吡咯亚胺配体与过渡金属的反应性及其催化烯烃聚合

在经典的Brookhart吡啶双亚胺后过渡金属烯烃聚合催化剂基础上,用吡咯五元环代替吡啶六元环骨架可得到具有不同电子效应的新型吡咯亚胺配体.通过吡咯环特殊的电子效应和位阻效应可设计出种类繁多的有别于吡啶亚胺配体的配合物.综述了吡咯亚胺配体与前过渡金属(Ti,Zr等)、后过渡金属(Fe,Co,Ni,Pd等)、稀土金属(Y...     

Zirconium Complexes of Two Different Iminopyrrolyl Ligands – Syntheses and Structures

The reaction involving N‐aryliminopyrrolyl ligand, 2‐((p‐Me‐C₆H₃N=CMe)–C₄H₃NH) ( 1a ) (Imp^Me‐H), and Zr(OtBu)₄ in a 2:1 molar ratio in toluene at 90 °C afforded the corresponding bis(iminopyrrolyl) complex of zirconium, [(Imp^Me)₂Zr(OtBu)₂] ( 2a ) having two bidentate iminopyrrole groups in the coordination sphere. In contrast, the bulkier 2‐((2,6‐iPr₂C₆H₃N=CH)–C₄H₃NH) ( 1b ) (Imp^Dipp‐H) and Zr(OtBu)₄ in a 1:1 molar ratio under the same condition yielded the corresponding mono(iminopyrrolyl) complex of zirconium, [(Imp^Dipp)Zr(OtBu)₃(THF)] ( 2b ), which contains only one bidentate iminopyrrole moiety in the coordination sphere. Both complexes were characterized by single‐crystal X‐ray diffraction analysis. The solid‐state structures reveal that the bulky iminopyrrole ligands cause a steric crowding around the zirconium ion along with three tert‐butoxide ligands attached to the central metal atom.     

Donor-extended tripodal pyrroles: encapsulation, metallation, and H-bonded tautomers

A tripodal iminopyrrole provides an environment suited to the encapsulation of water through hydrogen-bonding, and the formation of metal complexes by deprotonation and imine-pyrrole tautomerisation.     

Designed synthesis for some transition metal clusters involving bridging-sulfido ligand

Designed synthesis for some transition metal clusters involving bridging-sulfido ligands is reviewed. The basic concept with the use of reactive fragments as building blocks is described. It is shown that the sulfido ligands with lone-pair electrons and the unsaturated coordination sites play important roles in this rational synthesis. The relationship between the metallic coordination types of the sulfido ligands and their assembling activity in the compounds is summarized. Examples of the six kinds of unit construction with reactive fragments as building blocks are shown, indicating clearly that the unit construction is a reasonable way in the synthesis of transition metal clusters involving bridging sulfido ligands. Finally, the potential application of the unit construction schemes in the synthesis of transition metal clusters involving other bridging ligands is presented.     

Distinct nanostructures from isomeric molecules of bis(iminopyrrole) benzenes: effects of molecular structures on nanostructural morphologies

The effects of molecular structures on nanostructural morphologies have been studied through the preparation of nanospheres, square nanowires, and nanocubes from three isomeric molecules of bis(iminopyrrole)benzene.     

Paramagnetic metal complexes of diamido donor ligands

Recently, considerable attention has been given to the use of multi-dentate amido ligands in the coordination chemistry of a range of transition metals as a means of accessing novel structural motifs and unusual reactivity. Presented herein is a perspective on transition and f-block metal complexes containing diamido donor ligands of the general form [NDN](2-) (D = NR, O, PR). Particular focus is given to paramagnetic metals, which have in general been studied much less than their diamagnetic counterparts despite their potential to exhibit unique structures and diverse reactivity patterns, in addition to their magnetic properties.     

面手性二芳基膦-噁唑啉配体的开发及其在不对称催化反应中的应用

膦-噁唑啉配体形成的催化剂具有出色的催化活性和对映选择性, 被广泛应用于各种不对称催化反应中. 具有面手性的膦-噁唑啉配体是其中重要的一类. 综述了面手性二芳基膦-噁唑啉配体的开发, 并按反应类型介绍了它们在不对称催化反应中的应用.     

Novel chiral thiazoline‐containing N―O ligands in the asymmetric addition of diethylzinc to aldehydes: substituent effect on the enantioselectivity

Several novel chiral thiazoline primary and tertiary alcohols were easily synthesized from commercially available l ‐cysteine in three steps and with high yield. These ligands were subsequently applied to the asymmetric addition of diethylzinc (Et₂Zn) to various aldehydes. Products with S configuration were obtained when thiazoline‐containing tertiary alcohol ligands were used as catalysts. The primary alcohol induced corresponding products with R configuration in 68% enantiomeric excess, which was a higher value relative to other N―O ligands possessing a primary alcohol unit in the literature. Furthermore, a plausible transition state model was proposed to explain the observed enantioselectivities. Copyright © 2012 John Wiley & Sons, Ltd.     

