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An important challenge in enantioselective catalysis is developing strategies for the precise synthesis of neighboring congested all-carbon quaternary stereocenters. The well-defined transition states of [3,3]-sigmatropic rearrangements and their underlying stereospecificity render them powerful tools for the synthesis of such arrays. However, this type of pericyclic reaction remains notoriously difficult to catalyze, especially in an enantioselective fashion. Herein, we describe an enantioselective reductive Eschenmoser-Claisen rearrangement catalyzed by chiral 1,3,2diazaphospholene-hydrides. This developed transformation enables full control of the two newly formed acyclic stereogenic centers, leading to amides with vicinal all-carbon quaternary-tertiary or quaternary-quaternary carbon atoms. [ABSTRACT FROM AUTHOR]

Group 9 metals, in particular RhIII complexes with cyclopentadienyl ligands, are competent C−H activation catalysts. Recently, a Cp*RhIII‐catalyzed reaction of alkenes with N‐enoxyphthalimides showed divergent outcome based on the solvent, with carboamination favored in methanol and cyclopropanation in 2,2,2‐trifluoroethanol (TFE). Here, we create selectivity and activity maps capable of unravelling the catalyst‐solvent interplay on the outcome of these competing reactions by analyzing 42 cyclopentadienyl metal catalysts, CpXMIII (M=Co, Rh, Ir). These maps not only can be used to rationalize previously reported experimental results, but also capably predict the behavior of untested catalyst/solvent combinations as well as aid in identifying experimental protocols that simultaneously optimize both catalytic activity and selectivity (solutions in the Pareto front). In this regard, we demonstrate how and why the experimentally employed Cp*RhIII catalyst represents an ideal choice to invoke a solvent‐induced change in reactivity. Additionally, the maps reveal the degree to which even perceived minor changes in the solvent (e. g., replacing methanol with ethanol) influence the ratio of carboamination and cyclopropanation products. Overall, the selectivity and activity maps presented here provide a generalizable tool to create global pictures of anticipated reaction outcome that can be used to develop new experimental protocols spanning metal, ligand, and solvent space. [ABSTRACT FROM AUTHOR]

Au(I) catalysts promote the intramolecular cycloisomerization of 1,n‐enynes, as well as facilitate reactions with alcohols, characteristics that have led to their wide‐spread in the synthesis of complex natural products. Literature reports of Cu and Ag species catalyzing the same or similar reactions are much less common. Here, we utilize molecular volcano plots to assess the activity of 45 coinage metal phosphine/phosphite catalysts possessing a variety of stereoelectronic properties for the methoxycyclization reaction of a prototypical 1,5‐enyne. Our analysis reveals that the intrinsic properties of gold allow it to be coupled with a wide range of ligands, all of which exhibit high catalytic activity. On the other hand, the coupling of silver and copper with more traditional phosphines, such as triphenylphosphine, leads to catalysts with diminished catalytic ability. The activity of Ag and Cu species, however, can be enhanced by appending ligands with strong π‐accepting character, which shifts these species closer to the volcano peak. [ABSTRACT FROM AUTHOR]

A novel nickel pincer cofactor was recently discovered in lactate racemase. Reported here are three synthetic nickel pincer complexes that are both structural and functional models of the pincer cofactor in lactate racemase. DFT computations suggest the ipso‐carbon atom of the pyridinium pincer ligands act as a hydride acceptor for lactate isomerization, whereas an organometallic pathway involving nickel‐mediated β‐hydride elimination is less favored. [ABSTRACT FROM AUTHOR]

A novel nickel pincer cofactor was recently discovered in lactate racemase. Reported here are three synthetic nickel pincer complexes that are both structural and functional models of the pincer cofactor in lactate racemase. DFT computations suggest the ipso‐carbon atom of the pyridinium pincer ligands act as a hydride acceptor for lactate isomerization, whereas an organometallic pathway involving nickel‐mediated β‐hydride elimination is less favored. [ABSTRACT FROM AUTHOR]

The speed and precision of machine‐learning (ML) techniques in determining quantum chemical properties has resulted in a considerable computational speed up in comparison to traditional quantum chemical methods, and now allows a desired property of thousands of molecules to be assessed virtually instantaneously. The large databases that result from employing ML can, in turn, be mined with the goal of uncovering relationships that may be missed through more commonly used small scale screening procedures. Due to its prominent place in chemistry, catalysis represents a particularly fruitful playground, where drawing connections between the quantum chemical properties of catalysts and their overall catalytic performance may lead to the identification of new, highly functional species. In this spirit, we previously trained ML models to predict the performance of 18000 prospective catalysts for a Suzuki coupling reaction using molecular volcano plots. Here, we apply concepts from big data to probe a type of "C−C cross‐coupling genome" that explores results from many different named cross‐coupling reactions. The use of interactive dimensionality‐reducing data‐clustering maps facilitates the identification of relationships between the thermodynamics of different catalysts and the chemical properties of their constituent metal and ligands. Analyzing large numbers of species in this manner leads to the identification of not only unexpected catalysts that have thermodynamically ideal profiles to catalyze C−C cross‐coupling reactions, but also reveals a wealth of interesting chemical trends regarding the influence played by different metals and ligands, as well as their unique combinations. [ABSTRACT FROM AUTHOR]

