Rules governing asymmetric synthesis with organotransition metal complexes

A set of rules are presented which allow prediction of (1) the conformational properties of organotransition metal complexes of the type (η⁵-C₅H₅)M(Ph₃P)(L)R [M = Fe, Co, Re; L = CO, NO]; and (2) the stereochemical consequences of their reactions.     

Hartree-Fock complete basis set limit properties for transition metal diatomics

Numerical Hartree-Fock (HF) energies accurate to at least 1 microhartree are reported for 27 diatomic transition-metal-containing species. The convergence of HF energies toward this numerical limit upon increasing the basis set size has been investigated, where standard nonrelativistic all-electron correlation consistent basis sets and augmented basis sets, developed by Balabanov and Peterson [J. Chem. Phys. 123, 064107 (2005)], were employed. Several schemes which enable the complete basis set (CBS) limit to be determined have been investigated, and the resulting energies have been compared to the numerical Hartree-Fock energies. When comparing basis set extrapolation schemes, those in the form of exponential functions perform well for our test set, with mean absolute deviations from numerical HF energies of 234 and 153 microE(h), when the CBS limit has been determined using a two-point fit as proposed by Halkier et al. [Chem. Phys. Lett. 302, 437 (1999)] on calculations of triple- and quadruple-zeta basis set qualities and calculations of quadruple- and quintuple-zeta basis set qualities, respectively. Overall, extrapolation schemes in the form of a power series are not recommended for the extrapolation of transition metal HF energies. The impact of basis set superposition error has also been examined.     

Ethylene polymerization catalysts from supported organotransition metal complexes. II. Chromium alkyls

Another class of organochromium compounds, beta-stabilized chromium alkyls, has been synthesized and tested for catalytic activity in ethylene polymerization. Although not active alone, these compounds do exhibit remarkable activity when reacted with a partially dehydroxylated high surface area carrier. The best supports seem to be fluorided alumina or the aluminophosphates, depending on the particular chromium alkyl being tested. The worst was always silica. Both divalent and tetravalent chromium alkyls were tested and found to have high catalytic activity. Comparisons of activity and polymer structure were made between these compounds and previously studied organochromium compounds with pi-bonded ligands.     

Fluorocarbon metal compounds—role models in organotransition metal chemistry

Early studies on organo-transition metal complexes with fluorocarbon ligands are reviewed in a historical context in relation to the renaissance of organometallic chemistry which followed the discovery of ferrocene.     

The development of an organotransition metal synthesis of quinones

A new and very general synthesis of quinones is described from conception to the current state of maturity. The chemistry relies on a convergent joining of a transition metal complex and an alkyne to provide benzoquinones (from maleoylmetal complexes) and naphthoquinones (from phthaloylmetal complexes). Significant aspects of this chemistry are its generality (terminal, internal, electron rich, and electron deficient alkynes react), its mildness (reactions can be run between room temperature and 80°) and its functional group compatibility (aldehydes, ketones, esters, nitriles, olefins, halides acetals, ketals, etc. survive).     

Ethylene polymerization catalysts from supported organotransition metal complexes: I. Pentadienyl derivatives of Ti,V, and Cr

A new class of ethylene polymerization catalysts, namely the bis-(2,4-dimethyl pentadienyl) derivatives of titanium, vanadium, and chromium, have been synthesized and tested. When supported on a variety of inorganic carriers, these compounds yielded 0.2–1.0 million g polymer/g metal/h under typical slurry conditions. Sensitivity to H₂ as a molecular weight regulator varied among the three metals, but in the absence of H₂ all produced ultrahigh-molecular-weight polyethylene. The molecular weight distribution varied from moderately narrow to very broad (bimodal) depending on the metal and the carrier. Catalyst synthesis and polymer properties are discussed.     

The role of range-separated Hartree-Fock exchange in the calculation of magnetic exchange couplings in transition metal complexes

We assess the dependence of magnetic exchange couplings on the variation of Hartree-Fock exchange (HFX) admixture in global hybrid functionals and the range-separation parameter ω in range-separated hybrid functionals in a set of 12 spin-1/2 binuclear transition metal complexes. The global hybrid PBEh (hybrid Perdew-Burke-Ernzerhof) and range-separated hybrids HSE (Heyd-Scuseria-Ernzerhof) and LC-ωPBE (long-range corrected hybrid PBE) are employed for this assessment, and exchange couplings are calculated from energy differences within the framework of the spin-projected approach. It is found that these functionals perform optimally for magnetic exchange couplings with 35% HFX admixture for PBEh, ω = 0.50 a.u.(-1) for LC-ωPBE, and ω at or near 0.0 a.u.(-1) for HSE (which corresponds to PBEh). We find that in their standard respective forms, LC-ωPBE slightly outperforms PBEh, while PBEh with 35% HFX yields exchange couplings closer to experiment than those of LC-ωPBE with ω = 0.50 a.u.(-1). Additionally, we show that the profile of exchange couplings with respect to ω in HSE is appreciably flat from 0 to 0.2 a.u.(-1). This combined with the fact that HSE is computationally more tractable than global hybrids makes HSE an attractive alternative for the evaluation of exchange couplings in extended systems. These results are rationalized with respect to how varying the parameters within these functionals affects the delocalization of the magnetic orbitals, and conclusions are made regarding the relative importance of range separation versus global mixing of HFX for the calculation of exchange couplings.     

