A density functional study of alizarin two of its isomers and its transition metals and rare-earth complexes

Electronic structure of Alizarin, two of its isomers, 11 different transition metal complexes and five rare-earth complexes are studied using density functional theory (DFT). Complexation energies are evaluated and it is found that chelation has a negligible influence on the structure of the anthraquinone backbone; the molecule keeps a planar conformation except for some metals such as Cr, Al, and Zn where the metal atom M and the oxygen atoms are slightly out of the plane by few degrees. The M–O bonds involve p or d metal orbitals depending on whether the d shell is full or empty. The complexation effect leads to a red shift and hence to a colour change of the solutions of the complexes.

The calculated complexation energies are of the same order for metal transition and for rare-earth elements.     

Organometalloidal derivatives of the transition metals : V. A 1,2-alkyl shift from lead to a transition metal

The complexes (η⁵-C₅H₅)Fe(CO)₂PbR₃ (R = Me and Et) have been synthesized and characterized. The trimethyllead complex is extremely labile with respect to thermal and photochemical decomposition that leads to the formation of (Me)₄Pb, Pb, and (η⁵-C₅H₅)Fe(CO)₂Me. This new type of methyl transfer from Pb to Fe does not occur for the triethyllead complex thermally, but does occur to a limited extent photochemically, and helps explain certain zinc treatments for removal of organolead compounds from industrial effluents.     

NDDO/MC: A new semiempirical SCFMO method for transition metal complexes

A new semiempirical SCF MO procedure available for prediction of the transition-metal complexes' binding energy and molecular geometry is developed. The features of the method are (i) an explicit account of the orthogonality of the basis set; (ii) use of a new formula for the resonance integral; and (iii) an effective account of the Coulomb correlation of electrons in the calculation of the two-electron integrals based on approach of a model Coulomb hole function. The parameterization for H, C, N, O, Co, and Ni atoms is presented. The results of NDDO /MC (NDDO for Metal Compounds) calculations of molecular geometries and binding energies for a number of organic compounds and more than 30 cobalt and nickel complexes are compared with the available experimental and ab initio data. The average absolute errors for the binding energies of organic molecules and metal complexes are 8.8 and 5.0 kcal/mol, respectively. © 1992 John Wiley & Sons, Inc.     

A new class of electrocatalysts for hydrogen production from water electrolysis: metal monolayers supported on low-cost transition metal carbides

This work explores the opportunity to substantially reduce the cost of hydrogen evolution reaction (HER) catalysts by supporting monolayer (ML) amounts of precious metals on transition metal carbide substrates. The metal component includes platinum (Pt), palladium (Pd), and gold (Au); the low-cost carbide substrate includes tungsten carbides (WC and W(2)C) and molybdenum carbide (Mo(2)C). As a platform for these studies, single-phase carbide thin films with well-characterized surfaces have been synthesized, allowing for a direct comparison of the intrinsic HER activity of bare and Pt-modified carbide surfaces. It is found that WC and W(2)C are both excellent cathode support materials for ML Pt, exhibiting HER activities that are comparable to bulk Pt while displaying stable HER activity during chronopotentiometric HER measurements. The findings of excellent stability and HER activity of the ML Pt-WC and Pt-W(2)C surfaces may be explained by the similar bulk electronic properties of tungsten carbides to Pt, as is supported by density functional theory calculations. These results are further extended to other metal overlayers (Pd and Au) and supports (Mo(2)C), which demonstrate that the metal ML-supported transition metal carbide surfaces exhibit HER activity that is consistent with the well-known volcano relationship between activity and hydrogen binding energy. This work highlights the potential of using carbide materials to reduce the costs of hydrogen production from water electrolysis by serving as stable, low-cost supports for ML amounts of precious metals.     

