3,3-二{2,2-二[4-(N,N-二取代氨基)苯基]乙烯基}-4,5,6,7-四氯-2-苯并[c]呋喃酮的合成

在对甲苯磷酸存在下,采用1,1-二[4-(N,N-二取代氨基)苯基]乙烯(3)和四氯苯酐在乙酸酐溶液中的缩合反应合成了3,3-二{2,2-二[4-(N,N-二取代氨基)苯基]乙烯基}-4,5,6,7-四氯-2-苯并[c]呋喃酮(4),产率89～93％。3由4,4＇-二(N,N-二取代氨基)二苯甲酮(1)与甲基碘化镁进行Grignard反应的产物经水解再脱水制得,产率85％～88.5％(以1为基准)。     

Enantiopure synthesis of all four stereoisomers of carbapenam-3-carboxylic acid methyl ester

The retro-Dieckmann reaction has been used as a stereodivergent synthetic tool on N-Boc-7-azabicyclo[2.2.1]heptan-2-one-1-carboxylic acid methyl ester to obtain enantiopure trans- and cis-5-(carboxymethyl)pyrrolidine-2-carboxylic acid methyl esters. These disubstituted pyrrolidines have been used as starting materials to develop concise and straightforward syntheses of all four stereoisomers of carbapenam-3-carboxylic acid methyl esters. In this way, we have confirmed unequivocally the stereochemistry of two carbapenams isolated from strains of Serratia and Erwinia species.     

3,3-二{2,2-二[4-(N,N-二取代氨基)苯基]乙烯基}-4,5,6,7-四氯-2-苯并[c]呋喃酮的合成

在对甲苯磺酸存在下，采用1,1-二[4-(N,N-二取代氨基)苯基]乙烯(3)和四氯苯酐在乙酸酐溶液中的缩合反应合成了3,3-二{2,2-二[4-(N,N-二取代氨基)苯基]乙烯基}-4,5,6,7-四氯-2-苯并[c]呋喃酮(4)，产率89～93%。3由4,4'-二(N,N-二取代氨基)二苯甲酮(1)与甲基碘化镁进行Grignard反应的产物经水解再脱水制得，产率85%～88.5%(以1为基准)。     

Highly stereospecific, palladium-catalyzed cross-coupling of alkenylsilanols

[reaction: see text] Alkenylsilanols bearing methyl ((E)-1 and (Z)-1) or isopropyl ((E)-2 and (Z)-2)) substituents are converted to disubstituted alkenes by a palladium(0)-catalyzed cross-coupling reaction with aryl or vinyl iodides in the presence of tetrabutylammonium fluoride or hydroxide. Yields and stereoselectivities are generally high, and the reaction is compatible with a wide range of functional groups.     

A facile synthesis of some thieno/furo‐[2,3‐d]pyrimidine‐2‐yl‐thioacetic acid derivatives

The reaction of 2‐(α‐chloroacetamido)‐3‐cyano‐4,5‐disubstituted thiophenes/furanes with ammonium thiocyanate in methanol or ethanol afforded methyl or ethyl (4‐amino‐5,6‐disubstituted thieno/furo[2,3‐d]‐pyrimidine‐2‐yl)thioacetates in good yields.     

Structure of the charge separated state P865(+)Q(A)- in the photosynthetic reaction centers of Rhodobacter sphaeroides by quantum beat oscillations and high-field electron paramagnetic resonance: evidence for light-induced Q(A)- reorientation

