Molecular structure and internal rotation potential of perfluoro (2,4-dimethyl-3-oxa-2,4-diazapentane), (CF3)2N–O–N(CF3)2

Ab initio quantum chemical calculation were performed on R₂N–O–NR₂ type (R=H, F, CH₃ and CF₃) molecules, using the HF, B3LYP and MP2/6-31G* levels of theory. The equilibrium structures and the internal rotation potentials have been determined. Three stable conformers were found for R=H, F and CH₃ while only two in case of R=CF₃. The rotation potential energy curves do not change significantly upon fluorination. The calculations suggests that in the ED measurement of the title compound the NC and NO bond length might have been interchanged.     

Theoretical study on the reaction mechanisms of ethylene with Cp2TiR, Cp2Ti(Cl)R, and Cp2Ti(Cl:AlH2Cl)R (R=H and CH3)

The potential energy surfaces for reactions of ethylene with Cp₂Ti⁺R, Cp₂Ti(Cl)R, and Cp₂Ti(Cl:AlH₂Cl)R (R=H and CH₃) were calculated by ab initio molecular orbital methods. These six reaction mechanisms were compared. Of the two possible reaction paths, attack of ethylene at Ti and the Cl and R ligands (path IN) and that from the opposite side of the Cl ligand (path OUT), the former is found to be more favorable, with a very low activation energy for reaction of ethylene with Cp₂Ti(Cl)H. For reaction of ethylene with Cp₂Ti(Cl)CH₃, the insertion transition states on both paths have almost the same energy barrier height above the reactants. For reaction of ethylene with Cp₂Ti(Cl:AlH₂Cl)R, the bond alternation between Ti–Cl and Cl–Al plays an important role in the mechanisms.     

Normal coordinate analysis of MSiH3 moieties in transition metal complexes and comparison to results obtained for silyl halides

In order to examine the influence of the transition metal on the metal-silyl fragment MSiH₃ and the metal-silicon bond, polarized Raman spectra of the complexes (C₅R₅)(CO)₂FeSiH₃ R = H (Cp) (1a), Me (Cp^*) (1b)], (C₅H₅)(CO)(PPh₃)FeSiH₃ (1c), (C₅Me₅)(CO)₂RuSiH₃ (2), (C₅R₅)(CO)₂(PMc₃)MoSiH₃ [R = H (3a), Me (3b)], and (C₅R₅)(CO)₂(PMe₃)WSiH₃ [R = H(4a), Me (4b)] have been recorded. The spectral data have been evaluated and interpreted on the basis of a normal coordinate analysis of the MSiH₃ core and the derived force constants and potential energy distributions were compared to results obtained for analogous halogen derivatives in the series XSiH₃ [X = Br (5), I (6)].     

A comparative study on the nature and strength of O–O, S–S, and Se–Se bond

A computational study on dichalcogenide molecules (R₂X₂; X = O, S, Se; R = H, CH₃, NH₂) has been carried out employing B3LYP and MP2 levels using 6-31+G*, 6-311+G*, 6-311++G**, and PVDZ basis sets. The relative energies have been evaluated at G2MP2 also. The rotational barriers and bond dissociation energies indicate that S–S bond is stronger than Se–Se and O–O bond. NBO analysis at MP2/6-31+G* suggest the presence of partial π character between X–X bond that decreases in the order S–S > Se–Se > O–O. Fuki functions for nucleophilic and electrophilic attack fail to distinguish the reactivity of S and Se. The proton affinities of the O₂H₂, S₂H₂, Se₂H₂ decrease in the order Se > S > O.     

Iminophosphine-palladium(0) complexes as catalysts in the alkoxycarbonylation of terminal alkynes

In the presence of methanesulfonic acid, the palladium(0)-olefin complexes: [Pd(η²-ol)(P---N)] [ol=dimethyl fumarate or fumaronitrile, P---N=1-(Ph₂P)C₆H₄-2-CH=NR (R=CMe₃ or C₆H₄OMe-4)] catalyse the alkoxycarbonylation of terminal alkynes. Moderately good rates are obtained when the catalysts are promoted with two equivalents of the free P---N ligand and a large excess of acid at 120°C. The catalytic data suggest that derivatives of the type [Pd(alkyne)(P---N)_n] (n=2–3) are the active catalytic species.     