Organometalloidal derivatives of the transition metals : XXX. Mass spectrometry of transition metal substituted disilanes

Mass spectral fragmentation of a series of transition metal substituted disilanes, LMSiMe₂SiMe₂ML, LM = (η⁵-C₅H₅)Fe(CO)₂- (Fp), (η⁵-C₅H₅)Fe(η⁵-C₅H₄)- (Fc), RFe(CO)₂(η⁵-C₅H₄), are reported. They exhibit significant distinctions depending on the nature of LM. Direct cleavage of the Si---Si bond occurs in the order Fc å Fp å RFe(CO)₂(η⁵-C₅H₄) owing to the capacity of the LM fragment to stabilize positive charge. For complexes containing a direct Fe---Si bond, i.e. Fp-SiMe₂SiMe₂ML, disilene complexed ions are observed, and those complexes containing both an Fp group and a (η⁵-C₅H₄-SiMe₂SiMe₂) group exhibit significant formation of (C₅H₄=Si=SiMe₂) complexed ions. Little disproportionation is observed for any of the complexes studied, in contrast to organodisilanes.     

Dehydrogenation of ammonia by early transition metals: formation of metal nitride clusters

The dehydrogenation of NH₃ by Ti, Zr, and Nb cations, produced in a laser-induced plasma reactor, is found to form both neutral and cationic clusters. Depending on the conditions, either the production of neutral metal nitride clusters is favored or, the formation of cationic `precursor' metal nitride clusters containing additional intact NH₃ is observed. The neutral clusters are formed when full dehydrogenation of the NH₃ is achieved, while the cationic precursor species are formed under conditions where a large fraction of the NH₃ remains intact. Metastable dissociation studies show that intact NH₃ molecules are bound to the developing transition metal nitride clusters.     

Reactions involving transition metals : XIX. Some reactions of perfluoronorbornadiene with low valent transition metal complexes

Perfluoronorbornadiene reacts with the compounds [M(PPh₃)₄] (M = Pt, Pd) and [IrCl(CO)(PMePh₂)₂] to give the adducts [(C₇F₈)M(PPh₃)₂] and [(C₇F₈)IrCl(CO)(PMePh₂)₂] in which one of the double bonds is coordinated to the metal atom. The platinum complex reacts further with [Pt(PPh₃)₄] to give [(C₇F₈){Pt(PPh₃)₂}₂] having both double bonds coordinated to a Pt atom. The carbonylmetal anions [M^?] react to form the mono-substitution products [(C₇F₇)M] (M = Mn(CO)₅, Re(CO)₅, Ir(CO)₂(PPh₃)₂, Rh(CO)₂(PPh₃)₂), but the use of an excess of [Fe(CO)₂(η-C₅H₆)]^? leads to substitution of one fluorine atom on each of the double bonds. The complex having M = Mn(CO)₅ reacts with [Pt(PPh₃)₄] to afford the derivative [(C₇F₇){Mn(CO)₄(PPh₃)}{Pt(PPh₃)₂}], and the compound where M = Ir(CO)₂(PPh₃)₂ undergoes an oxidative addition reaction with acetyl chloride. Oxidative coupling products have been isolated on UV irradiation of a mixture of perfluoronorbornadiene and [Fe(η⁴-CH₂CRCHCH₂)(CO)₃] (R = H, Me), and under similar conditions the reaction with Fe(CO)₅ affords [(C₇F₈)Fe(CO)₄] in very low yield.     

过渡金属配合物与铀酰-有机框架复合:两例新型铀/铜异金属配合物的合成、晶体结构及其性能研究

在水热条件下,将铜金属配合物插入到铀酰有机框架化合物中,合成了两例新型铀/铜异金属杂化配合物[Cu(bipy)(UO2)(bdc)2·H2 O]n(1),{[Cu(phen)(UO2)(bdc)(bc)(H2O)]·H2O}n(2)(bipy=2,2′-联吡啶,bdc=对苯二甲酸,phen=1,10-邻菲罗琳,bc=苯...     

