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Herein, we disclose a simple copper‐catalyzed method for enantioselective allylic C(sp3)−H oxidation of unsymmetrical acyclic alkenes, specifically 1‐aryl‐2‐alkyl alkenes. The C−H substrates are used in limiting amounts, and the products are obtained with high enantioselectivity, E/Z‐selectivity, and regioselectivity. The method exhibits broad functional group tolerance, and E/Z‐alkene mixtures are suitable C−H substrates. The transformation is enabled by light irradiation, which sustains the enantioselective copper catalysis by photoinduced oxidant homolysis. [ABSTRACT FROM AUTHOR]

Decarboxylative alkylation of carboxylic acids with easily oxidizable functional groups such as phenol and indole functionalities was achieved using a catalytic amount of basic iron(III) acetate, Fe(OAc)2(OH), in the presence of benzimidazole under 427 nm LED irradiation. Kinetic analyses of this catalytic reaction revealed that the reaction rate is first‐order in alkenes and is linearly correlated with the light intensity; the faster reaction rate for the benzimidazole‐ligated species was consistent with the increased absorbance in the visible light region. Wide functional group tolerance for the easily oxidizable groups is ascribed to the weak oxidation ability of the in situ‐generated oxo‐bridged iron clusters compared with other iron(III) species. [ABSTRACT FROM AUTHOR]

The catalytic disproportionation of by non‐heme Fe(II) complexes of H2O2 the ligand N4Py (1,1‐bis(pyridin‐2‐yl)‐N,N‐bis(pyridin‐2‐ylmethyl)methanamine) and the formation and reactivity of Fe(III)‐OOH and Fe(IV)=O species is studied by UV/Vis absorption, NIR luminescence, (resonance) Raman and headspace Raman spectroscopy, 1O2 trapping and DFT methods. Earlier DFT studies indicated that disproportionation of H2O2 catalysed by Fe(II)‐N4Py complexes produce only 3O2, however, only the low‐spin state pathway was considered. In the present study, DFT calculations predict two pathways for the reaction between Fe(III)‐OOH and H2O2, both of which yield 3O2/H2O2 and involve either the S=1/2 or the S=3/2 spin state, with the latter being spin forbidden. The driving force for both pathways are similar, however, a minimal energy crossing point (MECP) provides a route for the formally spin forbidden reaction. The energy gap between the reaction intermediate and the MECP is lower than the barrier across the non‐adiabatic channel. The formation of 3O2 only is confirmed experimentally in the present study through 1O2 trapping and NIR luminescence spectroscopy. However, attempts to use the 1O2 probe (α ${\alpha }$ ‐terpinene) resulted in initiation of auto‐oxidation rather than formation of the expected endoperoxide, which indicated formation of OH radicals from Fe(III)‐OOH, e. g., through O−O bond homolysis together with saturation of methanol with 3O2. Microkinetic modelling of spectroscopic data using rate constants determined earlier, reveal that there is another pathway for Fe(III)‐OOH decomposition in addition to competition between the reaction of Fe(III)‐OOH with H2O2 and homolysis to form Fe(IV)=O and hydroxyl radical. Notably, after all H2O2 is consumed the decay of the Fe(III)‐OOH species is predominantly through a second order self reaction (with Fe(III)‐OOH). The conclusion reached is that the rate of O−O bond homolysis in the Fe(III)‐OOH species to form Fe(IV)=O and an hydroxyl radical is too low to be responsible for the observed oxidation of organic substrates. [ABSTRACT FROM AUTHOR]

A mononuclear, T‐shaped palladium(I) d9 metalloradical (3), stabilized by a bulky carbazole‐based PNP‐ligand, was obtained by reduction of palladium chloride or thermal Pd−C bond homolysis of the corresponding neopentyl complex. Pressurizing with CO gave the Pd(I) carbonyl complex, which was structurally characterized by X‐ray diffraction. Delocalization of the unpaired electron to the carbonyl carbon was detected by EPR spectroscopy and theoretically modeled by DFT and ab initio methods. The partially reduced and radicalized CO slowly reacts with di(tert‐butyl) disulfide under homolytic S−S cleavage and C−S bond formation to give the corresponding metallathioester. [ABSTRACT FROM AUTHOR]

A light‐driven radical oxy‐functionalization of non‐acidic aliphatic and benzylic C(sp3)−H bonds was achieved with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) in a single‐step by employing an aryl ketone as a sole catalyst. The transformation was initiated by homolysis of a C(sp3)−H bond in the starting substance by the photo‐excited aryl ketone. The derived carbon radical was then promptly trapped by TEMPO leading to the formation of the TEMPO‐adduct. The derived TEMPO‐adduct is synthetically versatile as an alcohol equivalent since it can be readily converted to the corresponding ketone by oxidation and to the corresponding alcohol by reduction. The key to realizing the present catalytic reaction relies on the distinctive triple role of TEMPO, which acts as the precursor of the oxygen functionality, the oxidant to regenerate the aryl ketone, and the protective group for the derived TEMPO‐adduct from over‐oxidation. [ABSTRACT FROM AUTHOR]

Dearomative spirocyclization reactions represent a promising means to convert arenes into three‐dimensional architectures; however, controlling the regioselectivity of radical dearomatization with nonactivated arenes to afford the spirocyclizative 1,2‐difunctionalization other than its kinetically preferred 1,4‐difunctionalization is exceptionally challenging. Here we disclose a novel strategy for dearomative 1,2‐ or 1,4‐amidoximation of (hetero)arenes enabled by direct visible‐light‐induced homolysis of N−NO bonds of nitrosamides, giving rise to various highly regioselective amidoximated spirocycles that previously have been inaccessible or required elaborate synthetic efforts. The mechanism and origins of the observed regioselectivities were investigated by control experiments and density functional theory calculations. [ABSTRACT FROM AUTHOR]

