膦配体电子和空间效应对钯催化羰化酯化反应的影响

膦配体修饰的钯催化剂在不饱和化合物羰化酯化反应中使用广泛,其催化活性在很大程度上取决于金属周围的配体环境。膦配体电子和空间效应的调变,可以实现定向催化,甚至可以预测催化行为。新催化反应的开发和现有催化反应的优化都可以通过膦配体的合理设计来实现。配体已经是成为公认的最重要的需要详细研究的变量之一。本文综述了钯催化烯烃羰化酯化反应中,单齿膦配体、双齿膦配体、半稳定膦配体电子和空间效应对活性和选择性的调控作用,并对面临的问题和未来的发展方向进行了探讨,以期对未来设计高效高选择性羰化酯化反应催化体系提供指导。     

Advances in the coordination chemistry of nitrogen ligand complexes of coinage metals

Coinage metals nitrogen chemistry has not been studied extensively until recently. The focus of this review is the base- and halide-free complexes of the monoanionic nitrogen ligands. This review describes how minor ligand modifications can result in a drastic change in the metal–metal interactions in multinuclear compounds. Crystal structures of these complexes show individual complexes, dimers, supramolecular columnar packing or more complex supramolecular aggregates. Bulky substituents on the ligands can prevent intermolecular metal–metal interactions or the formation of supramolecular architectures. The nuclearity and metal–metal interactions in these complexes are controlled by ligand steric and electronic factors and solvent of crystallization. Many classes of nitrogen ligand coordination compounds have given rise to advances in several fundamental and applied research aspects. Recent potential applications of nitrogen ligand complexes are highlighted particularly for those complexes included in this review.     

稀土-氨基多羧酸配合物的配位结构及变化规律I氨基三乙酸(nta)、乙二胺四乙酸(edta)和反式-1,2-环己二胺四乙酸(cydta)系列

本文综述了稀土金属离子与一系列氨基多羧酸配体(如nta(=氨基三乙酸),edta(=乙二胺四乙酸),cydta(=反式-1,2-环己二胺四乙酸),dtpa(=二乙三胺五乙酸)和ttha(=三乙四胺六乙酸)等)形成配合物的分子结构和晶体结构,发现了这些配合物的配位规律和结构变化,说明了稀土金属离子象其它过渡金属离子一样,与氨基多羧酸配体形成配合物的配位数和配位结构取决于稀土金属离子的离子半径,电子结构和配体形状以及配电离子等。     

Coulombic inter-ligand repulsion effects on the Pt(II) coordination chemistry of oligocationic, ammonium-functionalized triarylphosphines

The Pt(II) coordination chemistry of oligocationic ammoniomethyl- and neutral aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX(2)(L)(2) (X = Cl, I) have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1](6+) and [2](6+), two ligands always occupy a trans-configuration with respect to each other in complexes of the type PtX(2)(L)(2), while for the tri-para-ammoniomethyl-substituted ligand [7](3+), the trans/cis ratio is dependent on the ionic strength of the solution. This behaviour was not observed for the neutral aminomethyl-substituted ligands. In the crystal structure of trans-[PtI(2)(1)(2)]I(12), the geometrical parameters of the phosphine ligand [1](6+) are very similar to those found in the analogous complex of the benchmark ligand PPh(3), i.e. trans-PtI(2)(PPh(3))(2), indicating that no significant increase in the steric congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine ligands is dominated by repulsive Coulombic inter-ligand interactions.     

Transition-Metal Complexes with Nano-Sized Phosphine and Pyridine Ligands-Catalysis,Fluxional Behavior and Molecular Recognition

Nano-sized phosphine and pyridine ligands having tetraphenylphenyl-, m-terphenyl-, poly(benzylether) moieties were synthesized. These ligands showed a remarkable effect on homogeneous transition metal catalyzed reactions. Pd(II) complexes with tetraphenylphenyl substituted pyridine ligands show high catalytic activities for oxidation of ketones suppressing Pd black formation and maintains the catalytic activity for a long time. Rh(I) complex catalysts with m-terphenyl substituted phosphine ligands showed remarkable rate acceleration in the hydrosilylation of ketones. In addition, several phosphinocalixarene ligands were synthesized and their coordination studies with Pd(II), Pt(II), Ru(II), Ir(I), and Rh(I) metals were documented. Ir(I) and Rh(I) cationic complexes with a 1,3,5-triphosphinocalix[6]arene ligand showed dynamic behavior with size-selective molecular recognition.     

