BF3·OEt2-catalyzed synthesis of 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran and trans-fused hexahydropyrano[3,2-c]chromene derivatives

A novel intramolecular Prins cyclization of (E)-5-(2-(hydroxymethyl)phenyl)pent-4-en-1-ol with aldehydes has been achieved using 10 mol % BF₃·Et₂O to produce 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran derivatives in good to excellent yields with high selectivity. Similar type of coupling with salicylaldehydes provides the trans-fused hexahydropyrano[3,2-c]chromene derivatives in excellent yields.     

Reactions of (Me2C)(Me2Si)[(η-C5H3)Mo(CO)3]2 with nitrile and subsequent cleavage of the CN bond by cooperation of molybdenum and ruthenium

Reaction of the doubly bridged dinuclear molybdenum complex (Me₂C)(Me₂Si)[(η⁵-C₅H₃)Mo(CO)₃]₂ (1) with benzonitrile in refluxing xylene afforded complexes (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η²-η²(⊥)-NCPh)] (2) (50%) and (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η¹-η²-NCPh)] (3) (6%) with different coordination of nitrile. The corresponding μ-η²-η² acetonitrile and propionitrile complexes 4 and 5 could be obtained from the reactions of (Me₂C)(Me₂Si)(C₅H₄)₂ with (RCN)₃Mo(CO)₃ (R = Me, Et) in refluxing xylene. Reactions of 1 with isonitriles generated μ-η¹-η²-CNR (R = ^tBu, Ph, C₆H₁₁) bridged complexes 6-8 in 53-63% yields. Subsequent reaction of 4 with Ru₃(CO)₁₂ yielded two CN bond cleavaged MoRu clusters (Me₂C)(Me₂Si)(η⁵-C₅H₃)₂Mo₂Ru₃(CO)₁₀(μ-CO)(μ₃-CMe)(μ₄-N) (9) (7%) and [(Me₂C)(Me₂Si)(η⁵-C₅H₃)₂]₂Mo₄Ru₆(CO)₁₆(μ-CO)(μ₄-CO)₂(μ₃-η¹-η²-η²-NCMe)(μ₃-CMe)(μ₅-N) (10) (8%). All the new complexes have been fully characterized. The molecular structures of 2, 4, 6, 9, and 10 have been determined by X-ray diffraction analysis.     

Synthesis and structures of the silyl bridged bis(indenyl) diruthenium complexes and a novel indenyl nonanuclear ruthenium cluster Ru9(μ6-C)(CO)14(μ3-η:η:η-C9H7)2

Thermal treatment of C₉H₇SiMe₂C₉H₇ and C₉H₇Me₂SiOSiMe₂C₉H₇ with Ru₃(CO)₁₂ in refluxing xylene gave the corresponding diruthenium complexes (E)[(η⁵-C₉H₆)Ru(CO)]₂(μ-CO)₂ [E = Me₂Si (1), Me₂SiOSiMe₂ (2)]. A desilylation product [(η⁵-C₉H₇)Ru(CO)]₂(μ-CO)₂ (3) was also obtained in the latter case. Similar treatment of C₉H₇Me₂SiSiMe₂C₉H₇ with Ru₃(CO)₁₂ gave a novel indenyl nonanuclear ruthenium cluster Ru₉(μ₆-C)(CO)₁₄(μ₃-η⁵:η²:η²-C₉H₇)₂ (5) with carbon-centered tricapped trigonal prism geometry, in addition to the diruthenium complex (Me₂SiSiMe₂)[(η⁵-C₉H₆)Ru(CO)]₂(μ-CO)₂ (4) and the desilylation product 3. Complex 4 can undergo a thermal rearrangement to form the product [(Me₂Si)(η⁵-C₉H₆)Ru(CO)₂]₂ (6). The molecular structures of 1, 2, 4, 5, and 6 were determined by X-ray diffraction.     

