电极表面第二配位环境对水氧化分子催化剂O–O键形成机理的调控

水氧化反应可以提供四个电子和四个质子,反应产物是可以资源化的氧气,因而,水氧化反应是大规模能源转化和存储技术理想的阳极反应.但是,由于水氧化反应具有较高的热力学能垒,涉及四个电子和四个质子的转移过程以及氧-氧键(O–O)的形成,是一个耗能高且动力学缓慢的复杂反应.因此,开发高效的水氧化催化剂来加速水氧化反应速率,对于能源转化和存储相关技术至关重要.然而,人们对水氧化催化剂的合理设计和在催化反应中提高反应活性的方法了解甚少,在温和条件下促进O–O键的有效形成仍然是一个根本性的挑战.迄今为止,关于水氧化分子催化剂的研究主要集中在催化剂的配位结构(第一配位环境)和催化效率之间的关系上,水氧化分子催化剂的第二配位环境对其催化活性的影响尚未得到充分研究.将催化剂引入到电极表面时,其催化环境和均相反应时完全不同.因此,水氧化催化剂在电极表面的催化反应动力学、质子耦合电子转移过程以及其O–O键形成机理可能发生改变.本文以4-乙烯基吡啶为轴向配体的[Ru(bda)](络合物1,bda=2,2’-联吡啶-6,6’-二羧酸)水氧化分子催化剂,通过电化学聚合的方法将络合物1固载在玻璃碳电极表面,用于研究第二配位环境对电极表面水氧化分子催化剂催化机理的影响.通过直接聚合络合物1在玻璃碳表面得到电极材料poly-1@GC;将4-三氟甲基苯乙烯和苯乙烯作为限制单元分别与络合物1共聚,得到电极材料poly-1+P3F@GC和poly-1+PSt@GC.通过一系列电极表面动力学方法和DFT计算分别求出催化剂在三种电极材料中的反应级数ρcata、催化剂的溶液质子-原子转移性质、催化剂的水氧化氘动力学同位素效应KIEs_H/D,以及[Ru(bda)]催化剂在不同材料中的偶极矩的变化.通过对比催化剂在不同电极材料中的催化行为和相关关键参数发现,电极表面催化剂的第二层配位环境对其水氧化反应过程中的O–O键形成机制和质子耦合电子转移过程有着显著的影响.[Ru(bda)]在直接聚合的电极材料poly-1@GC中,通过自由基耦合机理(I2M)形成O–O键.而当[Ru(bda)]与4-三氟甲基苯乙烯和苯乙烯共聚时,由于[Ru(bda)]催化剂被分散,不利于自由基耦合机理的发生,[Ru(bda)]在电极材料poly-1+P3F@GC和poly-1+PSt@GC中主要通过水分子亲核进攻机理进行(WNA)催化水氧化.同时,具有强偶极矩的4-三氟甲基苯基能够稳定[Ru(bda)]在催化过程的中间体,可以使引发O–O键生成的关键物种Ru^V=O的氧化电位发生明显的负向移动,使得[Ru(bda)]在poly-1+P3F@GC可以更容易触发水氧化反应,进而加快了[Ru(bda)]采用水分子亲核进攻机理时的催化反应速率.     

Recent advances in click-derived macrocycles for ions recognition

Triazole-containing macrocycles using Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition click reaction for ions recognition, including anions, metal ions and ions pair, have been reviewed.     

Oligobisvelcraplex: self-assembled linear oligomer by solvophobic pi-pistacking interaction of bisvelcrands based on resorcin[4]arene

[reaction: see text] Bisvelcrand 3 based on resorcin[4]arene was obtained by a stepwise route, and the formation of oligobisvelcraplex 3(n) by solvophobic pi-pistacking interaction was observed. (1)H NMR spectroscopic studies revealed that DeltaG(++)(pseudorotation) of oligobisvelcraplex 3(n) is 16.7 kcal mol(-1) in C(6)D(5)NO(2) solution. The pulsed field gradient spin-echo (PGSE) NMR experiment and VPO experiment showed that the number of aggregation (n) ranges from 7 to 10 in CHCl(3) solution at 298 K. In high concentration, bisvelcrand 3 tends to form gels or fiber.     