Ab initio and DFT computer studies of complexes of trimethylphosphine and products of substituted phosphonium cations with hydroxide, chloride and fluoride anions: Phosphorus analogues of choline and acetylcholine

Theoretical calculations (DFT, MP2) are reported for up to four sets of reaction products of trimethylphosphine, (CH₃)₃P, each with H₂O, HCl and HF together with DFT calculations on up to three sets of reaction products of substituted phosphonium cations, (CH₃)₃P–R⁺. These products comprise (a) P(III) normal complexes (CH₃)₃PHY, (b) P(IV) ‘reverse’ complexes Y(H–CH₂)₃P–R, (c) P(IV) ylidic complexes YHCH₂(CH₃)₂P–R and (d) P(V) covalent compounds Y–P(CH₃)₃–R for Y=HO, Cl and F and R=H, CH₃, C₂H₅, C₂H₄OH and C₂H₄OC:OCH₃. Calculations are carried out at the B3LYP/6-31+G(d,p) level in all cases and also at the MP2/6-31+G(d,p) level for systems in which R=H. Minimum energy structures are determined for predicted complexes or structures and geometrical properties, harmonic vibrations and BSSE corrected binding energies are reported and compared with the limited experimental information available. Potential energy scans predict equilibria between covalent trigonal bipyramidal P(V) forms and reverse complexes comprising hydrogen bonded or ion pair, tetrahedral P(IV) forms separated by low potential energy barriers. Similar scans are also reported for equilibria between reverse complexes and ylidic complexes for Y=OH and R=CH₃, C₂H₅, C₂H₄OH and C₂H₄OC:OCH₃. Corrected binding energies, structures and values of harmonic modes are discussed in relation to bonding The names ‘pholine’ and ‘acetylpholine’ are suggested for phosphorus analogues to choline and acetylcholine.     

单层石墨相氮化碳负载Pt4团簇吸附O2的第一性理论研究

采用第一性原理密度泛函理论结合周期性平板模型模拟研究了Pt₄团簇吸附单层石墨相氮化碳(g-C₃N₄)的几何结构和电子性质,以及氧气在其表面上的吸附行为。同时,对比分析了氧气在纯净的石墨相氮化碳和Pt₄团簇上的吸附行为。计算结果表明, Pt₄团簇吸附在3-s-三嗪环石墨相氮化碳表面,并与四个边缘氮原子成键,形成两个六元环时为最稳定构型。Pt₄团簇倾向于吸附在三嗪环石墨相氮化碳的空位并与邻近三个氮原子成键。由于Pt与N原子较强的杂化作用,以及金属与底物之间较多电子转移增强了Pt₄团簇吸附g-C₃N₄的稳定性。另外,对比分析了氧气在纯净的g-C₃N₄和金属吸附的g-C₃N₄上吸附行为,发现金属原子的加入促进了电子转移,同时拉长了O―O键长。Pt₄吸附3-s-三嗪环g-C₃N₄比Pt₄吸附三嗪环g-C₃N₄表现出微弱的优势,表现出明显的基底扭曲以及较大的吸附能。这些结果表明,化学吸附通过调节电子结构和表面性质增强催化性能的较好方法。     

XVI. (2,5-C4Bu2RHN)MCl3 (M = Ti, Zr, Hf; R = H, SiMe3)—Azacyclopentadienyl-Komplexe der Gruppe 4-Metalle

The azacyclopentadienyl compounds (2,5-C₄^tBu₂RHN)MCl₃ (M = Ti, Zr, Hf; R = H, SiMe₃) have been prepared as stable solids from the lithiated pyrroles and MCl₄. The π-coordination of the azacyclopentadienyl ligands, as suggested from ¹³ C NMR data, has been confirmed for (2,5-C₄^tBu₂H₂N)TiCl₃ by an X-ray diffraction study.     

