Insertion of unactivated acetylenes into the metal-aryl bond of bis(triphenylphosphine)phenylbromonickel(II)

2-Butyne reacts stereospecifically with (PPh₃)₂Ni(Ph)(Br) in CH₃OH at room temperature, leading to the isolable vinyl complex trans-(PPh₃)₂-Ni(Br)[cis-C(CH₃)C(CH₃)(Ph)] in 70% yield. Carbonylation (CO/CH₃OH) of this material gives a 98% yield of cis-α,β-dimethylcinnamate. Reaction of the phenylnickel complex with 3-hexyne is more complicated; insertion again occurs, but the ultimate products of the reaction are phenyl-substituted styrenes and butadienes. Evidence is presented that free vinyl radicals are involved as intermediates in the 3-hexyne reaction.     

Vanadium(III) dithiophosphate complex [V(S2P(O-iso-Pr)2)3]: synthesis and structure

The reaction of [VO(OPr)₃] with (iso-PrO)₂P(S)SH (Pr is n-propyl, and iso-Pr is isopropyl) followed by the treatment with hexamethyldisilthiane (Me₃SiSSiMe₃) affords the vanadium(III) dithiophosphate complex [V(S₂P(O-iso-Pr)₂)₃]. The structure of the complex is determined by X-ray diffraction analysis (CIF file CCDC 986354).     

Thermodynamics of formation for the 18-crown-6-triglycine molecular complex in water-dimethylsulfoxide solvents

The effect of a water-dimethylsulfoxide (DMSO) solvent on the formation of a molecular complex of 18-crown-6 (18C6) with triglycine (diglycylglycine, 3Gly) is studied via calorimetric titration. It is found that switching from water to an H₂O-DMSO mixture with DMSO mole fraction of 0.30 is accompanied by a monotonic increase in the stability of [3Gly18C6] complex, from logK ^° = 1.10 to logK ^° = 2.44, and an increase in the exothermicity of the reaction of its formation, from ?5.9 to ?16.9 kJ/mol. It is shown that the [3Gly18C6] complex exhibits enthalpy stabilization with negative values of enthalpy and entropy over the investigated range of H₂O-DMSO solvents. Analysis of the reagents’ solvation characteristics reveals that the increase in the reaction’s exothermicity of transfer is due to differences in the solvation of [3Gly18C6] and 18C6 with a small solvation contribution from 3Gly. It is concluded that the change in the Gibbs energy of the reaction 3Gly_solv + 18C6_solv ? [3Gly18C6]_solv is due to differences in the change in the solvation state of the complex and the peptide (Δ_tr G ^°([3Gly18C6])-Δ_tr G ^°(3Gly)).     

Tert-butylborane: A bis (σ-B-H) ligand in ruthenium hydride chemistry

The reaction of tert-butylborane with the bis(dihydrogen) complex RuH₂(η²-H₂)₂(PCy₃)₂ leads to the corresponding bis σ-borane complex which is the first example of a monoalkylborane ruthenium bis σ-complex. An alternative route involves the reaction of RuHCl(η²-H₂)(PCy₃)₂ with lithium tert-butylborohydride.     

Formal aza-Michael additions to tropone: Addition of diverse aryl- and alkylamines to tricarbonyl(tropone)iron and [(C7H7O)Fe(CO)3]BF4

A formal aza-Michael addition to tropone by way of tricarbonyl(tropone)iron and/or the tetrafluoroborate salt formed via protonation of the complex is reported. Tricarbonyl(tropone)iron smoothly undergoes the direct aza-Michael reaction with unhindered aliphatic amines under solvent free conditions in good yields. Meanwhile, the known cationic complex [(C₇H₇O)Fe(CO)₃]BF₄ (whose reaction with a small number of nucleophiles was previously reported) undergoes addition with an even broader array of amine nucleophiles. Finally, it was discovered that protecting the aza-Michael adduct as a carbamate was necessary for oxidative demetallation of the complex.     

trans-Bis-[(−)ephedrinate]-palladium complex: synthesis, molecular modeling and use as catalyst

The reaction between palladium acetate, (−)-ephedrine and potassium acetate led to bis-chelate complex Pd[OCH(Ph)NH(Me)]₂ whose the trans-structure is obtained from calculations. The use of this complex to catalyze either the 1,4-hydrogenation of (E)-2-benzyliden-1-tetralone or Heck reaction of phenyl iodide with 3-methyl-3-buten-2-ol led to a low enantiomeric excess.     