The discovery of new homogeneous catalysts that preferentially form one product over another in regio‐ or enantioselective chemical reactions has traditionally been the province of experimental chemists. Today, computational‐based approaches have carved an increasingly important role, which, for computational catalytic designs, often rely on highly inefficient combinatorial‐based screening methods. To increase the pace of discovery, tools capable of rapidly assessing large numbers of prospective species and identify those possessing desirable properties, such as activity and selectivity, are vital. Here, through the examination of the hydroformylation of 2‐methylpropene, we demonstrate how a new tool built upon molecular volcano plots can be used to quickly predict the activity of molecular catalysts as well as estimate the intrinsic ability of each species to form one regioisomer over the other with striking accuracy. Following training and validation, these regioselective molecular volcanoes are employed to predict catalysts that preferentially form the branched product (2,2‐dimethylpropanal) in violation of Keulemans’ 70‐year‐old law. Eighteen species (out of a total of 68 predicted) were computationally predicted to have regiomeric excess (r.e.) values > 90. Overall, these tools can be used to quickly screen the activity and selectivity of potential catalysis based on two easily computed descriptor variables. [ABSTRACT FROM AUTHOR]

Abstract: As a heavily used technique for forming new C−C bonds, developing new catalysts and reaction conditions for Suzuki–Miyaura cross‐couplings is highly desirable. By using molecular volcano plots, the influence of the electrophilic coupling component in catalytic cycle thermodynamics is revealed. Less reactive electrophiles, such as iodine, broaden the volcano plateau, which leads to a larger number of catalysts having appealing thermodynamic profiles. Whereas, fluorine and other more reactive electrophiles compress the volcano plateau, which shrinks the pool of catalysts having good thermodynamic profiles. As a result, judicious selection of the electrophile employed in a reaction may represent an appealing strategy for further tuning the thermodynamics of cross‐coupling reactions. [ABSTRACT FROM AUTHOR]

Abstract: In homogeneous catalysis, the structure and electronic configuration of the active catalysts can vary significantly. Changes in ligation, oxidation, and spin states have the potential to influence the catalytic cycle energetics strongly that, to a large degree, dictate the catalytic performance. With the increased use of computational screening strategies aimed towards the identification of new catalysts, ambiguity surrounding structure/electronic configurations can be problematic, as it is unclear which species should be computed to determine a catalyst's properties. Here, we show that a single volcano plot constructed from linear free energy scaling relationships is able to account for variations in ligation, oxidation, and spin state. These linear scaling relationships can also be used to predict the free energies associated with a specific structure and electronic configuration of a catalyst based on a single descriptor. As a result, a single volcano plot can be used to screen prospective new catalysts rapidly. [ABSTRACT FROM AUTHOR]

Lactate racemase is the first enzyme known to possess a metal pincer active site. The enzyme interconverts D- and L-lactic acid, which is important for the assembly of cell walls in many microorganisms. Here, we report a synthetic model of the active site of lactate racemase, which features a pyridinium-based SCS pincer ligand framework bound to nickel. The model complex mediates the dehydrogenation of alcohols, a reaction relevant to lactate racemization. Experimental and computational data indicate ligand participation in the dehydrogenation reaction. [ABSTRACT FROM AUTHOR]

The alkynylation of thiols with EthynylBenziodoXolone (EBX) reagents is a fast and chemoselective method for the synthesis of thioalkynes. Combined experimental and computational studies are reported, which led to the identification of a new mechanism for this reaction, proceeding via an initial sulfur-iodine interaction followed by β-addition, α-elimination, and a 1,2-shift. Depending on the substituent on the alkyne, this mechanism can be favored over the previously disclosed concerted α-addition pathway. [ABSTRACT FROM AUTHOR]

