Geminally Diaurated Aryls Bridged by Semirigid Phosphine Pillars: Syntheses and Electronic Structure

Geminally diaurated μ₂‐aryl complexes have been prepared where gold(I) centers were bridged by the semirigid diphosphine ligands bis(2‐diphenylphosphinophenyl)ether (DPEphos) and 4,6‐bis(diphenylphosphanyl)dibenzo[b,d]furan (DBFphos). Diaurated complexes were synthesized in ligand redistribution reactions of the corresponding di‐gold dichlorides with di‐gold diaryls (six of them new) and silver(I) salts. Diaurated complexes were isolated as salts of the minimally coordinating anions SbF₆^? and ReO₄^?. Efforts to prepare salts of the tetraarylborate [B(3,5‐(CF₃)₂C₆H₃)₄]^? led to transmetalation from boron, with crystallization of the fluorinated aryl complex. The new complexes were characterized by multinuclear NMR, absorption and emission spectroscopies, 77 K emission lifetimes, and by combustion analysis; three are crystallographically characterized. Structures of geminally diaurated aryl ligands are compared to those of mono‐aurated analogues. Both crystal structures and density‐functional theory calculations indicate slight but observable disruptions of aryl ligand aromaticity by geminal di‐gold binding. An intermolecular aurophilic interaction in one structurally authenticated complex was examined computationally.     

Lithium aminoborohydrides 17. Palladium catalyzed borylation of aryl iodides, bromides, and triflates with diisopropylaminoborane prepared from lithium diisopropylaminoborohydride

The Alcaraz-Vaultier borylation of aryl halides and triflates is reported utilizing diisopropylaminoborane (BH₂N(ⁱPr)₂) prepared from the corresponding lithium aminoborohydride (LAB reagent). BH₂N(ⁱPr)₂, prepared by reacting lithium diisopropylaminoborohydride with trimethylsilyl chloride, provided the most consistent isolated yields from this reaction. Catalytic amounts of palladium dichloride produced the highest yields from aryl iodides, while catalytic tris(dibenzylideneacetone)dipalladium(chloroform) provided the best yields for aryl bromides and triflates. This route to boronic acids is mild enough to tolerate various functionalities and for the first time employs aryl triflates as substrates for the Alcaraz-Vaultier borylation. In addition, it was found that both boronic acid and ester compounds could be isolated from the reaction mixture utilizing simple work-up procedures. Treatment of the reaction intermediate with an acid/base work-up provided the corresponding boronic acid, while treating the same intermediate with a diol, such as neopentyl glycol, afforded the corresponding boronic ester.     

Non-empirical INDO-MO calculations on some vanadium(IV) halides

ODIN, a non-empirical INDO-MO scheme, has been used to determine the ground state electronic configurations for the tetrahedral molecules, VCl₄ and VBr₄. A ² E ground state was obtained for both molecules. The Photoelectron spectrum and the electronic spectrum have been calculated for VCl₄, and a satisfactory correlation with the corresponding experimental data was made. Also, ODIN was employed to evaluate electronic transition energies and the photoelectron spectrum of VBr₄.     

A CNDO-MO calculation of VCl4

The electronic structure of the tetrahedral molecule VCL₄ is investigated within the CNDO-MO approximations. The metal and ligand valence orbitals, 3d, 4s, 4p; and 3s, 3p; respectively, have been systematically varied in an attempt to minimize the total energy; “optimum” V 4s(χ₄ = 1.10) and 4p(d ³ p ²) orbitals have been established, but V 3d(d ⁿ ) and Cl(-δ) valence orbitals are only seen to favor lower energy for expanded orbitals. Since determining the one-electron molecular orbital level which is occupied by the vanadium lone electron is a major aspect of this investigation, all calculations have been performed in triplicate: calculations assuming the unpaired electron occupies the 3a ₁, 2 _e and 4t ₂ molecular orbital (ground state electronic configurations² A ₁,² E, and² T ₂, respectively). The Hartree-Fock equations have been solved by Roothaan's SCF method for open shells, but off-diagonal multipliers between filled and partly filled molecular orbitals of the same symmetry have been neglected. As a qualitative estimate of the error introduced by this simplification, the pertinent overlap integrals between the eigenfunctions from calculations for the three possible configurations,² A ₁,² E, and² T ₂, are investigated as functions of the component 3d(d ⁿ ) and Cl(-δ) valence orbitals. The overlap integrals from the relevant² A ₁ and² T ₂ calculations are reasonably small, but the neglect of off-diagonal multipliers in calculations on the² E state is found to be a poor approximation. An ordering of the non-filled molecular orbitals in VCl₄ of 4t ₂ < 3a ₁ < 2e < 5t ₂ seems most consistent with the numerous calculations. This suggested ground state electronic configuration of² T ₂ introduces new aspects to the consideration of a (dynamic) Jahn-Teller effect in VCl₄. Experimental data pertinent to the electronic structure of VCl₄ has been briefly summarized, but unfortunately it is inadequate to confirm or deny the present calculations.     

