Base-catalyzed diborylation of alkynes: synthesis and applications of cis-1,2-bis(boryl)alkenes

An efficient, transition-metal free, and practical approach to cis-bis(boryl)alkenes from various alkynes was disclosed in the presence of a catalytic amount of K_2CO_3 under mild conditions. Meanwhile, tetrasubstituted alkenes and phenanthrene derivatives were readily constructed from the target diborylalkenes via Suzuki-Miyaura cross coupling.     

One-pot synthesis of aromatic homoallylic alcohols from aldehydes and Grignard reagents promoted by Titanium(IV) tetraisopropanolate

An efficient method of Titanium(IV) mediated one-pot reaction approaching aromatic homoallylic alcohols from aldehydes and dual Grignard reagents was developed with good isolated yields. This method could use aromatic-, heteroaromatic-, or aliphatic-aldehydes as starting materials. However, electron-riched benzaldehyde or cinnamaldehyde tended to precede further hydroxyl eliminations to give all conjugated structures as demonstrated.     

Mizoroki-Heck type reaction of organoboron reagents with alkenes and alkynes. A Pd(II)-catalyzed pathway with Cu(OAc)2 as an oxidant

[reaction: see text]. In contrast to the Pd(0)-catalyzed mechanism by Uemura, Mizoroki-Heck type reaction of boronic acids is found to proceed under a Pd(II)-mediated pathway using a catalytic amount of Pd(OAc)2 in the presence of Cu(OAc)2 as an oxidant. Treatment of a variety of alkenes with boronic acids, boronates, and sodium tetraphenylborate furnishes beta-arylated and alkenylated products in good to excellent yields. The reactions with norbornene, norbornadiene, and diphenylacetylene are also performed to give 1:2 or 2:1 coupling products.     

Reactions and properties of some trimethyleneplatinum(IV) complexes: VII. Kinetics and mechanism of displacement of cyclopropane by alkenes

The kinetics of the reaction of alkenes (e.g. cis-pent-2-ene, hex-1-ene, cyclopentene) with [$\text{PtX}{}_2\text{(CH}{}_2\text{CH}{}_2\text{C}$H₂)(THF)₂] (X = Cl or Br, THF = tetrahydrofuran) or with [$\text{PtCl}{}_2\text{(CHPhCH}{}_2\text{C}$H₂)(THF)₂] in THF solution have been studied. The reactions occur with displacement of cyclopropane or phenylcyclopropane to give [PtCl₂(olefin)(THF)], and follow essentially second order kinetics, first order in both platinum complex and olefin. The mechanism of reaction is discussed.     

4-Methylpyrimidinium ylides. Part 7: 3+2 Dipolar cycloadditions to non-symmetrical substituted alkenes and alkynes

The ability of 4-methylpyrimidinium ylides (as 1,3-dipoles) to react with activated non-symmetrical substituted dipolarophiles (alkenes and alkynes) is presented. 4-Methylpyrimidinium ylides did not react with alkenes. With alkynes the reactions are regiospecific, a single regioisomer being obtained. A possible mechanism for the reaction pathway is proposed. For the first time in the pyrimidinium ylides series both isomers resulting from bonding to the 2-and 6-positions of the heterocycle ring were obtained. The appropriate conditions in order to increase the selectivity of one of the isomers were determined.     

Pyrolysis study of sol-gel derived TiO2 powders: Part IV. TiO2-anatase prepared by hydrolysing titanium(IV) isopropoxide without chelating agents

An amorphous TiO₂ gel was obtained by hydrolysing titanium(IV) isopropoxide with a stoichiometric amount of water using SnCl₂ as catalyst. In these operative conditions, a TiO₂ gel matrix containing a lower fraction of organic residual was obtained with respect to samples prepared by previously modifying the titanium alkoxide precursor with chelating ligands. Dried gel powders were characterized by N₂ adsorption analyses, FT-IR and XRD measurements. Thermogravimetric (TG) and differential thermal analysis (DTA) coupled with mass spectrometric (MS) and gas chromatographic (GC) measurements were performed in order to identify the organic products released from TiO₂ gel pyrolysis. The Tg-MS semiquantitative analysis of the main evolved species allowed to describe both the chemical composition of the initial TiO₂ gel and the chemical rearrangements occurring in the matrix during heating up to its crystallisation to anatase form at 420°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis and transformations of metallacycles. 28. Reactions of allenes with EtAlCl2 and Et2AlCl catalyzed by Ti and Zr complexes

Catalytic cycloalumination of allenes with EtAlCl₂ in the presence of Ti or Zr complexes afforded methylidene- and alkyl(benzyl)idenealuminacyclopropanes and the corresponding aluminacyclopentanes, which were identified by analyzing the hydrolysis products. The reactions with the use of Et₂AlCl instead of EtAlCl₂ produced 1,2- and 1,4-dialuminum compounds.     

