Selective [2+1+1] Fragmentation of P4 by heteroleptic Metallasilylenes

Small-molecule activation by low-valent main-group element compounds is of general interest. We here report the synthesis and characterization (¹H, ¹³C, ²⁹Si NMR, IR, sc-XRD) of heteroleptic metallasilylenes L¹(Cl)MSiL² (M=Al 1 , Ga 2 , L¹=HC[C(Me)NDipp]₂, Dipp=2,6-ⁱPr₂C₆H₃; L²=PhC(N^tBu)₂). Their electronic nature was analyzed by quantum chemical computations, while their promising potential in small-molecule activation was demonstrated in reactions with P₄, which occurred with unprecedented [2+1+1] fragmentation of the P₄ tetrahedron and formation of L¹(Cl)MPSi(L²)PPSi(L²)PM(Cl)L¹ (M=Al 3 , Ga 4 ).     

Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond Cleavage

It has been established that an electron-deficient cyclopentadienyl rhodium(III) (Cp^ERh^III) complex catalyzes the oxidative and decarboxylative [2+1+2+1] cycloaddition of benzoic acids with diynes through C≡C triple bond cleavage, leading to fused naphthalenes. This cyclotrimerization is initiated by directed ortho C−H bond cleavage of a benzoic acid, and the subsequent regioselective alkyne insertion and decarboxylation produce a five-membered rhodacycle. The electron-deficient nature of the Cp^ERh^III complex promotes reductive elimination giving a cyclobutadiene–rhodium(I) complex rather than the second intermolecular alkyne insertion. The oxidative addition of the thus generated cyclobutadiene to rhodium(I) (formal C≡C triple bond cleavage) followed by the second intramolecular alkyne insertion and reductive elimination give the corresponding [2+1+2+1] cycloaddition product. The synthetic utility of the present [2+1+2+1] cycloaddition was demonstrated in the facile synthesis of a donor–acceptor [5]helicene and a hemi-hexabenzocoronene by a combination with the chemoselective Scholl reaction.     

Kinetics of the reactions Br + NO2 + M and I + NO2+ M

The reactions Br + NO₂ + M → BrNO₂ + M (1) and I + NO₂ + M → INO₂ + M (2) have been studied at low pressure (0.6-2.2 torr) at room temperature and with helium as the third body by the discharge-flow technique with EPR and mass spectrometric analysis of the species. The following third order rate constants were found k₁₍₀₎ = (3.7 ± 0.7) × 10^?31 and k₂₍₀₎ = (0.95 ± 0.35) × 10^?31 (units are cm⁶ molecule^?2 s^?1). The secondary reactions X + XNO₂ → X₂ + NO₂ (X = Br, I) have been studied by mass spectrometry and their rate constants have been estimated from product analysis and computer modeling.     

Cycloaddition of Dialkylalumanyl Anion toward Unsaturated Hydrocarbons in (1+2) and (1+4) Modes

The reactivity of dialkylalumanyl anion ( 1 ) towards naphthalene, anthracene, diphenylacetylene, and (E)/(Z)-stilbenes was investigated. The compound 1 reacts with naphthalene and anthracene through (1+4) cyclization, giving Al-containing norbornadiene derivatives. In the reaction of 1 with diphenylacetylene and (E)/(Z)-stilbenes, (1+2) cyclization proceeded to form Al-C-C three-membered rings. Cyclization toward (E)- or (Z)-stilbenes solely gave a trans-cycloadduct. DFT calculations revealed that the cycloaddition of 1 with (Z)-stilbene proceeds via a single transition state with a carbanion character, which results in the selectivity towards the trans-cycloadduct.     

