选择性控制的配体工程在金团簇催化中的作用

金团簇表面的硫醇配体影响着团簇的催化性质,尤其是选择性.我们采用在真空条件下通过程序升温的方法逐渐剥除金团簇表面的硫醇配体来制备催化剂,利用透射电镜,红外光谱对催化剂结构进行表征,以硝基化合物催化还原反应为模型反应,详细研究了配体对催化活性和选择性的影响.研究发现因配体被剥离导致底物更容易接近团簇表面,最终使得反应转换率大幅升高.实验结果还表明金团簇催化剂催化不同官能团取代的底物显示了良好的官能团兼容性,有吸电子效应的硫配体使团簇表面带正电荷,进而避免苯胺衍生物的产生.     

Dinuclear Dy2 Single‐Molecule Magnets: Functional Modulation on the Bridging Ligand and Different Relaxation Performances within the Single‐Crystal to Single‐Crystal System

Crystal structures, single‐molecule magnetic behavior, and ab initio calculations of four new phenoxo‐bridged dinuclear dysprosium complexes and their gadolinium(III) analogues are explored. Complexes [Dy₂(DMOMP)₂(DBM)₄]₂ ? CHCl₃ ( 1 ; DMOMP=1‐methyl‐3,5‐dimethoxy‐4‐hydroxybenzene, DBM=1,3‐diphenylpropane‐1,3‐dione); [Dy₂(DMOAP)₂(DBM)₄]₂ ? CHCl₃ ( 2 ; DMOAP=syringaldehyde); Dy₂(DMOEP)₂(DBM)₄ ( 3 ; DMOEP=methyl syringate); and solvent‐free Dy₂(DMOMP)₂(DBM)₄ ( 4 ), which is obtained by the transformation of single crystal into single crystal from 1 , have nearly identical core structures and only differ in the substituents at the para position of the phenol moieties of the bridging ligand. In this system, the electronic effects are efficiently implemented to significantly modify the ligand field strength and exchange coupling by modulating the substituents on the phenol backbone. The effective energy barrier (U_eff) of magnetization reversal is improved significantly to fivefold magnitude, at most, and the hysteresis temperature up to 3.5 K by deliberately using the electron‐withdrawing substituent to replace the electron‐donating one. The origin of the two relaxation processes in 1 is mostly attributed to the existence of two molecules in one unit, which is illuminated by means of the transformation of single crystal into single crystal.     

Tunable Chiroptical Properties from the Plasmonic Band to Metal–Ligand Charge Transfer Band of Cysteine‐Capped Molybdenum Oxide Nanoparticles

Understanding the interactions between a semiconducting nanocrystal surface and chiral anchoring molecules could resolve the mechanism of chirality induction in nanoscale and facilitate the rational design of chiral semiconducting materials for chiroptics. Now, chiral molybdenum oxide nanoparticles are presented in which chirality is transferred via a bio‐to‐nano approach. With facile control of the amount of chiral cysteine molecules under redox treatment, circular dichroism (CD) signals are generated in the plasmon region and metal–ligand charge‐transfer band. The obtained enhanced CD signals with tunable lineshapes illustrate the possibility of using chiral molybdenum oxide nanoparticles as potentials for chiral semiconductor nanosensors, optoelectronics, and photocatalysts.     

Direct HPLC separation of carnosine enantiomers with two chiral stationary phases based on penicillamine and teicoplanin derivatives

Carnosine is present in high concentrations in specific human tissues such as the skeletal muscle, and among its biological functions, the remarkable scavenging activity toward reactive carbonyl species is noteworthy. Although the two enantiomers show almost identical scavenging reactivity toward reactive carbonyl species, only d ‐carnosine is poorly adsorbed at the gastrointestinal level and is stable in human plasma. Direct methods for the enantioselective analysis of carnosine are still missing even though they could find more effective applications in the analysis of complex matrices. In the present study, the use of two different chiral stationary phases is presented. A chiral ligand‐exchange chromatography stationary phase based on N,S‐dioctyl‐d‐ penicillamine resulted in the direct enantioseparation of carnosine. Indeed, running the analysis at 25°C and 1.0 mL/min with a 1.5 mM copper(II) sulfate concentration allowed us to obtain separation and resolution factors of 3.37 and 12.34, respectively. However, the use of a copper(II)‐containing eluent renders it hardly compatible with mass spectrometry detectors. With the teicoplanin‐based stationary phase, a mass spectrometry compatible method was successfully developed. Indeed, a water/methanol 60:40 v/v pH 3.1 eluent flowed at 1.0 mL/min and with a 25°C column temperature produced separation and resolution factors of 2.60 and 4.16, respectively.     