A convenient one‐step synthesis of β‐aminocyclobutane monoesters starting from commercially available reagents is reported. The obtained strained rings undergo (4+2) dearomative annulation with indole partners using silylium catalysis. This organocatalyzed annulation provided tricyclic indolines with four new stereocenters in up to quantitative yield and >95 : 5 diastereoselectivity and can proceed both intra‐ and intermolecularly. When performed intramolecularly, the tetracyclic structure of either akuamma or malagasy alkaloids was obtained selectively depending on the temperature of the reaction. This divergent outcome could be rationalized based on DFT calculations. [ABSTRACT FROM AUTHOR]

A convenient one‐step synthesis of β‐aminocyclobutane monoesters starting from commercially available reagents is reported. The obtained strained rings undergo (4+2) dearomative annulation with indole partners using silylium catalysis. This organocatalyzed annulation provided tricyclic indolines with four new stereocenters in up to quantitative yield and >95 : 5 diastereoselectivity and can proceed both intra‐ and intermolecularly. When performed intramolecularly, the tetracyclic structure of either akuamma or malagasy alkaloids was obtained selectively depending on the temperature of the reaction. This divergent outcome could be rationalized based on DFT calculations. [ABSTRACT FROM AUTHOR]

The chemistry of [Fe]-hydrogenase has attracted significant interest due to its ability to activate molecular hydrogen. The intriguing properties of this enzyme have prompted the synthesis of numerous small molecule mimics aimed at activating H2. Despite considerable effort, a majority of these compounds remain nonfunctional for hydrogenation reactions. By using a recently synthesized model as an entry point, seven biomimetic complexes have been examined through DFT computations to probe the influence of ligand environment on the ability of a mimic to bind and split H2. One mimic, featuring a bidentate diphosphine group incorporating an internal nitrogen base, was found to have particularly attractive energetics, prompting a study of the role played by the proton/hydride acceptor necessary to complete the catalytic cycle. Computations revealed an experimentally accessible energetic pathway involving a benzaldehyde proton/hydride acceptor and the most promising catalyst. [ABSTRACT FROM AUTHOR]

Iron-catalyzed alkyl–arylKumada coupling has developedinto an efficient synthetic method, yet its mechanism remains vague.Here, we apply a bis(oxazolinylphenyl)amido pincer ligand (Bopa) tostabilize the catalytically active Fe center, resulting in isolationand characterization of well-defined iron complexes whose catalyticroles have been probed and confirmed. Reactivity studies of the ironcomplexes identify an Fe(II) “ate” complex, [Fe(Bopa-Ph)(Ph)2]−, as the active species for the oxidativeaddition of alkyl halide. Experiments using radical-probe substratesand DFT computations reveal a bimetallic and radical mechanism forthe oxidative addition. The kinetics of the coupling of an alkyl iodidewith PhMgCl suggests that formation of the “ate” complex,rather than oxidative addition, is the turnover-determining step.This work provides insights into iron-catalyzed cross-coupling reactionsof alkyl halides. [ABSTRACT FROM AUTHOR]

Among all functional groups, alkynes occupy a privileged position in synthetic and medicinal chemistry, chemical biology, and materials science. Thioalkynes, in particular, are highly useful, as they combine the enhanced reactivity of the triple bond with a sulfur atom frequently encountered in bioactive compounds and materials. Nevertheless, general methods to access these compounds are lacking. In this article, we describe the mechanism and full scope of the alkynylation of thiols using ethynyl benziodoxolone (EBX) hypervalent iodine reagents. Computations led to the discovery of a new, three-atom concerted transition state with a very low energy barrier, which rationalizes the high reaction rate. On the basis of this result, the scope of the reaction was extended to the synthesis of aryl- and alkyl-substituted alkynes containing a broad range of functional groups. New sulfur nucleophiles such as thioglycosides, thioacids, and sodium hydrogen sulfide were also alkynylated successfully to lead to the most general and practical method yet reported for the synthesis of thioalkynes. [ABSTRACT FROM AUTHOR]

RhIII-catalyzed directed CH functionalizations of arylhydroxamates have become a valuable synthetic tool. To date, the regioselectivity of the insertion of the unsaturated acceptor into the common cyclometalated intermediate was dependent solely on intrinsic substrate control. Herein, we report two different catalytic systems that allow the selective formation of regioisomeric 3-aryl dihydroisoquinolones and previously inaccessible 4-aryl dihydroisoquinolones under full catalyst control. The differences in the catalysts are computationally examined using density functional theory and transition state theory of different possible pathways to elucidate key contributing factors leading to the regioisomeric products. The stabilities of the initially formed rhodium complex styrene adducts, as well as activation barrier differences for the migratory insertion, were identified as key contributing factors for the regiodivergent pathways. [ABSTRACT FROM AUTHOR]