The structure of the secondary radical pair, P865(+)Q(A)-, in fully deuterated and Zn-substituted reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides R-26 has been determined by high-time resolution and high-field electron paramagnetic resonance (EPR). A computer analysis of quantum beat oscillations, observed in a two-dimensional Q-band (34 GHz) EPR experiment, provides the orientation of the various magnetic tensors of P865(+)Q(A)- with respect to a magnetic reference frame. The orientation of the g-tensor of P865(+) in an external reference system is adapted from a single-crystal W-band (95 GHz) EPR study [Klette, R.; T?rring, J. T.; Plato, M.; M?bius, K.; B?nigk, B.; Lubitz, W. J. Phys. Chem. 1993, 97, 2015-2020]. Thus, we obtain the three-dimensional structure of the charge separated state P865(+)Q(A)- on a nanosecond time scale after light-induced charge separation. Comparison with crystallographic data reveals that the position of the quinone is essentially the same as that in the X-ray structure. However, the head group of Q(A)- has undergone a 60 degrees rotation in the ring plane relative to its orientation in the crystal structure. Analysis suggests that the two different QA conformations are functionally relevant states which control the electron-transfer kinetics from Q(A)- to the secondary quinone acceptor QB. It appears that the rate-limiting step of this reaction is a reorientation of Q(A)- in its binding pocket upon light-induced reduction. The new kinetic model accounts for striking observations by Kleinfeld et al. who reported that electron transfer from Q(A)- to QB proceeds in RCs cooled to cryogenic temperature under illumination but does not proceed in RCs cooled in the dark [Kleinfeld, D.; Okamura, M. Y.; Feher, G. Biochemistry 1984, 23, 5780-5786].     

Different C-C coupling reactions of permethyltitanocene and permethylzirconocene with disubstituted 1,3-butadiynes

Herein we describe different C-C coupling reactions of permethyltitanocene and -zirconocene with disubstituted 1,3-butadiynes. The outcomes of these reactions vary depending on the metals and the diyne substituents. The reduction of [Cp2*MCl2] (Cp* = C5Me5; M = Ti, Zr) with Mg in the presence of disubstituted butadiynes RC triple bond C-C triple bond CR' is suitable for the synthesis of different C-C coupling products of the diyne and the permethylmetallocenes, and provides a new method for the generation of functionalized pentamethyl-cyclopentadienyl derivatives. For M = Zr and R = R' = tBu, the reaction gives, by a twofold activation of one pentamethylcyclopentadienyl ligand, the complex [Cp*Zr[-C(=C=CHtBu)-CHtBu-CH2-eta5-C5Me3-CH2-]] (3), containing a fulvene ligand that is coupled to the modified substrate (allenic subunit). When using the analogous permethyltitanocene fragment "Cp2*Ti", the reaction depends strongly on the substituents R and R'. The coupling product of the butadiyne with two methyl groups of one of the pentamethylcyclopentadienyl ring systems, [Cp*Ti[eta5-C5Me3-(CH2-CHR-eta2-C2-CHR'-CH2)]], is obtained with R = R' = tBu (4) and R = tBu, R' = SiMe3 (5). In these complexes one pentamethylcyclopentadienyl ligand is annellated to an eight-membered ring with a C-C triple bond, which is coordinated to the titanium center. A different activation of both pentamethylcyclopentadienyl ligands is observed for R = R' = Me, resulting in the complex [[eta5-C5Me4(CH2)-]Ti[-C(=CHMe)-C(=CHMe)-CH2-eta5-C5Me4]] (6), which displays a fulvene as well as a butadienyl-substituted pentamethylcyclopentadienyl ligand. The influence exerted by the size of the metal is illustrated in the reaction of [Cp2*ZrCl2] with MeC triple bond C-C triple bond CMe. Here the five-membered metallacyclocumulene complex [Cp2*Zr(eta4-1,2,3,4-MeC4Me)] (7) is obtained. The reaction paths found for R = R' = Me are identical to those formerly described for R = R' = Ph.     