Tailor‐made Molecular Cobalt Catalyst System for the Selective Transformation of Carbon Dioxide to Dialkoxymethane Ethers

Herein a non‐precious transition‐metal catalyst system for the selective synthesis of dialkoxymethane ethers from carbon dioxide and molecular hydrogen is presented. The development of a tailored catalyst system based on cobalt salts in combination with selected Triphos ligands and acidic co‐catalysts enabled a synthetic pathway, avoiding the oxidation of methanol to attain the formaldehyde level of the central CH₂ unit. This unprecedented productivity based on the molecular cobalt catalyst is the first example of a non‐precious transition‐metal system for this transformation utilizing renewable carbon dioxide sources.     

联三吡啶配体及其衍生物合成进展

金属-配体间的配位作用是超分子化学中最重要的相互作用之一, 寡聚吡啶配体可以与许多过渡金属离子配位, 形成具有独特磁、光物理和电化学性质的过渡金属络合物, 因此联三吡啶配体的合成及其过渡金属络合物性能研究引起化学家的广泛关注. 综述了联三吡啶配体及其衍生物的合成方法, 主要包括成环缩合反应、过渡金属催化的偶联反应以及其它方法, 并选取具有代表性的实例对联三吡啶配体的结构和合成方法进行详细地阐述.     

How can enzymes be so efficient?

Dudley Williams and his colleagues discuss how ligands can gain binding energy to their receptors, and substrate transition states to their enzymes, by tightening the protein structures, with a decrease in their dynamic behaviour.     

Magneto-structural correlation in a series of bimetallic alternating chain complexes of [CrIIIL(CN)4]n[MnIII(salpn)]n.nsolvents (L=2,2'-bipy or 9,10-phen, salpn=substituted salicyldehyde, solvents=water and methanol)

Five chain compounds based on the building block of [Cr(L)(CN)4]- (L=2,2'-bipy, 1-4; L=9,10-phen, 5) and [Mn(salpn)]+ (salpn=substituted salicyldehyde-type Schiff base in Scheme 1) have been prepared and characterized structurally and magnetically. The four compounds (1-4) consisting of [Cr(bipy)(CN)4]- units possess straight bimetallic chains as the [Cr(bpy)(CN)4]- unit links the two neighbor [Mn(salpn)]+ units with the two trans-cyanide ligands, while in 5 the chain is zigzag because the [Cr(phen)(CN)4]- unit connects the [Mn(salpn)]+ units with its two cis-cyanide ligands. The bond angles of Mn-N-C-Cr are adjusted by different coligands of salpn and bipy/phen. The chains are stacking via mainly the aromatic pi-pi-type interactions. All compounds show 3D antiferromagnetic ordering with Néel temperatures ranging from 3.7 to 8.1 K, and they are metamagnets displaying antiferromagnetic to ferrimagnetic transition at critical fields of 4.0-13.1 kOe at 1.9 K. This is due to weak interchain antiferromagnetic interactions between the ferrimagnetic bimetallic chains in the materials. The intrachain couplings (J, in cm(-1)) in the materials, between cyanide-bridged CrIII and MnIII ions, from -1.84 to -5.35 cm(-1), follow a linear relationship (J=-33+0.18alpha) to the Mn-N-C angles (alpha, in deg). In addition, the weak interchain antiferromagnetic interactions and critical fields for antiferromagnetic-ferrimagnetic transition are closely related to some of their structural factors, which were studied very superficially only referring to the separations of nearest chains in each material.     

Metal binding studies with macrocyclic hexathioethers: Transition metal complexes of 22S6 and 20S6

The two macrocyclic hexathioethers, 1,4,7,12,15,18‐hexathiacyclodocosane (22S6) and 1,4,7,11,14,17‐hexathiacycloeicosane (20S6) have been examined with respect to their complexation behavior towards a variety of transition metals ions. In all of these complexes, the two ligands generate relatively strong ligand field, but their field strengths fall between the smaller ring and stronger field hexathioether ligands (such as 18S6) and larger ring and weaker field ligands, such as 24S6. The stability of the complexes towards hydrolysis parallels their reduced field strengths with first row transition metal complexes of both ligands showing enhanced sensitivity to solvolysis reactions compared to the analogous 18S6 complexes. In general, the electrochemical behavior of the hexathioether complexes shows metal centered oxidations which occur at higher potentials than those complexes involving trithioethers. We suggest that the hexathioether ligand is less able to expand and contract during the reduction and oxidation of the metal center. The complex [Pd(22S6)]²⁺ does not display the unusual spectroscopic and electrochemical properties observed in the analogous 18S6 complex.     

