Low Catalyst Loading Research Articles

(Invited) Electron Microscopy Investigation of PEM Electrolyzer Degradation at Low Iridium Loadings

The employment of hydrogen as an energy carrier provides a promising solution toward zero carbon emission and battling climate change. To meet the DOE’s Hydrogen Shot goal of $1 per kilogram of hydrogen by 2031, proton exchange membrane (PEM) water electrolysis is a key technology of hydrogen production from renewable energy sources. Successful deployment of PEM electrolyzers requires reducing cost while simultaneously improving performance and lifetime. While cost reduction is expected from a variety of strategies including scaling up, operation optimization, and advanced manufacturing, it remains vital to reduce the use of noble-metal catalyst due to its scarcity and vulnerable supply chain subject to market disturbance. [1]Reducing the loading of iridium catalyst on the anode while maintaining electrolyzer performance and durability is of great challenge. In this talk, we discuss issues in PEM electrolyzer component development and advanced manufacturing of electrode layers related to catalyst loading reduction with an emphasize on analytical electron microscopy which provides valuable insight on materials morphology, crystalline structure, and chemical compositions. The batch-to-batch variance of catalyst morphology and elemental composition/distribution from commercial suppliers will be examined for catalyst down-selection. We then analyze the effect of reducing Ir loading on the electrode layer structure and ionomer distribution. These results are correlated with electrochemical measurements in the electrolyzer cell, which help elucidate the effect of low catalyst loading on electrolyzer performance. Morphologies of degraded low-loading anode catalyst layer and gas recombination layers will be investigated, and the dissolution and migration of iridium will be studied. We will also examine impact of different roll-to-roll manufacturing strategies for low-loading catalyst layers and on electrolyzer durability. Last but not least, we analyze MEAs subject to cation contamination and recovery procedure with electron microscopy. [2]References[1] Alia, S.M., Current Opinion in Chemical Engineering 2021, 33:100703.[2] Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Optimization of Transport Components and Electrode Interfaces for Low Iridium Oxide Loading PEM Electrolysis

Moving towards lower iridium oxide (IrOx) catalyst loadings for the anode side of polymer electrolyte membrane water electrolyzers (PEMWE) requires tuning of the catalyst layer-porous transport layer (PTL) interface. To see widespread deployment, PEMWE anodes need to lower the loadings from 1-2 mg/cm2 IrOx down to 0.1 mg/cm2 [1]. The catalyst layer can become less uniform and more disconnected at these lower loadings, so the addition and optimization of a microporous layer (MPL) onto the PTL to improve interfacial contact and in-plane connectivity is essential to move toward the more sustainable lower loadings [2]. First, a set of PTLs with MPLs are made such that morphological properties are varied between them. Then, the PTLs with MPLs are combined with anode catalyst layers with IrOx loadings of 0.7, 0.5, 0.3, and 0.1 mg/cm2 to create cells to record polarization curves, stability tests, and catalyst degradation rates. The morphology of the PTLs and MPLs is quantified using X-ray computed tomography (CT). The important morphological characteristics that can be varied and measured with X-ray CT include porosity, pore size distribution, tortuosity, and thickness for each the MPL and base PTL. Using operando X-ray CT and radiography, oxygen transport through the PTL and channel can be observed to provide further information to the performance of the novel PTLs and MPLs. By using a two-dimensional continuum PEMWE model, insights into the effects on the cell performance and the contact resistance present at the MPL-catalyst layer brought about from PTL and MPL morphology alterations can be extracted to help guide the optimization efforts. Through combining these results, an optimal set of manufacturing/morphological parameters can be found to tune PTL and MPL production for the low-loaded catalyst layers that are needed for the future of PEMWEs.