Carbamates,thiolcarbamates, dithiocarbamates and thioncarbamates derived from 2-benzothiazolinone and benzoxazolinone

The reaction of 3-(2-hydroxyethyl)-2-benzothiazoline with methyl, phenyl isocyanate, or dimethylcarbamoyl chloride afforded the carbamates 1–4 . The carbanilate 5 was prepared by the reaction of 2-benzothiazolinone with 3-chloropropyl-N-methylcarbanilate under basic conditions. The reaction of the appropriate 2-benzothiazolinone with the appropriate 2-chloro or 3-chloropropyl disubstituted thiolcarbamate under basic conditions furnished the thiolcarbamates 6–14 . The thiolcarbamate 15 was prepared by the reaction of sodium di-isopropylthiolcarbamate with 3-(chloromethyl)-2-benzothiazolinone. The reaction of 3-(chloromethyl)-2-ben-zothiazolinone and related compound with the appropriate sodium or triethylamine salt of disubstituted dithiocarbamate afforded the dithiocarbamate 16–22 . The reaction of the appropriate xanthate with the potassium salt of bromoacetic acid and the appropriate secondary amine afforded the thionocarbamates 23–29 . The thionocarbamate 30 was synthesized by the reaction of 5-chloro-2-benzothiazolinone with 3-chloropropyl diethylthionocarbamate.     

Iron(III) [bond] Salen complexes as enzyme models: mechanistic study of oxo(salen)iron complexes oxygenation of organic sulfides

The oxidation of a series of para-substituted phenyl methyl sulfides was carried out with several oxo(salen)iron (salen = N,N'-bis(salicylidine)ethylenediaminato) complexes in acetonitrile. The oxo complex [O=Fe(IV)(salen)](*+), generated from an iron(III) [bond] salen complex and iodosylbenzene, effectively oxidizes the organic sulfides to the corresponding sulfoxides. The formation of [O [double bond] Fe(IV)(salen)](*+) as the active oxidant is supported by resonance Raman studies. The kinetic data indicate that the reaction is first-order in the oxidant and fractional-order with respect to sulfide. The observed saturation kinetics of the reaction and spectral data indicate that the substrate binds to the oxidant before the rate-controlling step. The rate constant (k) values for the product formation step determined using Michaelis-Menten kinetics correlate well with Hammett sigma constants, giving reaction constant (rho) values in the range of -0.65 to -1.54 for different oxo(salen)iron complexes. The log k values observed in the oxidation of each aryl methyl sulfide by substituted oxo(salen)iron complexes also correlate with Hammett sigma constants, giving positive rho values. The substituent effect, UV-vis absorption, and EPR spectral studies indicate oxygen atom transfer from the oxidant to the substrate in the rate-determining step.     

Electron-transfer salts of 1,2,3,4,5-pentamethylferrocene, Fe(II)(C5Me5)(C5H5). Structure and magnetic properties of two 1:1 and two 2:3 Fe(C5Me5)(C5H5) electron-transfer salts of tetracyanoethylene

The reaction of Fe(II)(C5Me5)(C5H5), FeCpCp, with percyano acceptors, A [A = C4(CN)6 (hexacyanobutadiene), TCNQF4 (perfluoro-7,7,8,8-tetracyano-p-quinodimethane), and DDQ (2,3-dichloro-5,6-dicyanobenzoquinone)], results in formation of 1:1 charge-transfer salts of [Fe(III)CpCp]*]*+[A]*- composition. With A = TCNQ (7,7,8,8-tetracyano-p-quinodimethane) a 1:2 electron-transfer salt with FeCpCp forms. With A = TCNE (tetracyanoethylene) a pair of 1:1 salts as well as a pair of 2:3 salts of [FeCpCp]2[TCNE]3.S (S = CH2Cl2, THF) have been isolated and characterized by single-crystal X-ray diffraction. [FeCpCp][TCNE] consists of parallel 1-D.D(*+)A(*-)D(*+)A(*-)D(*+)A(*-). chains, while [FeCpCp][TCNE].MeCN has a herringbone array of D(*+)A2(2-)D(*+) dimers separated by solvent molecules. Although each [TCNE](-) is disordered, the diamagnetic [TCNE]2(2-) dimer is structurally different from those observed earlier with an intradimer separation of 2.79 A. The [TCNE](-) in the 2:3 [FeCpCp]2[TCNE]3.S exists as an eclipsed diamagnetic [TCNE]2(2-) dimer with an intradimer ethylene C.C separation of 2.833 and 2.903 A for the CH2Cl2- and THF-containing materials, respectively. The bond distances and angles for all the cations are essentially equivalent, and the distances are essentially equivalent to those previously reported for [FeCp2](*+) and [FeCp2](*+) cations. The average Fe-C5H5-ring and Fe-C5Me5-ring centroid distances are 1.71 and 1.69 A, respectively, which are 0.05 A longer than reported for Fe(II)CpCp. The one-electron reduction potential for Fe(II)CpCp is 0.11 V (vs SCE). The 5 K EPR of [FeCpCp](*+)[BF4](-) exhibits an axially symmetric powder pattern with g(parallel) = 4.36 and g(perpendicular) = 1.24, and the EPR parameters are essentially identical to those reported for ferrocenium and decamethylferrocenium. The high-temperature magnetic susceptibility for polycrystalline samples of these complexes can be fit by the Curie-Weiss law, chi = C/(T - theta), with low theta values and mu(eff) values from 2.08 to 3.43 mu(B), suggesting that the polycrystalline samples measured had varying degrees of orientation. [FeCpCp][TCNE] exhibits the highest effective moment of 3.43 mu(B)/Fe and weak ferromagnetic coupling, as evidenced from the theta of 3.3 K; however, unexpectedly, it does not magnetically order above 2 K. The formation of the four phases comprising FeCpCp and TCNE emphasizes the diversity of materials that may form and the present inability to predict neither solid-state compositions nor structure types.     