The reaction between HO and (H2O) n (n?=?1, 3) clusters: reaction mechanisms and tunneling effects

The reaction between the HO radical and (H₂O)n (n?=?1, 3) clusters has been investigated employing high-level quantum mechanical calculations using DFT-BH&HLYP, QCISD, and CCSD(T) theoretical approaches in connection with the 6-311?+?G(2df,2p), aug-cc-pVTZ, and aug-cc-pVQZ basis sets. The rate constants have also been calculated and the tunneling effects have been studied by means of time?Cdependent wavepacket calculations, performed using the Quantum?CReaction Path Hamiltonian method. According to the findings of previously reported theoretical works, the reaction between HO and H₂O begins with the formation of a pre-reactive complex that is formed before the transition state, the formation of a post-reactive complex, and the release of the products. The reaction between HO and (H₂O)₂ also begins with the formation of a pre-reactive complex, which dissociates into H₂O??HO?+?H₂O. The reaction between HO and (H₂O)₃ is much more complex. The hydroxyl radical adds to the water trimer, and then it occurs a geometrical rearrangement in the pre-reactive hydrogen-bonded complex region, before the transition state. The reaction between hydroxyl radical and water trimer is computed to be much faster than the reaction between hydroxyl radical and a single water molecule, and, in both cases, the tunneling effects are very important mainly at low temperatures. A prediction of the atmospheric concentration of the hydrogen-bonded complexes studied in this work is also reported.     

Catalysis of hydrosilyation.: XII. Spectrophotometric study of the reactivity of the [RhCl(COD)]2-bis(dipenylphosphinoethyl)-tetramethyldisiloxane complex with substrates of the hydrosilylation reaction

The reactivity of the model complex - [RhCl(COD)]₂ - bis(diphenylphosphineethyl)etramethyldisiloxane (I) with the substrates of the hydrosilylation (1-hexene and triethoxysilane) has been studied spectrophotometrically at room temperature. Disappearance of the band at 24.4 × 10³ cm⁻¹, characteristic for the square planar complex, I, enabled us to determine pseudo first-order rate constants (k_obs) for the reaction. Relative values of k_obs indicate that the reaction is four times faster with 1-hexene than with triethoxysilane. Inhibition by added siloxyphosphine (BPS-2) is evidence for preliminary replacement of phosphine by 1-hexene. Consequently, for silica-supported catalysts of the BPS ligand structure the anchored complex is released into solution during the reaction and catalyses the process homogeneously.     

Amino acid-functionalized cyclopentadienyl molybdenum tricarbonyl complex and its use in catalytic olefin epoxidation

The complex [(N-benzyloxycarbonylprolyl)cyclopentadienyl]-Mo(CO)₃Me was prepared by the reaction of the amino acid-functionalized cyclopentadienyl-lithium reagent with Mo(CO)₆, and subsequent methylation with CH₃I. The complex was characterized by FTIR, ¹H and ¹³C NMR, and elemental analysis. A single-crystal X-ray diffraction study showed that the complex is chiral, crystallizing in the orthorhombic P2₁2₁2₁ space group with the Flack parameter refining to –0.007(16), which unequivocally confirms the presence of an enantiomerically pure compound. The complex was examined as a catalyst precursor in the liquid-phase epoxidation of trans-β-methylstyrene at 280–330 K, using either tert-butylhydroperoxide (tert-BuOOH), cumylhydroperoxide or urea-hydrogen peroxide adduct as oxidant, and, optionally, a co-solvent. With chloroform and tert-BuOOH, the catalytic activity surpasses that previously reported for chiral complexes of the type CpMo(CO)₃X, giving the epoxide isomers ((R,R)-(+) and (S,S)-(?)-1-phenylpropylene oxide) in excellent selectivity, albeit with negligible enantiomeric excess. FTIR spectroscopy showed that the oxidative decarbonylation of the tricarbonyl complex with tert-BuOOH is fast under the reaction conditions used, and that the structural integrity of the amino acid-functionalized cyclopentadienyl group is retained during this process. The use of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate as a solvent for the catalyst generates a biphasic liquid–liquid reaction system that enables, at the end of a catalytic cycle, the separation and reutilization of the catalyst.     