Near Hartree-Fock limit study of the linear chain of hydrogen atoms

The linear, equidistant chain of hydrogen atoms has been studied with the aid of the crystal orbital method. Extended gaussin basis sets have been used, with the aim to obtain near Hartree—Fock limit ground state properties. The metallic type and the broken symmetry type solution yielded energies of ?0.5361 and ?0.5372 hartree, respectively, for the total energy per hydrogen atom. These values are estimated to be at most 0.5 millihartree above the Hartree-Fock limit. The corresponding values for the equilibrium distance r_e are 1.840 and 1.843 bohr, respectively.     

Singlet unrestricted Hartree-Fock Slater (UHFS) model for unstable metalmetal bonds

The electronic properties of weak metalmetal bonds are investigated on the basis of the singlet unrestricted Hartree-Fock Slater (¹UHFS) model. It is pointed out that the ¹UHFS model is sufficiently useful in describing the electron-transfer processes in cluster compounds which are regarded as models of organic semiconducting complexes.     

A localized-orbital Hartree-Fock description of alkali metal clusters

We propose a new variational method, based on the ab initio Hartree-Fock methods, for the purpose of calculating efficiently both the equilibrium geometry and stability of alkali metal microclusters. Applying this method to neutral and cationic lithium clusters, up to Li₃₆, we find that the calculated stable cluster size corresponds to the observed magic numbers. Our results also indicate that both neutral and cationic clusters exhibit very similar dependence on the number of electrons both in stability and cluster shape, which is quite similar to the one obtained by the shell model. Furthermore, we find that lithium clusters larger than Li₂₆ have an ordered structure while clusters smaller than this do not. This is suggestive of the occurrence of a structural transition to a solid-like phase.     

Nucleophilic addition to organotransition metal cations containing unsaturated hydrocarbon ligands : A survey and interpretation

Three simple rules are proposed that enable the prediction of the most favourable position of nucleophilic attack on 18 electron organotransition metal cations containing unsaturated hydrocarbon ligands.     

Thiosulfate metal complexes

The electronic structure of the thiosulfate ions was determined, which made it possible to predict and confirm experimentally for the first time the nature of their ³³S NMR spectra containing two signals of functionally different sulfur atoms. The results of NMR study on different nuclei and the EPR data indicated that the thiosulfate ions as bifunctional ligands enter the coordination sphere of metals with different nature in accordance with the principle of hard and soft acids and bases. The general scheme of the redox transformations of the thiosulfate ions as a result of homo-and heterolytic cleavage of the S-S bonds or the charge transfer in a metal-ligand system was proposed.     

Approaching the basis set limit for transition metal compounds with highly polar bonds: a benchmark coupled-cluster study of the ScF3 and FeF3 molecular structures and spectra

The molecular equilibrium geometries, quadratic and cubic force constants, vibrational frequencies, and infrared intensities of scandium and iron trifluorides are determined ab initio with a sequence of atomic natural orbital basis sets using the CCSD(T) treatment of electron correlation. The largest basis set of spdf ghi quality contains 462 contracted Gaussian functions. Relativistic corrections are applied to compute the equilibrium geometries and vibrational frequencies. The cubic force constants are used to estimate vibrational corrections to the effective r(g) internuclear distances determined in the gas electron diffraction experiments. The computed molecular properties are extrapolated to the complete basis-set limit. The predicted values are compared to the available experimental data; uncertainties and inconsistencies in these data are then discussed.     

One-pot metal templated synthesis for the preparation of 2-quinoxalinol salen metal complexes

Metal complexes of 2-quinoxalinol salen (salqu) ligands can be prepared in a one-pot metal templated synthesis resulting in significantly enhanced yields than if the ligand were prepared and isolated prior to introducing the metal for complexation. Using this method, 12 salqu metal complexes have been prepared and characterized from +2 metal ions.     

Approaching bulk limit for three‐dimensional solids via the cyclic cluster approximation: Semiempirical INDO study

The cyclic cluster method has been examined for a number of solids using a recently developed computer code, Solid 98. Calculations are based on the quasirelativistic (QR) INDO/1 (intermediate neglect of differential overlap) method that is simple enough to allow for a saturation of the (cyclic) clusters. Convergence toward the bulk limit (INDO/1) charge density with respect to the size of the model cyclic cluster is shown for diamond, silicon, germanium, boron nitride, gallium phosphide, gallium arsenide, and gallium antimonide. Results show that, as soon as the initial cluster size reaches 5 to 6 nm, one can safely use the obtained density matrix as a good approximation to the bulk limit. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 253–261, 1999     

Conformations of the transition metal complexes

A historical overview is given on the structural and conformational studies of tris(diamine)metal system. Studies on various coordination compounds revealed that energy minimization calculations can predict the detailed geometries of the complexes. The computed geometry of a coordination compound agrees with that observed in the crystal structure to within several standard deviations. Differences in thermodynamic properties between different conformers are well reproduced. Equilibrium distribution of conformers can be reasonably accounted for on the basis of the minimized strain energies.     

Paper chromatography of metal complexes : Realtionship between the rf and the stabiliiy of metal complexes

It is shown that the R_F values can be related to the stability constants of the corresponding metalligand coördination compounds. The relationship has been applied to prove graphically the stoichiometric identity of two or more complexes formed by paper chromatrography in a given system.