Structural and kinetic studies on uranyl(V) carbonate complex using 13C NMR spectroscopy

We have measured 13C NMR spectra of uranyl(V) carbonate complex in D2O solution containing 1.003 M Na2(13)CO3 at various temperatures. Two singlet signals corresponding to free and coordinated CO3(2-) were observed at 169.13 and 106.70 ppm, respectively. From the peak area ratio, the structure of the uranyl(V) carbonate complex was determined as [U(V)O2(CO3)3]5-. Furthermore, kinetic analyses of the exchange reaction of free and coordinated CO3(2-) in [U(V)O2(CO3)3]5- were carried out using 13C NMR line-broadening. As a result, the first-order rate constant at 298 K and the activation parameters for CO3(2-) exchange reaction in [U(V)O2(CO3)3]5- were evaluated as 1.13 x 10(3) s(-1) and deltaH(double dagger) = 62.0 +/- 0.7 kJ x mol(-1), deltaS(double dagger) = 22 +/- 3 J x mol(-1) x K(-1), respectively. We suggest that the exchange follows a dissociative mechanism as in the corresponding [U(VI)O2(CO3)3]4- complex.     

Carbon dioxide fixation by an unprecedented hydroxo lead-chromium carbonyl complex: synthesis, reactivity, and theoretical calculations

The novel hydroxo-bridged dimeric lead-chromium carbonyl complex [Et4N]2[{PbCr2(CO)10}2(mu-OH)2] ([Et4N]2[1]) was synthesized from the reaction of PbCl2 and Cr(CO)6 followed by metathesis with [Et4N]Br in a KOH/MeOH solution. The X-ray crystallographic structure shows that dianion 1 consists of two Pb{Cr(CO)5}2 units bridged by two hydroxo fragments in which the Pb atoms are further coordinated with two Cr(CO)5 groups, resulting in a distorted tetrahedral geometry. A CO2 molecule can insert itself into dianion 1 to form two new carbonate complexes, [Et(4)N]2[{PbCr2(CO)10}(CO3)] ([Et4N]2[2]) and [Et4N]2[{PbCr2(CO)10}2(CO3)] ([Et4N]2[3]), depending on the reaction conditions. In addition, complex 2 can be transformed into 3 in CH2Cl2 solution at an elevated temperature. While the carbonate group in dianion 2 is bonded to one Pb atom, which is coordinated with two Cr(CO)5 fragments, the carbonate group in 3 bridges the two Pb centers in a mu-1kappa2OO':2kappa2OO' fashion in which each Pb atom is further bonded to two Cr(CO)5 moieties. Complexes 2 and 3 can be converted back the hydroxo complex 1 under appropriate conditions. All three unprecedented lead-chromium compounds, 1-3, were fully characterized by spectroscopic methods and single-crystal X-ray diffraction analyses. The nature and formation of complexes 1-3 were also examined by molecular orbital calculations using the B3LYP method of the density functional theory.     

Ag_2~-催化CO氧化反应机理的理论研究

用密度泛函理论B3LYP方法详细研究了Ag_2~-催化CO氧化反应的机理.计算结果表明,O2分子在Ag_2~-和Au_2~-上吸附能相差不大,而CO分子在Ag_2~-上吸附要比在Ag_2~-上弱得多.Ag_2~-催化CO氧化反应共有四条反应途径.最可能反应通道为CO插入Ag2O_2~-中的Ag—O键形成中间体[Ag—AgC(O—O)O]-,然后直接分解形成产物CO2和Ag2O-,或另一分子CO进攻中间体[Ag—AgC(O—O)O]-形成两分子产物CO2和Ag_2~-.在动力学上最难进行的反应通道为经历碳酸根双银中间体,需要克服约0.24eV的能垒.Ag_2~-催化CO氧化反应活性要高于Au_2~-.     