Enantioselective conjugate addition of dialkylzinc and diphenylzinc to enones catalyzed by a chiral copper(I) binaphthylthiophosphoramide or binaphthylselenophosphoramide ligand system

The enantioselective conjugate addition of dialkylzinc or diphenylzinc to enones was catalyzed by a copper(I)-axially chiral binaphthylthiophosphoramide or binaphthylselenophosphoramide ligand system at room temperature (20 degrees C) or 0 degrees C, affording the Michael adducts in high yields with excellent ee for cyclic and acyclic enones. The enantioselectivity and reaction rate achieved here are one of the best results yet for the Cu-catalyzed conjugate addition to enones. It was revealed that this series of chiral phosphoramides was a novel type of S,N-bidentate ligands on the basis of (31)P NMR and (13)C NMR spectroscopic investigations. The mechanism of this asymmetric conjugate addition system has been investigated as well. We found that the acidic proton of phosphoramide in these chiral ligands play a significant role in the formation of the active species. A bimetallic catalytic process has been proposed on the basis of previous literature. The linear effect of product ee and ligand ee further revealed that the active species is a monomeric Cu(I) complex bearing a single ligand [Cu(I):ligand 1:1].     

Diverse reactions of 1,4-dilithio-1,3-dienes with nitriles: facile access to tricyclic Delta1-bipyrrolines, multiply substituted pyridines, siloles, and (Z,Z)-dienylsilanes by tuning of substituents on the butadienyl skeleton

Addition cyclization of 1,2,3,4-tetrasubstituted 1,4-dilithio-1,3-dienes (Type I) with four equivalents of various aromatic nitriles in the presence of hexamethylphosphoramide (HMPA) gives exclusively fully substituted pyridines in moderate to good yields. Similarly, trisubstituted pyridines can be prepared by the reaction of 2,3-dialkyl- or diaryl-substituted 1,4-dilithio-1,3-dienes (Type II) with nitriles. However, five- or six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-dienes (Type III) reacted with various aromatic and aliphatic nitriles without alpha-hydrogen atoms to afford tricyclic Delta1-bipyrrolines in high yields. The reaction of six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-diene (Type III) with 2-cyanopyridine afforded the corresponding pyridine, and no tricyclic Delta1-bipyrroline was observed. Seven-membered-ring fused dilithiodienes reacted with PhCN or trimethylacetonitrile to afford the corresponding pyridines in good yield. When 1,2,3,4-tetrasubstituted dilithio reagents (Type I) were treated with Me3SiCN, a tandem silylation/intramolecular substitution process readily occurred to yield siloles, whereas the reaction of 2,3-disubstituted dilithio reagents (Types II and III) with Me3SiCN gave rise to (Z,Z)-dienylsilanes with high stereoselectivity. These results revealed that the formation of tricyclic Delta1-bipyrrolines, pyridines, siloles, and (Z,Z)-dienylsilanes are strongly dependent on the substitution patterns of the dilithio butadienes and the nature of the nitriles employed.     

Spectrophotometric study of interaction of iodine with 4'-aminobenzo-15-crown-5 in chloroform, dichloromethane and 1,2-dichloroethane solutions

The formation of charge transfer complex between 4'-aminobenzo-15-crown-5 (AB15C5) and iodine is investigated spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 degrees C. The continuous variation method clearly revealed the formation of 1:1 charge transfer complex in solution. The observed time dependence of the charge transfer band and subsequent formation of I 3- in solution were related to the slow transformation of the initially formed 1:1 AB15C5.I2 outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants for the transformation process were evaluated from the absorbance-time data and found to vary in the order of 1,2-DCE>DCM>CHCl3. The values of the formation constant, KDA, for each complex are evaluated from Benesi-Hilebrand equation. Stability of the resulting complex in three solvents was also found to vary in the order of 1,2-DCE>DCM>CHCl3.     

Synthesis, crystal structures and reactivity of copper(I) amidate complexes with aryl halides: insight into copper(I)-catalyzed Goldberg reaction

In this paper, copper(I) amidate complexes (2-3), proposed intermediates in copper-catalyzed Goldberg reaction, have been prepared and characterized by elemental analysis, IR, (1)H NMR and X-ray crystallography. Ancillary ligand bis(diphenylphosphino)ferrocene (dppf) has contributed greatly to the stability of the copper-amidate complexes due to its strong chelating ability and weak intermolecular interactions. Thermal gravimetric analyses are carried out to determine the thermal competency of complexes 2-3 as the intermediates of the high-temperature Goldberg reactions. Reaction of complexes 2 and 3 with aryl halides generates the N-arylation products 5-8, accompanied by the formation of a copper(I) complex Cu(dppf)X (X = I or Br) 4, which has been determined by LC-MS analysis. These results provide new evidence for the mechanism of copper(I)-catalyzed Goldberg reaction.     