Themechanism of alkyl–aryl Kumada coupling catalyzed bythe nickel pincer complex Nickamine was studied. Experiments usingradical-probe substrates and DFT calculations established a bimetallicoxidative addition mechanism. Kinetic measurements showed that transmetalationrather than oxidative addition was the turnover-determining step.The transmetalation involved a bimetallic pathway. [ABSTRACT FROM AUTHOR]

A convenient one‐step synthesis of β‐aminocyclobutane monoesters starting from commercially available reagents is reported. The obtained strained rings undergo (4+2) dearomative annulation with indole partners using silylium catalysis. This organocatalyzed annulation provided tricyclic indolines with four new stereocenters in up to quantitative yield and >95 : 5 diastereoselectivity and can proceed both intra‐ and intermolecularly. When performed intramolecularly, the tetracyclic structure of either akuamma or malagasy alkaloids was obtained selectively depending on the temperature of the reaction. This divergent outcome could be rationalized based on DFT calculations. [ABSTRACT FROM AUTHOR]

Tetra-n-butylammonium (TBA) (η6-biphenyl)diphenylferrate was formed unexpectedly in the reaction of (TBA)2[Fe4S4Cl4] with an excess of phenyllithium. This complex belongs to a novel type of organoferrate. [ABSTRACT FROM AUTHOR]

While frequently employed as an experimentaltechnique, the mechanisticpicture surrounding the gas-phase dissociation of peptides carryingmultiple positive charges during electron capture and electron transferdissociation tandem mass spectrometry remains incomplete. Despitethis mechanistic uncertainty, most proposals agree that the peptidebackbone N–Cαbond located to the C-terminal(right) side of an aminoketyl radical formed in a peptide backboneduring the electron capture process is homolytically cleaved. Recently,we introduced the “enol” mechanism, which proposes thata backbone N–Cαbond located to the N-terminal(left) side of an aminoketyl radical is cleaved heterolytically. Here,we further validate this mechanism using replica-exchange moleculardynamics to create unbiased representative sets of low-energy conformersfor several model tryptic peptide systems (H-Alax-Lys-OH2+, x= 3–5). Transitionstate barrier enthalpies for the cleavage of N–Cαbonds proceeding via the homolytic (right-side) and heterolytic(left-side) pathways, determined by density functional computations,identify the preferred cleavage route for each conformer. These findingssupport our original hypothesis that heterolytic N–Cαcleavage can exist in a competitive balance with homolytic cleavages,independent of the relative energy of the precursor dication species.Smaller peptide systems see decreased heterolytic N–Cαcleavage probabilities, likely resulting from an insufficient hydrogen-bondingnetwork needed to stabilize and ultimately annihilate the transitionstate zwitterion. This observation may explain the early dismissalof left-side cleavage pathways based on computational studies employingsmall model systems. [ABSTRACT FROM AUTHOR]

Electroncapture and electron transfer dissociation (ECD/ETD) tandemmass spectrometry (MS/MS) are commonly employed techniques for biomolecularanalysis. The ECD/ETD process predominately cleaves N–Cαpeptide backbone bonds, leading to primary sequenceinformation complementary to other mass spectrometry techniques. Despitefrequent laboratory use, the mechanistic underpinnings surroundingN–Cαbond cleavage remain debated. While themajority of mechanisms assume a homolytic bond rupture, we recentlyshowed that heterolytic cleavage is also thermodynamically viable.For a cleavage of this type to be feasible, the charge separationcreated upon breaking of the N–Cαbackbonebond must be quickly annihilated. In this work, we show, using densityfunctional computations, that specific hydrogen-bonding motifs andstructural rearrangements involving proton transfers stabilize thetransition state associated with heterolytic cleavage and eliminatethe ensuing charge separation from the final product fragments. Themovement of protons can occur either directly from the z- to c-fragment or in a more complex manner includinga ping-pong-type mechanism. The nature of these diverse hydrogen-bondingmotifs reveals that not only those functional groups proximate tothe bond rupture site, but also the entire global chemical environment,play important roles in backbone cleavage characteristic of ECD/ETDMS/MS. For doubly charged systems, both conformation and electronlocalization site dictate which of the two fragments retains the finalpositive charge. [ABSTRACT FROM AUTHOR]

[Fe]-hydrogenase, one of three types of hydrogenases, activates molecular hydrogen. Here, using DFT computations, we examine the electronic elements governing the binding of small ligands to a recently synthesized [Fe]-hydrogenase biomimic. Computed reaction free energies indicate that anionic species, such as CN- and H-, and π acceptors, such as CO, bind favourably with the Fe centre. Ligands such as H2O, CH3CN, and H2, however, do not bind iron. Protonation of an adjacent thiolate ligand on the mimic significantly increases the energies of ligand binding. Additional computational analysis reveals that the degree of electron donation from the ligand to the mimic correlates strongly with overall binding ability. The results give insights into the electronic elements of iron-small-molecule interaction in these model complexes. [ABSTRACT FROM AUTHOR]