α‐Aminoalkylation of sulfonylarenes with alkylamines was found to be induced by photoirradiation. Here various types of alkylamines, such as trialkylamines, dialkylamines, N,N‐dialkylanilines and N‐alkylanilines as well as sulfonylarenes containing an azole, azine, heterole or benzene ring are available. The reaction proceeds through a homolytic aromatic substitution (HAS) process consisting of addition of an α‐aminoalkyl radical to a sulfonylarene and elimination of the sulfonyl radical to give the α‐arylalkylamine, where photoirradiation is considered to induce homolysis of sulfonylarenes leading to the generation of α‐aminoalkyl radicals that make a radical chain operative. [ABSTRACT FROM AUTHOR]

1,5‐X insertions of alkylidene carbenes are powerful methods to construct five‐membered carbocycles and heterocycles, but the mechanisms of these 1,5‐X insertions of alkylidene carbenes remain unclear (concerted or stepwise?). Here we disclose different mechanisms of 1,5‐X insertions of free alkylidene carbenes based on DFT calculations. Except for the 1,5 S−H insertion, all 1,5‐X insertions proceed through stepwise processes via forming ylide intermediates. However, subsequent 1,2 rearrangements of ylides occur through different mechanisms. The formal 1,5 O−H/N−H insertion except S−H insertion happens through deprotonation rather than insertion reaction, while other pathways including nucleophilic substitution, 2,3‐sigmatropic rearrangement, and homolysis of O−C bond are invoked in various 1,5 O−C insertions. The competition between 1,5‐X insertions and other side reactions (such as 1,2 migration, dealkylation) has been discussed to answer why the target insertion products were not obtained in some cases. [ABSTRACT FROM AUTHOR]

Hydrophosphination activity has been solicited from the parent and decamethyl zirconocene dichloride compounds, Cp2ZrCl2 and Cp*2ZrCl2. Given recent reports of photocatalytic hydrophosphination, these compounds were irradiated in the near ultraviolet (UV) as precatalysts resulting in the successful hydrophosphination of styrene substrates and activated alkenes. Irradiation appears to induce homolysis of the Cp or Cp* ligand, resulting in radical hydrophosphination. Successful detection of this radical reactivity was achieved by monitoring for EPR signals with in situ irradiation, a methodology proving to be general for the determination of radical versus closed‐shell reactivity in transition‐metal photocatalysis. [ABSTRACT FROM AUTHOR]

Transition metal intermediates bearing M−X σ‐bonds are ubiquitous in metal‐mediated C−X bond transformations. Thermodynamic knowledge of M−X bond cleavage is crucial to explore relevant reactions; but little was accumulated till present due to lack of suitable determination methods. We here report the first systematic study of the Pd−X bond homolysis dissociation free energies [BDFE(Pd−X)] of representative [(tmeda)Pd(4‐F−C6H4)X] (tmeda=N,N,N′,N′‐tetramethylethylenediamine, X=OR or NHAr) in DMSO on the basis of reliable measurement of their bond heterolysis energies (ΔGhet(Pd−X)). Despite ΔGhet(Pd−O)s of palladium‐phenoxides are generally found about 8 kcal/mol smaller than ΔGhet(Pd−N)s of palladium‐amidos, their BDFE(Pd−X)s are observed comparable. The structure‐property relationship was investigated to disclose an enhancement effect of electron‐withdrawing groups on BDFE(Pd−X)s. Linear free energy relationship analysis revealed that Pd−X bonds are more sensitive than X−H bonds to structural variation. The energetic propensity of reductive elimination from arylpalladium complexes was evaluated by combinatorial use of BDFE(Pd−X)s and BDFE(C−X)s, indicating an overall thermodynamic bias to C−N bond formation. [ABSTRACT FROM AUTHOR]

Herein, we report visible light‐promoted single nickel catalysis for diverse carbon–heteroatom couplings under mild conditions. This mild, general, and robust method to couple diverse nitrogen, oxygen, and sulfur nucleophiles with aryl(heteroaryl)/alkenyl iodides/bromides exhibits a wide functional group tolerance and is applicable to late‐stage modification of pharmaceuticals and natural products. On the base of preliminary mechanistic studies, a NiI/NiIII cycle via the generation of active NiI complexes that appear from homolysis of NiII−I rather than NiII−aryl bond was tentatively proposed. [ABSTRACT FROM AUTHOR]

Enzymes that use a [4Fe‐4S]1+ cluster plus S‐adenosyl‐l‐methionine (SAM) to initiate radical reactions (radical SAM) form the largest enzyme superfamily, with over half a million members across the tree of life. This review summarizes recent work revealing the radical SAM reaction pathway, which ultimately liberates the 5′‐deoxyadenosyl (5′‐dAdo•) radical to perform extremely diverse, highly regio‐ and stereo‐specific, transformations. Most surprising was the discovery of an organometallic intermediate Ω exhibiting an Fe‐C5′‐adenosyl bond. Ω liberates 5′‐dAdo• through homolysis of the Fe–C5′ bond, in analogy to Co–C5′ bond homolysis in B12, previously viewed as biology's paradigmatic radical generator. The 5′‐dAdo• has been trapped and characterized in radical SAM enzymes via a recently discovered photoreactivity of the [4Fe‐4S]+/SAM complex, and has been confirmed as a catalytically active intermediate in enzyme catalysis. The regioselective SAM S–C bond cleavage to produce 5′‐dAdo• originates in the Jahn–Teller effect. The simplicity of SAM as a radical precursor, and the exquisite control of 5′‐dAdo• reactivity in radical SAM enzymes, may be why radical SAM enzymes pervade the tree of life, while B12 enzymes are only a few. [ABSTRACT FROM AUTHOR]

