failed
Post-carbonization acid leaching of metal-impregnated carbons applied to transition metal-doped carbon electrocatalysts. Reason: Severe dissolution and loss of poorly coordinated metal dopants during acid purification
Carbon electrode for the oxygen reduction reaction · Imperial
Considered and rejected
Considered and rejected: Rejected bare MXenes as viable NRR catalysts despite favorable overpotentials because Pourbaix and selectivity analyses show they are unstable and poison/favor HER under operating conditions.
Considered and rejected
Considered and rejected: Rejected 500 °C calcination for single-site catalyst synthesis because it caused Cu agglomeration into metallic particles and destroyed ligand framework.
Regulating Molecular Interactions for Electrochemical Energy Conversion and Storage · JScholarship
Difficult catalyst separation and metal contamination hindered synthetic routes
Separation of homogeneous metal residues, persistent colored impurities, and phosphine byproducts proved challenging and caused product loss. Potential metal leaching and magnetic contamination also motivated abandoning metal-mediated pathways for cleaner alternatives.
Considered and rejected
Considered and rejected: Rejected transition-metal-mediated cross-coupling polymerizations (Stille, Suzuki-Miyaura, Kumada) due to the requirement of electron-rich co-monomers, toxicity of organostannanes, and tedious palladium catalyst purification.
Considered and rejected
Considered and rejected: Two-step recrystallisation for purifying catalyst 1 was replaced by column chromatography of ligand HL1 and solvent evaporation due to higher yield (89% vs 22%).
Considered and rejected
Considered and rejected: Rejected standard dppf iron-catalyzed cyanation protocol, adopting an iron-free dppb catalytic route despite much lower yields to eliminate magnetic contamination in VSM/EPR.
Tried and failed
solid-supported scavenger for catalyst removal applied to living ring-opening metathesis polymerization. Reason: cleaved catalyst byproduct retained catalytic activity and underwent side reactions with unreacted scavenger
Considered and rejected
Considered and rejected: Rejected ring-closing metathesis using Grubbs 2nd generation catalyst due to inability to separate tricyclohexylphosphine oxide and ruthenium impurities without yield loss.
Mechanistic Investigations into Catalytic Wittig Reactions · University of Nottingham Repository
Considered and rejected
Considered and rejected: Rejected Grubbs Ru catalyst 2.3 for biological studies due to persistent colored impurities, trace metal chelation, and lower water solubility.
Left open by the authors
Problems the authors named and did not get to.
Left open
Elucidate the structure of residual palladium clusters and determine their catalytic mechanism for proton reduction. Blocker: Requires advanced physical characterization techniques, wet lab chemistry, and specialized spectroscopy/microscopy equipment.
Left open
Screen palladium catalysts, solvents, temperatures, and additives for the homo-coupling reaction of biferrocenyl diiodide. Blocker: Requires a wet chemistry laboratory, synthetic reagents, and analytical instruments for reaction screening
Towards the synthesis of multinuclear, branched and cyclic metallocene-containing complexes · Imperial
Left open
Resolve Pd leaching and catalyst deactivation in Pd-MIL-101-PTA during sequential tandem synthesis of caprolactam from phenol. Blocker: Requires a wet chemistry laboratory and physical catalyst synthesis and characterization apparatus.
Left open
Develop an enantioselective decarboxylative functionalization of cyclopropenes using excited state palladium catalysis or dual photoredox/transition metal catalysis. Blocker: Requires a wet chemistry laboratory, reagents, and physical synthesis equipment.
Left open
Employ peracetic acid for the regioselective acetoxylation of triazole and oxazoline substrates using palladium catalysis. Blocker: Requires a wet chemistry laboratory and physical chemical reagents (PAA, Pd catalyst, triazole, oxazoline).
Left open
Develop enantioselective rhodium-catalyzed reductive coupling reactions using cheap, benign terminal reductants. Blocker: Requires a synthetic chemistry wet lab, reagents, catalysts, and analytical equipment
Carbon-carbon bond formation via transition metal-catalyzed transfer hydrogenative carbonyl addition · UT Austin
Left open
Expand Rh-catalyzed transfer hydrogenative coupling of alcohols to complex higher dienes beyond butadiene and isoprene. Blocker: Requires wet lab synthetic chemistry facilities, catalysts, and physical reagents
Carbon-carbon bond formation via transition metal-catalyzed transfer hydrogenative carbonyl addition · UT Austin
Left open
Extend the copper/tartramide catalyst system to cross-coupling of phenols, thiols, and alkynes in diethylene glycol. Blocker: Requires a synthetic chemistry wet laboratory, specialized reagents, and analytical equipment.
Exploring copper-catalysed Ullmann cross coupling reactions · Imperial
Left open
Develop atroposelective reductive biaryl cross-couplings between sterically hindered substrates using ruthenium catalysis. Blocker: Requires a synthetic chemistry wet lab, reagents, catalysts, and physical analytical equipment (e.g., HPLC, NMR).
Development of catalytic carbon-carbon bond forming reactions by leveraging the iodide effect · UT Austin
Left open
Develop catalytic perfluoroalkylation and C-C bond formation reactions using 1,3,2-diazaphospholenes while suppressing background uncatalyzed reactivity. Blocker: Requires wet lab synthetic chemistry experimentation and reagents
New Applications of 1,3,2-Diazaphospholenes in Catalysis · EPFL
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