Hydrocarbon radical stabilization energy (RSE) estimates based on the differences in R--H vs CH3--H bond dissociation energies have inherent advantages over RSEs based on R--CH3 vs CH3--CH3, as well as R--R vs CH3--CH3 comparisons, since the R--CH3 and R--R reference systems are prone to unbalanced contaminating intramolecular interactions involving the R groups. When the effects of steric crowding, branching protobranching, conjugation, and hyperconjugation are taken into account, R--CH3 and R--R based RSE values are nearly identical to R--H RSEs. Corrections for electronegativity differences between H and R are not needed to achieve agreement. [ABSTRACT FROM AUTHOR]

Despite the widespread use and numerous successful applications of density functional theory, descriptions of hydrocarbon reaction energies remain problematic. Illustrative examples include large underestimation of energies associated with alkane bond separation reactions and poor general description of intramolecular dispersion in hydrocarbons (e.g., B3LYP, MAD = 14.1 kcal mol). More recent, but not readily availably functionals, along with efficient posteriori corrections, not only show considerable improvement in the energy description of hydrocarbons but also help identify the sources of error in traditional DFT. Interactions in branched alkanes and compact hydrocarbons are adequately mimicked by systems compressed below their typical van der Waals distances. At these distances, standard DFT exchange functionals are overly repulsive for non-bonded density overlaps, and significant improvement is offered by the long-range corrected exchange functionals (e.g., LC-BLYP0.33, MAD = 5.5 kcal mol). For those systems, the neglect of long-range dispersion is found to be a critical shortcoming, as well as 'overlap dispersion', for which non-negligible amounts are captured by the correlation functional. Accounting for the missing dispersion interactions is of key importance. Accordingly, most noteworthy improvements over standard functionals are obtained by using non-local van der Waals density functionals (e.g., LC-S-VV09, MAD = 3.6 kcal mol, rPW86-VV09, MAD = 5.8 kcal mol), a dispersion corrected double hybrid (B2PLYP-D, MAD = 2.5 kcal mol), or by the addition of an atom pairwise density-dependent dispersion correction to a standard functional (e.g., PBE-dDXDM, MAD = 0.8 kcal mol). To a lesser extent, the reduction of the delocalization error (e.g., MCY3, MAD = 6.3 kcal mol) or careful parameter fitting (e.g., M06-2X, MAD = 5.6 kcal mol) also lowers the errors. [ABSTRACT FROM AUTHOR]

Bond separation reactions of highly branched alkanes are used to assess (de)stabilizing interactions associated with various 1,3-nonbonded substituent patterns. While n- and singly methylated alkanes show positive bond separation energies (BSEs), which increase systematically along the series, permethylated alkanes are characterized by decreasing BSEs. Analysis shows that singly methylated alkanes are more stabilized than linear alkane chains and that the unique destabilizing feature of permethylated alkanes arises from the close proximity of bulky methyl groups causing highly distorted geometries along the carbon backbone. [ABSTRACT FROM AUTHOR]

The trigonal planar geometry of the nitrogen atom in commonly used phosphoramidite ligands is not in line with the traditional valence shell electron pair repulsion (VSEPR) model. In this work, the effects governing nitrogen configuration in several substituted aminophosphines, A2PNB2 (A or B = H, F, Cl, Br, Me, OMe, BINOP), are examined using modern computational analytic tools. The electron delocalization descriptions provided by both electron localization function (ELF) and block localized wavefunction analysis support the proposed relationships between conformation and negative hyperconjugative interactions. In the parent H2PNH2, the pyramidal nitrogen configuration results from nitrogen lone pair electron donation into the σ* P&bond;H orbital. While enhanced effects are seen for F2PNMe2, placing highly electronegative fluorine substituents on nitrogen (i.e., Me2PNF2) eliminates delocalization of the nitrogen lone pair. Understanding and quantifying these effects can lead to greater flexibility in designing new catalysts. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A direct relationship exists between the properties of substituted semibullvalenes and their Cope rearrangement activation barrier. This unique correlation not only enables the determination of kinetic data from ground state information, but also provides a rationalization for the extent to which ground state properties are altered with respect to their "normal" values (i.e., that of their localized Lewis structure). Examination of electron density distribution, geometrical parameters, and J-coupling constant differences between canonical and Lewis structures deliver quantitative evidence for the structure--correlation principle. [ABSTRACT FROM AUTHOR]