锗硅烯与CH3OH加成反应机理及区域选择性

采用密度泛函理论方法,在B3LYP/6-311++G(d, p)水平,研究了几种锗硅烯与CH₃OH的加成反应的微观机理和势能剖面,分析了锗硅烯中Si=Ge双键的极性对加成反应区域选择性的影响.研究结果表明,锗硅烯可分别与CH₃OH的单聚体或二聚体发生加成反应.所有加成反应均从初始亲核或亲电复合物的形成开始.母体锗硅烯H₂Si=GeH₂与CH₃OH二聚体的加成反应比其与CH₃OH单聚体的相应反应在动力学上更容易些,但在其它锗硅烯与CH₃OH的反应中情况则相反.用Ph或SiMe₃基团取代H₂Si=GeH₂中的H原子在动力学上使反应变得不利且SiMe₃基团的影响更显著.加成反应的区域选择性与锗硅烯中Si=Ge双键的极性以及Si-O(Ge-H)和Ge-O (Si-H)键的相对强弱都有关.     

铂钌团簇及电荷对甲醇活性的理论研究

采用密度泛函理论(DFT)对钌掺杂的铂团簇阳离子([Pt_nRu_m]⁺, m + n = 3, n ≥ 1)活化甲醇C―H和O―H键反应进行了理论研究;探讨了电荷对[Pt_nRu_m]团簇反应活性的影响。电荷分析表明:(1) [Pt₃]⁺团簇中正电荷在三个Pt原子上均匀分布;掺杂Ru原子后,正电荷主要分布在Ru原子上; (2)首先活化C―H键时[Pt_nRu_m]⁺的反应活性比[Pt_nRu_m]明显提高;首先活化O―H键时只有[Pt₃]⁺比[Pt₃]团簇的反应活性有明显提高。本研究可为金属团簇调控的C―H键和O―H键的活化提供更深入的理解。     

The molecular structure of N-sulfinyl trimethylsilanamine, (CH3)3SiNSO

The geometric structure of (CH₃)₃Si---NSO in the vapour phase has been determined by gas electron diffraction. The molecule possesses a planar Si---N=S=O skeleton with syn conformation. The Si(CH₃)₃ group staggers the N=S double bond. The following skeletal parameters (r_a distances and angles with 3σ errors limits) were obtained: Si---N 1.750(6)Å, N=S 1.508(5)Å, S=O 1.444(4)Å, Si---N=S 133.9(9)°, N=S=O 122.5(10)°. Ab initio calculations (HF/3−21G*) were performed for H₃Si---NSO and confirm the planar syn structure for sulfinyl silanamines.     

一氯·四(对甲氧基苯基)卟啉合锰(Ⅲ)的分子和晶体结构

氯代四(对甲氧苯基)卟啉合锰(Ⅲ)的晶体属于正交晶系,空间群为P_bca。晶胞参数:a=23.3973(6)Å,b=22.5524(7)Å,c=15.1043(2)Å。V=7970.02ų,Z=8。收集衍射强度在Nicolet XRD R3系列四圆衍射仪上进行。数据收集范围3°< 2θ < 45°,以ω扫描,用MoK_α射线,共收集到独立衍射点5200个,可观察点2859个(Ⅰ>3σ(Ⅰ))。重原子法测定结构,用方块矩阵最小二乘法修正结构参数,Mn-N的平均键长为2.005Å,Mn-Cl的键长为2.370(3)Å。     

CpRu(PPh3)2SSiiPr3与SCNR(R=Ph,1-Naphthyl)反应的结构、成键与机理的理论研究

应用密度泛函理论(DFT), 通过CpRu(PH₃)₂SSiⁱPr₃ (Cp＝环戊二烯负离子; ⁱPr＝异丙基)与SCNH模型化反应, 探讨了CpRu(PPh₃)₂SSiⁱPr₃ 与SCNR (R＝苯基, 萘基)的反应机理, 分析了反应所涉及的各相关化合物的结构与成键特征. 反应中首先失去一个膦配体, 生成一个中间体. 该中间体中, 硫原子采取sp²杂化, 硫原子剩余的一个p轨道与金属中心上的d轨道具有相同的对称性, 因而该p轨道上的孤电子对可与金属中心上的d轨道形成π键, 导致Cp环中心, Ru, S1, P和Si原子在同一平面内, 而不是S1, P和Si原子偏离该平面. 计算结果预测, S＝C双键中的p键打开, 生成含金属中心的四元环螯合物一步为反应的决速步骤. 空间位阻的减小、p共轭体系的生成以及螯合环的存在, 是导致该反应热力学有利的重要原因.     