Preparation of a novel Cu‐Ni mixed nanoparticles immobilized on clay: An Eco-friendly Nanocatalyst for mild synthesis of Benzimidazoles and pyrimidines

In the present work, Cu‐Ni mixed nanoparticles immobilized in magnetic clay (MMT-BAC@Fe3O4@CuNi) nanocatalyst were successfully synthesized using a simple method for the first time. In the design of this catalyst, nickel and copper ions were reduced and deposited on clay layers using a benzalkonium chloride directing group. The proposed method offers a safe, sustainable, and selective approach for the synthesis of 2-substituted benzimidazole and 3,4-dihydropyrimidin-2(1H)-ones using an environmentally friendly nanocatalyst. The solid catalyst was distinguished using a diversity of methods, including EDX (Energy Dispersive X-Ray), XRD (X-ray Diffraction), ICP (Inductively Coupled Plasma), VSM (Vibrating Sample Magnetometer), FT-IR (Fourier Transform Infrared Spectroscopy), TEM (Transmission Electron Microscopy) and FE-SEM (Field Emission Scanning Electron Microscopy). The significant features of this new protocol include good to excellent efficiency, oxidant-free conditions, low catalyst loading, inexpensive and non-toxic catalyst, simple procedure, moderate conditions, straightforward work-up, short reaction times, and easy reuse of the nanocatalyst.

CFD modeling of a mini-pilot scale CO2 hydrogenation to hydrocarbons reactor using both direct and indirect pathway-based kinetic model

Both indirect CO2 hydrogenation (reverse water gas shift (RWGS) followed by CO-based Fischer-Tropsch synthesis (FTS)) and direct CO2-based FTS were considered for CO2 hydrogenation, and a kinetic model for the chain-length distribution of hydrocarbon products was developed. For independent estimation, the kinetic parameters were estimated by fitting the experimental data using powder catalysts under various conditions, mainly including CO/CO2 ratios. The contribution of indirect CO2 hydrogenation (RWGS followed by CO-FTS) was more favorable than that of direct CO2-FTS, and CO2 conversion and product selectivity were significantly dependent on the temperature and hydrogen fraction. The effectiveness factor was estimated for the pellet-type catalysts, and values less than one validated the existence of mass-transfer resistance. Computational fluid dynamics (CFD) modeling was used to simulate the three-dimensional thermal behaviors of a mini-pilot-scale reactor with a substantially large diameter loaded with a pellet-type catalyst and inert materials. Both a low catalyst loading in the early stage of the reactor and the use of an additional inner cooling tube showed a stable temperature profile, with the peak temperature maintained below 350 °C (the critical temperature to prevent the thermal decomposition of chemicals) and fast heating of cold feed in the early stage. The CFD results with no inner tube showed thermal runaway in the second reactor, and the simulation with arbitrarily reduced heat of the reaction (70 % of the actual value) resulted in a peak temperature higher than 410 °C. Further quantitative analysis indicated that the no-inner-tube case's reduced heat transfer area per unit volume was responsible for its thermally unstable behavior.

Flame made low Pt loading catalysts supported on different metal oxides for catalytic combustion of CO and CH4

Catalytic combustion is an effective approach to remove air pollutants from various emission sources. For this purpose, supported noble metal catalysts are preferred in commercial applications due to their outstanding catalytic activity for eliminating CO, hydrocarbon compounds and NOx. In this paper, we employ the flame spray pyrolysis method to prepare a series of Pt-based catalysts with four different supports (TiO2, ZrO2, MgO and ZnO) and variable low Pt loadings for catalytic combustion of CO and CH4. The performance of 0.5 Pt/TiO2 is the best in all samples, in which the T90 temperatures are 107 and 500 °C for 90% conversion of CO and CH4, respectively. To examine its thermal stability, a time-on-stream test at 700 °C for 420 min is carried out, resulting in a decrease of about 5% in the final conversion of CH4. The X-ray diffraction results show that TiO2 support is a mixed phase with a major amount of anatase and a small amount of rutile other than a pure phase of ZrO2, MgO and ZnO. Furthermore, X-ray photoelectron spectroscopy analysis and high-angle annular dark-field scanning transmission electron microscopy observation show that when the Pt loading is low, the Pt species exist as highly dispersed single atoms on the surface of the TiO2 support. As the Pt loading gradually increases, the state of the Pt species transitions from single atoms to Pt clusters, resulting in a decrease in dispersion. Ultimately, the Pt can successfully accumulate on the surface of the TiO2 nanoparticles, providing abundant active sites for efficient catalytic combustion reactions.