Amide bonds connect the amino acids in proteins and exist as a prevalent structural motif in biomolecules. Herein, we have exploited the concept of cross‐electrophile coupling by merging the photo‐redox and transition‐metal catalysis to construct carbamides from superabundant (hetero)aryl halides along with commercially feasible carbamoyl chlorides. The success of this method relies on the prior formation of NiII‐aryl halide intermediates, which involves in a photoexcited Ni‐halide homolysis event by energy transfer from aryl bromide and single‐electron transfer from aryl chloride to assist generation of the vital carbamoyl radical. The breadth of application of this technique is demonstrated both in inter‐ as well as intramolecular routes for the synthesis of a plethora of (hetero)aryl carbamides with diverse functionalities, and biologically important benzolactams. [ABSTRACT FROM AUTHOR]

A computational study of the pyrolysis of 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives is carried out employing density functional theory (DFT) and high‐level coupled‐cluster methods, such as coupled‐cluster singles and doubles with perturbative triples [DLPNO‐CCSD(T)]. Our results demonstrate that the reaction proceeds through the products formed by the electrocyclization, as opposed to the mechanism suggested by Mcnab (J. Chem. Soc. Chem. Commun. 1980, 422–423), in which the reaction proceeds by starting via formation of the iminyl radicals. Our results demonstrate that the products formed by electrocyclization are responsible for the formation of iminyl radicals, contrary to homolysis of N−N bond of 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives proposed by Mcnab. Besides, our results showing that the reaction starts with the electrocyclization very well clarify why the formation of ortho‐cyclization product, contrary to ipso‐cyclization from 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives as the main product. Therefore, our results are in agreement with the experimental results for pyrolysis of 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives. [ABSTRACT FROM AUTHOR]

Saddle‐shaped hemes have been discovered in the structures of most peroxidases. How such a macrocycle deformation affects the reaction of FeIII hemes with hydrogen peroxide (H2O2) to form high‐valent Fe‐oxo species remains uncertain. Through examination of the ESI‐MS spectra, absorption changes and 1H NMR chemical shifts, we investigated the reactions of two FeIII porphyrins with different degrees of saddling deformation, namely FeIII(OETPP)ClO4 (1OE) and FeIII(OMTPP)ClO4 (1OM), with tert‐butyl hydroperoxide (tBuOOH) in CH2Cl2 at −40 °C, which quickly resulted in O−O bond homolysis from a highly unstable FeIII‐alkylperoxo intermediate, FeIII‐O(H)OR (2) into FeIV‐oxo porphyrins (3). Insight into the reaction mechanism was obtained from [tBuOOH]‐dependent kinetics. At −40 °C, the reaction of 1OE with tBuOOH exhibited an equilibrium constant (Ka=362.3 M−1) and rate constant (k=1.87×10−2 sM−>1) for the homolytic cleavage of the 2 O−O bond that were 2.1 and 1.4 times higher, respectively, than those exhibited by 1OM (Ka=171.8 M−1 and k=1.36×10−2 s−1). DFT calculations indicated that an FeIII porphyrin with greater saddling deformation can achieve a higher HOMO ([Fe(dz2 ,dx2-y2)‐porphyrin(a2u)]) to strengthen the orbital interaction with the LUMO (O−O bond σ*) to facilitate O−O cleavage. [ABSTRACT FROM AUTHOR]

We report herein a modular catalytic method for the efficient enantioselective synthesis of chiral allylboronates from abundant feedstock chemicals through an asymmetric 1,1‐difunctionalization of alkenes. This protocol is distinguished by its use of an inexpensive chiral catalyst, mild and convenient reaction conditions, wide substrate scope, scalability and practicality. The utility of this method is demonstrated by the rapid synthesis of key intermediates of complex drug molecules. Mechanistic studies reveal that β‐H elimination is a highly regioselective step and the reversible homolysis and convergance to the lower energy pre‐reductive elimination intermediate is the enantio‐determining step. [ABSTRACT FROM AUTHOR]

Catalysis by radical enzymes dependent on coenzyme B12 (AdoCbl) relies on the reactive primary 5′‐deoxy‐5′adenosyl radical, which originates from reversible Co−C bond homolysis of AdoCbl. This bond homolysis is accelerated roughly 1012‐fold upon binding the enzyme substrate. The structural basis for this activation is still strikingly enigmatic. As revealed here, a displaced firm adenosine binding cavity in substrate‐loaded glutamate mutase (GM) causes a structural misfit for intact AdoCbl that is relieved by the homolytic Co−C bond cleavage. Strategically interacting adjacent adenosine‐ and substrate‐binding protein cavities provide a tight caged radical reaction space, controlling the entire radical path. The GM active site is perfectly structured for promoting radical catalysis, including "negative catalysis", a paradigm for AdoCbl‐dependent mutases. [ABSTRACT FROM AUTHOR]

Herein, we report a polar‐radical relay strategy for α‐C−H amination of cyclic amines with N‐chloro‐N‐sodio‐carbamates. The relay is initiated by in situ generation of cyclic iminium intermediate using N‐iodosuccinimide (NIS) oxidant as an initiator, which then operates through a series of polar (addition and elimination) and radical (homolysis, hydrogen‐ and halogen atom transfer) reactions to enable the challenging C−N bond formation in a controlled manner. A broad range of α‐amino cyclic amines were readily accessed with excellent regioselectivity, and the superb applicability was further demonstrated by functionalization of biologically relevant compounds. [ABSTRACT FROM AUTHOR]