An exceptionally stable cis-(hydride)(η2-dihydrogen) complex of iron

The cis-(H)(H₂ complex [(PP₃)Fe(H)(H₂)]BPh₄ (PP₃  P(CH₂CH₂PPh₂)₃) has been made by reaction of the chloride [(PP₃)FECl]BPh₄ in THF with NaBH₄ under 1 atm of H₂. In the solid state and in solution at low temperature the complex is octahedral, and the hydride and dihydrogen ligands occupy mutually cis positions. At ambient temperature in solution the complex is trigonal-bipyramidal, and an “H₃” unit occupies an axial position trans to the bridgehead phosphorus atom of PP₃; this results in exceptional thermal and chemical stability of the complex.     

Trindenyl[tris(rheniumtricarbonyl)]

Trindene is combined with KH and [Re(CO)₃(THF)Br]₂ (THF = tetrahydrofuran) in THF to yield the first trinuclear half-sandwich complex of the trindene trianion, (trindenyl)[Re(CO)₃]₃, in 50% yield. Two of the rhenium carbonyl units are rigidly held in close proximity and the carbonyl ligands on adjacent metals are vibrationally coupled. Both cis and trans isomers of the dirhenium complex, (trindenyl)[Re(CO)₃]₂, are also isolated from the above reaction in low yield.     

The isomerization of n-butenes catalyzed by RhCl(PPh3)3. II. The isomerization of 1-butene

1-butene is catalytically isomerized by RhCl(PPh₃)₃ in dichloromethane solution. The slow reaction starts with an induction period and reaches the equilibrium distribution of the three n-butenes. The pseudo first order reaction rate, as taken from the second half of the reaction, depends on the square root of the catalyst concentration and the inverse of the concentration of free triphenylphosphine. At relatively low butene concentrations the reaction rates fall off. This is interpreted as meaning that a PPh₃—butene ligand exchange equilibrium is essential for the activation of the catalyst. ³¹P n.m.r. spectroscopy suggested that a trans-RhCl(PPh₃)₂(C₄H₈) complex existed in solution. Because of the high cis-2-butene/trans-2-butene ratio formed at the beginning of the reaction the activation of the olefinic double bond is thought to occur via a π-allyl mechanism.     

Electron-Deficient Borinic Acid Polymers: Synthesis,Supramolecular Assembly,and Examination as Catalysts in Amide Bond Formation

The Lewis acidic character of borinic-acid-functionalized polymers suggests broad potential applications in supramolecular materials, chemo- and biosensors, as well as supported catalysts. Two highly electron-deficient borinic acid copolymers ( 3 a and 3 b ) with variable steric hindrance at the boron center were prepared by reaction of aryldibromoboranes ArBBr₂ ( 2 , Ar=2,4-Cl₂Ph, 3,5-Cl₂Ph) with a 10 % stannylated polystyrene random copolymer, followed by conversion to the desired PS-B(Ar)OH functionalities. The supramolecular assembly of these polymers through Lewis acid–Lewis base interactions and reversible covalent B−O−B bond formation was investigated. Exposure of a polymer solution of 3 a to pyridine triggered spontaneous gelation, whereas 3 b only gelled upon addition of molecular sieves to favor formation of boroxane crosslinks. The crosslinking process was readily reversed by addition of small amounts of water or wet solvent. The dynamic processes were studied in detail by variable-temperature (VT) NMR by using molecular model compounds. The polymers and their corresponding model compounds were also examined as catalysts in the amide bond formation reaction between phenylacetic acid and benzylamine. The 3,5-dichlorophenyl borinic acid derivatives proved to be the more effective catalysts. Mechanistic studies suggested that the borane Lewis acid-catalyzed coupling involves initial acid-induced protodeboronation to release the dichlorophenyl boronic acid as the active catalyst.     

