Bond length and the electron density at the bond critical point: X--X, Z--Z, and C--Z bonds (X = Li-F, Z = Na-Cl)

The aim was to investigate the relationship between the bond length and the electron density at the bond critical point in homonuclear X--X and Z--Z and heteronuclear C--Z bonds (X = Li-F, Z = Na-Cl). The d,rho(c) pairs were obtained from 472 target bonds in DFT-optimized (B3LYP/6-311+G(d,p)) small molecular species. These species were selected arbitrarily but with a view to maximize the range widths WR for each atom combination. It was found that (i) with one clear exception, the d(A - A) means (A = X or Z) correlate linearly with the bond lengths d(A(2)) of the respective diatomic molecules; (ii) the d(A - A) means correlate parabolically with n, the formal number of valence electrons in the atoms of the bond; and (iii) with increasing sample size N the ratio WR(rho(c))/WR(d) appears to converge toward a representation f [WR(rho(c))/WR(d)](N-->infinity) characteristic of A. Detailed analysis of the d,rho(c) relationship has shown that by and large simple power regression accounts best for the DFT data. The regression coefficients of d = arho(c) (-b) and rho(c) = alphad(-beta) (b, beta > 0) vary with n in a seemingly irregular manner but one that is consistent with simple chemical notions. The d(A(2)) can be approximated in terms of multilinear MO electron occupancies.     

一维链状[Mn(9-AC)_2(4,4′-bpy)(H_2O)_2]_n配位聚合物的合成及晶体结构

在水热条件下(120℃),将醋酸锰、4,4′-联吡啶(4,4′-bpy)与9-蒽酸(9-HAC)反应,得到了配位聚合物[Mn(9-AC)2(4,4′-bpy)(H2O)2]n,通过元素分析、红外光谱、X射线单晶衍射对其进行了表征,并用TGA研究了该配位聚合物的热稳定性.结构解析结果表明,该晶体属于正交晶系,Fdd2空间群,a=1.66772(12)nm,b=3.36471(16)nm,c=1.1687(4)nm,V=6.558(2)nm3,Z=8,Mr=689.60,Dc=1.397Mg/m3,R=0.0356,wR2=0.0604.在该配位聚合物中,中心锰原子采取略微变形的八面体构型,与两种配体共同构筑了一维直线形链结构,链与链之间通过氢键相互作用构筑成三维超分子网络.     

烯虫酯的立体选择性全合成

以香茅醛为起始原料, 通过羟醛缩合反应和Reformatskii反应得到3,7,11-三甲基-2,4,10-十二碳三烯酸异丙酯的双键顺反异构体混合物, 经苯硫酚两次催化双键顺反异构化, (2E,4E)-异构体3a的含量由原来的26%提高到85%. 再通过醚化反应, 立体选择性地全合成了具有保幼激素活性的昆虫生长调节剂烯虫酯及其异构体, 即11-甲氧基-3,7,11-三甲基-2,4-十二碳二烯酸异丙酯. 其中具有较高生物活性的(2E,4E)-异构体的含量达85%. 各步所合成的化合物的结构经IR, MS和NMR证实.     

烃类化合物碳氢键解离焓的密度泛函理论研究

通过比较10种密度泛函方法对烃类化合物碳氢键解离焓的计算精度, 发现新型密度泛函BMK方法具有最高的计算精度. 利用该方法计算了包含饱和链烃,、不饱和链烃、脂环烃和芳香烃在内的172个烃类化合物的碳氢键解离焓,计算均方根误差仅为7.95 kJ•mol^－1, 线性拟合常数为0.985. 通过自然键轨道法分析发现, 烃类物质的碳氢键解离焓与母体的碳氢键杂化轨道成分p%, 自由基奇电子轨道杂化成分p%及自由基的自旋密度三个参数之间存在较好的定量关系. 此外, 饱和链烷烃及不饱和链烃的碳氢键解离焓与碳氢键键长之间也存在较好的线性关系.     

Supramolecular assemblies based on some new methyl-substituted cucurbit[5]urils through hydrogen bonding

Three supramolecular assemblies based on three new partial methyl-substituted cucurbit[5]urils, which are tetramethylcucurbit[5]uril (α,γ-TMeQ[5]), hexamethyl cucurbit[5]uril (α,β,δ-HMeQ[5]), Nonamethylcucurbit[5]uril (NMeQ[5]), were synthesized and structurally characterized by single-crystal X-ray diffractions. For the comparison with these new Q[5]s, crystal structure of an assembly constructing with normal Q[5] and K₂PtCl₆ was also reported. They are (α,γ-TMeQ[5])·15(H₂O) (1), (α,β,δ-HMeQ[5])·2Cl⁻·2(H₃O)⁺·7(H₂O) (2), (NMeQ[5])·14(H₂O) (3), (4). In the corresponding crystal structures, the molecular encapsulates included a water molecule and lidded water molecules at both of the portals were observed. Moreover, these molecular encapsulates are connected through hydrogen bonding and formed supramolecular chains or joined in pair.     

Functionalized fluoroalkyl and alkenyl silanes: Preparations, reactions, and synthetic applications

Preparations, reactions, and synthetic applications of functionalized fluoroalkyl and alkenyl silanes have been summarized. This review focuses mainly on the chemistries of (1) 1-substituted difluoromethylsilanes (XCF₂SiR₃), (2) 1-substituted 2,2-difluorovinylsilanes (CF₂CXSiR₃), (3) trifluoroisopropenyl, trifluoroacetimidoyl, and trifluoroacetyl silanes [CF₃C(SiR₃)X, XCH₂, NAr, O] and (4) other fluorinated alicyclic silanes.     

New organobimetallic compounds containing catecholate and o-semiquinolate ligands

New organobimetallic compounds CatSn[CpM(CO)_n]₂ (2-4) were obtained by the insertion of CatSn(II) (1) into the metal-metal bond of [CpM(CO)_n]₂ (Cat - 3,6-di-tert-butylcatecholate dianion; M = Fe (2), n = 2; M = Mo (3), W (4), n = 3). The structure of CatSn[CpMo(CO)₃]₂ was determined by X-ray analysis. The oxidation of compounds 2-4 with silver(I) triflate was found to produce stable paramagnetic o-semiquinolate derivatives which keep both Sn-M bonds. New paramagnetic tin(IV) complexes were investigated by EPR spectroscopy.     

Synthesis and applications of a new palladacycle as a high active catalyst in the Suzuki couplings

The reaction of biphenyl-based phosphine P(o-C₆H₄Me)Ph₂ (1) with Pd(OAc)₂ in toluene affords the air and water stable palladacycle (2) as a binuclear compound which has been characterized by multi-nuclear NMR spectroscopy and elemental analysis as a mixture of cis and trans isomers with relative intensity of 1:3, respectively. This palladacycle is a highly efficient catalyst precursor for the coupling of aryl boronic acids and aryl halides. Both activated and deactivated aryl bromides and chlorides are efficiently coupled in the presence of 2 to furnish the corresponding cross-coupled products in excellent yields, and a wide variety of functional groups are tolerated in aryl halides. This methodology has also been extended for the coupling of bromoarylphosphines and bromoarylphosphine oxides with aryl boronic acids for the generation of hindered corresponding products.