Corrigendum: Ligand-Controlled Regio-divergent Pathways of Rhodium(III)-Catalyzed Dihydroisoquinolone Synthesis - Experimental and Computational Studies of Different Cyclopentadienyls GLO:OLD/18jun20:chem202001781-toc-0001.jpg PHOTO (COLOR): . gl The authors became aware that product B 4 aa b was erroneously assigned to 4-phenyl-3,4-dihydroisoquinolin-1(2 I H i )-one. Conditions B: 0.10 mmol B 1 b , 0.20 mmol B 2 b , 5 mol % Cp*Rh(OBz) SB 2 sb , 0.2 M in CF SB 3 sb CH SB 2 sb OH, 23 °C, 14 h. [Extracted from the article]

Ethynylbenziodoxol(on)e (EBX) cyclic hypervalent iodine reagents have become popular reagents for the alkynylation of radicals and nucleophiles, but only offer limited possibilities for further structure and reactivity fine‐tuning. Herein, the synthesis of new N‐heterocyclic hypervalent iodine reagents with increased structural flexibility based on amide, amidine and sulfoximine scaffolds is reported. Solid‐state structures of the reagents are reported and the analysis of the I−Calkyne bond lengths allowed assessing the trans‐effect of the different substituents. Molecular electrostatic potential (MEP) maps of the reagents, derived from DFT computations, revealed less pronounced σ‐hole regions for sulfonamide‐based compounds. Most reagents reacted well in the alkynylation of β‐ketoesters. The alkynylation of thiols afforded more variable yields, with compounds with a stronger σ‐hole reacting better. In metal‐mediated transformations, the N‐heterocyclic hypervalent iodine reagents gave inferior results when compared to the O‐based EBX reagents. [ABSTRACT FROM AUTHOR]

The reconstitution of [Mn]‐hydrogenases using a series of MnI complexes is described. These complexes are designed to have an internal base or pro‐base that may participate in metal–ligand cooperative catalysis or have no internal base or pro‐base. Only MnI complexes with an internal base or pro‐base are active for H2 activation; only [Mn]‐hydrogenases incorporating such complexes are active for hydrogenase reactions. These results confirm the essential role of metal–ligand cooperation for H2 activation by the MnI complexes alone and by [Mn]‐hydrogenases. Owing to the nature and position of the internal base or pro‐base, the mode of metal–ligand cooperation in two active [Mn]‐hydrogenases is different from that of the native [Fe]‐hydrogenase. One [Mn]‐hydrogenase has the highest specific activity of semi‐synthetic [Mn]‐ and [Fe]‐hydrogenases. This work demonstrates reconstitution of active artificial hydrogenases using synthetic complexes differing greatly from the native active site. [ABSTRACT FROM AUTHOR]

The reconstitution of [Mn]‐hydrogenases using a series of MnI complexes is described. These complexes are designed to have an internal base or pro‐base that may participate in metal–ligand cooperative catalysis or have no internal base or pro‐base. Only MnI complexes with an internal base or pro‐base are active for H2 activation; only [Mn]‐hydrogenases incorporating such complexes are active for hydrogenase reactions. These results confirm the essential role of metal–ligand cooperation for H2 activation by the MnI complexes alone and by [Mn]‐hydrogenases. Owing to the nature and position of the internal base or pro‐base, the mode of metal–ligand cooperation in two active [Mn]‐hydrogenases is different from that of the native [Fe]‐hydrogenase. One [Mn]‐hydrogenase has the highest specific activity of semi‐synthetic [Mn]‐ and [Fe]‐hydrogenases. This work demonstrates reconstitution of active artificial hydrogenases using synthetic complexes differing greatly from the native active site. [ABSTRACT FROM AUTHOR]

The intramolecular [4+2] cycloaddition between arenes and allenes first reported by Himbert gives rapid access to rigid polycyclic scaffolds. Herein, we report a one‐pot oxyalkynylation/cycloaddition reaction proceeding under mild conditions (23–90 °C) and providing complex polycyclic architectures with high efficiency, and atom and step economy. The bicyclo[2.2.2]octadiene products were obtained with a wide variety of useful functional groups and were successfully applied as chiral ligands for metal catalysis. Computational studies gave a first rationalization of the low activation energy for the cycloaddition based on counter‐intuitive favorable dispersive interactions in the transition state. [ABSTRACT FROM AUTHOR]