Kristallstrukturen von MgCr2O4-Typ Li2VCl4 und Spinell-Typ Li2MgCl4 und Li2CdCl4

Crystal Structures of MgCrO₄-type Li₂VCl₄ and Spinel-type Li₂MgCl₄ and Li₂CdCl₄ The crystal structures of the ternary lithium chlorides Li₂MCl₄ (M = Mg, V, Cd) have been determined firstly by X-ray single-crystal experiments. Li₂MgCl₄ and Li₂CdCl₄ crystallize in an inverse spinel structure (space group Fd3 m, Z = 8, a = 1 040.1(2) and 1 062.06(9) pm, structural parameters u = 0.25699(2) and 0.2550(1), R = 1.7 and 3.7% for 218 and 211 unique reflections). The Li? Cl distances of the tetrahedrally coordinated Li⁺ ions are significantly greater than calculated with Shannon's crystal radii ( > 238 ± 1 instead of 233 pm). Contrary to the results of X-ray powder data reported in the literature, Li₂VCl₄ crystallizes in the distorted spinel structure of MgCr₂O₄ type (space group F4 3m, Z = 8, a = 1 037.49(2) pm, R = 5.9% for 217 unique reflections). The decrease of the site symmetry of the octahedrally coordinated ions (V²⁺, Li⁺) from 3 m to 3m resulting in contracted and widened tetrahedral M₄ entities of the spinel structure is obviously caused by V? V metal—metal bonds (shortest V? V distance 366.2(7) pm).     

Group IB organometallic chemistry: XXIX. Synthetic and structural aspects of polynuclear arylcopperlithium compounds Ar4Cu2Li2 (“arylcuprates”) and interaggregate exchange phenomena in Ar4Cu4/Ar4Li4/Ar4Cu2Li2 systems

The thermally stable arylmetal-IB-lithium compounds (2-Me₂NCHZC₆H₄)₄M₂Li₂ (M = Cu, Ag or Au; Z = H or Me) and (2-Me₂NC₆H₄)₄M₂Li₂ have been prepared by a $\text{2}\text{1}$ molar reaction of the aryllithium compounds with the corresponding metal-IB halide (Cu or Ag) or metal-lB halide phosphine complex (BrAuPPh₃). These tetranuclear complexes were also made by an interaggregate exchange reaction of the pure arylmetal-IB clusters with the aryllithium compound.The structure of these compounds in solution consists of aryl groups bridging one metal-lB and one lithium atom of a trans M₂Li₂ core. The four built-in ligands coordinate to lithium resulting in two-coordination at M and four-coordination at Li. These conclusions were based on ¹H and ¹³C NMR spectroscopic data (J(AgC(1)), J(LiC(1)) of solutions of these tetranuclear compounds as well as on the ¹⁹⁷Au Mössbauer data of solid (2-Me₂NC₆H₄)₄Au₂Li₂ (IS 5.65 mm/s and QS 12.01 mm/s).The interaggregate exchange between the tetranuclear species is discussed in terms of an associative mechanism involving formation of an octanuclear intermediate in which the aryl groups can migrate via (3c-2e)edge-(2c-2e)corner(3c-2e)edge movements without M₂Ar bond cleavage.Some aspects of the organic reactions in which organocuprates are involved as intermediates are discussed in terms of the novel structural information.     