High-level ab initio calculations on CH+2(2A1) + PO(2II) reactions

We present ab initio calculations carried out in the framework of the G 2 theory on the singlet and triplet potential energy surfaces corresponding to the gas-phase between CH⁺₂ and PO. The global minimum of both potential energy surfaces is a cyclic singlet-state cation. Oxygen attachment of PO to CH⁺₂ in a triplet configuration is accompanied by a P(SINGLEBOND)O bond fission, with the result that the corresponding global minimum is an ion-dipole complex between P⁺(³P) and formaldehyde. This is also consistent with the fact that our results predict the formation of formaldehyde to be highly exothermic, either as a neutral or as radical cation. Both charge-transfer processes yielding CH₂(³B₁) or CH₂(¹A₁) are also exothermic. The formation of other carbon and oxygen containing species are endothermic. © 1996 John Wiley & Sons, Inc.     

[4+2] Cycloaddition of 2(1H)-pyrazinones and 1,2,4-triazoline-3,5-diones

The reaction of 2(1H)-pyrazinones 1 and 1,2,4-triazoline-3,5-diones 3 was investigated by comparing that of 1 with singlet oxygen. 2(1H)-Pyrazinones 1 reacted in Diels-Alder fashion with 1,2,4-triazoline-3,5-diones 3 to afford [4+2]-adducts 4–17 in high yields.     

[2 + 2]-Cycloadditions to Strained Bridgehead Olefins. I. 1, 1-Dichloro-2,2-difluoroethene

The strained bridgehead olefins bicyclo [3.3.1]non-1-ene ( 1 ), bicyclo [4.2.1] non--1-(8) ( 2 ), and bicyclo [4.2.1]non-1-ene ( 3 ) react rapidly with 1,1-dichloro-2, 2--difluoroethene ( 5 ) to yield mixtures of regioisomeric dichlorodifluorocyclobutanes 8/9, 10/11 and 12/13 , respectively. On the contrary, the reaction of 5 with the model compound (E)-l-methylcyclooctene ( 4 ) is completely regioselective. The structure of the cycloadducts has been elucidated mainly by ¹⁹F-NMR. and ¹³C-NMR. spectroscopy.     

Catalytic [2+2+1] Synthesis of Fused Thiophenes Using Thiocarbonyls as Sulfur Donors

The use of N‐(p‐chlorophenyl)methylbenzoxazole‐2‐thione as a sulfur‐atom donor enables the catalytic [2+2+1] cycloaddition of diynes in wet DMF at 80 °C when open to air, thus affording diverse fused thiophenes with good yields and wide functional‐group compatibility. A plausible mechanism, involving a cationic ruthenacycle intermediate, was also proposed on the basis of several control experiments.     

Viscosity of the systems m-xylene, +1-propanol, +2-propanol, +1-butanol, +t-butanol

Viscosities, η, of the systems, m-xylene, +1-propanol, +2-propanol, +1-butanol and +t-butanol have been measured for the whole range of composition at 303.15, 308.15, 313.15, 318.15 and 323.15?K. The variation of viscosities has been plotted against mole fraction of alkanols. Viscosities have been found to increase slowly up to a considerable concentration of alkanols, followed by a rapid rise of viscosities at higher concentrations. The slow rise of viscosity is attributed to dissociation of alkanols in m-xylene, while the rapid rise of viscosity is ascribed to self-association of alkanols. Excess viscosities, η^E, have been plotted as a function of mole fraction of alkanols. The curves show negative values for the whole range of composition, with minima occurring in alkanol-rich region.?η?and η^E have been fitted to appropriate polynomial equations. The study shows the effect of branching and chain length of alkanols on?η?and η^E.     

Photolysis of alkyl iodides at 147.0 nm. The reaction H + CnH2n + 1I → HI + CnH2n + 1

The 147 nm (8.4 eV) photolysis of gaseous C₂H₅I, n-C₃H₇I, and sec-C₃H₇I was investigated in the presence of and absence of HI. The main overall processes are: These dissociative processes occur mainly as a result of initial cleavage of the weak C? I bond, followed by decomposition of the internally excited alkyl radicals. In all cases, approximately 5-10% of the alkyl radicals thus formed do not undergo dissociation at pressures around 3-7 torr. There is also evidence for the elimination of HI as well as C? C cleavage in the primary dissociation. The former is indicated by deuterium labeling experiments and the formation of cyclopropane (Φ = 0.04) as a product in the photolysis of n-C₃H₇I. Because the processes listed above provide a constant source of H atoms whose quantum yield can be exactly determined, it was feasible to obtain accurate values for k_a/k_b: For thermally equilibrated H atoms (300 K), k_a/k_b is 0.44 ± 0.04, 0.57 ± 0.06, 0.95 ± 0.1, and 0.024 ± 0.01 for C₂H₅I, n-C₃H₇I, sec-C₃H₇I, and C₂H₅Br, respectively.     