Reductive C−N Bond Formation of Nitroarenes Using Pd@rGO‐CuFe2O4 Magnetic Nanoparticles in Water towards the Synthesis of N‐Aryl Formamide and Azole Derivatives

Abstract.Reductive C−N bond generation strategies of nitroarenes to form N‐arylformamide and azole derivatives were developed under the influences of magnetically separable Pd@rGO‐CuFe2O4 nanoparticle‐catalyzed reaction conditions. These reactions proceed at a very low catalyst loading in H2O as the solvent, which leads to a higher percentage of yields (up to 96 %) of the products. The catalyst is recovered from the reaction medium by using an external magnet and recycled for four consecutive reaction cycles with a less amounts of leaching.

Manganese Complexes with Consecutive Mn(IV) → Mn(III) Excitation for Versatile Photoredox Catalysis.

Manganese complexes stand out as promising candidates for photocatalyst design, attributed to their eco- and biocompatibility, versatile valence states, and capability for facilitating multiple electronic excitations. However, several intrinsic constraints, such as inadequate visible light response and short excited-state lifetimes, hinder effective photoinduced electron transfer and impede photoredox activation of substrates. To overcome this obstacle, we have developed a class of manganese complexes featuring boron-incorporated N-heterocyclic carbene ligands. These complexes enable prolonged excited-state durations encapsulating both Mn(IV) and Mn(III) oxidation stages, with lifetimes reaching microseconds for Mn(IV) and nanoseconds for Mn(III), concurrently exhibiting robust redox capabilities. They efficiently catalyze direct, site-selective cross-couplings between diverse arenes and aryl bromides, at a low catalyst loading of 0.5 mol %. Their proficiency spans an extensive array of substrates including both highly electron-rich and electron-deficient molecules, which underscore the superior performance of these manganese complexes in tackling intricate transformations. Furthermore, the versatility of these complexes is further highlighted by their successful applications in various photochemical transformations, encompassing reductive cross-couplings for the formation of C-P, C-B, C-S and C-Se bonds, alongside oxidative couplings for creating C-N bonds. This study sheds light on the distinctive photoredox properties and the remarkable catalytic flexibility of manganese complexes, highlighting their immense potential to drive progress in photochemical synthesis and green chemistry applications.

Synthesis, crystal structure, and DFT studies of NHC mediated Pd-PEPPSI complex: Application for Suzuki reaction

A novel air and moisture resistant Pd-PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) complex was synthesized via the reaction of benzimidazolium salt, PdCl2, KBr, K2CO3, and pyridine. The structure was characterized by spectroscopic methods such as 1H and 13C NMR, FT-IR, UV–vis. and single X-ray diffraction techniques. In order to evaluate the synthesized Pd complex in a detailed manner in terms of structural, bonding, electronic, and thermodynamic characteristics, DFT-based calculations were carried out at the B3LYP/6-311++G (d, p)/LANL2TZ theory level. Natural bond orbital (NBO) analysis was implemented to provide more insights about the possible donor-acceptor interactions and types of hybridization. Also, TD-DFT calculations were performed to rationalize the nature of the observed electronic transitions. The complex showed high catalytic activity in the Suzuki–Miyaura cross coupling of aryl chlorides with phenylboronic acid. Aryl chlorides bearing either electron- donating or withdrawing substituents afforded a wide range of biaryl derivatives that were isolated in the range of 55–97 % yields (7 examples). The reactions were carried out at very low catalyst loading (0.25 mol%) in the presence of air using a green water-based solvent (ipr:H2O/ 1:3). The palladium complex was found to be efficient for the coupling of aryl chlorides with arylboronic acids under aerobic conditions, affording the corresponding biaryls in high yields.

Half‐sandwich iridium complexes: Synthesis and catalytic activity in dehydrogenation of alcohols to carboxylic acids

A series of N,N‐chelate half‐sandwich iridium complexes were synthesized by a simple method with good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been successfully achieved by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half‐sandwich iridium catalyst system showed desirable stability and catalytic activity, and the achievement of a high TOF of 372.0 h−1 could be observed with an extremely low catalyst loading of only 0.05 mol%. Furthermore, the sustainable catalyst could be reused for a minimum of five cycles without obviously losing its activity, highlighting its potential application in industry. Structure of N,N‐chelate iridium complexes 1 and 3 were determined by single‐crystal X‐ray analysis.

Photoinduced Intermolecular Hydroamination and Hydroetherification of Electron-rich Alkenes with Low Catalyst Loadings.