"Switching on" the properties of single-molecule magnetism in triangular manganese(III) complexes

The reaction between oxide-centered, triangular [MnIII3O(O2CR)6(py)3](ClO4) (R = Me (1), Et (2), Ph (3)) compounds and methyl 2-pyridyl ketone oxime (mpkoH) affords a new family of Mn/carboxylato/oximato complexes, [MnIII3O(O2CR)3(mpko)3](ClO4) [R = Me (4), Et (5), and Ph (6)]. As in 1-3, the cations of 4-6 contain an [MnIII3(mu3-O)]7+ triangular core, but with each Mn2 edge now bridged by an eta1:eta1:mu-RCO2- and an eta1:eta1:eta1:mu-mpko- group. The tridentate binding mode of the latter causes a buckling of the formerly planar [MnIII3(mu3-O)]7+ core, resulting in a relative twisting of the three MnIII octahedra and the central O2- ion now lying approximately 0.3 A above the Mn3 plane. This structural distortion leads to ferromagnetic exchange interactions within the molecule and a resulting S = 6 ground state. Fits of dc magnetization data for 4-6 collected in the 1.8-10.0 K and 10-70 kG ranges confirmed S = 6 ground states, and gave the following D and g values: -0.34 cm(-1) and 1.92 for 4, -0.34 cm(-1) and 1.93 for 5, and -0.35 cm(-1) and 1.99 for 6, where D is the axial zero-field splitting (anisotropy) parameter. Complexes 4-6 all exhibit frequency-dependent out-of-phase (chi" M) ac susceptibility signals suggesting them possibly to be single-molecule magnets (SMMs). Relaxation rate vs T data for complex 4 down to 1.8 K obtained from the chi" M vs T studies were supplemented with rate vs T data measured to 0.04 K via magnetization vs time decay studies, and these were used to construct Arrhenius plots from which was obtained the effective barrier to relaxation (Ueff) of 10.9 K. Magnetization vs dc field sweeps on single-crystals of 4.3CH2Cl2 displayed hysteresis loops exhibiting steps due to quantum tunneling of magnetization (QTM). The loops were essentially temperature-independent below approximately 0.3 K, indicating only ground-state QTM between the lowest-lying Ms = +/-6 levels. Complexes 4-6 are thus confirmed as the first triangular SMMs. High-frequency EPR spectra of single crystals of 4.3CH2Cl2 have provided precise spin Hamiltonian parameters, giving D = -0.3 cm(-1), B40 = -3 x 10(-5) cm(-1), and g = 2.00. The spectra also suggest a significant transverse anisotropy of E > or = 0.015 cm(-1). The combined work demonstrates the feasibility that structural distortions of a magnetic core imposed by peripheral ligands can "switch on" the properties of an SMM.     