Stereospecific polymerization of isobutyl vinyl ether. III. Polymerization with VCl3 • LiCl

The polymerization of isobutyl vinyl ether by vanadium trichloride in n-heptane was studied. VCl₃ ? LiCl was prepared by the reduction of VCl₄ with stoichiometric amounts of BuLi. This type of catalyst induces stereospecific polymerization of isobutyl vinyl ether without the action of trialkyl aluminum to an isotactic polymer when a rise in temperature during the polymerization was depressed by cooling. It is suggested that the cause of the stereospecific polymerization might be due to the catalyst structure in which LiCl coexists with VCl₃, namely, VCl₃ ? LiCl or VCl₂ ? 2LiCl as a solid solution in the crystalline lattice, since VCl₃ prepared by thermal decomposition of VCl₄ and a commercial VCl₃ did not produce the crystalline polymer and soluble catalysts such as VCl₄ in heptane and VCl₃ ? LiCl in ether solution did not yield the stereospecific polymer. It was found that some additives, such as tetrahydrofuran or ethylene glycol diphenyl ether, to the catalyst increased the stereospecific polymerization activity of the catalysts. Influence of the polymerization conditions such as temperature, time, monomer and catalyst concentrations, and the kind of solvent on the formed polymer was also examined.     

Polymerization of styrene with VCl4–aluminum alkyls

Polymerization of styrene has been carried out with VCl₄–AlEt₃ and VCl₄–Al(i-Bu)₃ catalyst systems. These two systems have been found to behave in a similar manner but their behavior is different from those systems where VOCl₃ has been used instead of VCl₄. Reaction is first order with respect to monomer concentration for both the systems and first order with respect to catalyst in the case of VCl₄–AlEt₃. In the case of VCl₄–Al(i-Bu)₃, the rate of polymerization is independent of catalyst concentration but intrinsic viscosities increase with increasing catalyst concentration. The average valence of vanadium in the catalyst complexes has been discussed in relation to nature of catalyst sites. Activation energy and effect of diethyl zinc support the anionic mechanism for the two systems.     

Synthesis,spectroscopic and structural characterisation of vanadium(IV) and oxovanadium(IV) complexes with arsenic donor ligands

The reaction of o-C₆H₄(AsMe₂)₂ with VCl₄ in anhydrous CCl₄ produces orange eight-coordinate [VCl₄{o-C₆H₄(AsMe₂)₂}₂], whilst in CH₂Cl₂ the product is the brown, six-coordinate [VCl₄{o-C₆H₄(AsMe₂)₂}]. In dilute CH₂Cl₂ solution slow decomposition occurs to form the V^III complex [V₂Cl₆{o-C₆H₄(AsMe₂)₂}₂]. Six-coordination is also found in [VCl₄{MeC(CH₂AsMe₂)₃}] and [VCl₄{Et₃As)₂]. Hydrolysis of these complexes occurs readily to form vanadyl (VO²⁺) species, pure samples of which are obtained by reaction of [VOCl₂(thf)₂(H₂O)] with the arsines to form green [VOCl₂{o-C₆H₄(AsMe₂)₂}], [VOCl₂{MeC(CH₂AsMe₂)₃}(H₂O)] and [VOCl₂(Et₃As)₂]. Green [VOCl₂(o-C₆H₄(PMe₂)₂}] is formed from [VOCl₂(thf)₂(H₂O)] and the ligand. The [VOCl₂{o-C₆H₄(PMe₂)₂}] decomposes in thf solution open to air to form the diphosphine dioxide complex [VO{o-C₆H₄(P(O)Me₂)₂}₂(H₂O)]Cl₂, but in contrast, the products formed from similar treatment of [VCl₄{o-C₆H₄(AsMe₂)₂}_x] or [VOCl₂{o-C₆H₄(AsMe₂)₂}] contain the novel arsenic(V) cation [o-C₆H₄(AsMe₂Cl)(μ-O)(AsMe₂)]⁺. X-ray crystal structures are reported for [V₂Cl₆{o-C₆H₄(AsMe₂)₂}₂], [VO(H₂O){o-C₆H₄(P(O)Me₂)₂}₂]Cl₂, [o-C₆H₄(AsMe₂Cl)(μ-O)(AsMe₂)]Cl·[VO(H₂O)₃Cl₂] and powder neutron diffraction data for [VCl₄{o-C₆H₄(AsMe₂)₂}₂].     