A photochemical method based on visible-light irradiation (blue LEDs/sunlight) has been developed for the intermolecular hydroamination and hydroetherification of electron-rich alkenes. This photochemical method is compatible with a wide range of azoles and electron-rich alkenes, such as vinyl ethers, vinyl sulfides and enamides, and is performed with low concentrations of photocatalyst (1000 ppm). Comprehensive mechanistic studies indicate that this process is initiated by the formation of an active radical cation intermediate through single electron oxidation of azole, which is mediated by excited Acr-Mes+ BF4-.

Silicomolybdic Acid Cluster as Biocompatible Catalyst for One-Pot Tandem Synthesis of Orthogonally Protected Glycosides.

The present paper describes a new and practical approach for the one-pot preparation of O-isopropylidene derivatives and also orthogonally protected S- and O-glycosides from the corresponding unprotected saccharides by employing 2 mol % of a silicomolybdic acid (SMA) cluster as a versatile and biocompatible catalyst. The present protocol is applicable to two-step one-pot tandem transformations, which include the O-isopropylidation, spiroketal functionalization, 4,6-O-arylidene acetalations, and arylidene acetylation processes under relatively mild reaction conditions. One-pot sequential transformations, low catalyst loading, rapid transformation, high to excellent reaction yields, mild reaction conditions, and a nontoxic biocompatible workup procedure are the notable advantages of devised protocol.

Natural product synthesis by a nanoporous In-MOF Catalyst: Crystallographic insight by incorporating substrate inside its nanopores

Metal-organic frameworks (MOFs) are promising candidates as nanoporous heterogeneous catalysts over other solid catalysts. Herein, utilizing a new tetra-acid ligand and employing high-valent Indium metal source we have strategically developed a 3D robust nanoporous framework, IITKGP-53, which retained its crystallinity over a wide range of pH solutions (2–12). Considering the green synthesis approach IITKGP-53 was explored as a heterogeneous catalyst toward one-pot three-component Strecker reaction under solvent-free condition, with low catalyst loading for a broad range of substrates. Considering practical utility, biologically important natural product, Girgensohnine, was synthesized for the first time by using this catalyst with excellent conversion rate. The substrate binding sites inside the nanopores and host–guest interactions were verified crystallographically by obtaining a substrate inside nanopores of this MOF (aniline@IITKGP-53) and computational modeling. An in-depth theoretical investigation unveiled the most plausible transition states for the first time. This study inaugurates the usage of nanoporous MOFs as heterogeneous catalysts for natural product synthesis.

Oxidation of Ammonia Catalyzed by a Molecular Iron Complex: Translating Chemical Catalysis to Mediated Electrocatalysis.

Ammonia is a promising candidate in the quest for sustainable, clean energy. With its capacity to serve as an energy carrier, the oxidation of ammonia opens avenues for carbon-neutral approaches to address worldwide growing energy needs. We report the catalytic chemical oxidation of ammonia by an Earth-abundant transition metal complex, trans-[LFeII(MeCN)2][PF6]2, where L is a macrocyclic ligand bearing four N-heterocyclic carbene (NHC) donors. Using triarylaminium radical cations in MeCN, up to 182 turnovers of N2 per Fe were obtained from chemical catalysis with an extremely low loading of the Fe catalyst (0.043 mM, 0.004 mol % catalyst). This chemical catalysis was successfully transitioned to mediated electrocatalysis for the oxidation of ammonia. Molecular electrocatalysis by the Fe catalyst and the mediator (p-MeOC6H4)3N exhibited a catalytic half-wave potential (Ecat/2) of 0.18 V vs [Cp2Fe]+/0 in MeCN, and achieved 9.3 turnovers of N2 at an applied potential of 0.20 V vs [Cp2Fe]+/0 at -20 °C in controlled-potential electrolysis, with a Faradaic efficiency of 75 %. Based on computational results, the catalyst undergoes sequential oxidation and deprotonation steps to form [LFeIV(NH2)2]2+, and thereafter bimetallic coupling to form an N-N bond.