The intramolecular [4+2] cycloaddition between arenes and allenes first reported by Himbert gives rapid access to rigid polycyclic scaffolds. Herein, we report a one‐pot oxyalkynylation/cycloaddition reaction proceeding under mild conditions (23–90 °C) and providing complex polycyclic architectures with high efficiency, and atom and step economy. The bicyclo[2.2.2]octadiene products were obtained with a wide variety of useful functional groups and were successfully applied as chiral ligands for metal catalysis. Computational studies gave a first rationalization of the low activation energy for the cycloaddition based on counter‐intuitive favorable dispersive interactions in the transition state. [ABSTRACT FROM AUTHOR]

The reaction tolerates alkyl and aryl ethynyl substituted benziodoxolone reagents equipped with various functional groups. [ABSTRACT FROM AUTHOR]

Depending on the choice of Rh-catalyst and reaction solvent the directed C-H functionalization of arylhydroxamates (I) with styrenes can be controlled to yield either 4- or 3-arylated products (III) and (IV) with high regioselectivity. [ABSTRACT FROM AUTHOR]

A gram-scale synthesis of psiguadial B, a purported inhibitor of human hepatoma cell growth, has been achieved in one step by a biomimetic three-component coupling of caryophyllene, benzaldehyde, and diformylphloroglucinol. This cascade reaction is catalyzed by N,N′-dimethylethylenediamine, and proceeds at ambient temperature to generate four stereocenters, two rings, one C−O bond, and three C−C bonds. Combined computational and experimental investigations suggest the biosynthesis of the natural product is non-enzyme mediated, and is the result of a Michael addition between caryophyllene and a reactive ortho-quinone methide, followed by two sequential intramolecular cationic cyclization events. [ABSTRACT FROM AUTHOR]

A gram-scale synthesis of psiguadial B, a purported inhibitor of human hepatoma cell growth, has been achieved in one step by a biomimetic three-component coupling of caryophyllene, benzaldehyde, and diformylphloroglucinol. This cascade reaction is catalyzed by N,N′-dimethylethylenediamine, and proceeds at ambient temperature to generate four stereocenters, two rings, one C−O bond, and three C−C bonds. Combined computational and experimental investigations suggest the biosynthesis of the natural product is non-enzyme mediated, and is the result of a Michael addition between caryophyllene and a reactive ortho-quinone methide, followed by two sequential intramolecular cationic cyclization events. [ABSTRACT FROM AUTHOR]

First synthesized in 1991, EthynylBenziodoXolones (EBXs) – cyclic hypervalent iodine reagents derived from 2‐iodobenzoic acid – are now among the most versatile electrophilic alkynylation reagents. Due to their cyclic structure, these reagents exhibit enhanced stability compared to previously used alkynyl iodonium salts. Over the last decade, both the iodoheterocycle and the arene ring have been extensively modified to fine‐tune the reactivity of the reagents, resulting in new analogues such as Ethynylbenziodoxoles (EBxs) or N‐heterocyclic reagents. In this article, we have for the first time compiled the structural data available for EBXs and their analogues, focusing especially on X‐Ray and NMR data. For selected compounds, molecular electrostatic potentials (MEP) have also been calculated. When considering the tight relationship between structure and reactivity in hypervalent iodine reagents, the collected data is expected to be highly useful for further developments in the field. [ABSTRACT FROM AUTHOR]

[Fe]-Hydrogenase catalyzes the hydrogenation of a biological substrate via the heterolytic splitting of molecular hydrogen. While many synthetic models of [Fe]-hydrogenase have been prepared, none yet are capable of activating H2 on their own. Here, we report the first Fe-based functional mimic of the active site of [Fe]-hydrogenase, which was developed based on a mechanistic understanding. The activity of this iron model complex is enabled by its unique ligand environment, consisting of biomimetic pyridinylacyl and carbonyl ligands, as well as a bioinspired diphosphine ligand with a pendant amine moiety. The model complex activates H2 and mediates hydrogenation of an aldehyde. [ABSTRACT FROM AUTHOR]

Computational studies of organic systems are frequently limited to static pictures that closely align with textbook style presentations of reaction mechanisms and isomerization processes. Of course, in reality chemical systems are dynamic entities where a multitude of molecular conformations exists on incredibly complex potential energy surfaces (PES). Here, we borrow a computational technique originally conceived to be used in the context of biological simulations, together with empirical force fields, and apply it to organic chemical problems. Replica-exchange molecular dynamics (REMD) permits thorough exploration of the PES. We combined REMD with density functional tight binding (DFTB), thereby establishing the level of accuracy necessary to analyze small molecular systems. Through the study of four prototypical problems: isomer identification, reaction mechanisms, temperature-dependent rotational processes, and catalysis, we reveal new insights and chemistry that likely would be missed using static electronic structure computations. The REMD-DFTB methodology at the heart of this study is powered by i-PI, which efficiently handles the interface between the DFTB and REMD codes. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A new method for the cyanation of thiols and disulfides using cyanobenziodoxol(on)e hypervalent iodine reagents is described. Both aliphatic and aromatic thiocyanates can be accessed in good yields in a few minutes at room temperature starting from a broad range of thiols with high chemioselectivity. The complete conversion of disulfides to thiocyanates was also possible. Preliminary computational studies indicated a low energy concerted transition state for the cyanation of the thiolate anion or radical. The developed thiocyanate synthesis has broad potential for various applications in synthetic chemistry, chemical biology and materials science. [ABSTRACT FROM AUTHOR]