Rhodium assisted CH activation of N-(2′-hydroxyphenyl)benzaldimines. Synthesis, structure and electrochemical properties of a group of organorhodium complexes

Reaction of a group of N-(2′-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes (the para substituents are OCH₃, CH₃, H, Cl and NO₂), with [Rh(PPh₃)₃Cl] in refluxing toluene in the presence of a base (NEt₃) afforded a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallography. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh₃ ligands are trans. The complexes are diamagnetic (low-spin d⁶, S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry shows a Rh(III)Rh(IV) oxidation within 0.63-0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine ligand. A reduction of the coordinated benzaldimine is also observed within −0.96 to −1.04 V vs SCE. Potential of the Rh(III)Rh(IV) oxidation is found to be sensitive to the nature of the para-substituent.     

Preparation of ultrafine metal particles in processes of pulse mechanical action

Ultrafine metal particles (UFMP) (iron and cobalt) have been obtained in solid-state redox reactions of cyclopentadienyl--(3)-1,2-dicarbollyliron or cyclopentadienyl--(3)-1,2-dicarbollylcobalt with elemental sulfur ((C₅H₅)Fe³⁺(C₂B₉H₁₁)-S, (C₅H₅)Co⁵⁺C₂B₉H₁₁-S). These reactions are realized by the action of elastic wave (EW) pulses on powder compositions of these substances. Study of the UFMP obtained by the ferromagnetic resonance (FMR) method has shown that the sizes ofn · Co⁰ UFP lie in the range from 1 to 13 nm. UFP of cobalt and iron are also formed under the action of EW on samples containing (C₅H₅)Fe³⁺(C₂B₉H₁₁)-S or (C₅H₅)Co³⁺(C₂B₉H₁₁)-S within the film of tetrafluoroethylene and perfluoro-4-methyl-3,6-dioxaoct-7-ene-1-sulfonyl fluoride copolymer (CP). It is shown by the FMR method that FMR lines broaden on going from powder systems to systems containing CP films. It is supposed thatn · Co⁰ and n · Fe⁰ particles interact with polymeric matrices in the course of formation and stabilization of UFMP in the matrices.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2355–2358, December, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-09632).     

Group 9 complexes of an N-heterocycle carbene bearing a pentafluorobenzyl substituent: attempted dehydrofluorinative coupling of cyclopentadienyl and N-heterocycle carbene ligands

Treatment of N-methylimidazole with pentafluorobenzyl bromide produces 1-pentafluorobenzyl-3-methylimidazolium bromide (1), which reacts with silver(I) oxide to give the N-heterocycle carbene (NHC) complex 1-pentafluorobenzyl-3-methylimidazolin-2-ylidene silver(I) bromide (2). Complex 2 acts as a carbene transfer reagent giving the complexes [(η⁵-C₅Me₅)MCl₂(NHC)] (3a, M = Rh; 3b M = Ir) on reaction with [(η⁵-C₅Me₅)MCl(μ-Cl)]₂. An attempt to use intramolecular dehydrofluorinative coupling methodology to link the carbene and the pentamethylcyclopentadienyl ligands of [(η⁵-C₅Me₅)RhCl(CN^tBu)(NHC)]BF₄ was unsuccessful.     

Theoretical studies on the imine germylenoid HNGeNaF and its insertion reaction with R-H (R = F, OH, NH2, CH3)

