Theoretical insight into stereodynamics of the O(D) + H2 (v = 0–3, j = 0) → OH + H reaction: A quasiclassical trajectory (QCT) study

In this work, the reaction O(¹D) + H₂ → OH + H has been theoretically studied using the quasiclassical trajectory (QCT) method developed by Han and co-workers. All the quasiclassical trajectory calculations are performed on the DK (Dobbyn and Knowles) potential energy surface (PES). The vector correlation information on the reaction O(¹D) + H₂ → OH + H has been obtained. It has been demonstrated that the product alignment is sensitive to the reactant vibrational quantum number (v) at collision energy of 19 kcal/mol. Moreover, with increasing the value of v, backward scattering becomes weaker and forward scattering becomes stronger.     

On the synthesis and structures of the complexes [RuCl(L)(dppb)(N–N)]PF6 (L = CO,py or 4-NH2py; dppb = 1,4-bis(diphenylphosphino)butane; N–N = 2,2′-bipyridine or 1,10-phenanthroline) and [(dppb)(CO)Cl2-Ru-pz-RuCl2(CO)(dppb)] (pz = pyrazine)

The “Ru(P–P)” unit (P–P = diphosphine) is recognized to be an important core in catalytic species for hydrogenation of unsaturated organic substrates. Thus, in this study we synthesized six new complexes containing this core, including the binuclear complex [(dppb)(CO)Cl₂Ru-pz-RuCl₂(CO)(dppb)] (pz = pyrazine) which can be used as a precursor for the synthesis of cationic carbonyl species of general formula [RuCl(CO)(dppb)(N–N)]PF₆ (N–N = diimine). Complexes with the formula [RuCl(py)(dppb)(N–N)]PF₆ were synthesized by exhaustive electrolysis of these carbonyl compounds or from the precursors [RuCl₂(dppb)(N–N)]. The new complexes were characterized by microanalysis, conductivity measurements, IR and ³¹P{¹H} NMR spectroscopy, cyclic voltammetry and X-ray crystallography.     

Germylene and stannylene (Me2NCH2CH2O)2E as strong σ-donor ligands for transition metal complexes [ML(CO)n] (E = Ge, Sn; M = Cr, Mo, W, n = 4 or 5; M = Fe, n = 4). Synthesis, spectroscopic and theoretical study

A series of germylene and stannylene (Me₂NCH₂CH₂O)₂E (E = Ge, 1; E = Sn, 2) complexes of group 6 metals and iron carbonyls L·M(CO)_n (M = Cr, Mo, W, n = 5 (3-8), n = 4 (9, 10); M = Fe, n = 4 (11, 12)) were prepared. These complexes were characterized by ¹H, ¹³C NMR, FTIR and elemental analysis. Ligand properties of 1 and 2 were compared to PPh₃ and dmiy (N,N′-dimethylimidazolin-2-ylidene) using theoretical calculations (PBE/TZ2P) and FTIR. Ligand dissociation energies increase in the order Ph₃P < 2∼1 < dmiy, while donor strength rise in the order PPh₃ < dmiy < 2 < 1.     

Hydrolytic disproportionation of coordinated white phosphorus in [CpRu(dppe)(η-P4)]PF6 [dppe = 1,2-bis(diphenylphosphino)ethane]

The reaction of [CpRu(dppe)Cl] (1), dppe = 1,2-bis(diphenylphosphino)ethane, with one equivalent of P₄ in the presence of TlPF₆ affords the stable complex [CpRu(dppe)(η¹-P₄)]PF₆ (2) which contains the tetrahedral P₄ molecule η¹-bound to the metal. The tetraphosphorus ligand readily reacts with water upon mixing acetone or THF solutions of the complex with excess water. The complexes [CpRu(dppe)(PH₃)]PF₆ (5) and [CpRu(dppe){P(OH)₃}]PF₆ (6), identified among the hydrolysis products, contain the PH₃ molecule and, respectively, the unstable P(OH)₃ tautomer of the phosphorous acid bound to the CpRu(dppe) fragment. In CH₂Cl₂ the coordinated P(OH)₃ molecule in 6 easily yields the compound [CpRu(dppe){PF(OH)₂}]PF₂O₂ (8), via hydrolysis of the hexafluorophosphate anion and F/OH substitution in the coordinated P(OH)₃ molecule. All the compounds have been characterized by elemental analyses and NMR measurements. The crystal structures of 2 and 8 have been determined by X-ray diffraction methods.     