Mechanism of formation of organic carbonates from aliphatic alcohols and carbon dioxide under mild conditions promoted by carbodiimides. DFT calculation and experimental study

Dicyclohexylcarbodiimide (CyN=C=NCy, DCC) promotes the facile formation of organic carbonates from aliphatic alcohols and carbon dioxide at temperatures as low as 310 K and moderate pressure of CO2 (from 0.1 MPa) with an acceptable rate. The conversion yield of DCC is quantitative, and the reaction has a very high selectivity toward carbonates at 330 K; increasing the temperature increases the conversion rate, but lowers the selectivity. A detailed study has allowed us to isolate or identify the intermediates formed in the reaction of an alcohol with DCC in the presence or absence of carbon dioxide. The first step is the addition of alcohol to the cumulene (a known reaction) with formation of an O-alkyl isourea [RHNC(OR')=NR] that may interact with a second alcohol molecule via H-bond (a reaction never described thus far). Such an adduct can be detected by NMR. In alcohol, in absence of CO2, it converts into a carbamate and a secondary amine, while in the presence of CO2, the dialkyl carbonate, (RO)2CO, is formed together with urea [CyHN-CO-NHCy]. The reaction has been tested with various aliphatic alcohols such as methanol, ethanol, and allyl alcohol. It results in being a convenient route to the synthesis of diallyl carbonate, in particular. O-Methyl-N,N'-dicyclohexyl isourea also reacts with phenol in the presence of CO2 to directly afford for the very first time a mixed aliphatic-aromatic carbonate, (MeO)(PhO)CO. A DFT study has allowed us to estimate the energy of each intermediate and the relevant kinetic barriers in the described reactions, providing reasonable mechanistic details. Calculated data match very well the experimental results. The driving force of the reaction is the conversion of carbodiimide into the relevant urea, which is some 35 kcal/mol downhill with respect to the parent compound. The best operative conditions have been defined for achieving a quantitative yield of carbonate from carbodiimide. The role of temperature, pressure, and catalysts (Lewis acids and bases) has been established. As the urea can be reconverted into DCC, the reaction described in this article may further be developed for application to the synthesis of organic carbonates under selective and mild conditions.     

Crystal structures and topological aspects of the high-temperature phases and decomposition products of the alkali-metal oxalates M2[C2O4] (M=K, Rb, Cs)

The high-temperature phases of the alkali-metal oxalates M2[C2O4] (M = K, Rb, Cs), and their decomposition products M2[CO3] (M = K, Rb, Cs), were investigated by fast, angle-dispersive X-ray powder diffraction with an image-plate detector, and also by simultaneous differential thermal analysis (DTA)/thermogravimetric analysis (TGA)/mass spectrometry (MS) and differential scanning calorimetry (DSC) techniques. The following phases, in order of decreasing temperature, were observed and crystallographically characterized (an asterisk denotes a previously unknown modification): *alpha-K2[C2O4], *alpha-Rb2[C2O4], *alpha-Cs2[C2O4], alpha-K2[CO3], *alpha-Rb2[CO3], and *alpha-Cs2[CO3] in space group P6(3)/mmc; *beta-Rb2[C2O4], *beta-Cs2[C2O4], *beta-Rb2[CO3], and *beta-Cs2[CO3] in Pnma; gamma-Rb2[C2O4], gamma-Cs[C2O4], gamma-Rb2[CO3], and gamma-Cs2[CO3] in P2(1)/c; and delta-K2[C2O4] and delta-Rb2[C2O4] in Pbam. With respect to the centers of gravity of the oxalate and carbonate anions, respectively, the crystal structures of all known alkali-metal oxalates and carbonates belong to the AlB2 family, and adopt either the AlB2 or the Ni2In arrangement depending on the size of the cation and the temperature. Despite the different sizes and constitutions of the carbonate and oxalate anions, the high-temperature phases of the alkali-metal carbonates M2[CO3] (M = K, Rb, Cs), exhibit the same sequence of basic structures as the corresponding alkali-metal oxalates. The topological aspects and order-disorder phenomena at elevated temperature are discussed.     

温和条件下电催化CO2与环氧丙烷合成碳酸丙烯酯

 在常温常压下研究了CO2的电化学活化及其与环氧丙烷反应合成碳酸丙烯酯,考察了支持电解质对碳酸丙烯酯产率的影响. 结果表明,含有Br-的支持电解质对合成碳酸丙烯酯起到明显的催化效果. 在实验研究基础上,对反应机理进行了初步推测,认为Mg2+起到路易斯酸的作用并与环氧丙烷的氧原子配位,同时Br-作为亲核试剂进攻环氧丙烷的 C-O 键使其断裂开环,形成的中间物与CO2还原产生的活化物质结合形成碳酸丙烯酯.     