The geometries and isomerization of the imine germylenoid HNGeNaF as well as its insertion reactions with R-H (R = F, OH, NH₂, CH₃) have been systematically investigated at the B3LYP/6-311+G^∗ level of theory. The potential barriers of the four insertion reactions are 117.2, 172.6, 219.7, and 322.3 kJ/mol, respectively. Here, all the mechanisms of the four reactions are identical to each other, i.e., an intermediate has been formed first during the insertion reaction. Then, the intermediate could dissociate into the substituted germylene (HNGeHR) and NaF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies for the four reactions are 185.0, 208.1, 224.4, and 266.9 kJ/mol, respectively, which are linearly correlated with the calculated barrier heights. Compared with the insertion reaction of HNGe: and R-H, the introduction of NaF makes the insertion reaction occur easily though it is more difficult to proceed than that of insertion reaction between H₂GeNaF and R-H. Furthermore, the effects of halogen (F, Cl, Br) substitution and inorganic salts employed on the reaction activity have also been discussed. As a result, the relative reactivity among the four insertion reactions should be as follows: H-F > H-OH > H-NH₂ > H-CH₃.     

Facile hydrosilylation of norbornadiene by silanes R3SiH and R2SiH2 with molybdenum catalysts

Photochemically activated [Mo(CO)₆] and [Mo(CO)₄(η⁴-nbd)] have been demonstrated to be very effective catalysts for hydrosilylation of norbornadiene (nbd) by tertiary (Et₃SiH, Cl₃SiH) and secondary (Et₂SiH₂ and Ph₂SiH₂) silanes to give 5-silyl-2-norbornene, which under the same reaction conditions transform in ring-opening metathesis polymerization (ROMP) to unsaturated polymers and to a double hydrosilylation product, 2,6-bis(silyl)norbornane. The yield of a particular reaction depends very strongly on the kind of silane involved. The reaction products were identified by means of chromatography (GC–MS) and ¹H and ¹³C NMR spectroscopy. In photochemical reaction of [Mo(CO)₄(η⁴-nbd)] and Ph₂SiH₂ in cyclohexane-d₁₂, η²-coordination of the SiH bond to the molybdenum atom is supported by ¹H NMR spectroscopy due to the detection of two equal-intensity doublets with ²J_HH = 5.4 Hz at δ 6.12 and −5.86 ppm.     

Spin-crossover complexes in solution,II solvent effects on the high spin-low spin-equilibrium of [Fe(bzimpy)2](ClO4)2

Summary The influence of the solvent on the spin-equilibrium of [Fe(bzimpy)₂](ClO₄)₂ (bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) has been investigated in several nonaqueous solvents by means of UV-Vis spectroscopy and magnetic susceptibility measurements. In methanol, a bis-tris ligation equilibrium is found. Both, the FeL ₂ ²⁺ and FeL ₃ ²⁺ species show spin-crossover behaviour in solution. Photometric and magnetic properties of the complex in various solvents are related. The spin-equilibrium of [Fe(bzimpy)₂](ClO₄)₂ shows the strongest sensitivity towards changes of the solvent that has ever been observed for spin-crossover compounds. Increase in solvent donor number (DN) from DN=14.1 (Acetonitril) to DN=19.1 (Methanol) causes a shift from _exp=4.21 (78% High-Spin (HS)) to _exp=3.0 (56% HS). In solvents with DN 30 deprotonation of the complex occurs yielding a low-spin species. The solvent effects are discussed in terms of the donor-acceptor concept.Dedicated to Professor Harry J. Emeléus with heartiest congratulations to his 90^th birthday on 22^th June 1993.     

Ruthenium carbene complexes containing bidentate and tridentate PO ligands

Treatment of [Ru(CHR)Cl₂(PCy₃)₂] (Cy = cyclohexyl) with Tl[N(Pr₂ⁱPO)₂] and AgL_OEt (L_OEt⁻ = [CpCo{P(O)(OEt)₂}₃]⁻) afforded the Ru carbene complexes [Ru(CHPh)(PCy₃)Cl{N(Pr₂ⁱPO)₂}] (1) and [L_OEtRu(CHR)(PCy₃)Cl] (2), respectively. Chloride abstraction of complex 2 with TlPF₆ in MeCN afforded [L_OEtRu(CHPh)(PCy₃)(MeCN)][PF₆] (3). Complexes 1 and 2 are capable of catalyzing ring-closing metathesis of diethyl 1,2-diallylmalonate. The crystal structure of complex 2 has been determined.     