稀土-氨基多羧酸配合物的配位结构及变化规律的研究 II.二乙三胺五乙酸(dtpa)和三乙四胺六乙酸(ttha)系列

在前文的基础上,本文继续综述了氨基多羧酸类-dtpa和ttha配体与一系列稀土金属离子形成配合物的分子结构和配位结构。发现了dtpa和ttha配体与稀土金属离子的配位规律和结构变化规律。研究结果表明,稀土金属离子与dtpa和ttha配体形成配合物的配位数和配位结构明显地取决于稀土金属离子的离子半径,电子结构和氧化态以及配体的形状。     

Extraction and coordination behavior of diphenyl hydrogen phosphine oxide towards actinides

Extraction behavior of some selected actinides like U(VI), Th(IV), and Am(III) was investigated with three different H-phosphine oxides, viz. diphenyl hydrogen phosphine oxide (DPhPO), dihexyl hydrogen phosphine oxide (DHePO) and diphenyl phosphite (DPP). The H-phosphine oxides exhibited a dual nature towards the extraction of actinides where the ligand not only extracts the metals by cation exchange but also by coordination with the phosphoryl group at lower and higher acidic concentrations, respectively. Among all ligands employed, DPhPO showed highest extraction with actinides with a substituent dependent trend as follows: DPhPO > DHePO > DPP. This trend emphasizes the importance of substituents around the phosphine oxide towards their extraction of actinides. The coordination behavior of DPhPO was studied by investigating its corresponding complexes with Th(NO₃)₄ and UO₂(NO₃)₂. The metal complexes of these actinides were characterized using FT-IR, ¹H and ³¹P NMR spectroscopic techniques. Density Functional Theory (DFT) calculations were also performed to understand the electronic and geometric structure of the ligand and the corresponding metal complexes.     

Coordination chemistry of amine bis(phenolate) titanium complexes: tuning complex type and structure by ligand modification

The coordination chemistry of titanium(IV) complexes of amine bis(phenolate) ligands was investigated by synthesizing various types of complexes and analyzing them specroscopically and structurally. Steric effects of tridentate [ONO]- and tetradentate [ONNO]-type ligands were studied by reacting the ligand precursors with titanium tetra(isopropoxide). [ONNO]-type ligands featuring an amine donor located on a pendant arm led to octahedral bis(isopropoxide) complexes, regardless of the steric bulk around the metal. Several such complexes having varying steric crowding were thus synthesized. On the other hand, steric effects were found to play a major role in determining the complex constitution when [ONO]-type ligands, featuring no side donor, were involved. Relatively sterically undemanding ligands led to octahedral bis(homoleptic) complexes, whereas increased steric bulk resulted in the formation of pentacoordinate bis(isopropoxide) complexes. These pentacoordinate complexes readily lead to bis(heteroleptic) complexes by reaction with nonsterically demanding [ONO]- and [ONNO]-type ligand precursors. In the latter case the sidearm nitrogen remains uncoordinated to the metal. The bis(isopropoxide) complexes of the [ONNO]-type ligands may also lead to bis(heteroleptic) complexes, however, these reactions are much slower.     

Novel vanadium(III) complexes with tridentate phenoxy‐phosphine [O,P(O),O] ligands: Synthesis,characterization, and catalytic behavior of ethylene polymerization and copolymerization with 10‐undecen‐1‐ol

A series of novel vanadium(III) complexes bearing tridentate phenoxy‐phosphine [O,P,O] ligands and phosphine oxide‐bridged bisphenolato [O,P?O,O] ligands, which differ in the steric and electronic properties, have been synthesized and characterized. These complexes were characterized by Fourier transform infrared spectroscopy (FTIR) and mass spectra as well as elemental analysis. Single‐crystal X‐ray diffraction revealed that complexes 3c and 4e adopt an octahedral geometry around the vanadium center. In the presence of Et₂AlCl as a cocatalyst, these complexes displayed high catalytic activities up to 22.8 kg PE/mmol_V.h.bar for ethylene polymerization, and produced high‐molecular‐weight polymers. Introducing additional oxygen atom on phosphorus atom of [O,P,O] ligands has resulted in significant changes on the aspect of steric/electronic effect, which has an impact on polymerization performance. 3c and 4c /Et₂AlCl catalytic systems were tolerant to elevated temperature (70 °C) and yielded unimodal polyethylenes, indicating the single‐site behavior of these catalysts. By pretreating with equimolar amounts of alkylaluminums, functional α‐olefin 10‐undecen‐1‐ol can be efficiently incorporated into polyethylene chains. 10‐Undecen‐1‐ol incorporation can easily reach 14.6 mol % under the mild conditions. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, Al/V (molar ratio), and comonomer concentration, are also examined in detail. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Non-valent interactions and structural features of monomeric guanidinate complexes of rare earth metals: analyses and predictions based on the ligand solid angle