The unimolecular decomposition pathways of n‐butyl nitroxyethylnitramine (BuNENA) were computationally investigated. The O−NO2 bond dissociation energies (BDEs) are found to be smaller than the N−NO2 BDEs. The consecutive NO2 elimination via TSA1 is more favorable kinetically than that via TSA2 although both of them form the same intermediate of n‐butyl‐aminoacetaldehyde (BuAAA). Isomerization of n‐butyl‐nitramineethyloxidanyl radical (BuNEȮ) formed by homolytic cleavage of O−NO2 bond was found to eliminate NO2 with a negative bond dissociation energy. Among the NO2 elimination pathways, the formation of C4H9NCH2 (PB2b), CH2O, and NO2 from BuNEȮ via the saddle point TSB2a was found to be the most kinetically favorable with a low activation energy barrier. In contrast, the consecutive HONO elimination is the most thermodynamically favorable with a high exothermicity (−▵H0). The first‐principle kinetic Monte Carlo (kMC) simulations show that the NO2 elimination of BuNEȮ via TSB2a plays an important role in driving the decomposition of BuNENA. [ABSTRACT FROM AUTHOR]

Advanced oxidation technologies often use peroxymonosulfate in the presence of CoIIaq. It is commonly assumed that the reaction of Co(H2O)62+ with HSO5− yields CoIIIaq and SO4.−. DFT results point out that first CoII(SO5)(H2O)2 is formed. The homolysis of CoII(SO5)(H2O)2 to yield (H2O)CoII(SO5)OH.+SO4.−, is exothermic but has a large activation energy. However the cobalt is not oxidized in this reaction. CoII(SO5)(H2O)2 reacts with a second HSO5− to form CoII(SO5)2(H2O)2− that decomposes via disproportionation of the monoperoxysulfate ions without oxidation of the central cobalt ion. Surprisingly even in the presence of ligands, L, that stabilize CoIII, i. e., pyrophosphate; tri‐polyphosphate and ATP, the experimentally observed reaction mechanism involves the formation of LCoII‐OOSO3aq which then reacts with another HSO5− to form LCoII‐(OOSO32−)2. The latter complex decomposes via disproportionation of the monoperoxysulfate ligands followed by oxidation of the central cobalt cation. Alternatively, in the presence of excess CoIILaq, LCoII‐OOSO3aq reacts with CoIILaq to form 2CoIIILaq. These results point out that the mechanism of advanced oxidation processes initiated by a mixture of Co(H2O)62+ and HSO5− must be re‐considered. [ABSTRACT FROM AUTHOR]

We describe herein that the cross‐coupling of bromodifluoroacetamides with (iodoethynyl)arenes proceeds without recourse to any photocatalyst when exposed to visible light at room temperature to afford alkynyldifluoroacetamides in 62–83% yields (27 examples). Several control experiments suggest that the reaction involves the homolysis of bromodifluoroacetamides and the coupling of the resultant difluoromethyl radical species with the 1‐iodoalkynes via a radical chain process. Divergent transformations of the coupling products led to various organofluorine compounds, demonstrating the synthetic utility of the developed photo‐coupling method. [ABSTRACT FROM AUTHOR]

A tunable photocatalytic method is reported for anti‐Markovnikov hydro‐ and aminooxygenation of unactivated alkenes using readily accessible ketoxime carbonates as the diverse functionalization reagents. Mechanistic studies reveal that this reaction is initiated through an energy‐transfer‐promoted N−O bond homolysis of ketoxime carbonates leading to alkoxylcarbonyloxyl and iminyl radicals under visible‐light photocatalysis, followed by the addition of alkoxylcarbonyloxyl radical to alkenes. By taking advantage of the different stability of the iminyl radicals, the generated carbon radical either abstracts a hydrogen atom from the media to form the anti‐Markovnikov hydrooxygenation product, or it is trapped by the persistent iminyl radical to furnish the aminooxygenation product. Notably, this is the first example of direct hydrooxygenation of unactivated olefins with anti‐Markovnikov regioselectivity involving an oxygen‐centered radical. [ABSTRACT FROM AUTHOR]

The mainstream applications of visible‐light photoredox catalysis predominately involve outer‐sphere single‐electron transfer (SET) or energy transfer (EnT) processes of precious metal RuII or IrIII complexes or of organic dyes with low photostability. Earth‐abundant metal‐based MnLn‐type (M=metal, Ln=polydentate ligands) complexes are rapidly evolving as alternative photocatalysts as they offer not only economic and ecological advantages but also access to the complementary inner‐sphere mechanistic modes, thereby transcending their inherent limitations of ultrashort excited‐state lifetimes for use as effective photocatalysts. The generic process, termed visible‐light‐induced homolysis (VLIH), entails the formation of suitable light‐absorbing ligated metal–substrate complexes (MnLn‐Z; Z=substrate) that can undergo homolytic cleavage to generate Mn−1Ln and Z. for further transformations. [ABSTRACT FROM AUTHOR]

One of the challenges of catalysis is the transformation of inert C−H bonds to useful products. Copper‐containing monooxygenases play an important role in this regard. Here we show that low‐temperature oxygenation of dinuclear copper(I) complexes leads to unusual tetranuclear, mixed‐valent μ4‐peroxo [CuI/CuII]2 complexes. These Cu4O2 intermediates promote irreversible and thermally activated O−O bond homolysis, generating Cu2O complexes that catalyze strongly exergonic H‐atom abstraction from hydrocarbons, coupled to O‐transfer. The Cu2O species can also be produced with N2O, demonstrating their capability for small‐molecule activation. The binding and cleavage of O2 leading to the primary Cu4O2 intermediate and the Cu2O complexes, respectively, is elucidated with a range of solution spectroscopic methods and mass spectrometry. The unique reactivities of these species establish an unprecedented, 100 % atom‐economic scenario for the catalytic, copper‐mediated monooxygenation of organic substrates, employing both O‐atoms of O2. [ABSTRACT FROM AUTHOR]