Characterization and oxidative addition reactions for iridium cod complexes

Three different [Ir(LL′)(cod)] complexes (LL′ = N-aryl-N-nitrosohydroxylaminato) (cupf), trifluoroacetylacetonato (tfaa), and (methyl 2-(methylamino)-1-cyclopentene-1-dithiocarboxylato-κN,κS) (macsm)) were synthesized, characterized, and their rates of oxidative addition with methyl iodide were determined. Formation of an isosbestic point during the oxidative addition of methyl iodide with the complexes containing tfaa and cupf as bidentate ligands indicated formation of only one product, while an increase in absorbance maximum observed for macsm confirms that the same reaction between the complex and methyl iodide occurs. Kinetic results for all complexes, except [Ir(tfaa)(cod)], showed simple second-order kinetics with a zero intercept (within experimental error). Rates of oxidative addition for bidentate ligands in acetonitrile showed an increase of an order of magnitude with a change in the type of bidentate ligands. Computational chemistry using density functional theory calculations showed that the oxidative addition reaction proceeds through a “linear” transition state with the methyl iodide unit tilted towards the LL′-bidentate ligand.     

Synthesis and application of C2-symmetric diamino FERRIPHOS as ligands for enantioselective Rh-catalyzed preparation of chiral α-amino acids

C₂-Symmetrical ferrocenyl diamino diphosphines (diamino FERRIPHOS ligands) proved to be excellent ligands for the rhodium-catalyzed enantioselective reduction of methyl α-acetamidoacrylates. The straightforward synthesis, their air stability and the easy modification of their structure makes these ligands especially interesting for transition metal-catalyzed hydrogenations. α-Amino acids with enantioselectivities greater than 95% (and up to 99.3% ee) were obtained with no need of further recrystallization.     

One-photon photophysics and two-photon absorption of 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes

The synthesis, one-photon photophysics and two-photon absorption (2PA) of three dipolar D-π-A 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes with different linkers between the donor and acceptor are reported. All ligands exhibit (1)π,π* transition in the UV and (1)π,π*/(1)ICT (intramolecular charge transfer) transition in the visible regions, while the complexes display a lower-energy (1)π,π*/(1)CT (charge transfer) transition in the visible region in addition to the high-energy (1)π,π* transitions. All ligands and the complexes are emissive at room temperature and 77 K, with the emitting excited state assigned as the mixed (1)π,π* and (1)CT states at RT. Transient absorption from the ligands and the complexes were observed. 2PA was investigated for all ligands and complexes. The two-photon absorption cross-sections (σ(2)) of the complexes (600-2000 GM) measured by Z-scan experiment are much larger than those of their corresponding ligands measured by the two-photon induced fluorescence method. The ligand and the complex with the ethynylene linker show much stronger 2PA than those with the vinylene linker.     

General Enantioselective C−H Activation with Efficiently Tunable Cyclopentadienyl Ligands

Cyclopentadienyl (Cp) ligands enable efficient steering of various transition‐metal‐catalyzed transformations, in particular enantioselective C−H activation. Currently only few chiral Cp ligands are available. Therefore, a conceptually general approach to chiral Cp ligand discovery would be invaluable as it would enable the discovery of applicable Cp ligands and to efficiently and rapidly vary and tune their structures. Herein, we describe the three‐step gram‐scale synthesis of a structurally diverse and widely applicable chiral Cp ligand collection (JasCp ligands) with highly variable and adjustable structures. Their modular nature and their amenability to rapid structure variation enabled the efficient discovery of ligands for three enantioselective Rh^III‐catalyzed C−H activation reactions, including one unprecedented transformation. This novel approach should enable the discovery of efficient chiral Cp ligands for various further enantioselective transformations.     

Subduction of coset representations. An application to enumeration of chemical structures with achiral and chiral ligands

Molecules derived from a parent skeleton are enumerated where both achiral ligands as well as chiral ligands are allowed. Chirality fittingness of an orbit is proposed in order to permit chiral ligands. The enumeration is conducted with and without consideration of obligatory minimum valency (OMV). The effect of the OMV is formulated by assigning different weights to the respective orbits of the parent skeleton. The importance of coset representations and their subduction by subgroups is discussed. The subduced representations are classified into three classes through their chirality fittingness, which determines the mode of substitution with chiral and achiral ligands. Several novel concepts such as a unit subduced cycle index and a subduced cycle index are given in general forms.     

The role of inner- and outer-sphere ligands in pivalate and cymantrenecarboxylate complexes of transition metals

The formation of transition metal complexes with pivalate and cymantrenecarboxylate ligands in the presence of axial cyclopentadienyl and α-substituted pyridine ligands is discussed. The latter present steric hindrances due to repulsion from the O atoms of the carboxylate bridges. Particular emphasis is placed on the role of outer-sphere ammonium cations: their hydrogen bonding to fluoride bridges limits the growth of cyclic chromium(III) complexes with the pivalate and fluoride ligands that possess the properties of molecular magnets.     

Tetrathiafulvalene hydrazone an efficient precursor of various chelating electroactive ligands

Novel bidentate electroactive ligands containing one or two tetrathiafulvalene (TTF) cores as redox active unit have been synthesized thanks to the condensation of various carbonyl derivatives with TTF hydrazone. The electron donating ability of these redox active ligands determined by cyclic voltammetry is described together with the investigations of their molecular structures by X-ray diffraction studies. The chelating ability of these ligands has been exemplified through the coordination to molybdenum carbonyl fragment or the complexation to difluoroboron moiety.