Synthesis,structure and bioactivity of Ni2+ and Cu2+ acylhydrazone complexes

Two acylhydrazone complexes, bis{6‐methyl‐N′‐[1‐(pyrazin‐2‐yl‐κN¹)ethylidene]nicotinohydrazidato‐κ²N′,O}nickel(II), [Ni(C₁₃H₁₂N₅O)₂], (I), and di‐μ‐azido‐κ⁴N¹:N¹‐bis({6‐methyl‐N′‐[1‐(pyrazin‐2‐yl‐κN¹)ethylidene]nicotinohydrazidato‐κ²N′,O}nickel(II)), [Cu₂(C₁₃H₁₂N₅O)₂(N₃)₂], (II), derived from 6‐methyl‐N′‐[1‐(pyrazin‐2‐yl)ethylidene]nicotinohydrazide (HL) and azide salts, have been synthesized. HL acts as an N,N′,O‐tridentate ligand in both complexes. Complex (I) crystallizes in the orthorhombic space group Pbcn and has a mononuclear structure, the azide co‐ligand is not involved in crystallization and the Ni²⁺ centre lies in a distorted {N₄O₂} octahedral coordination environment. Complex (II) crystallizes in the triclinic space group P and is a centrosymmetric binuclear complex with a crystallographically independent Cu²⁺ centre coordinating to three donor atoms from the deprotonated L^? ligand and to two N atoms belonging to two bridging azide anions. The two‐ and one‐dimensional supramolecular structures are constructed by hydrogen‐bonding interactions in (I) and (II), respectively. The in vitro urease inhibitory evaluation revealed that complex (II) showed a better inhibitory activity, with the IC₅₀ value being 1.32±0.4 µM. Both complexes can effectively bind to bovine serum albumin (BSA) by 1:1 binding, which was assessed via tryptophan emission–quenching measurements. The bioactivities of the two complexes towards jack bean urease were also studied by molecular docking. The effects of the metal ions and the coordination environments in the two complexes on in vitro urease inhibitory activity are preliminarily discussed.     

Triangular Arrangement of Ferromagnetic Iron Chains in the High-TC Ferromagnet TiFe1−xOs2+xB2

Transition-metal borides (TMBs) containing B_n-fragment (n>3) have recently gained interest for their ability to enable exciting magnetic materials. Herein, we show that the B₄-containing TiFe_0.64(1)Os_2.36(1)B₂ is a new ferromagnetic TMB with a Curie temperature of 523(2) K and a Weiss constant of 554(3) K, originating from the chain of M₃-triangles (M=64 %Fe+36 %Os). The new phase was synthesized from the elements by arc-melting, and its structure was elucidated by single-crystal X-ray diffraction. It belongs to the Ti_1+xOs_2−xRuB₂-type structure (space group P 2 m, no. 189) and contains trigonal-planar B₄ boron fragments [B−B distance of 1.87(4) Å] interacting with M₃-triangles [M–M distances of 2.637(8) Å and 3.0199(2) Å]. The experimental results were supported by computational calculations based on the ideal TiFeOs₂B₂ composition, which revealed strong ferromagnetic interactions within and between the Fe₃-triangles. This discovery represents the first magnetically ordered Os-rich TMB, thus it will help expand our knowledge of the role of Os in low-dimensional magnetism of intermetallics and enable the design of such materials in the future.     