Analysis of steric saturation of rare earth metal centers in monomeric guanidinate coordination complexes with the use of ligand solid angles indicates that the observed optimal metal shielding is 85(3)%. Non-valent ligand–ligand interactions in the metal coordination sphere affect the shielding of the metal and can facilitate or preclude formation of agostic interactions. Analysis of all structurally characterized to date guanidinate complexes of Ln is presented and general and unique features of such complexes are identified.     

Synthesis and coordination chemistry of a photoswitchable bis(phosphine) ligand

A 1,2-dithienylethene compound bearing bis(phosphine) groups (1o) represents a new class of photoresponsive ligands where there are steric and electronic differences between two photogenerated isomers. The coordination chemistry of this ligand class is demonstrated by preparing a gold(I) complex (2o) and a phosphine selenide (3o).     

DFT studies of structural preference of coordinated ethylene in W(CO)3(PX3)2(CH2CH2) (X=H, CH3, F, Cl, Br, and I)

A set of phosphine complexes of the type W(CO)₃(PX₃)₂(CH₂CH₂) (X=H, CH₃, F, Cl, Br, and I) were investigated by density functional theory method (BP86) to examine the effect of the substituent X on the orientation of C-C vector of the ethylene ligand with respect to one of the metal-ligand bonds as well as the donation and the backdonation in the bonding ligands of phosphine and ethylene. When X=CH₃, H, F, and Cl, the ethylene C-C vector prefers to be coplanar with metal-phosphine bonds, while for the ethylene complexes containing PBr₃ and PI₃ ligands, the structural preference is coplanarity of the ethylene and the metal-carbonyl bonds. The molecular orbital calculations and natural bond orbital analysis were used to examine the structural consequences derived from these complexes. It can be concluded that the structural preferences in the complexes have a clear relation to electronic effects of phosphine ligands. Our calculations for halide phosphine complexes, particularly for PBr₃ and PI₃, allow us to conclude that in addition to electronic effects, steric factors can also affect the orientation of the ethylene ligand in complexes.     

Cationic terminal gallylene complexes by halide abstraction: coordination chemistry of a valence isoelectronic analogue of CO and N2

While N(2) and CO have played central roles in developing models of electronic structure, and their interactions with transition metals have been widely investigated, the valence isoelectronic diatomic molecules EX (E = group 13 element, X = group 17 element) have yet to be isolated under ambient conditions, either as the "free" molecule or as a ligand in a simple metal complex. As part of a program designed to address this deficiency, together with wider issues of the chemistry of cationic systems [L(n)M(ER)](+) (E = B, Al, Ga; R = aryl, amido, halide), we have targeted complexes of the type [L(n)M(GaX)](+). Halide abstraction is shown to be a viable method for the generation of mononuclear cationic complexes containing gallium donor ligands. The ability to isolate tractable two-coordinate products, however, is strongly dependent on the steric and electronic properties of the metal/ligand fragment. In the case of complexes containing ancillary pi-acceptor ligands such as CO, cationic complexes can only be isolated as base-trapped adducts, even with bulky aryl substituents at gallium. Base-free gallylene species such as [Cp*Fe(CO)(2)(GaMes)](+) can be identified only in the vapor phase by electrospray mass spectrometry experiments. With bis(phosphine) donor sets at the metal, the more favorable steric/electronic environment allows for the isolation of two-coordinate ligand systems, even with halide substituents at gallium. Thus, [Cp*Fe(dppe)(GaI)](+)[BAr(f)(4)](-) (9) can be synthesized and shown crystallographically to feature a terminally bound GaI ligand; 9 represents the first experimental realization of a complex containing a valence isoelectronic group 13/group 17 analogue of CO and N(2). DFT calculations reveal a relatively weakly bound GaI ligand, which is confirmed experimentally by the reaction of 9 with CO to give [Cp*Fe(dppe)(CO)](+)[BAr(f)(4)](-). In the absence of such reagents, 9 is stable for weeks in fluorobenzene solution, presumably reflecting (i) effective steric shielding of the gallium center by the ancillary phosphine and Cp* ligands; (ii) a net cationic charge which retards the tendency toward dimerization found for putative charge neutral systems; and (iii) (albeit relatively minor) population of the LUMOs of the GaI molecule through pi overlap with the HOMO and HOMO-2 of the [Cp*Fe(dppe)](+) fragment.     