Insertion reaction of elemental sulfur into the Ln–C bond: Synthesis and characterization of [(C5H4SiMe2Bu)2Ln(μ-SR)]2 (R = Me,Ln = Yb,Er, Dy,Y; R = Bu,Ln = Yb,Dy)

Treatment of (C₅H₄SiMe₂^tBu)₂LnR with 1 equiv of elemental sulfur in toluene at ambient temperature gives dimeric complexes [(C₅H₄SiMe₂^tBu)₂Ln(μ-SR)]₂ [R = Me, Ln = Yb (1), Er (2), Dy (3), Y (4); R = ⁿBu, Ln = Yb (5), Dy (6)]. All these complexes have been characterized by elemental analysis, IR and mass spectroscopies. The structures of complexes 1, 3, 5 and 6 are also determined through X-ray single crystal diffraction analysis, indicating that only one sulfur atom from elemental sulfur inserts into Ln–C σ-bond.     

[M(dipicH2)(H2O)3], M = Ni,Cu, Zn (dipicH2 = dipicolinic acid) – A combined crystallographic,spectroscopic and computational study

Cationic metal complexes of dipicolinic acid (dipicH₂) are stabilized by [Ce(dipic)₃]²⁻ ions in the three isomorphous crystals [M(dipicH₂)(OH₂)₃][Ce(dipic)₃] · 3H₂O (M = Ni, 1; Cu, 2; Zn, 3). Magnetic dilution provided by the bulky anions leads to well-resolved EPR spectra in polycrystalline samples of 2. The cations have 4+2 coordination, the carbonyl atom of the carboxylic acid groups coordinating weakly from trans positions. In the case of 2 this steric distortion is augmented by Jahn–Teller distortion. All the three structures are satisfactorily modelled by calculations based on density functional theory (DFT). The switch of the Jahn–Teller axis upon deprotonation of the complex, leading to the neutral species Cu(dipic)(H₂O)₃, is also reproduced by DFT. Electronic transition energies as well as the g-tensor component of the d⁹ complex obtained are in good agreement with experiment. However, the calculated hyperfine coupling constants are in error. DFT also fails to satisfactorily account for the electronic transition in the d⁸ ion in 1.     

Dependence of the product on the P–P ligand in reactions of [RuCl3(NO)(P–P)] complexes (P–P = aromatic diphosphines) with 2-mercaptopyridine

This study presents the syntheses and characterization of 2-mercaptopyridine (pyS⁻) complexes containing ruthenium(II) with the following general formula [Ru(pyS)₂(P–P)], P–P = (c-dppen) = cis-1,2-bis(diphenylphosphino)ethylene) (1); (dppe) = 1,2-bis(diphenylphosphino)ethane (2); (dppp) = 1,3-bis(diphenylphosphino)propane (3) and (dppb) = 1,4-bis(diphenylphosphino)butane (4). The complexes were synthesized from the mer- or fac-[RuCl₃(NO)(P–P)] precursors in the presence of triethylamine in methanol solution with dependence of the product on the P–P ligand. The reaction of pyS⁻ with a ruthenium complex containing a bulky aromatic diphosphine dppb disclosed a major product with a dangling coordinated dppbO-P, the [Ru(pyS)₂(NO)(η¹-dppbO-P)]PF₆(5). In addition, this work also presents and discusses the spectroscopic and electrochemical behavior of 1–5, and report the X-ray structures for 1 and 5.     

Synthesis and structural characterisation of five copper(I) and silver(I) complexes with 2-aminopyridine (2-APy), [Cu(μ-Cl)(2-Apy)(PPh3)]2, [Ag(μ-X)(2-Apy)(PPh3)]2 (X = Cl,Br), [Ag(μ-ONO2)(2-Apy)(EPh3)]2 (E = P,As)