Synthesis of 5,5-diallyl-substituted oxazolidin-2-one derivatives,based on reductive diallylation of amino acids

An efficient synthesis of 5,5-diallyl-substituted oxazolidinone derivatives, based on reductive diallylation of available α-amino acids, was developed. It was demonstrated that the obtained oxazolidinones can be readily converted into the corresponding derivatives of 3-azaspiro[4,4]-non-7-en-2-one via the metathesis reaction in the presence of the 1st generation Grubbs catalyst.

     

CO_2和丙三醇直接合成碳酸甘油酯的新方法

报道了一种以CO_2和丙三醇为原料,Cs_2CO_3为碱,DMF为溶剂,bmimBF_4为增溶剂,直接合成碳酸甘油酯(GC)的新方法。在最优反应条件[丙三醇5 mmol,Cs_2CO_310 mmol,CH_2Cl_25 m L,bmimBF_41 m L,DMF 5 m L,P(CO_2)1 MPa,于100℃反应24 h]下,GC收率76%,其结构经1H NMR和ESI-MS确证。在最优条件下进行50倍放大实验,GC收率72%。     

The Reaction of the Bis-spirocyclic Phosphazene [N 3 P 3 (O 2 C 12 H 8 ) 2 Cl 2 ] (O 2 C 12 H 8 = 2,2′-Dioxybiphenyl) with Thiophenols,in the Presence of Alkali Carbonates

The reactions of the spirocyclic phosphazene [N 3 P 3 (O 2 C 12 H 8 ) 2 Cl 2 ] (O 2 C 12 H 8 = 2,2'-dioxybiphenyl) with the thiophenols HS--C 6 H 4 --R and M 2 CO 3 (M = K or Cs) in refluxing acetone gave respectively the spirocyclic substituted derivatives [N 3 P 3 (O 2 C 12 H 8 ) 2 (SC 6 H 4 --R) 2 ] R = H ( 2a ), Br ( 2b ), OMe ( 2c ), NO 2 ( 2d ). The reaction is a two-step process the second of which is much faster than the first and the monosubstituted intermediate [N 3 P 3 (O 2 C 12 H 8 ) 2 (SC 6 H 4 --R)Cl] cannot be detected. By contrast, in the analogous reactions with the phenols HO--C 6 H 4 --R and M 2 CO 3 (M = K or Cs) in acetone or THF, to give the known derivatives [N 3 P 3 (O 2 C 12 H 8 ) 2 (OC 6 H 4 --R) 2 ], the first step is faster although both are very dependent on R, M and the solvent. Thus, in the case of the phenol HO--C 6 H 4 --OMe the reaction conditions could be adjusted to give the useful synthetic intermediate monosubstituted derivative [N 3 P 3 (O 2 C 12 H 8 ) 2 (OC 6 H 4 --OMe)Cl] ( 3 ). The reaction of [N 3 P 3 (O 2 C 12 H 8 ) 2 Cl 2 ] with the bifunctional reagent mercaptophenol HS--C 6 H 4 --OH was not specific and led to mixtures of cyclic and oligomeric products.     

离子液体中CO_2与炔醇在温和条件下高效合成-亚甲基环状碳酸酯

本文研究了离子液体1-乙基-3-甲基咪唑二乙基磷酸酯([EMIM][(EtO)2PO2])中醋酸银(AgOAc)对CO2与炔醇反应生成-亚甲基环状碳酸酯的催化性能,发现该反应可以在温和的条件下进行.在AgOAc/[EMIM][(EtO)2PO2]催化体系中,30℃、4 MPa CO2压力下,反应6h时-亚甲基环状碳酸酯的产率为97%;当压力降到0.5 MPa时,反应24 h产物产率为65.8%.[EMIM][(EtO)2PO2]在反应中起到了溶剂和碱的双重作用.AgOAc/[EMIM][(EtO)2PO2]体系重复利用3次活性仅略有下降.另外,该体系也可用于催化CO2与其他炔醇(3-甲基-1-戊炔-3-醇、3,5-二甲基-1-己炔-3-醇和2-苯基-3-丁炔-2-醇)的反应.     