Quantifying the electronic effect of substituted phosphine ligands via molecular electrostatic potential

Values of the molecular electrostatic potential minimum (V(min)) corresponding to the lone pair region of several substituted phosphine ligands (PR(3)) have been determined at the DFT level. The V(min) value is proposed as a quantitative measure of the electronic effect of the PR(3) ligands. Good linear correlation between V(min) and Tolman electronic parameter of PR(3) has been obtained. V(min) is also proportional to the pK(a) values of the conjugate acids of PR(3), viz., [PR(3)H](+). Further, the DeltaE values of the reaction Ni(CO)(3) + PR(3) --> Ni(CO)(3)PR(3) and ScH(3) + PR(3) --> ScH(3)PR(3) are also linearly proportional to the V(min) values. However, if there is a strong metal to phosphorus pi-back-bonding, the DeltaE and V(min) do not fit to a line. It is also found that the standard reduction potential as well as the enthalpy change corresponding to the electrochemical couple eta-Cp(CO)(PR(3))(COMe)Fe(+)/eta-Cp(CO)(PR(3))(COMe)Fe(0) is linearly proportional to the V(min) values of PR(3). These correlations suggest that V(min) is a quantitative measure of the sigma-donating ability of the phosphine. It is hoped that, in phosphine-metal coordination chemistry, the V(min) based electronic parameter could be more advantageous than nu-CO and pK(a) based electronic parameters as it solely represents the inherent electronic property of the ligand.     

Hemilability of Hybrid Ligands and the Coordination Chemistry of Oxazoline-Based Systems

Ligand design is becoming an increasingly important part of the synthetic activity in chemistry. This is of course because of the subtle control that ligands exert on the metal center to which they are coordinated. Ligands which contain significantly different chemical functionalities, such as hard and soft donors, are often called hybrid ligands and find increasing use in molecular chemistry. Although the interplay between electronic and steric properties has long been recognized as essential in determining the chemical or physical properties of a complex, predictions remain very difficult, not only because of the considerable diversity encountered within the Periodic Table-different metal centers will behave differently towards the same ligand and different ligands can completely modify the chemistry of a given metal-but also because of the small energy differences involved. New systems may-even through serendipity-allow the emergence of useful concepts that can gain general acceptance and help design molecular structures orientated towards a given property. The concept of ligand hemilability, which finds numerous illustrations with hybrid ligands, has gained increased acceptance and been found to be very useful in explaining the properties of metal complexes and in designing new systems for molecular activation, homogeneous catalysis, functional materials, or small-molecule sensing. In the field of homogeneous enantioselective catalysis, in which steric and/or electronic control of a metal-mediated process must occur in such a way that one stereoisomer is preferentially formed, ligands containing one or more chiral oxazoline units have been found to be very valuable for a wide range of metal-catalyzed reactions. The incorporation of oxazoline moieties in multifunctional ligands of increasing complexity makes such ligands good candidates to display hemilabile properties, which until recently, had not been documented in oxazoline chemistry. Herein, we briefly recall the definition and scope of hemilabile ligands, present the main classes of ligands containing one or more oxazoline moieties, with an emphasis on hybrid ligands, and finally explain why the combination of these two facets of ligand design appears particularly promising.     

Pd(II) and Ni(II) complexes featuring a "phosphasalen" ligand: synthesis and DFT study

A phosphorus analog of salen ligands featuring iminophosphorane functionalities in place of the imine groups was synthesised in 2 steps from o-diphenylphosphinophenol via the preparation of the corresponding bis-aminophosphonium salt. This novel tetradentate ligand (1), which we named phosphasalen, was coordinated to Pd(II) and Ni(II) metal centres affording complexes 6 and 7 respectively, which were characterised by multinuclear NMR, elemental and X-ray diffraction analyses. Both neutral complexes adopt a nearly square-planar geometry around the metal with coordination of all iminophosphorane and phenolate moieties. The electronic properties of these new complexes were investigated by cyclic voltammetry and comparison with known salens was made when possible. Moreover, the particular behaviour of the phosphasalen nickel complex 7 was further investigated through magnetic moment measurements and a DFT study.     