Five new copper(I)/silver(I) complexes containing 2-aminopyridine, [Cu(μ-Cl)(2-Apy)(PPh₃)]₂(1), [Ag(μ-Cl)(2-Apy)(PPh₃)]₂(2), [Ag(μ-Br)(2-Apy)PPh₃)]₂(3), [Ag(μ-ONO₂)(2-Apy)(PPh₃)]₂(4), [Ag(μ-ONO₂)(2-Apy)(AsPh₃)]₂(5) have been synthesised for the first time. Complexes 1–5 are obtained by the reactions of MX (MX = CuCl for 1; M = Ag for 2–5; X = Cl, Br for 2–3; X = NO₃ for 4–5) with the monodentate ligands EPh₃ (E = P for 1–4; E = As for 5) and 2-Apy in the molar ratio of 1:1:2 in the mixed solvent of CH₂Cl₂ and MeOH. Complexes 1–5 are characterised by IR and X-ray diffraction. In 1–5, chloride, bromide and nitrate ions bridge two metal atoms to form dinuclear complexes containing the parallelogram cores M₂X₂ (M = Cu, Ag).     

Solid–liquid phase equilibria in the systems K2SO4–MSO4–H2O (M = Co,Ni, Cu) from ambient to enhanced temperatures

Reviewing the literature solubility isotherms in the ternary systems K₂SO₄–MSO₄–H₂O (M = Co, Ni, Cu, Zn) revealed a lack at ambient temperatures. The solid–liquid phase equilibria have been determined in the systems K₂SO₄–MSO₄–H₂O (M = Co, Ni, Cu) at T = 313 K. With increasing bivalent metal sulfate concentration, the solubility of potassium sulfate rises until the two-salt point is reached. Reciprocally, the solubility of the bivalent metal sulfate hydrates (CoSO₄·7H₂O, α-NiSO₄·6H₂O, CuSO₄·5H₂O) increases with rising potassium sulfate concentration. In all three systems the double salts of Tutton's type K₂SO₄·MSO₄·6H₂O (M = Co, Ni, Cu) are formed.     

Synthesis and characterization of mono and polymeric cyclopalladated compounds: Crystal and molecular structure of [{Pd(dmba)(ONO2)}2(μ-pz)] · H2O (pz = pyrazine)

In the treatment of cyclometallated dimer [Pd(dmba)(μ-Cl)]₂ (dmba = N,N-dimethylbenzylamine) with AgNO₃ and acetonitrile the result was the monomeric cationic precursor [Pd(dmba)(NCMe)₂](NO₃) (NCMe = acetonitrile) (1). Compound 1 reacted with m-nitroaniline (m-NAN) and pirazine (pz), originating [Pd(dmba)(ONO₂)(m-NAN)] (2) and [{Pd(dmba)(ONO₂)}₂(μ-pz)] · H₂O (3), respectively. These compounds were characterized by elemental analysis, IR and NMR spectroscopy. The IR spectra of (2–3) display typical bands of monodentade O-bonded nitrate groups, whereas the NMR data of 3 are consistent with the presence of bridging pyrazine ligands. The structure of compound 3 was determined by X-ray diffraction analysis. This packing consists of a supramolecular chain formed by hydrogen bonding between the water molecule and nitrato ligands of two consecutive [Pd₂(dmba)₂(ONO₂)₂(μ-pz)] units.     

Polymer-supported tertiaryphosphine (JJ-TPP) as a green and recyclable organocatalyst for α-addition of carbon nucleophiles to α,β-unsaturated compounds

JJ-TPP has been demonstrated as an effective and reusable organocatalyst for α-addition of carbon nucleophiles to α,β-unsaturated compounds under very mild and environmentally friendly conditions. Under the optimized reaction conditions, the desired addition products were obtained as only E isomer with 18-90% isolated yields.     

A series of multinuclear homo- and heterometallic complexes with bridging tellurolato ligands derived from [CpIr(CO)(TeTol)2] (Cp = η-C5Me5, Tol = p-tolyl)

Reactions of [Cp^∗Ir(CO)(TeTol)₂] (1; Tol = p-tolyl) with certain organometallic Pd(II), Pt(II), Ir(III), Rh(III), and Ru(II) species afforded IrPd, IrPt, IrPt₂, Ir₂, IrRh, IrRu₃, and IrRu complexes having tellurolato-bridged dinuclear or trinuclear cores. This finding demonstrates that 1 is a versatile precursor to synthesize a variety of multinuclear homo- and heterometallic μ-tellurolato complexes, whose chemistry is still less advanced as compared with that of μ-thiolato complexes.     