TiCl4-mediated olefination of aldehydes with acetic acid and alkyl acetates: a stereoselective approach to (E)-α,β-unsaturated carboxylic acids and esters

A new method has been developed for the preparation of α,β-unsaturated carboxylic acids and corresponding esters with (E)-stereoselectivity via the TiCl₄-mediated olefination of aldehydes. The method, which uses readily available acetic acid or its alkyl esters as active methylene partners, is more flexible and complementary to conventional routes in the preparation of (E)-cinnamic acid derivatives.     

Synthesis and crystal structure of copper halide complexes with triethylallylammonium (teaa) chloride: [(teaa)Cu3ICl4], [(teaa)Cu3IBr3.86Cl0.14], and (teaa)2CuIICl4

The results of X-ray diffraction analysis of novel triethylallylammonium chloride compounds with copper(I) chloride, copper(I) bromide, and copper(II) chloride are reported. The [(CH₃CH₂)₃(CH₂=CHCH₂xN]Cu ₃ ^I Cl₄ and [(CH₃CH₂)₃(CH₂=CHCH₂Cu ₃ ^I Br_3.86)Cl_0.14 -complexes are isostructural: space group P2₁/a; a= 17.58(1) Å, b = 12.059(8)Å, c = 7.184(4) Å, = 98.37(5)° and a = 17.972(9) Å, b=12.479(8) Å, c = 7.290(5) Å, = 98.81(5)°, respectively. ²-Coordination of the copper atom by the olefinic bond plays a key role in the structural ordering of the tetraalkylammonium cation. In contrast, the structure of {(CH₃CH₂)₃x(CH₂=CHCH₂)N}₂Cu^IICl₄ (P4₂/nmc; a = 8.839(3) Å, c =15.660(9) Å) follows the ionic salt pattern.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

Investigations on the spin-crossover complex [Fe(bzimpy)2](ClO4)2 and its Mn2+, Co2+, Ni2+ and Zn2+ analogues

Summary A series of transition metal complexes [M(bzimpy)₂](ClO₄)₂ (M=Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺;bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) was synthesized and characterized by elemental analysis, UV-Vis and far-IR spectroscopy. The electronic spectra of [Ni(bzimpy)₂](ClO₄)₂ in solution and solid state reveal a ligand field splitting parameter ₀ in the range of 11470 cm^–1 to 11840 cm^–1. The simultaneous existence of two species with distinct spin state is found for [Fe(bzimpy)₂](ClO₄)₂ by means of variable temperature far-IR measurements. Assignments of the observed far-IR bands are given on the basis of the investigations of the variation of the metal ion in [M(bzimpy)₂](ClO₄)₂.This paper is dedicated to Professor Ulrich Wannagat on the occasion of his 70^th birthday with warmest personal wishes.     

Intermolecular hydrogen bonding in the binary mixture [(C2H5)2CO + CH3OH] probed by polarized Raman measurements and DFT calculations