Mono- and dinuclear copper(II) complexes with meta-phenylene-bridging ligands: Synthesis,structure and magnetic properties

The new double-Schiff-base ligand H₆ipa-bhea has been synthesized by condensation of a 4,6-diformylresorcinol derivative (ipa) with two equivalents of N,N-bis-(2-hydroxyethyl)ethylenediamine (bhea). Reaction with copper(II) perchlorate leads to the formation of two different products depending on the reaction conditions. The directed synthesis of either a mononuclear or dinuclear copper(II) complex is reported. The reaction in methanol results in the formation of a dinuclear complex [Cu₂(H₄ipa-bhea)](ClO₄)₂ (1). Whereas in the presence of water as solvent for the reaction, one imine side chain of the ligand is hydrolyzed regenerating the formyl moiety with the mononuclear complex [Cu(H₃hyforsa-bhea)]ClO₄ · 2H₂O (2) as final product. Subsequent reaction of complex 2 with N,N-bis-(pyridin-2-ylmethyl)ethylenediamine (unspenp) as additional amine component results in the formation of the mononuclear complex [Cu(Hhyforsa-unspenp)]ClO₄ (3). All complexes are characterized by IR spectroscopy, elemental analysis and X-ray crystallography. Temperature-dependent magnetic measurements on the dinuclear complex indicate weak antiferromagnetic exchange interactions between the copper(II) ions with a coupling constant of J = ?16.4 cm^?1. Density functional calculations have been used to evaluate the magnetic properties. The exchange coupling constant can be nicely reproduced with the use of the broken symmetry approach. The exchange pathway through the meta-phenylene-linkage is discussed in terms of a competitive spin-polarization and superexchange mechanism as well as geometrical changes at the copper(II) ions.     

Microwave-assisted dissolution of ceramic uranium dioxide in TBP–HNO3 complex

Microwave-assisted dissolution of ceramic uranium dioxide in tri-n-butyl phosphate (TBP)–HNO₃ complex was investigated. The research on dissolution of ceramic uranium dioxide in TBP–HNO₃ inclusion complex under microwave heating showed the efficiency of the use of this method. Nitric acid present in the inclusion complex participates both dissolution of UO₂, and oxidation of U(IV)–U(VI), the resulting UO₂(NO₃)₂ extracted with tri-n-butyl phosphate. Dissolution rate depends on both temperature of microwave dissolution process, and concentration of nitric acid present in the inclusion complex. The most intensive dissolution process is when the concentration of nitric acid ≥2 mol/L and the temperature of 120 °C. From the experimental data obtained by two kinetic models activation energies were calculated. At the average activation energy of UO₂ dissolution in TBP–HNO₃ complex equal 70 kJ/mol, and reaction order is close to one, i.e. the reaction takes place in an area close to kinetic.     

Kinetische und mechanistische untersuchungen von übergansmetallkomplex-reaktionen: XXI. Einfluss von zentralmetall,trans-X-ligand und carbinsubstituent auf die MCO-dissoziation in carbin-komplexen des typs trans-X(CO)4MCR

The influence of the central metal atom, the trans-X ligand, and the carbyne substituent R on the MCO dissociation step of seventeen different carbyne complexes, trans-(CO)₄MCR (X = Cl, Br, I, SePh; M = Cr, W; R = Me, aryl, NEt₂), in 1,1,2-trichloroethane was studied by means of the substitution of one CO ligand by PPh₃. All complexes react with PPh₃ according to the first-order rate equation: — d[complex]/dt = k[complex]. The activation enthalpies ΔH³ are in the range 97–116 kJ mol⁻¹, the activation entropies ΔS³ are 34 to 72 J mol⁻¹ K⁻¹. The reaction rate, (i) is virtually independent of the electronic properties of R, (ii) decreases slightly with increasing steric requirements of R, (iii) increases strongly in the series trans-X = I, Br, Cl, SePh, and (iv) is faster for chromium complexes than for analogous tungsten compounds by a factor of ca. 30 to 50. There is no general correlation between the rate constants k and the CO force constants k(CO). The variation in the reaction rate is essentially determined by the different levels of stabilization of energy in the transition state. The thermolysis of carbyne complexes is also initiated by CO dissociation. The rate of thermolysis when [CO] = 0 is equal to the rate of CO/PPh₃ substitution; it decreases rapidly with increasing CO concentration in the solution; and when [CO] = constant it increases significantly with increasing concentration of the complex. A mechanistic scheme is proposed for the thermolysis which involves three different reaction pathways for the coordinatively unsaturated fragment X(CO)₃MCR formed by CO dissociation from trans-X(CO)₄MCR: readdition of CO, monomolecular decomposition, and reaction with trans-X(CO)₄MCR.     