POLYMERIZATION OF ETHYLENE AND PROPYLENE WITH VCL4-BUTYLLITHIUM CATALYSTS

Polymerization of ethylene and propylene with VCl₄-BuLi (Bu = n-Bu, sec-Bu, tert-Bu) catalysts was investigated. The VCl₄-BuLi catalysts were found to initiate the polymerization of ethylene and propylene. The VCl₄-BuLi catalysts gave an ultra high molecular polyethylene. The effect of the Li /V mole ratio on the polymerization of ethylene with the VCl₄-BuLi catalysts was observed, an the catalyst gave an optimum rate at the Li/V ratio of about 3.0. The polyethylene obtained with the VCl₄-BuLi catalyst was found to be a linear structure. In the polymerization of propylene with the VCl₄-BuLi catalyst, the polymers contain mm contents of 56–66% were produced.     

(AsPh4)2[(μ-N2S2) (VCI5)2] Synthese,IR-Spektrum und Kristallstruktur

(AsPh₄)₂[(μ-N₂S₂)(VCl₅)₂]. Synthesis, I.R. Spectrum, and Crystal Structure From the reaction of VCl₄ and S₃N₂Cl₂ in CCl₄ solution a solid, black product mixture is obtained. From this, the title compound can be extracted by reaction with AsPh₄Cl in CH₂Cl₂ solution. It can also be synthesized from AsPh₄VCl₅ and S₃N₃Cl₃ in CH₂Cl₂ solution. The i.r. spectra of (AsPh₄)₂[(μ-N₂S₂)(VCl₅)₂] (black crystal plates) and AsPh₄VCl₅ (brown needles) are reported. The crystal structure of (AsPh₄)₂[(μ-N₂S₂)(VCl₅)₂] was determined by X-ray diffraction. It crystallizes in the monoclinic space group P2₁/c with two formula units per unit cell. The lattice constants are a = 1113.9, b = 1712.8, c = 1508.8 pm, β = 106.68°. The centrosymmetric [(μ-N₂S₂)(VCl₅)₂]^2? ion consists of two quadratic-pyramidal VCl₅ units which are linked via the N atoms of a N₂S₂ ring. The N₂S₂ ring shows positional disorder in two different orientations in the crystal. The AsPh₄⊕ ions form (AsPh₄⊕)₂ pairs via inversion centers, each pair is surrounded by eight anions.     

Stereoselective formation of Z-monofluoroalkenes by nickel-catalyzed defluorinative coupling of gem‑difluoroalkenes with lithium organoborates

A method for stereoselective construction of Z-monofluoroalkenes by nickel-catalyzed defluorinative coupling of gem?difluoroalkenes in mild conditions was described. The combination of lithium organoborate and ZnBr₂ generated in situ lithium aryl zincates, which facilitates the transmetalation step of the nickel-catalyzed cross coupling reaction.     

Aryl N- and O-trimethylsilyl substituents: reactivity toward organolithium compounds

The efficacy of using the trimethylsilyl group for protection of aryl amino and hydroxy substituents during reactions involving organolithium reagents has been assessed. Bromotrimethylsiloxy-benzenes or -pyrimidines reacted with $\text{n}$-butyl lithium by initial metal-halogen exchange followed by intra- or intermolecular rearrangement of trimethylsilyl from oxygen to the carbanionic center. Trimethysilyl groups on aryl nitrogen are stable to conditions of organolithium coupling reactions. It is suggested that for aryl 0- and aryl N-trimethylsilanes, the observed differences in reactivity at silicon are owing to the marked differences in basicity of the respective leaving groups (PhOH ? Ph0-, pK_A - 10, pHNH₂ ? PhNH^?, pK_A ? 25).     

Preparation and characterization of Cu supported on 2-(1H-benzo[d]imidazol-2-yl)aniline-functionalized Fe3O4 nanoparticles as a novel magnetic catalyst for Ullmann and Suzuki cross-coupling reactions

Copper supported on 2-(1H-benzo[d]imidazol-2-yl)aniline (BIA)-functionalized Fe₃O₄ nanoparticles (Cu-BIA-Si-Fe₃O₄) as a novel magnetic catalyst was designed and used for the synthesis of new products via Ullmann and Suzuki cross-coupling reactions. The Ullmann reaction was performed by mixing arylboronic acid with aniline derivatives in dimethylsulfoxide solvent. Also, diaryls were synthesized via Suzuki C–C reactions between aryl halides and phenylboronic acid in the same solvent. The prepared materials and catalyst were characterized with various analytical techniques. The Cu-BIA-Si-Fe₃O₄ catalyst demonstrated catalytic efficiency with good to excellent yields for both types of reactions in comparison with commercial palladium catalysts. Also, the catalyst could be recovered by a simple filtration and retained its activity even after several cycles.     