C‐aryl glycosyl compounds offer better in vivo stability relative to O‐ and N‐glycoside analogues. C‐aryl glycosides are extensively investigated as drug candidates and applied to chemical biology studies. Previously, C‐aryl glycosides were derived from lactones, glycals, glycosyl stannanes, and halides, via methods displaying various limitations with respect to the scope, functional‐group compatibility, and practicality. Challenges remain in the synthesis of C‐aryl nucleosides and 2‐deoxysugars from easily accessible carbohydrate precursors. Herein, we report a cross‐coupling method to prepare C‐aryl and heteroaryl glycosides, including nucleosides and 2‐deoxysugars, from glycosyl esters and bromoarenes. Activation of the carbohydrate substrates leverages dihydropyridine (DHP) as an activating group followed by decarboxylation to generate a glycosyl radical via C−O bond homolysis. This strategy represents a new means to activate alcohols as a cross‐coupling partner. The convenient preparation of glycosyl esters and their stability exemplifies the potential of this method in medicinal chemistry. [ABSTRACT FROM AUTHOR]

The pyrogallol autoxidation method has been widely utilized to evaluate various antioxidants in antioxidative bioactivities. However, this method is generally not appropriate for estimating the.O2− radical scavenging capacity of bioflavonoids, as it enables bioflavonoids to generate.O2− radical in oxygen‐alkaline (pH 8.2) surroundings. In the present study, an improved DMSO (dimethyl sulfoxide) system (pH 7.25, versus pH 8.2 of the pyrogallol autoxidation) was successfully developed to evaluate the.O2− radical scavenging capacity of bioflavonoids by EPR technique and using the spin trapping reagent DMPO (5,5‐dimethyl‐1‐pyrroline‐N‐oxide). The non‐protonic environment supplied by the system promotes the stabilization of the.O2−radical and therefore ensures a much more accurate measurement of.O2−radical scavenging capacity in bioflavonoids if compared to protonic solvents. The results demonstrated that the effects of scavenging.O2−radicals in natural bioflavonoids follows the order: dihydromyricetin>myricetin>quercetin>kaempferol>baicalein>chrysin, which are well associated with numbers of hydroxyl groups attached to their molecular skeletons and/or active H of their configurations. Interestingly, the higher superoxide‐anion scavenging effect measured for dihydromyricetin with respect to myricetin is possibly attributed to the fact that dihydromyricetin can be transformed into myricetin in the presence of.O2− radical, resulting from the homolysis of active H donated from C3−H bond of DMY via.O2− radicals. [ABSTRACT FROM AUTHOR]

A "one‐shot" cross coupling between benzyl alcohols and alkenyl halides has been established. A combination of low‐valent Ti‐mediated C−OH homolysis and the prominent chemistry of Ni‐based radical catalysis afforded the desired cross‐coupled product with good efficiency. The reaction proceeded regardless of the electronic property of benzyl alcohols, and Ar−B bond remained intact throughout the reaction. Alkenyl bromides with various substitution patterns were applicable to this reaction. Attempts for utilizing sterically demanding tri‐substituted alkenes indicated that the steric hinderance mainly inhibited the radical‐trapping by Ni species. This reaction can be a simple and efficient strategy for synthesizing densely substituted allylbenzene derivatives. [ABSTRACT FROM AUTHOR]

Pnictanes Cp*(Ph)ECl (E = As 1, Sb 2; Cp* = C5Me5) react with group 13 diyls LM (M = Al, Ga, In; L = HC[C(Me)N(Dip)]2, Dip = 2,6‐iPr2C6H3) with oxidative addition of the E‐Cl bond to a unique series of metalylpnictanes [L(Cl)M](Ph)ECp* (E = As, M = Al 3, Ga 4, In 5; E = Sb, M = Al 6, Ga 7, In 8). Thermal treatment of 4 and 6–8 results in homolytic E‐C bond scission with Cp* radical liberation, yielding the corresponding dipnictanes {[L(Cl)M](Ph)E}2 (E = As, M = Ga 9; E = Sb, M = Al 10, Ga 11, In 12). Compounds 1–12 were characterized by NMR (1H, 13C) and IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction (3–12). [ABSTRACT FROM AUTHOR]

Fascinating oscillations of color, kinetics of pH, cyclic voltammetry (CV) and UV‐vis spectra, ensued from supplementing of VO(acac)2‐acetonitrile solutions with micro‐amounts of H2O2, were greatly affected by the small additives of glyoxal and oxalic acid. Such effect was consisted in sufficient decreasing the sensitivity of samples by means of it pH, CV and UV‐vis response onto H2O2 additives. The revealed peculiarities substantiate the responsibility of free radicals (particularly.OH generated in the course of H2O2 homolysis) for the discussed parameters alteration. In view of.OH are identified as most active and destructive (especially, in respect to the cellular constituents) agents can be originated in vivo, it overproduction is responsible for developing of many related severe diseases. In practical aspect the undertaken research may be recommended for the oxidative stress evaluation and tracking. [ABSTRACT FROM AUTHOR]

A mild visible‐light‐induced Pd‐catalyzed intramolecular C−H arylation of amides is reported. The method operates by cleavage of a C(sp2)−O bond, leading to hybrid aryl Pd‐radical intermediates. The following 1,5‐hydrogen atom translocation, intramolecular cyclization, and rearomatization steps lead to valuable oxindole and isoindoline‐1‐one motifs. Notably, this method provides access to products with readily enolizable functional groups that are incompatible with traditional Pd‐catalyzed conditions. [ABSTRACT FROM AUTHOR]

Ab initio molecular dynamics simulations were performed to investigate the thermal decomposition mechanisms of the energetic benzotrifuroxan (BTF):1,3,3‐trinitroazetidine (TNAZ) cocrystal at high temperature. It is found that there are four initial reaction mechanisms involved in the decomposition of the cocrystal. Subsequent decomposition channels can be divided into three types: BTF‐chain isomerization, C─NO2 bond homolysis, and ring opening. After that, one main path is that long chains decomposed into small radicals gradually after the ring opening. The other is that a new ring was formed after the ring opening and then it will break by degrees. Releasing of the H radicals and oxygen‐containing groups plays an important role in the whole decomposition process. We also studied the release mechanisms of nitrogen gas and carbon dioxide in the later decomposition stage. Our study may provide new insights into the initiation mechanisms and subsequent decomposition of cocrystal explosives at high temperature. [ABSTRACT FROM AUTHOR]