Reactions of nickel(II) 2,21-dimethyl-2-aza-21-carbaporphyrin with phenyl Grignard reagents, phenyllithium, and n-butyllithium

Addition of a phenyl Grignard reagent to a toluene solution of the nickel(II) chloride complex of a dimethylated inverted porphyrin, (2-NCH3-21-CH3CTPP)NiIICl (1), at 203 K results in the formation of a rare paramagnetic (sigma-phenyl)nickel(II) species, (2-NCH3-21-CH3CTPP)NiIIPh (2). The coordination of the sigma-phenyl in 2 is determined by a unique pattern of three sigma-phenyl resonances (ortho 375.0 ppm; meta 108.94 ppm; para 35.68 ppm (at 283 K)) in the 1H NMR and 2H NMR spectra. The (sigma-phenyl)nickel(II) compound 2 is in the high-spin ground electronic state (dxy)2(dxz)2(dyz)2(dz2)1(dx2-y2)1, as confirmed by similarity of the NMR spectra of the equatorial ligand in 1 and 2. Titration of 1 with phenyllithium produces (2-NCH3-21-CH3CTPP)NiIIPh (2). One-electron reduction with excess PhLi yields [(2-NCH3-21-CH3CTPP)NiIIPh]- (3), which can be also generated by independent routes, e.g., by reduction of (2-NCH3-21-CH3CTPP)NiIIPh using lithium triethylborohydride or tetrabutylammonium borohydride. The spectroscopic data indicate that (2-NCH3-21-CH3CTPP)NiIIPh (2) undergoes one-electron reduction without a substantial disruption of the molecular geometry. The presence of two paramagnetic centers in 3, i.e., the high-spin nickel(II) and the carbaporphyrin anion radical, produces remarkable variations in a spectral patterns, such as the upfield and downfield positions of pyrrole resonances (103.78, 96.66, -25.35, -50.97, -92.15, -114.83 ppm (at 253 K)) and sign alternations of the meso-phenyl resonances (ortho -77.81, -79.34 ppm; meta 48.77, 48.04 ppm; para -85.65, -86.46 ppm (at 253 K)). A single species, 4, is detected in the 1H NMR titration of 1 with n-butyllithium. The formation of one- or two-electron-reduced species, [(2-NCH3-21-CH3CTPP)NiBu]- or [(2-NCH3-21-CH3CTPP)NiBu]2-, respectively, is considered to account for the spectroscopic properties of 4 (pyrrole 17.33, 15.45, -5.79, -7.74, -14.62, -58.14 ppm; 21-CH3 3 ppm (at 203 K)). The temperature dependence of the hyperfine shifts of 4 demonstrates pronounced anti-Curie behavior, interpreted in terms of a temperature-dependent spin equilibrium between diamagnetic and paramagnetic states with diamagnetic properties approached as the temperature is lowered. Warming of 2-4 results in complete decomposition via homolytic/heterolytic cleavage of an axial nickel-apical carbon bond. In the case of 2 or 3, the process yields a mixture of two compounds, 5 and 6, which are detected by EPR spectroscopy, demonstrating the anisotropy of the g tensor (5, g1 = 2.237, g2 = 2.092, g3 = 2.090; 6, g1 = 2.115, g2 = 2.030, g3 = 1.940 (in frozen toluene solution at 77 K)).     

Cross [2 + 2] cycloaddition of bicyclic alkenes with alkynes mediated by cobalt complexes: a facile synthesis of cyclobutene derivatives.

Bicyclic alkenes 1a-e and 5 undergo [2 + 2] cycloaddition with a variety of alkynes PhC(triple bond)CPh, (TMS)C(triple bond)CH, HC(triple bond)C(CH(3))(2)OH, (TMS)C(triple bond)CCO(2)Et, PhC(triple bond)CCH(3), C(2)H(5)C(triple bond)CC(2)H(5), CH(3)C(triple bond)CC(3)H(7), and CH(3)C(triple bond)CC(2)H(5) in the presence of Co(PPh(3))(2)I(2), PPh(3), and Zn powder in toluene to afford the corresponding exo-cyclobutene derivatives 3a-m, 6, and 8a-g in fair to excellent yields. The yield of this cycloaddition is highly sensitive to the cobalt catalyst, solvent, ligand, and temperature used. A mechanism involving a metallacyclopentene intermediate is proposed to account for this cobalt-catalyzed cyclization.     

Reactive iron carbonyl reagents via reaction of metal alkoxides with Fe(CO)5 or Fe2(CO)9: synthesis of cyclobutenediones via double carbonylation of alkynes

Alkoxy bases such as t-BuOK react with Fe(CO)(5) to give reactive iron carbonyl intermediates that in turn react with alkynes at 70 °C in THF to give 1,2-cyclobutenediones in 70-93% yields after CuCl(2)·2H(2)O oxidation. A novel 1,2-diacyloxyferrole derivative was isolated in the reaction of diphenylacetylene with Fe(CO)(5)/t-BuOK in the presence of acetyl chloride in contrast to the formation of a 1,4-diacyloxyferrole complex formed in the reaction using Fe(CO)(5)/Me(3)NO. The Fe(2)(CO)(9)/t-BuOK reagent system also converts the alkynes to corresponding cyclobutenediones in 63-90% yields under similar reaction conditions.     