The Raman spectra of neat (C₂H₅)₂CO (pentanone) and its binary mixtures with hydrogen donor solvent (CH₃OH), [(C₂H₅)₂CO + CH₃OH] having different mole fractions of the reference system, (C₂H₅)₂CO in the range 0.1-0.9 at a regular interval of 0.1 were recorded in the CO stretching region. In neat liquid, the Raman peak appears asymmetric. The asymmetric nature of the peak has been attributed to the CO stretching mode of the two conformers of (C₂H₅)₂CO having C₂ and C_2v point groups and the corresponding bands at ∼1711 and ∼1718 cm⁻¹, respectively. A careful analysis of the I_iso (isotropic component of the Raman scattered intensity) at different concentrations reveals that upon dilution with methanol, at mole fraction C = 0.6, an additional peak in the CO stretching region is observed at ∼1703 cm⁻¹ which is attributed to the hydrogen bonding with methanol. A peculiar feature in this study is that upon dilution, the peak at ∼1718 cm⁻¹ shows a minimum at C = 0.6, but on further dilution it shows a blue shift. However, the other peak at ∼1711 cm⁻¹ shows a continuous red shift with dilution as well as a maximum at C = 0.7 in the linewidth vs. concentration plot, which is essentially due to competition between motional narrowing and diffusion phenomena. A significant amount of narrowing in the Raman band at ∼1718 cm⁻¹ can be understood in terms of caging effect of the reference molecule by the solvent molecules at high dilution. A density functional theoretic (DFT) calculation on optimized geometries and vibrational frequencies of two conformers of neat (C₂H₅)₂CO in C₂ ad C_2v forms and the complexes with one and two CH₃OH molecules with both the conformers was performed. The experimental results and theoretical calculations together indicate a co-existence of two conformers as well as hydrogen bonded complex with methanol in the binary mixture, [(C₂H₅)₂CO + CH₃OH] at intermediate concentrations.     

Copper-catalyzed oxidative cleavage of carbon-carbon double bond of enol ethers with molecular oxygen

A novel CC bond cleavage reaction of aromatic enol ethers (1) to give ketones (2) using molecular oxygen as oxidant is described. Among the examined catalysts (Cu(II), Pd(II), Ru(II), and H⁺), CuCl₂ exhibited the highest activity. The reaction proceeded smoothly with several kinds of substrates.     

InBr3-catalyzed stereoselective synthesis of 3,4-disubstituted hexahydro-1H-furo[3,4-c]pyran derivatives

An ?,δ-unsaturated alcohol tethered with a hydroxyl group, that is, (E)-2-styrylbutane-1,4-diol (1) undergoes a smooth bicyclization with various aldehydes in the presence of 10 mol % InBr₃ and at 0 °C to afford a novel series of hexahydro-1H-furo[3,4-c]pyran derivatives in good yields with high diastereoselectivity.     

Synthesis, crystal structure and in vitro antibacterial activity of two novel silver(I) complexes

Two silver(I) complexes [Ag₂(dppm)₂(L¹)₂(CH₂Cl₂)₂] (1) and [Ag₄(dppm)₂(L²)₂(NO₃)₂] (2) have been prepared by the reactions of [Ag₂(dppm)₂(NO₃)₂] with HL¹ and HL² [dppm = bis(diphenylphosphino)methane, HL¹ = 2-(9H-carbazol-9-yl) acetic acid and HL² = (E)-3-(4-(9H-carbazole-9-yl) phenyl) acrylic acid], respectively. Both complexes have been structurally characterized by X-ray crystallography, confirming that 1 is a binuclear complex whereas 2 is a tetranuclear one. Both complexes were assayed for antibacterial activity against two Gram-positive bacterial strains (Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 6538) and two Gram-negative bacterial strains (Pseudomonas aeruginosa ATCC 13525 and Escherichia coli ATCC 35218) by MTT method. Complex 2 exhibited powerful antibacterial activities against B. subtilis ATCC 6633 with MIC of 0.78 μg/mL, which was superior to the positive controls penicillin G. On the basis of the biological results, structure-activity relationships were discussed.     

Synthesis of Enantiomerically Pure 2-Isoxacephems

Summary. (R,6R,7R)-7-(1-Acetoxyethyl)-3-methyl-2-isoxacephem-4-carboxylic acid and its enantiomer have been prepared. The ring systems were formed from the corresponding enantiomerically pure N-unsubstituted -lactams. The reduction of methyl [(R,2S,3R)-3-(1-acetoxyethyl)-1-(4-methoxyphenyl)-4-oxoazetidine-2-carboxylate] has been solved via a hemi-acetal. The structure and the configuration of a new stereogenic center in this intermediate was predicted by using 2D NMR technique and unambiguously proven by x-ray.