Reductive elimination is an elementary organometallic reaction step involving a formal oxidation state change of −2 at a transition‐metal center. For a series of formal high‐valent NiIV complexes, aryl–CF3 bond‐forming reductive elimination was reported to occur readily (Bour et al. J. Am. Chem. Soc. 2015, 137, 8034–8037). We report a computational analysis of this reaction and find that, unexpectedly, the formal NiIV centers are better described as approaching a +II oxidation state, originating from highly covalent metal–ligand bonds, a phenomenon attributable to σ‐noninnocence. A direct consequence is that the elimination of aryl–CF3 products occurs in an essentially redox‐neutral fashion, as opposed to a reductive elimination. This is supported by an electron flow analysis which shows that an anionic CF3 group is transferred to an electrophilic aryl group. The uncovered role of σ‐noninnocence in metal–ligand bonding, and of an essentially redox‐neutral elimination as an elementary organometallic reaction step, may constitute concepts of broad relevance to organometallic chemistry. [ABSTRACT FROM AUTHOR]

Reductive elimination is an elementary organometallic reaction step involving a formal oxidation state change of −2 at a transition‐metal center. For a series of formal high‐valent NiIV complexes, aryl–CF3 bond‐forming reductive elimination was reported to occur readily (Bour et al. J. Am. Chem. Soc. 2015, 137, 8034–8037). We report a computational analysis of this reaction and find that, unexpectedly, the formal NiIV centers are better described as approaching a +II oxidation state, originating from highly covalent metal–ligand bonds, a phenomenon attributable to σ‐noninnocence. A direct consequence is that the elimination of aryl–CF3 products occurs in an essentially redox‐neutral fashion, as opposed to a reductive elimination. This is supported by an electron flow analysis which shows that an anionic CF3 group is transferred to an electrophilic aryl group. The uncovered role of σ‐noninnocence in metal–ligand bonding, and of an essentially redox‐neutral elimination as an elementary organometallic reaction step, may constitute concepts of broad relevance to organometallic chemistry. [ABSTRACT FROM AUTHOR]

Design of precursors for thin film growth by chemical vapor deposition (CVD) can be informed by knowledge of the precursor decomposition mechanism. However, the vast majority of decomposition characterization is done by techniques that do not capture CVD conditions. This work used a custom CVD reactor with in situ Raman spectroscopy capabilities to investigate the gas phase thermal decomposition of the tungsten imido complex Cl4(CH3CN)WNiPr, a known precursor for the aerosol‐assisted (AA)CVD of tungsten carbonitride thin films. In combination with previous computational and ex situ data, we propose a decomposition mechanism for this precursor under CVD conditions, based on observation of gas phase products of N(imido)‐C bond homolysis and σ‐bond metathesis between the precursor W–Cl bond and H2. [ABSTRACT FROM AUTHOR]

A tetrahedral CuII alkylperoxido complex [CuII(TMG3tach)(OOCm)]+ (1OOCm) (TMG3tach={2,2′,2′′‐[(1s,3s,5s)‐cyclohexane‐1,3,5‐triyl]tris‐(1,1,3,3‐tetramethyl guanidine)}, OOCm=cumyl peroxide) is prepared and characterized by UV/Vis, cold‐spray ionization mass spectroscopy (CSI‐MS), resonance Raman, and EPR spectroscopic methods. Product analysis of the self‐decomposition reaction of 1OOCm in acetonitrile (MeCN) indicates that the reaction involves O−O bond homolytic cleavage of the peroxide moiety with concomitant C−H bond activation of the solvent molecule. When an external substrate such as 1,4‐cyclohexadiene (CHD) is added, the O−O bond homolysis leads to C−H activation of the substrate. Furthermore, the reaction of 1OOCm with 2,6‐di‐tert‐butylphenol derivatives produces the corresponding phenoxyl radical species (ArO.) together with a CuI complex through a concerted proton‐electron transfer (CPET) mechanism. Details of the reaction mechanisms are explored by DFT calculations. [ABSTRACT FROM AUTHOR]

N‐arylthiophene‐2‐carboxamidoxime derivatives (a‐e) were synthesized by using two methods and then subjected to thermolysis at 200–250 °C for 2 h under nitrogen atmosphere either alone or in the presence of tetralin and/or naphthalene as radical scavengers yielded imidazole, oxazole, triazine and amide derivatives. The pyrolysates from both reactions were separated with their constituents by column chromatography and analyzed then identified 1H NMR, 13C NMR and GC‐MS. A plausible mechanism is suggested through two competitive pathways involving the homolysis of N‐O and/or C‐N bonds to account for the thermolysis products. [ABSTRACT FROM AUTHOR]

We report the formation of a new copper peroxynitrite (PN) complex [CuII(TMG3tren)(κ1‐OONO)]+ (PN1) from the reaction of [CuII(TMG3tren)(O2.−)]+ (1) with NO.(g) at −125 °C. The first resonance Raman spectroscopic characterization of such a metal‐bound PN moiety supports a cis κ1‐(−OONO) geometry. PN1 transforms thermally into an isomeric form (PN2) with κ2‐O,O′‐(−OONO) coordination, which undergoes O−O bond homolysis to generate a putative cupryl (LCuII−O.) intermediate and NO2.. These transient species do not recombine to give a nitrato (NO3−) product but instead proceed to effect oxidative chemistry and formation of a CuII–nitrito (NO2−) complex (2). [ABSTRACT FROM AUTHOR]