Heterocyclization of 2-chloro-1-cyano-1-diethoxyphosphoryl-2-trifluoromethylethylene and 2-chloro-2-chlorodifluoromethyl-1-cyano-1-diethoxyphosphorylethylene

The reactions of 2-chloro-1-cyano-1-diethoxyphosphoryl-2-trifluoromethylethylene (2a) and 2-chloro-2-chlorodifluoromethyl-1-cyano-1-diethoxyphosphorylethylene (2b) with arylamines, arylhydrazines, amidines, 2-aminopyridines, and 5-aminopyrazoles were studied. Alkenes 2a, b can serve as precursors of aminopyrazoles, pyrimidines, pyrido[1,2-a]pyrimidines, and pyrazolo[1,5-a]pyrimidines modified with the fluoroalkyl and diethoxyphosphoryl groups. Intermediates of some heterocyclization reactions were detected by NMR spectroscopy. The structures of the compounds were confirmed by X ray diffraction analysis.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1977–1986, September, 2004.     

Accurate DMBE Potential Energy Surface For the N(2D) + H2(1Σ g + ) Reaction Using an Improved Switching Function Formalism

A single-sheeted double many-body expansion (DMBE) potential energy surface is reported for the 1 ² A′′ state of NH₂. To approximate its true multi-sheeted nature, a novel switching function that imposes the correct behavior at the H₂(X ¹Σ _g ⁺)+ N(² D) and NH(X ³Σ^-) + H(² S) dissociation limits has been suggested. The new DMBE form is shown to fit with high accuracy an extensive set of new ab initio points (calculated at the multi-reference configuration interaction level using the full valence complete active space as reference and aug-cc-pVQZ and aug-cc-pV5Z basis sets) that have been semiempirically corrected at the valence regions by scaling the n-body dynamical correlation terms such as to account for the finite basis set size and truncated configuration interaction expansion. A detailed study of the N(² D) ... H₂(X ¹Σ _g ⁺) van der Waals region has also been carried out. These calculations predict a nearly free rigid-rotor with two shallow van der Waals wells of C _2v and C _{∞ v} symmetries. Such a result contrasts with previous cc-pVTZ calculations which predict a single T-shaped van der Waals structure. Except in the vicinity of the crossing seam, which is replaced by an avoided intersection, the fit shows the correct physical behavior over the entire configurational space. The topographical features of the new DMBE potential energy surface are examined in detail and compared with those of other potential functions available in the literature. Amongst such features, we highlight the barrier for linearization (11,802 cm^-1) which is found to overestimate the most recent empirical spectroscopic estimate by only 28 cm^-1. Additionally, the T-shaped N(² D) ... H₂ van der Waals minimum is predicted to have a well depth of 90 cm^-1, being 11 cm^-1 deeper than the C _{∞ v} minimum. The title DMBE form is therefore recommendable for dynamics studies of both non-reactive and reactive N(² D)+H₂ collisions.     

Photocatalyzed Intramolecular [2+2] Cycloaddition of N-Alkyl-N-(2-(1-arylvinyl)aryl)cinnamamides

N-Alkyl-N-(2-(1-arylvinyl)aryl)cinnamamides are converted into natural product inspired scaffolds via iridium photocatalyzed intramolecular [2+2] photocycloaddition. The protocol has a broad substrate scope, whilst operating under mild reaction conditions. Tethering four components forming a trisubstituted cyclobutane core builds rapidly high molecular complexity. Our approach allows the design and synthesis of a variety of tetrahydrocyclobuta[c]quinolin-3(1H)-ones, in yields ranging between 20–99 %, and with excellent regio- and diastereoselectivity. Moreover, it was demonstrated that the intramolecular [2+2]-cycloaddition of 1,7-enynes—after fragmentation of the cyclobutane ring—leads to enyne-metathesis-like products.     

Influence of 2,2'-bipyridyl on the stability of Cu2+ -glycine-1:1 complexes

The stability constant of the Cu²⁺-2,2′-bipyridyl-glycine complex (log K = 7,88) was measured and compared with that of the binary Cu²⁺-glycine complex (log K = 8,27). The value Δ log K = ?0,4 (cf. equation (3)) is in the order which should be expected for the coordination of a mixed O? N-ligand to (Cu-Bipy)²⁺ which results in the formation of a ternary complex (cf. [1]).     