Electron transfer. 157. Reactions of hypervalent manganese species with S(2) metal-ion reductants

Solutions of the complexes of hypervalent manganese, [Mn(III)(C(2)O(4))(3)](3)(-) (in oxalate buffers), [Mn(IV)(bigH)(3)](4+) (in biguanide buffers), and [(bipy)(2)Mn(III)(O)(2)Mn(IV)(bipy)(2)](3+) (in bipyridyl buffers) may be reduced by s(2) center reductants In(I), Sn(II), and Ge(II), yielding Mn(II) quantitatively. In all cases, rates are determined by the initial act of electron transfer, giving an s(1) transient (In(II), Sn(III), or Ge(III)); subsequent steps are rapid and kinetically silent. The In(I)-Mn(III) and Ge(II)-Mn(III) reactions are inhibited by added oxalate, whereas the Sn(II)-(Mn(III)Mn(IV)) reaction is strongly accelerated by Cl(-). The In(I)-Mn(IV) reaction is complicated by formation of a 1:1 addition compound In(I).Mn(IV). We find no evidence for two-unit steps in any of these systems.     

C-S bond formation reaction between a phenolate and disulfide-bridged dicopper(I) complexes

A novel C-S bond formation reaction took place, when a lithium phenolate derivative was treated with a disulfide-bridged dicopper(I) complex or a bis(micro-thiolato)dicopper(II) complex under very mild conditions. The reaction has been suggested to proceed via a disulfide-bridged (micro-phenoxo)dicopper(I) complex as the common reaction intermediate. Copper(II) complexes of the modified ligands containing a thioether group (products of the C-S bond formation reaction) have been isolated and structurally characterized by X-ray analysis as model compounds of the active site of galactose oxidase. Mechanism of the C-S bond formation reaction is also discussed in relation to the biosynthetic mechanism of the organic cofactor Tyr-Cys of galactose oxidase.     

Reactions forming and recyclizing heterocycles

It has been shown that 1,3-thiazolidine-2,4-dione and 1,3-oxazolidine-2,4-dione react with hydrazine with a rearrangement of the ring to form a triazolinone ring. In each case, the reaction begins with the formation of an ionic adduct of hydrazine with the azolidinedione. On heating, the adduct undergoes decyclization (water catalyzes the process). The further course of the reaction is governed by the temperature and pH of the medium, which determine whether dehydration of the intermediate product with the formation of a triazolinone ring (in acid media) or rearrangement into a 1-acylsemicarbazide (at elevated temperatures) predominates. The influence of substituents in the thiazolidinone ring on the course of the reaction has been studied.For Communication I, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 7, pp. 991–996, July, 1970.     

Reaction of arylthallium (III) compounds with Copper (II) and (I) cyanides. Synthesis of aryl cyanide

Various kinds of arylthallium(III) salts react with copper (II) or (I) cyanide in acetonitrile or pyridine to give the corresponding aryl cyanides in good yield. In acrylonitrile the reaction using copper(I) cyanide was revealed to be of an ionic concerted intermolecular and not radical type.     

The formation of 3(or 5)-methylcyclopent-2-en-2-ol-1-one from acetone

The original observation that 3(or 5)-methylcyclopent-2-en-2-ol-1-one (I) was formed (in low yield) by the treatment of glycidaldehyde with acetone in the presence of aqueous alkali, and speculations concerning the reaction mechanism, led to the realization that the reaction could also be carried out with glyceraldehyde. This suggested an explanation for the previously known formation of I by drastic alkali-treatment of carbohydrates.     

Novel Bis- and Mono-Pyrrolo[2,3-d]pyrimidine and Purine Derivatives: Synthesis,Computational Analysis and Antiproliferative Evaluation

Novel symmetrical bis-pyrrolo[2,3-d]pyrimidines and bis-purines and their monomers were synthesized and evaluated for their antiproliferative activity in human lung adenocarcinoma (A549), cervical carcinoma (HeLa), ductal pancreatic adenocarcinoma (CFPAC-1) and metastatic colorectal adenocarcinoma (SW620) cells. The use of ultrasound irradiation as alternative energy input in Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) shortened the reaction time, increased the reaction efficiency and led to the formation of exclusively symmetric bis-heterocycles. DFT calculations showed that triazole formation is exceedingly exergonic and confirmed that the presence of Cu(I) ions is required to overcome high kinetic requirements and allow the reaction to proceed. The influence of various linkers and 6-substituted purine and regioisomeric 7-deazapurine on their cytostatic activity was revealed. Among all the evaluated compounds, the 4-chloropyrrolo[2,3-d]pyrimidine monomer 5f with 4,4′-bis(oxymethylene)biphenyl had the most pronounced, although not selective, growth-inhibitory effect on pancreatic adenocarcinoma (CFPAC-1) cells (IC₅₀ = 0.79 µM). Annexin V assay results revealed that its strong growth inhibitory activity against CFPAC-1 cells could be associated with induction of apoptosis and primary necrosis. Further structural optimization of bis-chloropyrrolo[2,3-d]pyrimidine with aromatic linker is required to develop novel efficient and non-toxic agent against pancreatic cancer.     