Front Cover: Facile Multicomponent Synthesis of Oxazolidinones from Primary Amines and Cesium (Hydrogen)Carbonate (Eur. J. Org. Chem. 27/2023)

A facile multicomponent, catalyst-free oxazolidinone synthesis from primary aliphatic or aromatic amines, dibromoethane (DBE), and the usage of either cesium carbonate or cesium hydrogencarbonate as the simultaneous base and C1 source is reported. The applicability of this technically simple reaction was demonstrated by a broad scope with generally high yields, enabling concise late-stage functionalization of amino groups into N-substituted oxazolidinones. The proposed operating reaction mechanism consists of a first-step nucleophilic substitution reaction between DBE and the primary amine, followed by the formation of a carbamate or carbonate intermediate and subsequent cyclization. Additional versatility of the herein-developed protocol has been showcased in a medicinal chemistry approach by the generation of an oxazolidinone-modified dipeptidyl peptidase 8 (DPP8) inhibitor.     

Proximal regioselectivity of the O,O'-dialkylation of tetrahydroxyketocalix[4]arene

The only dialkylated products obtained in the reaction of tetrahydroxyketocalixarene 2a with MeI/K(2)CO(3) or PhCH(2)Br/K(2)CO(3) are the corresponding proximal (i.e., 1,2) O,O'-dialkyl ethers, in contrast to the parent tetrahydroxycalix[4]arene 1a which affords the distal (1,3) dialkyl ether derivatives. Pairs of geminally alkylated phenoxy groups in the conformationally rigid dibenzylated and tetrabenzylated derivatives are oriented in an anti fashion. These results can be rationalized assuming that the 1,3-alternate arrangement of the rings preferred by 2a is adopted during all the intermediate stages of the alkylation. The NMR spectra (in CDCl(3)) of the monomethyl, dimethyl, trimethyl, and tetramethyl ether derivatives of 2a are in agreement with a 1,3-alternate conformation.     

Fine-tuning of metallaborane geometries: chemistry of iridaboranes derived from the reaction of

From reaction of [(Cp*Ir)2HxCl(4-x)] (x=1, 0) and LiBH4, arachno-[[Cp*IrH2]B3H7](1) is produced in moderate yield concurrently with [Cp*IrH4]. In contrast, reaction of [(Cp*Ir)2H2Cl2] with LiBH4 results in arachno-[[Cp*IrH]2(mu-H)B2H5] (3) in high yield at room temperature but a mixture of 1 and [[Cp*IrH]2(mu-H)BH4] (2) at 0 degrees C. BH3 x THF converts 1 to arachno-[(Cp*IrHB4H9] (4) and 2 to 3 with 1 as a minor product. Further, reaction of 3 with excess of BH3 x THF results in formation of nido-[[Cp*Ir]2-(mu-H)B4H7] (6) formed by loss of H2 from the intermediate arachno-[[Cp*IrH]2B4H8] (5). Reaction of 1 with [Co2(CO)8] permits the isolation of two metallaboranes, arachno-[[Cp*Ir(CO)]-B3H7] (7) and nido-[1-[Cp*Ir]-2,3-Co2-(CO)4(mu-CO)B3H7] (8). Treatment of 4 with [Co2(CO)8] gives only one single mixed-metal metallaborane nido-[1-[Cp*Ir]-2-Co(CO)3B4H7 (9) in high yield. Finally, pyrolysis of 8 results in loss of hydrogen and formation of pileo-[1-[Cp*Ir]-2,3-Co2(CO)5B3H5] (10) with a BH-capped square-pyramidal structure. With kinetic control rational synthesis of a variety metallaboranes has been achieved by varying the number of chlorides in the monocyclopentadienylmetal halide dimer, reaction temperature, types of monoborane, and metal fragment sources.     