Oxidation of Ammonia Catalyzed by a Molecular Iron Complex: Translating Chemical Catalysis to Mediated Electrocatalysis

Ammonia is a promising candidate in the quest for sustainable, clean energy. With its capacity to serve as an energy carrier, the oxidation of ammonia opens avenues for carbon‐neutral approaches to address worldwide growing energy needs. We report the catalytic chemical oxidation of ammonia by an Earth‐abundant transition metal complex, trans‐[LFeII(MeCN)2][PF6]2, where L is a macrocyclic ligand bearing four N‐heterocyclic carbene (NHC) donors. Using triarylaminium radical cations in MeCN, up to 182 turnovers of N2 per Fe were obtained from chemical catalysis with an extremely low loading of the Fe catalyst (0.043 mM, 0.004 mol % catalyst). This chemical catalysis was successfully transitioned to mediated electrocatalysis for the oxidation of ammonia. Molecular electrocatalysis by the Fe catalyst and the mediator (p‐MeOC6H4)3N exhibited a catalytic half‐wave potential (Ecat/2) of 0.18 V vs [Cp2Fe]+/0 in MeCN, and achieved 9.3 turnovers of N2 at an applied potential of 0.20 V vs [Cp2Fe]+/0 at −20 °C in controlled‐potential electrolysis, with a Faradaic efficiency of 75%. Based on computational results, the catalyst undergoes sequential oxidation and deprotonation steps to form [LFeIV(NH2)2]2+, and thereafter bimetallic coupling to form an N−N bond.

Pd–PEPPSI-type expanded ring N-heterocyclic carbene complexes: synthesis, characterization, and catalytic activity in Suzuki–Miyaura cross coupling

ABSTRACT In this work, we synthesized a series of six unsymmetrical benzimidazolium salts 2 and their pyridine-enhanced precatalyst preparation stabilization and initiation (PEPPSI)-themed palladium N-heterocyclic carbene complexes [PdCl2(NHC)(Py)]. All the products were isolated in satisfactory yields (75-85%). The synthesis of these novel palladium PEPPSI complexes involved in reacting NHC precursors with PdCl2 in pyridine at 60°C in the presence of excess K2CO3. The structures of all compounds have been characterized by 1H NMR, 13C NMR, HRMS and IR spectroscopy, as well as elemental analysis techniques, which support the proposed structures. The catalytic activity of the six complexes was assessed in the Suzuki-Miyaura cross-coupling of phenylboronic acid and aryl halides. The reactions required only a low catalyst loading (0.1 mol%) and were carried out under mild aerobic conditions in a green, water-based solvent mixture.

D4-Symmetric Dirhodium Tetrakis(binaphthylphosphate) Catalysts for Enantioselective Functionalization of Unactivated C-H Bonds.

Dirhodium tetrakis(2,2'-binaphthylphosphate) catalysts were successfully developed for asymmetric C-H functionalization with trichloroethyl aryldiazoacetates as the carbene precursors. The 2,2'-binaphthylphosphate (BNP) ligands were modified by introduction of aryl and/or chloro functionality at the 4,4',6,6' positions. As the BNP ligands are C2-symmetric, the resulting dirhodium tetrakis(2,2'-binaphthylphosphate) complexes were expected to be D4-symmetric, but X-ray crystallographic and computational studies revealed this is not always the case because of internal T-shaped CH-π and aryl-aryl interactions between the ligands. The optimum catalyst is Rh2(S-megaBNP)4, with 3,5-di(tert-butyl)phenyl substituents at the 4,4' positions and chloro substituents at the 6,6' positions. This catalyst adopts a D4-symmetric arrangement and is ideally suited for site-selective C-H functionalization at unactivated tertiary sites with high levels of enantioselectivity, outperforming the best dirhodium tetracarboxylate catalyst developed for this reaction. The standard reactions were conducted with a catalyst loading of 1 mol % but lower catalyst loadings can be used if desired, as illustrated in the C-H functionalization of cyclohexane in 91% ee with 0.0025 mol % catalyst loading (29,400 turnover numbers). These studies further illustrate the effectiveness of donor/acceptor carbenes in site-selective intermolecular C-H functionalization and expand the toolbox of catalysts available for catalyst-controlled C-H functionalization.

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The method for the homogeneous hydrogenation of nitroarenes to produce aromatic amines using low catalyst loading (1 mo%) of air‐stable copper N‐heterocyclic carbene complexes as the catalyst and ammonia borane as the source of hydrogen is reported. More details are discussed in the article by Han et al. on page 1721—1726.image

Direct Multi-Deuterium Labelling of Pirtobrutinib.