Rh(I)-catalyzed Pauson-Khand reaction and cycloisomerization of allenynes: selective preparation of monocyclic, bicyclo[m.3.0], and bicyclo[5.2.0] ring systems

[reaction: see text] Rhodium(I)-catalyzed PKR of allenynes was found to be applicable for constructing azabicyclo[5.3.0]decadienone as well as oxabicyclo[5.3.0]decadienone frameworks. In addition, a reliable procedure for constructing a 10-monosubstituted bicyclo[5.3.0]deca-1,7-dien-9-one ring system by the rhodium(I)-catalyzed PKR of allenynes was developed under the condition of 10 atm of CO. Investigation of the rhodium(I)-catalyzed cycloisomerization of 4-phenylsulfonylnona-2,3-dien-8-ynes under nitrogen atmosphere gave the corresponding cyclohexene derivatives, whereas the C1-homologated allenynes produced cycloheptene derivatives and/or bicyclo[5.2.0]nonene skeletons depending on the substitution pattern at the allenic terminus. Thus, proper choice of the starting allenynes and reaction conditions led to the selective formation of 2-phenylsulfonylbicyclo[5.3.0]deca-1,7-dien-9-ones (Pauson-Khand-type product), 3-alkylidene-1-phenylsulfonyl-2-vinylcycloheptene derivatives, and bicyclo[5.2.0]nonene frameworks.     

Mechanistic studies of the O2-dependent aliphatic carbon-carbon bond cleavage reaction of a nickel enolate complex

The mononuclear nickel(II) enolate complex [(6-Ph(2)TPA)Ni(PhC(O)C(OH)C(O)Ph]ClO(4) (I) was the first reactive model complex for the enzyme/substrate (ES) adduct in nickel(II)-containing acireductone dioxygenases (ARDs) to be reported. In this contribution, the mechanism of its O(2)-dependent aliphatic carbon-carbon bond cleavage reactivity was further investigated. Stopped-flow kinetic studies revealed that the reaction of I with O(2) is second-order overall and is ～80 times slower at 25 °C than the reaction involving the enolate salt [Me(4)N][PhC(O)C(OH)C(O)Ph]. Computational studies of the reaction of the anion [PhC(O)C(OH)C(O)Ph](-) with O(2) support a hydroperoxide mechanism wherein the first step is a redox process that results in the formation of 1,3-diphenylpropanetrione and HOO(-). Independent experiments indicate that the reaction between 1,3-diphenylpropanetrione and HOO(-) results in oxidative aliphatic carbon-carbon bond cleavage and the formation of benzoic acid, benzoate, and CO:CO(2) (～12:1). Experiments in the presence of a nickel(II) complex gave a similar product distribution, albeit benzil [PhC(O)C(O)Ph] is also formed, and the CO:CO(2) ratio is ～1.5:1. The results for the nickel(II)-containing reaction match those found for the reaction of I with O(2) and provide support for a trione/HOO(-) pathway for aliphatic carbon-carbon bond cleavage. Overall, I is a reasonable structural model for the ES adduct formed in the active site of Ni(II)ARD. However, the presence of phenyl appendages at both C(1) and C(3) in the [PhC(O)C(OH)C(O)Ph](-) anion results in a reaction pathway for O(2)-dependent aliphatic carbon-carbon bond cleavage (via a trione intermediate) that differs from that accessible to C(1)-H acireductone species. This study, as the first detailed investigation of the O(2) reactivity of a nickel(II) enolate complex of relevance to Ni(II)ARD, provides insight toward understanding the chemical factors involved in the O(2) reactivity of metal acireductone species.     

