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Alexander T. Radosevich

Bio: Alexander T. Radosevich is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Catalysis & Phosphine. The author has an hindex of 23, co-authored 60 publications receiving 1627 citations. Previous affiliations of Alexander T. Radosevich include University of California, Berkeley & Pennsylvania State University.


Papers
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Journal ArticleDOI
14 Aug 2020-Science
TL;DR: It is asserted that nature’s blueprint provides essential principles for vastly expanding the use of EAMs in sustainable catalysis, pointing to an overarching need for improved theories and computational methods that accurately treat their multiconfigurational electronic structure.
Abstract: BACKGROUND Catalysis has had a transformative impact on society, playing a crucial role in the production of modern materials, medicines, fuels, and chemicals. Precious metals have been the cornerstone of many industrial catalytic processes for decades, providing high activity, stability, and tolerance to poisons. In stark contrast, redox catalysis essential to life is carried out by metalloenzymes that feature exclusively Earth-abundant metals (EAMs). The terrestrial abundance of some EAMs is 104 times that of precious metals, and thus their increased use would lead to reduced cost and environmental footprint. In addition to these practical considerations, EAMs display distinct reactivity profiles that originate from their characteristic electronic structure, thermochemistry, and kinetics. The behavior of EAMs provides compelling scientific opportunities for catalyst design. We assert that nature’s blueprint provides essential principles for vastly expanding the use of EAMs in sustainable catalysis. ADVANCES Exquisite tuning of the local environment around EAM active sites is key to enabling their use in catalysis. Such control is achieved in enzymatic catalysis by directed evolution of the amino acid environment, resulting in engineered enzymes with extraordinary catalytic performance. Similarly in molecular catalysis, modifying the steric and electronic properties of ligands can lead to some EAM catalysts with performance superior to that obtained from precious metal catalysts. In addition, for heterogeneous catalysts, the local environment and electronic structure of active sites can be modified by bonding to other metals or main-group elements, facilitating reaction pathways distinct from those involving precious metals. Innovations in the design of EAM catalysts demonstrate their potential to catalyze many of the reactions that traditionally relied on precious metals, although further improvements are needed in activity, selectivity, lifetime, or energy efficiency. The characteristics of EAMs point to an overarching need for improved theories and computational methods that accurately treat their multiconfigurational electronic structure. OUTLOOK The remarkable ability of enzymes to catalyze a variety of reactions under mild conditions, using only EAMs, highlights compelling opportunities for the discovery of new catalysis. Although enzymes are versatile platforms for harnessing the properties of EAMs, they are insufficiently robust under the harsh pH, temperature, pressure, and solvent conditions required for some industrial catalytic processes. Thus, systematic strategies are needed for directed evolution to extend the reactivity and persistence of engineered enzymes. For molecular catalysts, the tunability of the ligands provides opportunities for systematically varying the activities of EAMs. Key challenges include enhancing metal-ligand cooperativity, controlling transport to EAM active sites, and mastering the interactions of EAM centers with both metal-based and organic-based redox-active ligands. In heterogeneous catalysis, tuning the lattice environment of EAMs offers new opportunities for catalyst discovery, but for practical applications EAM catalysts should exhibit long-term stability and high active-site density. Thus, advances are needed in the synthesis of materials with tunable phase and nanostructure, as well as insights into how EAM catalysts undergo electronic and structural changes under sustained catalytic turnover. Strategies for controlling EAM reactivity patterns, coupled with advances in synthetic methods and spectroscopic and computational techniques, are critical for the systematic use of EAMs in sustainable catalysis.

227 citations

Journal ArticleDOI
TL;DR: A planar, trivalent phosphorus compound is shown to undergo reversible two-electron redox cycling (P(III)/P(V)) enabling its use as catalyst for a transfer hydrogenation reaction, suggesting broader potential for this nonmetal platform to support bond-modifying redox catalysis of the type dominated by transition metal catalysts.
Abstract: A planar, trivalent phosphorus compound is shown to undergo reversible two-electron redox cycling (PIII/PV) enabling its use as catalyst for a transfer hydrogenation reaction. The trivalent phosphorus compound activates ammonia-borane to furnish a 10-P-5 dihydridophosphorane, which in turn is shown to transfer hydrogen cleanly to azobenzene, yielding diphenylhydrazine and regenerating the initial trivalent phosphorus species. This result constitutes a rare example of two-electron redox catalysis at a main group compound and suggests broader potential for this nonmetal platform to support bond-modifying redox catalysis of the type dominated by transition metal catalysts.

204 citations

Journal ArticleDOI
TL;DR: A mild method for the regioselective synthesis of propargyl ethers by the coupling of prop argyl alcohols with a range of other alcohols is described, which employs an air- and moisture-tolerant rhenium-oxo complex as a catalyst for the formation of sp3-carbon-oxygen bonds without the need for prior activation of the propargol alcohol or deprotonation of the alcohol nucleophile.
Abstract: A mild method for the regioselective synthesis of propargyl ethers by the coupling of propargyl alcohols with a range of other alcohols is described. The method employs an air- and moisture-toleran...