Linear and nonlinear feature of electronic excitation energy in carbon chains HC2n+1H and HC2nH

Density functional theory has been used to investigate the geometries, bonding, and vibrational frequencies of HC_2nH (n = 1–13) and HC_2n+1H (n = 2–12). Vertical excitation energies for the X¹Σ → 1¹Σ transition of HC_2nH (n = 1–5) and for the X³Σ → 1³Σ transition of HC_2n+1H (n = 2–5) have been calculated by the time‐dependent density functional theory and ab initio second‐order multiconfiguration perturbation method, respectively. On the basis of the present calculations, explicit expressions for the size dependence of excitation energy in linear polyynes HC_2n+1H and HC_2n+1H are suggested. Such analytical λ ? n relationships show good agreement with experimental observations. Theoretical investigations of relevant excited states demonstrate that distinct linear and nonlinear spectroscopic features in such polyynes can be ascribed to similarity and difference in bonding between the ground and excited states in HC_2n+1H and HC_2nH. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Complexation study of Schiff base ligand: pyridin-2-ylimino methyl naphthanol with Co+2, Mn+2 and Ni+2 ions in solid and solution phase

Schiff base pyridin-2-ylimino methyl naphthanol (HL) was synthesized and characterized by spectroscopic (FTIR, ESIMS, and NMR) techniques. The ligand was reacted with perchlorate salts of Mn⁺², Co⁺², and Ni⁺². ESIMS mass spectra indicate the formation of mononuclear complex ML₂ for all three complexes. CoL₂ crystallizes in P₂1/n space group, adopting a distorted tetrahedral geometry where Co is in a N₂O₂ donor environment. Structure of the Co complex was optimized by DFT calculation. Solution-phase complexation between the ligand and the three metals ions: Mn⁺², Co⁺², and Ni⁺² (pH 7.2 in tris buffer), in CH₃CN–H₂O was performed spectrophotometrically by UV–vis spectral study. Job’s plot from each titration suggests a 1 : 2 metal to ligand combination. The association constants for the formation of ML₂ are as follows: Mn (19.80 × 10³ M^?1), Co (14.54 × 10³ M^?1) and Ni (19.04 × 10³ M^?1).     

Experimental study of the D + H2 (v = 1) reaction by CARS spectroscopy

The reactions D + H₂ (v = 0, 1) → HD (v = 0, 1) + H have been studiedin a discharge flow reactor by CARS-spectroscopy. For H₂(v = 0) molecules a rate constant of (4, 0 ± 1, 0) 10^?16 cm³ s^?1 is obtained at 310 K from measured HD (v = 0, 1) product yields. Keeping the degree of vibrational excitation of H₂in the microwave discharge in the range of 1% from the increase of the HD (v = 0, 1) CARS signals a rate of k_{2a, b} = (1, 0 ± 0, 4) 10^?13cm³ s^?1 is derived. The total consumption of H₂ (v = 1) in the presence of D atoms gives a rate k₂ = (1, 9 ± 0, 2) 10^?13 cm³ s^?1 at 310 K. The resultsare discussed in regard to previous measurements and theoretical treatments.     

Valence electronic states of NH2+ and PH2+ dications

The ab initio second-order effective valence-shell Hamiltonian that is based on the multireference many-body perturbation theory has been applied to determine adiabatic potential energy curves for the valence states of NH²⁺ and PH²⁺ dications. For PH²⁺, three low-lying quasi-bound states (X¹∑⁺, a³ Π, A¹Π) are found and their spectroscopic constants are characterized. In NH²⁺, no quasi-bound states are found. The potential energy curves for NH²⁺ are compared with those for PH²⁺ to understand the difference between these two valence isoelectronic cations. © 1993 John Wiley & Sons, Inc.