Initial nucleation of platinum clusters after reduction of K(2)PtCl(4) in aqueous solution: a first principles study

The initial nucleation of platinum clusters after the reduction of K(2)PtCl(4) in aqueous solution is studied by means of first principles molecular dynamics simulations. A reaction mechanism leading to a Pt dimer is revealed both by gas-phase simulations and by simulations which model the solution environment. The key step of the observed reaction process is the formation of a Pt-Pt bond between a Pt(I) complex and an unreduced Pt(II) complex. In light of this result, we discuss the reduction process leading to the formation of platinum nanoparticles. In the generally accepted model, the nucleation of Pt particles starts only when a critical concentration of Pt(0) atoms is reached. Here, we discuss a complementary mechanism where metal-metal bonds form between Pt complexes in higher oxidation states. This is consistent with a number of experimental results which show that a high concentration of zerovalent atoms is not necessary to start the nucleation.     

Me3SiN(PPh3)-ICN]: a new labile donor-acceptor complex

The reaction behavior of trimethylsilyl phosphanimine, Me3SiNPPh3, toward the pseudohalogen species XCN (X = Cl, Br, and I), especially the intermediate formation of [Me3SiN(PPh3)-XCN] adduct complexes, was investigated in solution. Only the ICN adduct was shown to be metastable in solution, with respect to further reaction into Ph3PNCN and Me3SiX, and can be intercepted. Raman and X-ray data of the ICN adduct revealed a very labile donor-acceptor complex with the iodine atom of the ICN moiety loosely bound to the nitrogen atom of Me3SiNPPh3. There are two distinct rather long N...I bonds with bond lengths of 2.634(1) and 2.739(14) A. The structure and bonding are discussed on the basis of natural bond orbital analysis and valence bond considerations.     

Supramolecular catalysis at work: diastereoselective synthesis of a molecular bowl with dynamic inner space

The supramolecular assistance to Pd(0)/Cu(I)-catalyzed cyclotrimerization of stannylated norbornene 7 has been investigated to give molecular bowl 1syn in a stereoselective fashion. Following a divergent strategy, racemic norbornene 7 was synthesized in satisfactory yield. Self-coupling, promoted by Pd(0)/Cu(I) catalysis acting in synergy with CsF, yielded molecular bowl 1syn in a moderate 30% yield. The reaction diastereoselectivity is affected by the concentration of Cu(I) and Cs+: increasing quantities of the cations enhanced the syn/anti ratio of the isolated cyclotrimer from statistical (1:3) to a more desirable (4.5:1) ratio, in favor of the molecular bowl 1syn. 1H NMR spectroscopic studies suggested the coordinating affinity of 1syn toward transition metals Cu(I), Ag(I), and Au(I), to account for the observed templation effect. In particular, the tridentate 1syn has been shown to bind to one Ag(I) cation in the assembly process that is driven with enthalpy (Delta H degrees = -19 +/- 2 kcal/mol, Delta S degrees = -45 eu). The complete coordination was not cooperative, and was hypothesized to be impeded with the adverse entropy. Accordingly, density functional theory (BP86) calculations of 1syn and its mono-, bis-, and tris-Ag(I) complexes suggested that the coordination of one to three silver cations is highly exothermic. The calculations also revealed that the bowl constriction is necessary for the aromatic arms to become preorganized and bind to a silver cation(s) (Delta E approximately 8 kcal/mol). Ultimately, Ag(I) has been shown to assist the diastereoselective formation of 1syn, lending support to the notion of template-directed synthesis.     

Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents

The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 degrees C. The results indicate the formation of 1:1 charge-transfer complexes. The observed time dependence of the charge-transfer band and subsequent formation of I(3)(-) in solution were related to the slow transformation of the initially formed 1:1 antipyrine:I(2) outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.     

Quantum chemical simulation of the reaction of methane with gold(I) acetylacetonate and aquaacetylacetonate complexes

The interaction between methane and gold(I) acetylacetonate via electrophilic substitution (reaction (I)) and oxidative addition (reaction (II)) is simulated. In both cases, the formation of the products is thermodynamically favorable: the decrease in energy is 31 kcal/mol for reaction (I) and 26 kcal/mol for reaction (II). The product of reaction (II) is additionally stabilized by Au-H interaction. Both reactions have a low activation barrier and proceed via the formation of structurally different methane complexes reducing the energy of the system by 9.3 kcal/mol for reaction (I) and by 10.9 kcal/mol for reaction (II). The complex [Au(H₂O)(acac)] is also capable of forming methane complexes. These complexes result from a thermally neutral reaction and turn into products after overcoming a low energy barrier. The structure of the complex activating methane in the gold-rutin system is deduced from the data obtained.