Despite significant progress in aliphatic decarboxylation, an efficient and general protocol for radical aromatic decarboxylation has lagged far behind. Herein, we describe a general strategy for rapid access to both aryl and alkyl radicals by photosensitized decarboxylation of the corresponding carboxylic acids esters followed by their successive use in divergent carbon–heteroatom and carbon–carbon bond‐forming reactions. Identification of a suitable activator for carboxylic acids is the key to bypass a competing single‐electron‐transfer mechanism and "switch on" an energy‐transfer‐mediated homolysis of unsymmetrical σ‐bonds for a concerted fragmentation/decarboxylation process. [ABSTRACT FROM AUTHOR]

A comparative study of the homoleptic [M(CF3)4]− complexes of all three coinage metals (M=Cu, Ag, Au) reveals that homolytic M−C bond cleavage is favoured in every case upon excitation in the gas phase (CID‐MS2). Homolysis also occurs in solution by photochemical excitation. Transfer of the photogenerated CF3. radicals to both aryl and alkyl carbon atoms was also confirmed. The observed behaviour was rationalized by considering the electronic structure of the involved species, which all show ligand‐field inversion. Moreover, the homolytic pathway constitutes experimental evidence for the marked covalent character of the M−C bond. The relative stability of these M−C bonds was evaluated by energy‐resolved mass spectrometry (ERMS) and follows the order Cu

Surface frustrated Lewis pairs (SFLPs) have been implicated in the gas‐phase heterogeneous (photo)catalytic hydrogenation of CO2 to CO and CH3OH by In2O3−x(OH)y. A key step in the reaction pathway is envisioned to be the heterolysis of H2 on a proximal Lewis acid–Lewis base pair, the SFLP, the chemistry of which is described as In⋅⋅⋅In‐OH + H2 → In‐OH2+⋅⋅⋅In‐H−. The product of the heterolysis, thought to be a protonated hydroxide Lewis base In‐OH2+ and a hydride coordinated Lewis acid In‐H−, can react with CO2 to form either CO or CH3OH. While the experimental and theoretical evidence is compelling for heterolysis of H2 on the SFLP, all conclusions derive from indirect proof, and direct observation remains lacking. Unexpectedly, we have discovered rhombohedral In2O3−x(OH)y can enable dissociation of H2 at room temperature, which allows its direct observation by several analytical techniques. The collected analytical results lean towards the heterolysis rather than the homolysis reaction pathway. [ABSTRACT FROM AUTHOR]

The reaction profiles for the uni‐ and bimolecular decomposition of benzyl hydroperoxide have been studied in the context of initiation reactions for the (aut)oxidation of hydrocarbons. The unimolecular dissociation of benzyl hydroperoxide was found to proceed through the formation of a hydrogen‐bonded radical‐pair minimum located +181 kJ mol−1 above the hydroperoxide substrate and around 15 kJ mol−1 below the separated radical products. The reaction of toluene with benzyl hydroperoxide proceeds such that O−O bond homolysis is coupled with a C−H bond abstraction event in a single kinetic step. The enthalpic barrier of this molecule‐induced radical formation (MIRF) process is significantly lower than that of the unimolecular O−O bond cleavage. The same type of reaction is also possible in the self‐reaction between two benzyl hydroperoxide molecules forming benzyloxyl and hydroxyl radical pairs along with benzaldehyde and water as co‐products. In the product complexes formed in these MIRF reactions, both radicals connect to a centrally placed water molecule through hydrogen‐bonding interactions. [ABSTRACT FROM AUTHOR]

Radical hydrosilylation, hydrogermylation and hydrostannylation without any added initiator may be initiated by alkene‐assisted homolysis of the respective Si‐H, Ge‐H and Sn‐H bond, three more examples of molecule‐assisted homolysis (MAH). We studied the thermally initiated radical addition of tris(trimethylsilyl) silane 1a, tributylgermane 1b, and tributylstannane 1c to methyl 10‐undecenoate 2a and of 1a to 1‐decene 2b. Computed reaction enthalpies and pathways support the radical formation by MAH. These results give evidence that many respective radical reactions without any added initiator reported in literature may be initiated analogously by MAH. [ABSTRACT FROM AUTHOR]

Over the past 150 years, a certain mythology has arisen around the mechanistic pathways of the oxygenation of organometallics with non‐redox‐active metal centers as well as the character of products formed. Notably, there is a widespread perception that the formation of commonly encountered metal alkoxide species results from the auto‐oxidation reaction, in which a parent metal alkyl compound is oxidized by the metal alkylperoxide via oxygen transfer reaction. Now, harnessing a well‐defined zinc ethylperoxide incorporating a β‐diketiminate ligand, the investigated alkylperoxide compounds do not react with the parent metal alkyl complex as well as Et2Zn to form a zinc alkoxide. Upon treatment of the zinc ethylperoxide with Et2Zn, a previously unobserved ligand exchange process is favored. Isolation of a zinc hydroxide carboxylate as a product of decomposition of the parent zinc ethylperoxide demonstrates the susceptibility of the latter to O−O bond homolysis. [ABSTRACT FROM AUTHOR]

Enzyme‐mediated cascade reactions are widespread in biosynthesis. To facilitate comparison with the mechanistic categorizations of cascade reactions by synthetic chemists and delineate the common underlying chemistry, we discuss four types of enzymatic cascade reactions: those involving nucleophilic, electrophilic, pericyclic, and radical reactions. Two subtypes of enzymes that generate radical cascades exist at opposite ends of the oxygen abundance spectrum. Iron‐based enzymes use O2 to generate high valent iron‐oxo species to homolyze unactivated C−H bonds in substrates to initiate skeletal rearrangements. At anaerobic end, enzymes reversibly cleave S‐adenosylmethionine (SAM) to generate the 5′‐deoxyadenosyl radical as a powerful oxidant to initiate C−H bond homolysis in bound substrates. The latter enzymes are termed radical SAM enzymes. We categorize the former as "thwarted oxygenases". [ABSTRACT FROM AUTHOR]