Silver(I) thiosemicarbazone complex [Ag(catsc)(PPh3)2]NO3: Synthesis,characterization, crystal structure,and antibacterial study

We report the synthesis, characterization and crystal structure of a new mononuclear silver(I) complex, [Ag(catsc)(PPh₃)₂]NO₃ (catsc = 3-phenylpropenalthiosemicarbazone). The complex was prepared by the reaction of catsc and AgNO₃ in the presence of PPh₃ and characterized by elemental analysis (CHN), FTIR, ¹H, ¹³C and ³¹P NMR spectroscopy, and single-crystal X-ray diffraction. In the complex, catsc acts as a bidentate NS ligand while the nitrate is a counter ion. The silver ion is coordinated by a bidentate ligand and two PPh₃ in the form of a distorted tetrahedron. In addition, the antibacterial effect of the complex was studied against the standard strains of two gram-positive (Staphylococcus aureus and Enterococcus faecalis) and two gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria.     

Preparation and properties of the formamidino complexes [M(π-C5H5){HC(NR)2}(CO)2] (M = molybdenum or tungsten; R = aryl or alkyl)

The preparation and properties of the complexes [M(π-C₅H₅){HC(NR)₂}CO)₂] (M = Mo, W; R = aryl or alkyl) are reported. The complex [Mo(π-C₅H₅){HC(N-p-tolyl)₂}(CO)₂] could be prepared by (a) reaction of MoCp(CO)₃Cl with M′{HC(N-p-tolyl)₂} (M′ = K, Ag or Cu); (b) irradiation of MoCp(CO)₃Cl with HC(HN-p-tolyl)N-p-tolyl); and (c) reaction of [MoCp(CO)₃]₂ with M′{HC(N-p-tolyl)₂} (M′ = Ag or Cu). The several routes to this complex give indications of the mechanisms of formation. The structure of these complexes and the bonding nature of the metal with the formamidino group is discussed on basis of the ¹H and ¹³C NMR and IR spectra.Reaction of N,N′-dimethyl formamidine with MCp(CO)₃Cl gave the complex [M(π-C₅H₅){HC(NMe)N(CO)Me}(CO)₂], containing a carbonyl inserted between the metal and the formamidino group. Irradiation of this carbamoyl complex caused decarbonylation, yielding the complex [M(π-C₅H₅){HC(NMe)₂}CO)₂].     

Reaction of trans-[Co(en)2(SO3)(H2O)]+ with imidazole and containing ligands

trans-[Co(en)₂(SO₃)(H₂O)]⁺ reacts with imidazole (ImH) and imidazole containing ligands (L) to form trans-[Co(en)₂(SO₃)L]⁺ in the pH range 6.0–9.0. The complex seems to react both in the hydroxy and in the aquo form. The rate constant for the reaction of imidazole with the aquo form is 6.0±0.7 and 4±1M^?1s^?1 for the reaction with the hydroxy form at 25°C. The apparent equilibrium constant for formation of the imidazole complex at pH 7 is consistent with the value of 3 x 10² measured previously. Appreciable amounts of complex form only in the pH 6–9 range. Above pH 9 NMR spectra show that even the immediate products are different. In aged solutions at all pHs other products form.     

Interaction of LnCl3 · 6H2O crystal hydrates with the alkoxy derivatives of aluminum in organic solvents

The interaction of LnCl₃ · 6H₂O (Ln = Pr, Nd, and Tb) with the alkoxy derivatives of aluminum (RO)_nAlCl_3?n (where R = Et or iso-Bu; n = 1–3) in organic solvents was studied. It was found that the reaction of the crystal water of LnCl₃ · 6H₂O with (RO)_nAlCl_3?n resulted in the partial dehydration of the crystal hydrates with the formation of an alcohol (ROH) and the LnCl₃ · 3H₂O · 3(RO)_mAl(OH)Cl_2?m complex (m = 1, 2). The solid colloidal particles of this complex and a solvent form a lanthanide-containing gel. The physicochemical (including luminescence) and catalytic properties of the complex in butadiene polymerization and 1,1-gem-dibromo-2-phenylcyclopropane dehalogenation were studied.