The interactions between some N-acetyl-N′-methyl-l-α-amino acid amides and urea in water at 298.15 K

The enthalpies of solution of N-acetyl-N′-methylglycinamide, N-acetyl-N′-methyl-l-α-alaninamide, N-acetyl-N′-methyl-l-α-leucinamide and N-acetyl-N′-methyl-l-α-serinamide have been measured in water and in aqueous urea solutions with molalities from 0.25 to 3.0 mol kg⁻¹ at 298.15 K. From these data the standard dissolution enthalpies of amides in aqueous urea solutions have been determined. The results have been treated according to McMillan-Mayer's theory in order to obtain the enthalpic coefficients of the interactions between amino acid derivatives and urea molecules. The obtained parameters were compared with the hydrophobic scale for the amino acid side chains.     

Further revisions on the diterpenoid alkaloids reported in a JNP paper (2012, 75, 1145–1159)

We have corrected (Tetrahedron2013, 69, 5859–5866) the structures of diterpenoid alkaloids reported in the Journal of Natural Products2012, 75, 1145–1159. Our follow-up experiments compel us to present further revisions and clarifications on the diterpenoid alkaloids:     

Synthesis,crystal structure and magnetic properties of a new dinuclear copper(II) amino acid complex [Cu2(l-arg)2(μ-HPO4-O)(μ-HPO4-O,O′)(μ-OH)] · (H3O) · (H2O)6

A novel dinuclear copper(II) complex with the amino acid l-arginine (l-arg), with mono and bidentate HPO₄²⁻ oxoanions and an OH⁻ anion. [Cu₂(l-arg)₂(μ-HPO₄-O)(μ-HPO₄-O,O′)(μ-OH)]⁻ · (H₃O)⁺ · 6H₂O (1) was prepared and its structure was determined by X-ray diffraction methods. The two independent copper ions are in a distorted square pyramidal coordination, each bonded to one l-arginine molecule. These two Cu(l-arg) units are bridged by two monoatomic equatorial–apical oxygen ligands belonging to a monodentate hydrogenphosphate group, and to the hydroxyl group. The copper ions in the dinuclear unit at d = 3.1948(8) Å are also connected by two equatorial oxygen belonging to a bidentate hydrogenphosphate. This dinuclear character and bridging scheme, not common for metal–amino acid compounds, is a consequence of the properties of the phosphate anions. The magnetic susceptibility at temperatures between 2 and 300 K and the isothermal magnetization curves at T = 2.29(1) K with applied fields up to 9 T were measured. The magnetic data indicate an antiferromagnetic intradinuclear exchange coupling J/k_B = −3.7(1) K and using a molecular field approximation we estimated a weaker ferromagnetic interaction J′/k_B ∼ 0.3 K between neighbour dinuclear units.     

A unique example of a co-crystal of [Ag(atr)2][Cr(dipic)2] (dipic = dipicolinate; atr = 3-amino-1H-1,2,4-triazole) and dinuclear [Cr(H2O)(dipic)(μ-OH)]2, with different coordination environment of Cr(III) ions

Treatment of a neutral aqueous solution of dipicolinic acid (dipicH₂), 3-amino-1H-1,2,4-triazole (atr) and CrCl₃·6H₂O in the presence of AgNO₃ (in molar ratio 1:1:1:3) under hydrothermal condition led to the formation of a co-crystal of {[Ag(atr)₂][Cr(dipic)₂]}₂·[Cr(H₂O)(dipic)(μ-OH)]₂·4H₂O (1). Compound 1 was characterized by elemental analyses, IR and UV-Vis spectroscopy as well as X-ray diffraction studies. The structure consists of two [Ag(atr)₂]⁺ cations, two [Cr(dipic)₂]⁻ anions, one co-crystallized neutral dinuclear chromium(III) complex, [Cr(H₂O)(dipic)(μ-OH)]₂, and four co-crystallized water molecules. Silver(I) ion in [Ag(atr)₂]⁺ is coordinated by two monodentate 3-amino-1H-1,2,4-triazole ligands, bound via endocyclic nitrogen atoms, in a linear fashion. Chromium(III) ion is octahedrally coordinated by two O,N,O-tridentate dipicolinate ligands in anionic complex. Each chromium(III) ion in neutral dinuclear complex, [Cr(H₂O)(dipic)(μ-OH)]₂, is octahedrally coordinated by one O,N,O-tridentate dipicolinate ligand, one water molecule and two bridging μ-OH ions in cis position. Thermal methods (TGA/DTA) confirm the number of co-crystallized water molecules in 1.     

Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(en)(X) (M = Mo, W; X = Br, N3, CN) and [(en)(η-C3H5)(CO)2M(μ-CN)M(CO)2(η-C3H5)(en)]Br (M = Mo, W)

Mononuclear compounds M(CO)₂(η³-C₃H₅)(en)(X) (X = Br, M = Mo(1), W(2); X = N₃, M = Mo(3), W(4); X = CN, M = Mo(5), W(6)) and cyanide-bridged bimetallic compounds [(en)(η³-C₃H₅)(CO)₂M(μ-CN)M(CO)₂(η³-C₃H₅)(en)]Br (M = Mo (7), W(8)) were prepared and characterized. These compounds are fluxional and display broad unresolved proton NMR signals at room temperature. Compounds 1-6 were characterized by NMR spectroscopy at −60 °C, which revealed isomers in solution. The major isomers of 1-4 adopt an asymmetric endo-conformation, while those of 5 and 6 were both found to possess a symmetric endo-conformation. The single crystal X-ray structures of 1-6 are consistent with the structures of the major isomer in solution at low temperature. In contrast to mononuclear terminal cyanide compounds 5 and 6, cyanide-bridged compounds 7 and 8 were found to adopt the asymmetric endo-conformation in the solid state.     

Mechanistic studies on reaction of [ReH4(η-H2)(Cyttp)] with ketones to give the hydrido-oxo complex [ReH2(O)(Cyttp)] (Cyttp = PhP(CH2CH2CH2PCy2)2)

Mechanistic studies were conducted on reaction of [ReH₄(η²-H₂)(Cyttp)]OTf (1(OTf); Cyttp = PhP(CH₂CH₂CH₂PCy₂)₂, OTf = O₃SCF₃) with ketones, both neat and in solution. Treatment of 1(OTf) with excess acetone at 60-65 °C affords [ReH₂(O)(Cyttp)]OTf (2(OTf)) in high yield, nearly 1 equiv. of H₂, 2 equiv. of 2-propanol, 1 equiv. of each of 4-hydroxy-4-methyl-2-pentanone (B) and 4-methylpent-3-en-2-one (C), and smaller amounts of other organic products derived by condensation or related reactions of acetone. The presence of C, apparently arising by dehydration of B, points to the formation of 1 equiv. of H₂O in the reaction system. Use of acetone-d₆ in conjunction with 1(OTf) gives 2(OTf) containing no deuterium, as well as 1 equiv. of each of (CD₃)₂CHOH/OD and (CD₃)₂CDOD/OH. Reactions of 1(OTf) with cyclohexanone, including cyclohexanone-2,2,6,6-d₄, under comparable conditions, give analogous results. The ketones cyclopentanone, 2-butanone, and 3-pentanone also convert 1(OTf) to 2(OTf) upon heating, as does isobutyraldehyde, but only in the presence of the stabilizer BHT. In contrast, the more robust ketones 2,4-dimethyl-3-pentanone, 2,6-dimethylcyclohexanone, and 2-adamantanone, which do not undergo condensation, failed to effect this transformation. Other organooxygen compounds, i.e., methanol, cyclohexanol, 1,2-butene oxide, cyclohexene oxide, DMSO, and Me₃NO, also are ineffective. A mechanism is proposed which begins with loss of H₂ by 2 to give a 16-electron “[ReH₄(Cyttp)]⁺” which, depending on the experimental conditions, binds a solvent or ligand molecule. A [ReH₄(R₂CO)(Cyttp)]⁺ intermediate generated in this manner reacts spontaneously by elimination of R₂CHOH (containing methine hydrogen even when deuteriated ketone is used), which results from transfer of two hydride ligands to coordinated ketone. Continued reaction leads to the formation of 2 and another molecule of R₂CHOH (containing methine deuterium when deuteriated ketone is employed), with the added hydrogens coming from H₂O, which derives from solvent/reactant ketone.