A three‐coordinate low‐spin cobalt(I) complex generated using a pincer ligand is presented. Since an empty dx2-y2 orbital is sterically exposed at the site trans to the N donor of an acridane moiety, the cobalt(I) center accepts the coordination of various donors such as H2 and PhSiH3 revealing σ‐complex formation. At this low‐spin cobalt(I) site, homolysis of H–H and Si−H bonds preferentially occurs via bimolecular hydrogen atom transfer instead of two‐electron oxidative addition. When the resulting CoII–H species was exposed to N2, H2 evolution readily occurs at ambient conditions. These results suggest single‐electron processes are favored at the structurally rigidified cobalt center. [ABSTRACT FROM AUTHOR]

Here, a new approach to further improve graphdiyne (GDY) based materials by using benzyl disulfide (BDS) as the sulfur source is demonstrated. The S radicals, generated from the homolysis of BDS, can react with the acetylenic bonds and be well confined in the triangle‐like pores of GDY, forming S‐GDY. The as‐prepared S‐GDY, which possesses numerous heteroatom defects and active sites, is suitable for applications in many electronic devices, such as lithium ion batteries (LIBs). As expected, the assembled LIBs based on S‐GDY displayed improved electrochemical properties, including larger capacity and superior rate capability. [ABSTRACT FROM AUTHOR]

The carbonylation of a nickel(II) anilido species 2 led to the formation of a dinickel(0)–CO complex (P2P‐PP2){Ni(CO)}23 with a P−P bond along with isocyanate generation. In this reaction, the central phosphide moiety of an anionic PPP ligand (PPP−=−P[2‐PiPr2C6H4]2) acts as a single‐electron donor to form a P radical. Alternatively, 3 can be synthesized from the reduction of (PPP)NiCl (1) in the presence of CO; thus, the reaction proceeds by radical coupling of a.P−Ni0−CO species. The reverse reaction occurred to generate 1 when 3 was treated with AgCl. Since the P−P bond is light‐sensitive, its homolysis is possible and was explored by EPR spectroscopy and DFT analysis. Finally, various bond‐activation reactions of 3 occurred under visible‐light conditions, thus indicating that a P−P bond can act as an active reaction site. [ABSTRACT FROM AUTHOR]

Simple monocyclic diketopiperazine (DKP)‐derived alkoxyamines exhibit unprecedented activation of a remote C−O bond for homolysis by amide distortion. The combination of strain‐release‐driven amide planarization and the persistent radical effect (PRE) enables a unique, irreversible, and quantitative trans→cis isomerization under much milder conditions than typically observed for such homolysis‐limited reactions. This isomerization is shown to be general and independent of the steric and electronic nature of both the amino acid side chains and the substituents at the DKP nitrogen atoms. Homolysis rate constants are determined, and they significantly differ for both the labile trans diastereomers and the stable cis diastereomers. To reveal the factors influencing this unusual process, structural features of the kinetic trans diastereomers and thermodynamic cis diastereomers are investigated in the solid state and in solution. X‐ray crystallographic analysis and computational studies indicate substantial distortion of the amide bond from planarity in the trans‐alkoxyamines, and this is believed to be the cause for the facile and quantitative isomerization. Thus, these amino‐acid‐derived alkoxyamines are the first examples that exhibit a large thermodynamic preference for one diastereomer over the other upon thermal homolysis, and this allows controlled switching of configurations and configurational cycling. Strain release drives isomerization: Amide pyramidalization in diketopiperazine‐derived trans‐alkoxyamines is the reason for facile homolytic bond cleavage at mild temperatures and quantitative isomerization into cis isomers with nearly planar amide geometry. PRE=persistent radical effect. [ABSTRACT FROM AUTHOR]

Abstract: The first N‐heterocyclic silylene (NHSi)–silane scaffold LSi−R−Si(H)Mes2 (1) (L=PhC(NtBu)2; R=1,12‐xanthendiyl spacer; Mes=2,4,6‐Me3C6H2) was synthesized and used to form the unique rhodium(III) complex (LSi−R−SiMes2)Rh(H)Cl 2 through its reaction with 0.5 molar equivalents of [Rh(coe)2Cl]2 (coe=cyclooctene). An X‐ray diffraction analysis revealed that 2 has a (SiIISiIV)Rh(H)Cl core with three short Rh⋅⋅⋅H−C contacts with Me groups of the ligand 1, which cause a distorted pentagonal bipyramidal coordination of the Rh center. Unexpectedly, the reaction of 2 with tBuONa gives the new bis(silyl)hydridorhodium(III) complex 4. Due to the strong donor ability of the chelate SiII–SiIV ligand, 2 and 4 can act as highly efficient pre‐catalysts in the Rh‐mediated selective C−H functionalization of 2‐phenylpyridines with C−C unsaturated organic substrates under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Abstract: Localized singlet diradicals have attracted much attention, not only in the field of bond‐homolysis chemistry, but also in nonlinear optical materials. In this study, an extremely long lived localized singlet diradical was obtained by using a new molecular design strategy in which it is kinetically stabilized by means of a macrocycle that increases the molecular strain of the corresponding σ‐bonded compound. Notably, the lifetime of this diradical (14 μs) is two orders of magnitude longer than that of a standard singlet diradical without a macrocyclic structure (≈0.2 μs) at 293 K. The species is persistent below a temperature of 100 K. In addition to the kinetic stabilization of the singlet diradical, the spontaneous oxidation of its corresponding ring‐closed compound at 298 K produced oxygenated products under atmospheric conditions. Apparently, the “stretch effect” induced by the macrocyclic structure plays a crucial role in extending the lifetime of localized singlet diradicals and increasing the reactivity of their corresponding σ‐bonded compounds. [ABSTRACT FROM AUTHOR]