A new strategy for ratiometric fluorescence detection of transition metal ions

A novel design strategy for ratiometric fluorescence signaling of transition metal ions, involving both photoinduced electron transfer and resonance energy transfer mechanisms, has been tested on a model system comprising dual fluorophores.     

Growth of new ternary intermetallic phases from Ca/Zn eutectic flux

The eutectic 7.3:2.7 molar ratio mixture of calcium and zinc metal melts at 394 °C and was explored as a solvent for the growth of new intermetallic phases for potential use as hydrogen storage materials. The reaction of nickel in this molten mixture produces two new phases—the CaCu₅-related structure CaNi₂Zn₃ (P6/mmm, a=8.9814(5) Å, c=4.0665(5) Å) and a new cubic structure Ca₂₁Ni₂Zn₃₆ (Fd-3m, a=21.5051(4) Å). Palladium-containing reactions produced CaPd_0.85Zn_1.15 with the orthorhombic TiNiSi structure type (Pnma, a=7.1728(9) Å, b=4.3949(5) Å, c=7.7430(9) Å). Reactions of platinum in the Ca/Zn mixture produce Ca₆Pt₃Zn₅, with an orthorhombic structure related to that of W₃CoB₃ (Pmmn, a=13.7339(9) Å, b=4.3907(3) Å, c=10.7894(7) Å).     

Synthesis of iminoaziridines from carbodiimides and diazoesters : A new example of transition metal salt catalysed reactions of carbenes

Alkyl diazoacetates react with N,N′-diisopropylcarbodiimide in the presence of transition metal salts (e.g. copper triflate or rhodium (II) acetate) to give 1-isopropyl-2-alkoxycarbonyl-3- isopropyliminio-aziridine in good yield. The reaction takes place at room temperature without formation of the formal dimer of the carbene (maleate and fumarate).     

含烯烃配体的过渡金属卡宾配合物的研究VI: 两个新奇的铁内盐配合物的合成和晶体结构

肉桂醛缩(2,4-二甲基苯胺)三羰基铁(1)与苯基锂和对氯苯基锂在低温下反应,所生成的加合物继后Et3OBF4在CH2Cl2中于-60℃烷基化, 分别生成两个组成为C19H22N(CO)3FeC6H5(2)和C19H22N(CO)3FeC6H4Cl(3)的新奇的铁内盐配合物. 2晶体属单斜晶系, 空间群为P21/n, 晶胞参数为: α=10.624(3), b=25.155(6),c=19.375(9)A, β=101.13(3)°, V=5042.2A^3, Z=8, Dc=1.27g/cm^3. 2的结构用直接法解出, 并用矩阵最小二乘法修正后得最后偏离因子R为0.071.     

Removal of residual metal catalysts with iron/iron oxide nanoparticles from coordinating environments

The application of Fe@FexOy nanoparticles was examined for the sequestration of catalytic metal impurities from organic reaction products. An X-ray photoelectron spectroscopy (XPS) study of the recovered particles confirmed Fe@FexOy sequestered Co2+, Cu2+, Ni2+, RhX+, Pd2+, Ag+, and Pt4+ by coordination of the metal ion to the iron oxide surfaces and followed by subsequent reduction of the surface-bonded ions to their metallic state. Fe@FexOy metal sequestration was found to be effective for catalyst impurities in the absence of strongly coordinating environments but was inhibited by the presence of phosphines. Sequestration of phosphine-coordinated metal impurities was achieved through the addition of either cysteamine or 3-mercaptopropionic acid to the Fe@FexOy during sequestration. This approach was applied to model syntheses using Grubbs' Catalyst (first generation), Pd(PPh3)4, Pd2(dba)3, and Wilkinson's Catalyst (RhCl(PPh3)3).     