Facile Synthesis of Derivatives of 1,1,3‐Trioxo‐2H,4H‐pyrrolo[1,2‐b][1,2,4,6]thiatriazine: A New Heterocyclic System

We reported a facile and efficient methodology to synthesize derivatives of pyrrolo[1,2‐b][1,2,4,6]thiatriazine (PTTD): a new bridgehead nitrogen heterocyclic system. Treatment of methyl pyrrole‐2‐carboxylate with N‐benzylsulfamoyl chlorides followed by subsequent hydrolysis reaction afforded 1‐benzylsulfamoyl‐1H‐pyrrole‐2‐carboxylic acids, which underwent ring‐closing reaction by treatment with diphenyl phosphorazidate via Curtius rearrangement; subsequent alkylation reaction afforded the desired 2,4‐disubstituted‐1,1,3‐trioxo‐2H,4H‐PTTDs.     

A novel undecametallic iron(III) cluster with an S = (11)/(2) spin ground state

The reaction of [NEt(4)](2)[Fe(2)OCl(6)] with sodium benzoate, 4,6-dimethyl-2-hydroxypyrimidine (dmhp), and 1,1,1-tris(hydroxymethyl)ethane (H(3)thme) gives the undecametallic compound [NEt(4)][Fe(11)O(4)(O(2)CPh)(10)(thme)(4)(dmhp)(2)Cl(4)]. X-ray crystallography, EPR spectroscopy, bulk magnetic susceptibility studies, and low-temperature single-crystal magnetic measurements were used to characterize the compound. Magnetic measurements indicate an S = (11)/(2) ground state with the parameters g = 2.03 and D = -0.46 cm(-)(1). Single-crystal magnetic studies show hysteresis of molecular origin at T < 1.2 K with fast quantum mechanical tunneling at zero field.     

Highly Diastereo‐ and Enantioselective Palladium‐Catalyzed [3+2] Cycloaddition of Vinyl Aziridines and α,β‐Unsaturated Ketones

A palladium‐catalyzed asymmetric [3+2] cycloaddition reaction of vinylaziridines with α,β‐unsaturated ketones, wherein the alkenes have a single activator, is realized in high diastereo‐ and enantioselectivity, thus affording 3,4‐disubstituted pyrrolidines in high yields with excellent ee values. The introduction of a methyl group at C1 of the vinyl group the vinylaziridines greatly improves the stereochemistry of the reaction. A plausible transition state is proposed.     

Antimony (III) Sulfate Catalyzed One-Pot Synthesis of 2,3-Disubstitutedindoles

A novel one-pot Fischer indole synthesis approach has been developed by using antimony (III) sulfate as the catalyst. Good yields were obtained after reacting phenylhydrazines hydrochlorides and ketones in refluxing methanol. The exclusive formation of 2,3- disubstituted indoles was observed in the reaction of ethyl methyl ketone with phenylhydrazines. One-pot synthesis of indole-3-propanol using dihydropyran has also been described. The use of reusable antimony (III) sulfate as a catalyst makes this method both economically and environmentally friendly.     

Kinetics and mechanism of hydrogen-atom abstraction from rhodium hydrides by alkyl radicals in aqueous solutions

The kinetics of the reaction of benzyl radicals with [L(1)(H(2)O)RhH{D}](2+) (L(1)=1,4,8,11-tetraazacyclotetradecane) were studied directly by laser-flash photolysis. The rate constants for the two isotopologues, k=(9.3±0.6) × 10(7) M(-1) s(-1) (H) and (6.2±0.3) × 10(7) M(-1) s(-1) (D), lead to a kinetic isotope effect k(H)/k(D)=1.5±0.1. The same value was obtained from the relative yields of PhCH(3) and PhCH(2)D in a reaction of benzyl radicals with a mixture of rhodium hydride and deuteride. Similarly, the reaction of methyl radicals with {[L(1)(H(2)O)RhH](2+) + [L(1)(H(2)O)RhD](2+)} produced a mixture of CH(4) and CH(3)D that yielded k(H)/k(D)=1.42±0.07. The observed small normal isotope effects in both reactions are consistent with reduced sensitivity to isotopic substitution in very fast hydrogen-atom abstraction reactions. These data disprove a literature report claiming much slower kinetics and an inverse kinetic isotope effect for the reaction of methyl radicals with hydrides of L(1)Rh.     