Heterobimetallic Mo---Sn complexes. Reactions of [Mo(CO)3(CH3CN)2(Cl)(SnRCl2)] (R = Me, Ph) with 4(4-XC6H4)3 (X = Cl, F, H, Me, MeO)

Three families of heterobimetallic compounds were obtained by reaction of [Mo(CO)₃(CH₃CN)₂(Cl)(SnRCl₂)] (R = Ph, Me) with P(4-XC₆H₄)₃ (X = Cl, F, H, Me, MeO). The type of compound obtained dependent on the solvent and concentration of the starting compound. So, [Mo(CO)₂(CH₃COCH₃)₂(PPh₃)(Cl)(SnRCl₂)]·nCH₃COCH₃ (R = Ph, n = 0.5; R = Me, n = 1) (type I) and [Mo(CO)₃{P(4-XC₆H₄)₃}(μ-Cl)(SnRCl₂)]₂ (R = Ph, X = Cl, F, H, Me, MeO; R = Me, X = Cl, F) (type II) were isolated from acetone solution in ca 0.05 M and 0.1 M concentrations, respectively. However, [Mo(CO)₃(CH₃CN) {P(4-XC₆H₄)₃}(Cl)(SnRCl₂)] (R = Ph, X = H; R = Me, X = Cl, F, H) (type III) were obtained from dichloromethane solution independently of the concentration used. All new complexes showed a seven-coordinate environment at molybdenum, containing Mo---Cl and Mo---Sn bonds. Mössbauer spectra indicated a four-coordination at tin for type III complexes.     

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen : XLV. Eigenschaften und Reaktionsverhalten von Hydrogenchalkogenid-Komplexen der Metalle Chrom, Molybdän und Wolfram

Hydrogensulfido and hydrogenselenido complexes of general composition (η⁵-C₅R₅(CO)3M(EH) (R = H, CH₃; M = Cr, Mo, W; E = S, Se) react at the EH functions by deprotonation, bimolecular elimination of H₂E, or by loss of the chalcogen atoms E. Reactions with Lewis-acidic complex cations such as [((η⁵-C₅R₅)(CO)₃M]⁺ (R = H, CH₃; M = Mo, W) are useful for the synthesis of chalcogen bridged compounds (μ-E)[(η⁵-C₅R₅)(CO)₃M]₂. The heterodinuclear chalcogen bridge complexes thus generated form metathesis equilibria with their corresponding homodinuclear systems.     

铂钌团簇活化甲醇C―H和O―H键的理论研究

采用密度泛函理论研究了Pt_nRu_m (n+m=3, n≠0)团簇活化甲醇C―H和O―H键的反应活性和机理. 分别给出以O―H和C―H键活化为初始步骤的势能曲线. 计算结果表明反应是以C―H键的活化为初始步骤; 三种团簇与甲醇反应的活性顺序为Pt₂Ru>Pt₃>PtRu₂. 前线轨道分析表明Pt_nRu_m团簇活化初始的C―H和O―H键的活化过程是质子转移(PT). 此外还讨论了溶剂化对反应的影响. 本研究可为C―H键和O―H键的活化提供更深入的理解, 为甲醇活化反应催化剂选择以及其使用条件的优化提供新思路.     