Caging the mercurous ion: a tetradentate tripodal nitrogen ligand enhances stability and J(1H199Hg)

The dimeric mercurous ion has been encapsulated by a pair of the tetradentate tripodal nitrogen ligands tris[(2-(6-methylpyridyl))methyl]amine (TLA). The complex [Hg₂(TLA)₂](ClO₄)₂ (1) was isolated directly from an acetonitrile solution of Hg(ClO₄)₂ 3H₂O and TLA. Complex 1 crystallizes in the triclinic space group with a = 10.537(2) Å, b = 10.751(2) Å, c = 10.907(2) Å, = 75.20(3), = 73.73(3), = 75.73(3), and Z = 1. The cation is located an inversion center. The Hg–Hg and Hg–N_amine bond distances are 2.5469(8) and 2.297(6) Å, respectively, and the average Hg–N_pyridyl bond length is 2.75(7) Å. Complex 1 was stable indefinitely in acetonitrile-d ₃ solution, permitting detection of 13 and 22 Hz heteronuclear couplings between the Hg(I) ions and the methylene protons of the ligand. Comparisons with the structures and spectroscopic properties of related mercuric and mercurous complexes are made.     

Room temperature ligand fragmentation in the reaction between PhCCo3(CO)9 and Ph2PN(Me)N(Me)PPh2. X-ray diffraction structure of PhCCo3(CO)8[Ph2PP(O)Ph2]

The cobalt cluster PhCCo₃(CO)₉ reacts with the bis(phosphanyl)hydrazine ligand bis(diphenylphosphino)dimethylhydrazine (dppdmh) in CH₂Cl₂ with added Me₃NO to give the monosubstituted cluster PhCCo₃(CO)₈[Ph₂PP(O)PPh₂] as the major isolable product. The solid-state structure of this new cluster was unequivocally established by X-ray diffraction analysis, which has confirmed the presence of a noncoordinated (O)PPh₂ moiety. PhCCo₃(CO)₈[Ph₂PP(O)Ph₂] crystallizes in the triclinic space group P , a = 12.036(2), b = 12.037(2), c = 15.124(3) Å, = 84.82(1)°, = 89.44(2)°, = 60.09(1)°, V = 1890.0(6) ų, Z = 2, and d_calc = 1.540 g/cm³.     

Pincer ligand coordination at Co3 and Ru6 clusters: Syntheses, reactivity studies, and X-ray diffraction structures of [PhCCo3(CO)8]2(dppx) and [Ru6(μ6-C)(CO)16]2(dppx)

The reaction of the pincer diphosphine ligand 4,6-bis(diphenylphosphinomethyl)-m-xylene (dppx) with the metal cluster compounds PhCCo₃(CO)₉ and Ru₆(μ₆-C)(CO)₁₇ has been explored. Both clusters react with dppx to afford the simple substitution products [PhCCo₃(CO)₈]₂(dppx) and [Ru₆(μ₆-C)(CO)₁₆]₂(dppx), where two cluster units are tethered by the pincer ligand. The molecular structures of the title products and the 2:1 cluster-pincer ligand stoichiometry have been established by X-ray crystallography. The stability of [PhCCo₃(CO)₈]₂(dppx) and [Ru₆(μ₆-C)(CO)₁₆]₂(dppx) has been investigated under gentle thermolysis conditions (ca. 55–65°C). Both dppx-substituted clusters are unstable with [PhCCo₃(CO)₈]₂(dppx) decomposing and [Ru₆(μ₆-C)(CO)₁₆]₂(dppx) transforming into the diphosphine-bridged cluster Ru₆(μ₆-C)(CO)₁₅(μ-dppx) as the major observable product. The identity of the latter cluster has been ascertained by IR and NMR spectroscopies and mass spectrometry.     