Pt羰基簇合物在NaY内的合成机理

利用IR，EXAFS, ~(13)CO同位素交换反应及与NO作用等手段研究了Pt羰基簇合物[Pt_3(CO)_6]~(2-)_n(n＝3,4)在NaY分子筛超笼内的合成机理．在氧化样品Pt~(2+)/NaY上300－373 K的还愿羰基化过程中，首先Pt~(2+)与CO反应生成PtO(CO)物种(波数σ_(CO)＝2110 cm~(-1))，然后聚集成“Pt_3(CO)_6”(σ_(CO)＝2112，1896和1841 cm~(-1))，最后生成深绿色的Pt羰基簇合物Pt_(12)(CO)_(24)]~(2-)/NaY(σ_(CO)＝2080，1824 cm~(-1))．“Pt_3(CO)_6”的羰基在室温下能迅速地与~(13)CO发生交换，而[Pt_3(CO)_6]~(2-)_n(n＝3,4)的羰基与~(13)CO的同位素交换即使在343 K也进行得很慢，室温下，NO能逐步破坏Pt羰基簇合物的层间和层内Pt－Pt键，得到中间物种“Pt_3(CO)_6”和PtO(CO)，同时在气相产生CO_2和N_2O．而由上述两中间物种出发，300－353 K温度下，在CO气氛中的还原羰基化又能可逆地得到原羰基簇合物．     

从超临界二氧化碳和甲醇直接合成碳酸二甲酯

Dimethyl carbonate (DMC), an environmentally benign intermediate for organic synthesis, has been mainly synthesized through non-phosgene route of oxidative carbonylation[1]. Direct synthesis of DMC from carbon dioxide and methanol is of more significance due to atom economy. Organometallic compounds of formulae R2M(OR)2, M(OR)2 or M(OR)4[2,3] were employed as catalysts in direct synthesis of DMC, where an activation mechanism of CO2 insertion into metal-oxygen bond was supposed. Unfortunately, the yield of DMC was low even in the presence of chemical dehydrants because mainly of thermodynamic limit.     

Inclined N2 desorption in a steady-state N2O + CO reaction on Pd(110)

The angular and velocity distributions of desorbing products were analyzed in the course of a catalyzed N2O + CO reaction on Pd(110). The reaction proceeded steadily above 450 K, and the N2 desorption merely collimated sharply along 45 degrees off the surface normal toward the [001] direction. It is proposed that this peculiar N2 desorption is induced by the decomposition of adsorbed N2O oriented along the [001] direction. On the basis of the observation of similar inclined N2 desorption in both NO + CO and N2O + CO reactions, the N2 formation via the intermediate N2Oa dissociation was confirmed in catalytic NO reduction.     

Preparation and wittig reactions of organotrifluoroborato phosphonium ylides

[reaction: see text] Potassium [(trifluoroboratophenyl)methyl]triphenylphosphonium chlorides have been prepared from the corresponding benzyl chlorides and PPh3. In the presence of 1.2 equiv of K2CO3 and various aldehydes, these mixed salts are easily converted to the corresponding unsaturated organotrifluoroborates via the intermediate phosphorus ylides. A protocol for a one-pot transformation has also been developed.     

甲醇和碳酸丙烯酯合成碳酸二甲酯的研究

采用浸渍法以ZrO2为载体，以碱金属氢氧化物和碳酸盐为前驱体制备了不同的固体碱催化剂，在温和反应条件下考察了催化剂的酯交换扳应性能，并通过BET、XRD和CO2－TPD等方法对催化剂进行了表征，结果表明：Na2CO3负载到不同载体上，其催化性能明显不同，Na2CO3/ZrO2催化剂获得了较高的酯交换活性。载体的比表面和孔结构与催化剂的反应活性无一定的依存关系。而催化剂表面的酸碱性是影响酯交换活性的重要因素。     

Synthesis and P-P cleavage reactions of [P(X)X']2; X-ray structures of [Co[P(X)X'](CO)3] and P4[P(X)X']2[X = N(SiMe3)2, X'= NPri2

Treatment of P(X)(X')Cl with KC8 gave the crystalline diphosphine [P(X)X']2 (1) which dissociated reversibly into the phosphinyl radical *P(X)X' (2), a plausible intermediate in the reaction of with [Cr(CO)6], [Co(NO)(CO)3] or P4, yielding [Cr[P(X)X']2(CO)3] (3), [Co[P(X)X'](CO)3] (4), or 1,4-P4[P(X)X']2 (5); the P(X)X' substituent is pyramidal at P in but planar in [X = N(SiMe3)2, X'= NPri2].