Herein, we demonstrate an efficient method for multi-deuterium labelling of pirtobrutinib-a Bruton's tyrosine kinase inhibitor recently approved by the FDA-using a straightforward hydrogen isotope exchange (HIE) reaction. A remarkably high level of deuterium incorporation was achieved using an excess of a Kerr-type iridium catalyst. The key factor in the significant deuterium labelling was the decision to employ a deuterium uniformly labelled solvent, chlorobenzene-d5, at an elevated temperature. Virtually, no d0-d3 species were detected, with only traces of d4-d5 isotopomers (< 5%) observable in the mass spectrum of pirtobrutinib-d8, fulfilling requirements for stable isotope-labelled internal standard. The labelled compound-mainly consisting of isotopomers d6-d9 at 82.4% of the total abundance-was isolated in a high yield (73%) and purity (99%). Noteworthy, fluorine group acting as a directing group was observed for the first time. Significant incorporation of deuterium in ortho-positions, exceeding 87%, was observed. Interestingly, chlorinated solvent used in the HIE reactions was non-specifically deuterated yielding up to 0.42 deuterium per chlorobenzene molecule even at an exceptionally low iridium catalyst loading of 4.17 × 10-2 mol%.

Ligand Effects in Carboxylic Ester- and Aldehyde-Assisted β-C-H Activation in Regiodivergent and Enantioselective Cycloisomerization-Hydroalkenylation and Cycloisomerization-Hydroarylation, and [2 + 2 + 2]-Cycloadditions of 1,6-Enynes.

Herein, we report room temperature, atom-economic protocols for high regio- and enantioselective tandem cycloisomerization-hydroarylation and cycloisomerization-hydroalkenylation of 1,6-enynes leading to vicinal carba-functionalized pyrrolidines, tetrahydrofurans, and cyclopentanes. The latter steps in these processes involve carbonyl-coordination-assisted ortho-C-H activation of aromatic aldehydes and esters, and, a similar, yet rarely seen, β-C-H activation in the case of the acrylates. Synthetically useful enantioselective versions of such reactions are rare and are limited to the C2-H activation of indoles and pyrroles. A similar reaction is also observed with N-vinylphthalimide, which also has a carbonyl group suitable for C-H activation. A dibenzooxaphosphole ligand, (2S,2S',3S,3S')-MeO-BIBOP was uniquely identified as crucial to achieving the challenging regio- and enantioselectivity. This methodology gives access to substituted five-membered carbo- and heterocyclic compounds in good yields and excellent enantioselectivities under a low catalyst loading. A primary KIE of 3.5 is observed in an intermolecular competition experiment with methyl benzoate and d5-methyl benzoate, which indicates that the C-H cleavage is the turnover-limiting step of this process. Unlike the acrylates, which undergoes exclusive hydroalkenylation, a β, γ-unsaturated ester, methyl but-3-enoate, undergoes the highly enantioselective cycloisomerization-coupling sequence with a 1,6-enyne giving either a [2 + 2 + 2]-cycloaddition with (S, S)-BDPP or hydroalkenylation with (2S,2'S,3S,3'S)-MeO-BIBOP depending on the ligand employed. The (E)-configuration of the newly formed double bond at the terminal alkynyl carbon (of the starting enyne) in the hydroalkenylation product of β,γ-unsaturated ester suggests a more classical migratory insertion-β-hydride elimination route for the formation of this product.

Phase transfer catalysts shift the pathway to transmetalation in biphasic Suzuki-Miyaura cross-couplings

The Suzuki-Miyaura coupling is a widely used C-C bond forming reaction. Numerous mechanistic studies have enabled the use of low catalyst loadings and broad functional group tolerance. However, the dominant mode of transmetalation remains controversial and likely depends on the conditions employed. Herein we detail a mechanistic study of the palladium-catalyzed Suzuki-Miyaura coupling under biphasic conditions. The use of phase transfer catalysts results in a remarkable 12-fold rate enhancement in the targeted system. A shift from an oxo-palladium based transmetalation to a boronate-based pathway lies at the root of this activity. Furthermore, a study of the impact of different water loadings reveals reducing the proportion of the aqueous phase increases the reaction rate, contrary to reaction conditions typically employed in the literature. The importance of these findings is highlighted by achieving an exceptionally broad substrate scope with benzylic electrophiles using a 10-fold reduction in catalyst loading relative to literature precedent.