EPR- und Ligandenfeld-Spektren von Chlorovanadaten(IV). Die Kristallstruktur von PPh4[VxTi2–xCl9] (x = 0,15)

E.P.R. and Ligand Field Spectra of Chlorovanadates(IV). The Crystal Structure of PPh₄[V_xTi_2–xCl₉] (x = 0.15) Black, moisture-sensitive crystals of PPh₄[V_xTi_2–xCl₉] (x = 0.15) are formed by the reaction of titanium tetrachloride and PPh₄[VCl₅] in dichloromethane. Its EPR and ligand field spectra as well as those of PPh₄[VCl₅] and (PPh₄)₂[V₂Cl₉][VCl₅] · CH₂Cl₂ were recorded. In the mixed crystals of PPh₄[V_0.15Ti_1.85Cl₉], the existence of [VTiCl₉]^? ions consisting of trigonally distorted, face sharing octahedra can be proven by the spectra. The spectra of the compounds with [VCl₅]^? ions can only be explained when a significant Jahn-Teller distortion of the trigonal bipyramids is assumed; this distortion was not detected in the crystal structure determination of (PPh₄)₂[V₂Cl₉][VCl₅] · CH₂Cl₂. The crystal structure of PPh₄[V_0.15Ti_1.85Cl₉] was determined by X-ray diffraction (2588 independent observed reflexions, R = 0.044). Crystal data: triclinic, space group P1 , a = 1090.4, b = 1217.4, c = 1287.7 pm, α = 73.19°, β = 69.87°, γ = 82.15°, Z = 2. The compound consists of PPh₄^⊕ and [V_0.15Ti_1.85Cl₉]^? ions. In the anions, Ti and V atoms are distributed statistically in the two face sharing octahedra.     

(PPh4)2[V2Cl9][VCl5] · CH2Cl2 Synthese,IR-Spektrum und Kristallstruktur

(PPh₄)₂[V₂Cl₉][VCl₅] · CH₂Cl₂. Synthesis, I.R. Spectrum, and Crystal Structure The title compound was obtained by addition of CCl₄ to a solution of PPh₄Cl and excess VCl₄ in CH₂Cl₂. It forms black crystals which are light and moisture sensitive. The i.r. spectrum is reported. The crystal structure was determined by X-ray diffraction (3044 independent reflexions, R = 0.063). Crystal data: triclinic, space group P1 , Z = 2, a = 1186, b 1325, c = 1995 pm, α 97.5, β 105.6°, γ 93.4°. The structure consists of PPh₄⁺ cations, V₂Cl₉? and VCl₅? anions and CH₂Cl₂ molecules. The V₂Cl₉? ions consist of face-sharing octahedra with a long V…?V distance of 333 pm; the VCl₅? ions form nearly ideal trigonal bipyramids with V? Cl bonds of 228 pm (axial) and 218 pm (equatorial). Both anions deviate only marginally from D_3h symmetry. Half of the cations is arranged to (PPh₄⁺)₂ pairs about inversion centers.     

Spectrophotometric investigation of the mechanism of polymerization of isobutylene with vanadium tetrachloride and visible light

The spectra of n-heptane solution of VCl₄, isobutylene, and their mixture at temperatures ranging from +25 to ?80°C in the range of wavelengths from 200 to 2000 nm were investigated. In the region of wavelengths of visible light (400–700 nm) in which the absorption of isobutylene alone and of VCl₄ (concentration lower than 2.2 × 10^?4 mole/l.) is practically zero, their mixtures exhibit an absorption which depends on the concentration of both components and on temperature. A colored complex of VCl₄ and isobutylene is thus obtained, the concentration of which increases with decreasing temperature and is in equilibrium with that of the starting components. The polymerization of isobutylene under the experimental conditions investigated here probably is initiated with the isobutylene–VCl₄ complex after its excitation with light or heat. At low temperatures (t < ?20°C), when the polymerization of isobutylene with VCl₄ virtually does not take place at all in the dark, only excitation with light is operative in the initiation, while at higher temperatures (t > +10°C) thermal excitation plays the predominant role.     