Synthesis and structural characterization of five new coordination polymer chain structures using a new,Z-shaped ligand, 2,2′-bis-(4-pyridylethynyl)tolane

Using the new ligand, 2,2-bis-(4-pyridylethynyl)tolane we have synthesized five new coordination polymers: HgBr₂[2,2-bis-(4-pyridylethynyl)tolane] (1), HgI₂[2,2-bis-(4-pyridylethynyl)tolane] (2), Ni(acetylacetonate)₂[2,2-bis-(4-pyridylethynyl)tolane] (3), Zn(acetylacetonate)₂[2,2-bis-(4-pyridylethynyl)tolane] (4), and Cu(hexafluoro acetylacetonate)₂[2,2-bis-(4-pyridylethynyl)tolane]CHCl₃ (5). 2,2-Bis-(4-pyridyl ethynyl)tolane is a rigid ligand with a Z-shape that promotes the formation of zig-zag chains. Compounds 1– 5 were characterized by single crystal X-ray diffraction; and compounds 1– 3 were additionally characterized by IR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic space group C2/c with a = 29.761(3) Å, b = 5.0531(5) Å, c = 16.7823(15) Å, = 104.090(2), V = 2447.9(4) ų, Z = 4. Each mercury is bound to two tolane ligands and two bromine anions, resulting in a tetrahedral coordination environment. Compound 2 crystallizes in the monoclinic space group P2/c, with a = 20.3061(17) Å, b = 5.6303(5) Å, c = 24.5459(19) Å, = 110.338(2), V = 2631.4(4) ų, Z = 4. Here also, each mercury is bound to two tolane ligands and two iodine anions in a tetrahedral coordination environment. The ligand orientation differs in compounds 1 and 2 being trans oriented in 1 and cis oriented in 2. Compound 3 crystallizes in the monoclinic space group P2₁/c with a = 14.5947(14) Å, b = 6.3082(6) Å, c = 18.3939(18) Å, = 112.112(2), V = 1568.9(3) ų, Z = 2. Each nickel is bound to two tolane ligands and two bidentate AcAc anions, resulting in an octahedral coordination environment. Compound 4, which is isostructural with 3, also crystallizes in the monoclinic space group P2₁/c with a = 14.6990(9) Å, b = 6.2724(4) Å, c = 18.6433(11) Å, = 112.8610(10), V = 1583.86(17) ų, Z = 2. Compound 5 crystallizes in the triclinic space group P-1 with a = 6.5487(4) Å, b = 11.6471(7) Å, c = 14.3225(9) Å, = 70.1360(10), = 89.3990(10), = 88.7680(10), V = 1027.18(11) ų, Z = 1. Each copper in 5 is bound to two tolane ligands and two bidentate hfAcAc anions, resulting in an octahedral coordination environment identical to that found in 3 and 4.     

Synthesis and crystal structure of an infinite double- stranded chain manganese(II) coordination polymer bridged through 1,2-bis(imidazol-1-yl)ethane ligand

The manganese complex [Mn(bim)₂(NCO)₂]_n (1) (bim = 1,2-bis(imidazol-1-yl)ethane) has been synthesized and structurally characterized by X-ray diffraction analysis. It crystallizes in the monoclinic space group C2/c, a = 9.896(3) Å, b = 15.383(4) Å, c = 13.949(4) Å, β = 98.966(5)^∘, V = 2097.5(9) ų, Z = 4. The coordination geometry of Mn(II) atom is distorted octahedral; it is coordinated equatorially by four nitrogen atoms from the imidazole rings of four symmetry-related bim ligands, and axially by two nitrogen atoms from two symmetry-related cyanate anions. The structure is polymeric, with 18-membered spiro-fused rings and each 18-membered ring involving two inversion-related bim molecules.     

Reaction of 1,2-bis(diphenylphosphino)cyclobutenedione (bpcbd) with fac-BrRe(CO)3(THF)2: X-ray diffraction structure of the dimeric complex [BrRe(CO)3]2(bpcbd) ⋅ CH2Cl2

Treatment of the diphosphine ligand 1,2-bis(diphenylphosphino)cyclobutenedione (bpcbd) with the THF adduct fac-BrRe(CO)₃(THF)₂ at room temperature furnishes the new dirhenium compound [BrRe(CO)₃]₂(bpcbd) instead of the expected mononuclear compound fac-BrRe(CO)₃(bpcbd). [BrRe(CO)₃]₂(bpcbd) was characterized in solution by IR spectroscopy, and the solid-state structure was solved by X-ray crystallography. [BrRe(CO)₃]₂(bpcbd), as the CH₂Cl₂ solvate, crystallizes in the space group P , a = 11.173(1), b = 13.362(1), c = 15.250(1) Å, = 108.973(7)°, = 99.477(8)°, = 110.466(7)°, V = 1915.0(3) ų, Z = 2, and d _calc = 2.143 g-cm^–3. The structure of [BrRe(CO)₃]₂(bpcbd) consists of two rhenium centers that are six-coordinate and possess nearly ideal octahedral geometry. The two Re(CO)₃ units are linked together by the bridging diphosphine ligand and two bridging bromide groups.