Detection of nanocrystallinity by X-ray absorption spectroscopy in thin film transition metal/rare-earth atom,elemental and complex oxides

Nanocrystallinity has been detected in the X-ray absorption spectra of transition metal and rare-earth oxides by (i) removal of d-state degeneracies in the (a) Ti and Sc L₃ spectra of TiO₂ and LaScO₃, respectively, and (b) O K₁ spectra of Zr(Hf)O₂, Y₂O₃, LaScO₃ and LaAlO₃, and by the (ii) detection of the O-atom vacancy in the O K₁ edge ZrO₂–Y₂O₃ alloys. Spectroscopic detection is more sensitive than X-ray diffraction with a limit of ∼2 nm as compared to >5 mm. Other example includes detection of ZrO₂ nanocrystallinity in phase-separated Zr(Hf) silicate alloys.     

A review of enantioselective dual transition metal/photoredox catalysis

Transition metal catalysis is one of the most important tools to construct carbon-carbon and carbon-heteroatom bonds in modern organic synthesis. Visible-light photoredox catalysis has recently drawn considerable attention of the scientific community owing to its unique activation modes and significance for the green synthesis. The merger of photoredox catalysis with transition metal catalysts, termed metallaphotoredox catalysis, has become a popular strategy for expanding the synthetic utility of visiblelight photocatalysis. This strategy has led to the discovery of novel asymmetric transformations, which are unfeasible or not easily accessible by a single catalytic system. This contemporary area of organic chemistry holds promise for the development of economical and environmentally friendly methods for the asymmetric synthesis of chiral compounds. In this review, the advances in the enantioselective metallaphotoredox catalysis(EMPC) are summarized.     

Local magnetic anisotropy in amorphous transition metals: A problem of metal physics treated with methods of quantum chemistry

A microscopic cluster model for the calculation of the magnetic ansisotropy in amorphous transition metals is presented. The local spin-orbit coupling is calculated by means of an uncoupled Hartree-Fock (HF) perturbational approach defined on the basis of a semi-empirical self-consistent-field (SCF) formalism in the zero differential overlap (ZDO) approximation. The simplifications presumed in the definition of the spin-orbit interaction are in line with the design of the employed ZDO Hamiltonian. The theoretical approach is applied to amorphous iron. The required finite Fe clusters of 12 to 14 atoms have been isolated from a large amorphous matrix generated by a molecular dynamics (MD) simulation. The local easy directions and the local anisotropy energy of the amorphous material show a random distribution. The analytic structure of the surface of the spin-orbit coupling depends on the atomic short-range order. The anisotropy energies in an amorphous Fe matrix are of the same order of magnitude as of uniaxial crystalline solids. Bifurcation and quasi-degeneracy in the underlying electronic-structure calculations have been analyzed in some detail. It is shown that statistical data of high significance can be derived in multi-level systems although individual HF calculations are influenced by “instabilities”. A comparison of the SCF solutions emerging from crystalline and amorphous structural units shows the close interrelation between the “symmetry dilemma” and the more general “continuity dilemma” of the HF wavefunction. The one-electron properties of representative Fe arrangements are discussed.     

Studies on olefin-coordinating transition metal carbene complexes: VI. Synthesis and crystal structure of two novel inner salt complexes of iron

Reaction of N-cinnamylidenyl-m-4-xylidine (tricarbonyl) iron ( 1 ) with phenyllithium and p-chlorophenyllithium at low temperature, and subsequent alkylation of the resulting adducts with Et₃OBF₄ in CH₂Cl₂ at ?60°C gave two novel zwitter-ion iron complexes with the compositions of C₁₉H₂₂ N(CO)₃ FeC₆H₅(2) and C₁₉H₂₂N(CO)FeC₆H₄Cl (3), respectively. The complex 2 crystallizes in the monoclinic system, space group P2₁/_n with a = 10.624(3), b = 25.155(6), c = 19.375(9)Å, β = 101.1 (3)°, V= 5042.2ų, Z=8, D_c = 1.27g/cm³. The structure of 2 has been solved by direct method and refined by block-matrix least-squares method to give the final R of 0.071.