Positively charged GdIII cryptates: slow, associative water exchange

A combined variable-temperature and multiple field 17O NMR, EPR and NMRD study has been performed for the first time on gadolinium(III) complexes of cryptand ligands, L1 and L2, where L1 contains three 2,2'-bipyridine units ([bpy.bpy.bpy]) and L2 is the disubstituted methyl ester derivative of L1. The experimental data have been analysed in a simultaneous fit in order to determine parameters for water exchange, rotational dynamics and electronic relaxation for both complexes. The cryptates have three water molecules in the inner sphere which exchange with a rate of k(ex)298 = 1.8 x 10(6) s(-1) and 0.97 x 10(6) s(-1) for [GdL1(H2O)3]3+ and [GdL2(H2O)3)]3+, respectively. The k(ex)298 values obtained for these positively charged cryptates are smaller than those of the negatively charged Gd-poly(amino carboxylate) complexes. The water exchange mechanism was assessed for [GdL2(H2O)3]3+ by variable-pressure 17O NMR relaxation measurements. Based on the activation volume, DeltaV++ = -2.5 cm3 mol(-1), the water exchange is an associative interchange process. The proton relaxivities, r1, of the cryptate complexes are 9.79 mM(-1) s(-1) for [GdL1(H2O)3]3+ and 11.18 mM(-1) s(-1) for [GdL2(H2O)3]3+ (298 K, 20 MHz), which, due to the presence of three inner sphere water molecules, represent much higher values than those obtained for Gd3+ poly(amino carboxylate) complexes of similar molecular weight.     

Complexation of dimethylmagnesium with alpha-diimines; structural and EPR characterisation of single electron and alkyl transfer products

Treatment of dimethylmagnesium with the alpha-diimine ligands Ar'N=C(R)C(R)=NAr' [R = naphth-1,8-diyl (1), H (2), CH3 (3); Ar' = 2,6-diisopropylphenyl] in diethyl ether provides the neutral methyl-bridged dimeric complexes [(alpha-diimine-.)Mg+(mu-CH3)]2 via single electron transfer (SET) to the coordinated diimine and elimination of a methyl radical. These biradical species have been characterised by EPR spectroscopy and, for the ligand , X-ray crystallography. In the presence of THF the reaction of ligand proceeds to the diamagnetic [(ene-1,2-diamide)Mg(THF)3] complex in which the diimine ligand has been doubly reduced to an ene-diamide by two successive SET processes. Comparison of the structural data for the free ligand with that obtained for the alpha-diimine radical anion and ene-diamide complexes shows the expected increases in C-N, and decreases in C-C, bond lengths within the N-C-C-N unit consistent with the progressive reduction of the ligand. In the case of ligand , reaction at low temperature provides the complex [Mg(mu2-Me){Ar'NC(Me)2C(Me)NAr'}]2 in which methyl transfer to a ligand imine carbon atom has occurred. This species has also been structurally characterised. This contrasts with the formation of the radical species at room temperature, and indicates the involvement of an intermediate in which the radical products of the SET process are held in close proximity by the solvent cage. Two competing processes of methyl radical escape and methyl transfer to the ligand account for the formation of the observed products at different temperatures.     