Massenspektrometrische Beobachtungen und chemische Transportexperimente mit den Systemen VCl3/Al2Cl6 und VCl2/Al2Cl6

Mass Spectroscopic Observations and Chemical Transport Experiments with the Systems VCl₃/Al₂Cl₆ and VCl₂/Al₂Cl₆ By mass spectrometry the equilibrium VCl_3,s + 0.5 Al₂Cl_6,g ? VAlCl_6,g has been determined: ΔH°(298) = 25.6(±0.5) kcal; ΔS°(298) = 23.0(±3) cal/K, ΔCp (assumed) = ?4 cal/K. This is approximately in agreement with results determined by ligand field spectroscopy by ANUNDSKÅS and ØYE (A. and Ø.). For the dimerization of VCl_3,g values for ΔH and ΔS have been derived. The molecule VAl₂Cl₉ assumed by A. and Ø. could not been observed by mass spectrometry. For the VCl₂/Al₂Cl₆ complex, observed by chemical transport, A. and Ø. give the formula VAl₃Cl₁₁. This molecule could not been observed by mass spectrometry. This suggests a smaller concentration, compared with the results of A. and Ø. Stabilization of VCl_2,s (by metal-nietal-bonds) shifts the reaction to the left, whith explains the lower complex concentration as well as the larger molecular weight of the complex. With chlorides stabilized by stronger metal-metal bonds (MoCl₃, MoCl₂, Nb₃Cl₈) AlCl₃ complexes are not formed in observable concentrations. The chemical transport of VCl₂ with Al₂Cl₆ needs relatively high temperatures (973 → 873 K). In this case the addition of SiCl₄ hinders the attack of the quartz ampoule by Al₂Cl₆. Using a VCl₃ + VCl₂ mixture, VCl₃ is transported by Al₂Cl₆ (673 → 623 K) into the colder region. If afterwords the ampoule is reversed, VCl₃ again moves into the colder region, but the thermal decomposition of VCl₃ at the same time causes that a VCl₂-residue remains in the hot region.     

Neutron diffraction and electrochemical studies on LiIrSn4

Large quantities of single phase, polycrystalline LiIrSn₄ have been synthesised from the elements by melting in sealed tantalum tubes and subsequent annealing. LiIrSn₄ crystallises with an ordered version of the PdGa₅ structure: I4/mcm, a=655.62(8), . The lithium atoms were clearly localised from a neutron powder diffraction study: R_P=0.147 and R_F=0.058. Time-dependent electrochemical polarisation techniques, i.e. coulometric titration, chronopotentiometry, chronoamperometry and cyclic voltammetry were used to study the kinetics of lithium ion diffusion in this stannide. The range of homogeneity (Li_1+ΔδIrSn₄, −0.091?δ?+0.012) without any structural change in the host structure and the chemical diffusion coefficient (∼10⁻⁷-10⁻⁹ cm²/s) point out that LiIrSn₄ is a first example of a large class of intermetallic compounds with lithium and electron mobility. Optimised materials from these ternary lithium alloys may be potential electrode material for rechargeable lithium batteries.     

Lithium aluminate-doped lithium orthosilicate: Sol-gel ceramics and lithium dynamics

Dense ceramics (Li_4+xSi_1−xAl_xO₄ with 0 ≤ x ≤ 0.3) are obtained by sintering at 700–900°C, without prior calcination, of sol-gel powders prepared by an alkoxide-hydroxide route. In comparison with the pure lithium orthosilicate (3 × 10⁻⁴ S · cm⁻¹ at 350°C), only a slight enhancement of the ionic conductivity is noted for monophase ceramics with Li₄SiO₄-type structure (5 × 10⁻⁴ S · cm⁻¹ at 350°C for x = 0.3). Higher conductivity (2 × 10⁻² S · cm⁻¹ at 350°C) is observed for an heterogeneous material formed of a lithium silicoaluminate phase (x = 0.2) with the Li₄SiO₄-type structure coexisting with lithium hydroxide. In this two-phase material, ac conductivity and ⁷Li spin-lattice relaxation data are consistent with the formation of a new kinetic path, via a thin layer along the interface, which enhances the lithium mobility.