Many nickel-based catalysts have been reported for cross-coupling reactions of nonactivated alkyl halides. The mechanistic understanding of these reactions is still primitive. Here we report a mechanistic study of alkyl–alkyl Kumada coupling catalyzed by a preformed nickel(II) pincer complex ([(N2N)Ni–Cl]). The coupling proceeds through a radical process, involving two nickel centers for the oxidative addition of alkyl halide. The catalysis is second-order in Grignard reagent, first-order in catalyst, and zero-order in alkyl halide. A transient species, [(N2N)Ni-alkyl2](alkyl2-MgCl), is identified as the key intermediate responsible for the activation of alkyl halide, the formation of which is the turnover-determining step of the catalysis. [ABSTRACT FROM AUTHOR]

Chemically induced bond cleavage of nitrous oxide typically proceeds by rupture of the N-O bond with concomitant O-atom transfer and liberation of dinitrogen. On a few occasions, N-N bond scission has been observed instead. We report a reaction sequence involving an N-heterocyclic carbene and a vanadium complex that results in cleavage of both the N-O bond and the N-N bond. [ABSTRACT FROM AUTHOR]

Abstract: Atropo‐enantioselective C−H functionalization reactions are largely limited to the dynamic kinetic resolution of biaryl substrates through the introduction of steric bulk proximal to the axis of chirality. Reported herein is a highly atropo‐enantioselective palladium(0)‐catalyzed methodology that forges the axis of chirality during the C−H functionalization process, enabling the synthesis of axially chiral dibenzazepinones. Computational investigations support experimentally determined racemization barriers, while also indicating C−H functionalization proceeds by an enantio‐determining CMD to yield configurationally stable eight‐membered palladacycles. [ABSTRACT FROM AUTHOR]

Abstract: Atropo‐enantioselective C−H functionalization reactions are largely limited to the dynamic kinetic resolution of biaryl substrates through the introduction of steric bulk proximal to the axis of chirality. Reported herein is a highly atropo‐enantioselective palladium(0)‐catalyzed methodology that forges the axis of chirality during the C−H functionalization process, enabling the synthesis of axially chiral dibenzazepinones. Computational investigations support experimentally determined racemization barriers, while also indicating C−H functionalization proceeds by an enantio‐determining CMD to yield configurationally stable eight‐membered palladacycles. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a new class of neutral aminyl radicals is reported. Monoradicals were obtained by reduction of azoimidazolium dyes with potassium. Structural, spectroscopic, and computational data suggest that the spin density is centered on one of the nitrogen atoms of the former azo group. The reduction of a dimeric dye with an octamethylbiphenylene bridge between the azo groups resulted in the formation of a biradical with largely independent unpaired electrons. Both the monoradicals and the biradical were found to display high stability in solution as well as in the solid state. [ABSTRACT FROM AUTHOR]

[Fe]-Hydrogenase catalyses the reversible hydrogenation of a methenyltetrahydromethanopterin substrate, which is an intermediate step during the methanogenesis from CO2 and H2. The active site contains an iron-guanylylpyridinol cofactor, in which Fe2+ is coordinated by two CO ligands, as well as an acyl carbon atom and a pyridinyl nitrogen atom from a 3,4,5,6-substituted 2-pyridinol ligand. However, the mechanism of H2 activation by [Fe]-hydrogenase is unclear. Here we report the reconstitution of [Fe]-hydrogenase from an apoenzyme using two FeGP cofactor mimics to create semisynthetic enzymes. The small-molecule mimics reproduce the ligand environment of the active site, but are inactive towards H2 binding and activation on their own. We show that reconstituting the enzyme using a mimic that contains a 2-hydroxypyridine group restores activity, whereas an analogous enzyme with a 2-methoxypyridine complex was essentially inactive. These findings, together with density functional theory computations, support a mechanism in which the 2-hydroxy group is deprotonated before it serves as an internal base for heterolytic H2 cleavage. [ABSTRACT FROM AUTHOR]