钒硼双原子阳离子活化甲烷研究

Methane activation by transition metal species has been extensively investigated over the past few decades. It is observed that ground-state monocations of bare 3d transition metals are inert toward CH₄ at room temperature because of unfavorable thermodynamics. In contrast, many mono-ligated 3d transition metal cations, such as MO⁺ (M = Mn, Fe, Co, Cu, Zn), MH⁺ (M = Fe, Co), and NiX⁺ (X = H, CH₃, F), as well as several bis-ligated 3d transition metal cations including OCrO⁺, Ni(H)(OH)⁺, and Fe(O)(OH)⁺ activate the C―H bond of methane under thermal collision conditions because of the pronounced ligand effects. In most of the above-mentioned examples, the 3d metal atoms are observed to cooperate with the attached ligands to activate the C―H bond. Compared to the extensive studies on active species comprising of middle and late 3d transition metals, the knowledge about the reactivity of early 3d transition metal species toward methane and the related C―H activation mechanisms are still very limited. Only two early 3d transition metal species HMO⁺ (M = Ti and V) are discovered so far to activate the C―H bond of methane via participation of their metal atoms. In this study, by performing mass spectrometric experiments and density functional theory calculations, we have identified that the diatomic vanadium boride cation (VB⁺) can activate methane to produce a dihydrogen molecule and carbon-boron species under thermal collision conditions. The strong electrostatic interaction makes the reaction preferentially proceed the V side. To generate experimentally observed product ions, a two-state reactivity scenario involving spin conversion from high-spin sextet to low-spin quartet is necessary at the entrance of the reaction. This result is consistent with the reported reactions of 3d transition metal species with CH₄, in which the C―H bond cleavage generally occurs in the low-spin states, even if the ground states of the related active species are in the high-spin states. For VB⁺ + CH₄, the insertion of the synergetic V―B unit (rather than a single V or B atom) into the H₃C―H bond causes the initial C―H bond activation driven by the strong bond strengths of V―CH₃ and B―H. The mechanisms of methane activation by VB⁺ discussed in this study may provide useful guidance to the future studies on methane activation by early transition metal systems.     

Synthesis and reactions of H3Ru3(μ3-CSet)(CO)9. Reductive elimination of C---H bonds and insertion of alkynes into Ru---C and Ru---H bonds

Synthesis of H₃Ru₃(μ₃-CSEt)(CO)₉, is accomplished by base-promoted attack of ethanethiol on H₃Ru₃(μ₃-CBr)(CO)₉. Thermolysis of this product under CO yields HRu₃(CH₂SEt)(CO)₉. Reactions of H₃Ru₃(μ₃-CSEt)(CO)₉ with alkynes C₂R₂ form HRu₃(μ₃-η³-EtSCCRCR)(CO)₉ (R = Me or Ph) and Ru₃ (cis-CR=CHR)(CSEt)(CO)₉ (R = Me). The chemistry of H₃Ru₃(μ₃-CSEt)(CO)₉ differs significantly from that of the analogous ether derivative H₃Ru₃(μ₃-COMe)(CO)₉.     

Theoretical studies on the metathesis processes, (Tp(PH3)MR(eta 2-H[bond]CH3)]-->[Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe,Ru, and Os; R=H and CH3)

Theoretical calculations on the metathesis process, [Tp(PH3)MR(eta 2-H[bond]CH3)] --> [Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe, Ru, and Os; R=H and CH3), have been systematically carried out to study their detailed reaction mechanisms. Other than the one-step mechanism via a four-center transition state and the two-step mechanism through an oxidative addition/reductive elimination pathway, a new one-step mechanism, with a transition state formed under oxidative addition, has been found. Based on the intrinsic reaction coordinate calculations, we found that the trajectories of the transferring hydrogen atom in the metathesis processes studied are similar to each other regardless of the nature of reaction mechanisms.     

Synthesis and X-ray structure of (η-C5H5)2W2Ir2(CO)7(CHCO2Et)2, a tetrahedral heterometal cluster with two different environments for ethylcarboxylatocarbene ligands

The tetrahedral heteronuclear cluster complex (η⁵-C₅H₅)₂W₂Ir₂(CO)₁₀ reacts with N₂CHCO₂R (R = Et, Me) at room temperature to form the dicarbene species (η⁵-C₅H₅)₂W₂Ir₂(CO)₇(CHCO₂R)₂. An X-ray diffraction study (R = Et) shows an intact tetrahedral metal framework with two distinct sites for the CHCO₂Et ligands. The first uses its carbon atom to bridge the Ir---Ir bond; the second uses its carbon atom to bridge an Ir---W bond and, additionally, forms a donor bond from a carbonyl oxygen atom to the second tungsten atom.