132 citations

Journal ArticleDOI
TL;DR: The results point to an inherent distinction in design criteria for organophosphorus-based catalysts operating via P(III)/P(V)═O redox cycling as opposed to Lewis base (nucleophilic) catalysis.
Abstract: A small-ring phosphacycle is found to catalyze the deoxygenative condensation of α-keto esters and carboxylic acids. The reaction provides a chemoselective catalytic synthesis of α-acyloxy ester products with good functional group compatibility. Based on both stoichiometric and catalytic mechanistic experiments, the reaction is proposed to proceed via catalytic PIII/PV═O cycling. The importance of ring strain in the phosphacyclic catalyst is substantiated by an observed temperature-dependent product selectivity effect. The results point to an inherent distinction in design criteria for organophosphorus-based catalysts operating via PIII/PV═O redox cycling as opposed to Lewis base (nucleophilic) catalysis.

114 citations

Journal ArticleDOI
TL;DR: Density functional calculations indicate that a concerted oxidative addition via a classical three-center transition structure is energetically inaccessible, and a stepwise heterolytic pathway is preferred, proceeding by initial amine-assisted N-H heterolysis upon complexation to the electrophilic phosphorus center followed by rate-controlling N → P proton transfer.
Abstract: Ammonia, alkyl amines, and aryl amines are found to undergo rapid intermolecular N–H oxidative addition to a planar mononuclear σ3-phosphorus compound (1). The pentacoordinate phosphorane products (1·[H][NHR]) are structurally robust, permitting full characterization by multinuclear NMR spectroscopy and single-crystal X-ray diffraction. Isothermal titration calorimetry was employed to quantify the enthalpy of the N–H oxidative addition of n-propylamine to 1 (nPrNH2 + 1 → 1·[H][NHnPr], ΔHrxn298 = −10.6 kcal/mol). The kinetics of n-propylamine N–H oxidative addition were monitored by in situ UV absorption spectroscopy and determination of the rate law showed an unusually large molecularity (ν = k[1][nPrNH2]3). Kinetic experiments conducted over the temperature range of 10–70 °C revealed that the reaction rate decreased with increasing temperature. Activation parameters extracted from an Eyring analysis (ΔH⧧ = −0.8 ± 0.4 kcal/mol, ΔS⧧ = −72 ± 2 cal/(mol·K)) indicate that the cleavage of strong N–H bonds by 1...

112 citations


Cited by
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01 Sep 2010
TL;DR: In this paper, the selection of the best choice of reaction conditions and ligand of this class for the most commonly encountered and practically important substrate combinations for Pd-catalyzed amination reactions is discussed.
Abstract: Dialkylbiaryl phosphines are a valuable class of ligand for Pd-catalyzed amination reactions and have been applied in a range of contexts. This perspective attempts to aid the reader in the selection of the best choice of reaction conditions and ligand of this class for the most commonly encountered and practically important substrate combinations.

966 citations

Journal ArticleDOI
TL;DR: Ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy, and often exhibit unusual reactivity.
Abstract: The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.

467 citations

Journal ArticleDOI
TL;DR: It is shown that the selective N-alkylation of amines with alcohols can be catalysed by defined PNP manganese pincer complexes and the chemoselective monomethylations of primary amines using methanol under mild conditions are reported.
Abstract: Borrowing hydrogen (or hydrogen autotransfer) reactions represent straightforward and sustainable C-N bond-forming processes. In general, precious metal-based catalysts are employed for this effective transformation. In recent years, the use of earth abundant and cheap non-noble metal catalysts for this process attracted considerable attention in the scientific community. Here we show that the selective N-alkylation of amines with alcohols can be catalysed by defined PNP manganese pincer complexes. A variety of substituted anilines are monoalkylated with different (hetero)aromatic and aliphatic alcohols even in the presence of other sensitive reducible functional groups. As a special highlight, we report the chemoselective monomethylation of primary amines using methanol under mild conditions.

436 citations

Journal ArticleDOI
TL;DR: This study describes for the first time specific molecular-defined manganese complexes that allow for the hydrogenation of various polar functional groups and achieves good functional group tolerance, and industrially important substrates, e.g., for the flavor and fragrance industry, are selectively reduced.
Abstract: Hydrogenations constitute fundamental processes in organic chemistry and allow for atom-efficient and clean functional group transformations. In fact, the selective reduction of nitriles, ketones, and aldehydes with molecular hydrogen permits access to a green synthesis of valuable amines and alcohols. Despite more than a century of developments in homogeneous and heterogeneous catalysis, efforts toward the creation of new useful and broadly applicable catalyst systems are ongoing. Recently, Earth-abundant metals have attracted significant interest in this area. In the present study, we describe for the first time specific molecular-defined manganese complexes that allow for the hydrogenation of various polar functional groups. Under optimal conditions, we achieve good functional group tolerance, and industrially important substrates, e.g., for the flavor and fragrance industry, are selectively reduced.

408 citations

Journal ArticleDOI
TL;DR: This Review highlights the substantial progress achieved in the past decade for the activation of robust single bonds by main-group compounds and the more recently realized activation of multiple bonds by these elements.
Abstract: Oxidative addition and reductive elimination are key steps in a wide variety of catalytic reactions mediated by transition-metal complexes. Historically, this reactivity has been considered to be the exclusive domain of d-block elements. However, this paradigm has changed in recent years with the demonstration of transition-metal-like reactivity by main-group compounds. This Review highlights the substantial progress achieved in the past decade for the activation of robust single bonds by main-group compounds and the more recently realized activation of multiple bonds by these elements. We also discuss the significant discovery of reversible activation of single bonds and distinct examples of reductive elimination at main-group element centers. The review consists of three major parts, starting with oxidative addition of single bonds, proceeding to cleavage of multiple bonds, and culminated by the discussion of reversible bond activation and reductive elimination. Within each subsection, the discussion is...

367 citations