Dithiolene complexes containing N coordinating groups and corresponding tetrathiafulvalene donors

The chemistry of transition metal dithiolene complexes containing N coordinating groups and the corresponding TTF donors, is reviewed starting from the ligand synthesis to the coordination structures where these dithiolene complexes are used as bridging units. The dithiolene ligands containing N coordinating atoms present two coordination poles which can selectively bind different metals and act as bridging units in a variety of coordination architectures. The transition metal dithiolene complexes based on these N containing ligands and the corresponding TTF donors can be themselves regarded as ligands. These can be used to coordinate other metals, potentially leading to a diversity of hetero metallic coordination architectures. With the use of appropriate auxiliary ligands they can lead to discrete metal complexes. In addition they can lead to more extended polymeric structures of different dimensionality such as 1D chains, 2D layers or even 3D polymers can also be obtained.     

Synthesis, characterization and catalytic activity of lithium and sodium iminophenoxide complexes towards ring-opening polymerization of L-lactide

A series of lithium and sodium iminophenoxide complexes have been successfully synthesized and characterized by X-ray crystallography and investigated as catalysts for the ring opening polymerization of L-lactide. The nature and steric bulk of the ligands coordinated to the central metal ions greatly influence the catalytic properties. Complexes with bidenate ligands exhibit higher catalytic activity than tridentate counterparts because the third coordination atom contends with L-lactide, which decreases activity. Oxygen is the third atom in the tridentate ligand, providing stronger chelation ability with Li and Na than nitrogen or sulfur and occupies the space with which L-lactide is coordinated.     

Gas-phase reactions of divalent Ni complex ions with acetonitrile: Chelate ring size,inductive, and steric effects

Ni(II) complexes of a series of pentadentate polyamine ligands have been reacted with CH₃CN in the gas phase using a modified quadrupole ion trap mass spectrometer. The ligands have structural features such that upon complexation, chelate ring size, sterics, and inductive effects can be evaluated in the gas phase. Rate and equilibrium constants for CH₃CN addition to the metal complexes show that there is a general decrease in the gas-phase reactivity as the chelate ring size is increased. Density functional theory calculations at the B3LYP/LANL2DZ level of theory have been used to obtain minimum energy structures and Mulliken charges for the complexes. The decreased reactivity observed as the chelate ring size is increased correlates with a decrease in the atomic charge on the metal. A larger chelate ring size enhances ligand flexibility and improves the overlap of the ligand’s donor atoms with the metal center. Adding methyl groups adjacent to or on the nitrogen donor groups of a ligand also decreases the rate and equilibrium constants for the reactions of a given complex with CH₃CN. Analysis of Mulliken charges for these complexes indicates that both inductive and steric effects are responsible for lower complex reactivity. These results suggest that while the gas-phase reactivity of a metal complex with CH₃CN is very dependent on the functional groups directly bound to the metal, in some cases steric effects can conceal the correlation between reactivity and coordination structure.     

Heteroleptic copper dipyrromethene complexes: synthesis, structure, and coordination polymers

The synthesis of neutral [Cu(dpm)2] and [Cu(dpm)(acac)] (dpm = dipyrromethene, acac = acetylacetonato) complexes is presented. The formation of the asymmetric metal complexes was monitored by electronic absorption and infrared spectroscopy. Two of the complexes investigated, containing pyrdpm ligands (pyrdpm = pyridyldipyrromethene), form 1-dimensional coordination polymers. The coordination polymers formed by these complexes have been characterized by single-crystal X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. The complexes possess square pyramidal coordination geometries with the apical position occupied by the meso-pyridyl donor of a neighboring complex in the crystal lattice. The features of these coordination complexes that facilitate formation of extended solids have been probed. Symmetric [Cu(pyrdpm)2] complexes are unable to form coordination solids due to steric hindrance at the metal center. Use of cyano donors in complexes such as [Cu(cydpm)(acac)] (cydpm = cyanodipyrromethene) in lieu of pyridyl donors also fail to form network solids. Through these systematic studies, both the basic coordination chemistry of these complexes and the fundamental design requirements for synthesizing this novel class of coordination polymers have been defined.