Electron-nuclear double resonance spectroscopic evidence that S-adenosylmethionine binds in contact with the catalytically active [4Fe-4S](+) cluster of pyruvate formate-lyase activating enzyme

Pyruvate formate-lyase activating enzyme (PFL-AE) is a representative member of an emerging family of enzymes that utilize iron-sulfur clusters and S-adenosylmethionine (AdoMet) to initiate radical catalysis. Although these enzymes have diverse functions, evidence is emerging that they operate by a common mechanism in which a [4Fe-4S](+) interacts with AdoMet to generate a 5'-deoxyadenosyl radical intermediate. To date, however, it has been unclear whether the iron-sulfur cluster is a simple electron-transfer center or whether it participates directly in the radical generation chemistry. Here we utilize electron paramagnetic resonance (EPR) and pulsed 35 GHz electron-nuclear double resonance (ENDOR) spectroscopy to address this question. EPR spectroscopy reveals a dramatic effect of AdoMet on the EPR spectrum of the [4Fe-4S](+) of PFL-AE, changing it from rhombic (g = 2.02, 1.94, 1.88) to nearly axial (g = 2.01, 1.88, 1.87). (2)H and (13)C ENDOR spectroscopy was performed on [4Fe-4S](+)-PFL-AE (S = (1)/(2)) in the presence of AdoMet labeled at the methyl position with either (2)H or (13)C (denoted [1+/AdoMet]). The observation of a substantial (2)H coupling of approximately 1 MHz ( approximately 6-7 MHz for (1)H), as well as hyperfine-split signals from the (13)C, manifestly require that AdoMet lie close to the cluster. (2)H and (13)C ENDOR data were also obtained for the interaction of AdoMet with the diamagnetic [4Fe-4S](2+) state of PFL-AE, which is visualized through cryoreduction of the frozen [4Fe-4S](2+)/AdoMet complex to form the reduced state (denoted [2+/AdoMet](red)) trapped in the structure of the oxidized state. (2)H and (13)C ENDOR spectra for [2+/AdoMet](red) are essentially identical to those obtained for the [1+/AdoMet] samples, showing that the cofactor binds in the same geometry to both the 1+ and 2+ states of PFL-AE. Analysis of 2D field-frequency (13)C ENDOR data reveals an isotropic hyperfine contribution, which requires that AdoMet lie in contact with the cluster, weakly interacting with it through an incipient bond/antibond. From the anisotropic hyperfine contributions for the (2)H and (13)C ENDOR, we have estimated the distance from the closest methyl proton of AdoMet to the closest iron of the cluster to be approximately 3.0-3.8 A, while the distance from the methyl carbon to the nearest iron is approximately 4-5 A. We have used this information to construct a model for the interaction of AdoMet with the [4Fe-4S](2+/+) cluster of PFL-AE and have proposed a mechanism for radical generation that is consistent with these results.     

The Development of Copper‐Catalyzed Aerobic Oxidative Coupling of H‐Tetrazoles with Boronic Acids and an Insight into the Reaction Mechanism

The development of a highly efficient and practical protocol for the direct C?N coupling of H‐tetrazole and boronic acid was presented. A careful and patient optimization of a variety of reaction parameters revealed that this conventionally challenge reaction could indeed proceed efficiently in a very simple system, that is, just by stirring the tetrazoles and boronic acids under oxygen in the presence of different Cu^I or Cu^II salts with only 5 mol % loading in DMSO at 100 °C. Most significantly, the reaction could proceed very smoothly in a regiospecific manner to afford the 2,5‐disubstituted tetrazoles in high to excellent yields. A mechanistic study revealed that both tetrazole and DMSO are crucial for the generation of catalytically active copper species in the reaction process in addition to their role as reactant and solvent, respectively. It is demonstrated that in the reaction cycle, the Cu^I catalyst could be oxidized to Cu^II by oxygen to form a [CuT₂D] complex (T=tetrazole anion; D=DMSO) through an oxidative copper amination reaction. The Cu^II complex thus formed was confirmed to be the real catalytically active copper species. Namely, the Cu^II complex disproportionates to aryl Cu^III and Cu^I in the presence of boronic acid. Facile elimination of the Cu^III species delivers the C?N‐coupled product. The results presented herein not only provide a reliable and efficient protocol for the synthesis of 2,5‐disubstituted tetrazoles, but most importantly, the mechanistic results would have broad implications for the de novo design and development of new methods for Cu‐catalyzed coupling reactions.