New vanadium(IV) and titanium(IV) oxyfluorotellurates(IV): V2Te2O7F2 and TiTeO3F2

As part of a continuing study of oxyfluorotellurates(IV), materials likely to present interesting nonlinear optical properties, two new phases, titanium(IV) tellurium(IV) trioxide difluoride, TiTeO₃F₂, and divanadium(IV) ditellurium(IV) heptaoxide difluoride, V₂Te₂O₇F₂, have been characterized and present, respectively, titanium and vanadium in the tetravalent state. The TiTeO₃F₂ structure is based on linear double rows of TiO₃F₃ polyhedra sharing vertices. These rows are connected to adjacent rows via two vertices of Te₂O₅ bipolyhedra. The Te, Ti, one F and two O atoms are on general positions, with one O and F statistically occupying the same site with half‐occupancy for each anion. One O and one F occupy sites with .m. symmetry. The V₂Te₂O₇F₂ structure consists of zigzag chains of VO₄F₂ octahedra alternately sharing O—O and F—F edges. These chains are connected via Te₂O₅ bipolyhedra, forming independent mixed layers. The Te, V, one F and three O atoms are on general positions while one O atom occupies a site of symmetry. In both phases, the electronic lone pair E of the Te^IV atom is stereochemically active. A full O/F anionic ordering is observed in V₂Te₂O₇F₂, but in TiTeO₃F₂ one of the six anionic sites is occupied by half oxygen and half fluorine, all the others being strictly ordered. These compounds represent new members of a growing family of oxyfluorotellurates(IV), including the recently characterized members of formula MTeO₃F, M being a trivalent cation. As was true for the previous members, they are characterized by an unusually high thermal and chemical stability in relation to the absence of direct Te—F bonds.     

Pyrolysis study of Sol-gel derived TiO2 Powders: Part II. TiO2-anatase prepared by reacting titanium(IV) isopropoxide with oxalic acid

Homogeneous TiO₂ powders were obtained, via sol-gel method, hydrolysing titanium(IV) isopropoxide, previously reacted with oxalic acid in order to better control the gelling process. The characterization of the amorphous TiO₂ powders was carried out by using different techniques such as FT-IR, XRD and N2 adsorption analysis. Coupled thermogravimetric (TG) gas chromatographic (GC) and mass spectrometric (MS) analyses were performed to quantify the organic content present in the titania gel and its release during pyrolysis. A detailed semiquantitative analysis of the evolved chemical species from TG-MS data allowed to describe the chemical composition of the TiO₂ gel and the chemical rearrangements occurring in matrix during pyrolysis up to its crystallization to anatase form at 530°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pyrolysis study of Sol-gel derived TiO2powders: Part I. TiO2-anatase prepared by reacting titanium(IV) isopropoxide with formic acid

A homogeneous TiO₂ gel sample was prepared, via sol-gel method, hydrolysing titanium(IV) isopropoxide, previously modified by reaction with formic acid. The amorphous TiO₂ gel was characterized using various techniques such as FT-IR, XRD and N₂ adsorption analysis. Thermoanalyses (TG, DTA) coupled with gas chromatographic (GC) and mass spectrometric measurements (MS), by means of a home-assembled instrumental interfaces, were performed in order to quantify the organic component still present in the titania gel and its release during pyrolysis. Several chemical species were evolved and detected in gas phase for temperatures up to 350°C, before crystallization of TiO₂-anatase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intramolecular Gas-Phase Reactions of Synthetic Nonheme Oxoiron(IV) Ions: Proximity and Spin-State Reactivity Rules

The intramolecular gas-phase reactivity of four oxoiron(IV) complexes supported by tetradentate N(4) ligands (L) has been studied by means of tandem mass spectrometry measurements in which the gas-phase ions [Fe(IV) (O)(L)(OTf)](+) (OTf=trifluoromethanesulfonate) and [Fe(IV) (O)(L)](2+) were isolated and then allowed to fragment by collision-induced decay (CID). CID fragmentation of cations derived from oxoiron(IV) complexes of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmc) and N,N'-bis(2-pyridylmethyl)-1,5-diazacyclooctane (L(8) Py(2) ) afforded the same predominant products irrespective of whether they were hexacoordinate or pentacoordinate. These products resulted from the loss of water by dehydrogenation of ethylene or propylene linkers on the tetradentate ligand. In contrast, CID fragmentation of ions derived from oxoiron(IV) complexes of linear tetradentate ligands N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane (bpmen) and N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane (bpmpn) showed predominant oxidative N-dealkylation for the hexacoordinate [Fe(IV) (O)(L)(OTf)](+) cations and predominant dehydrogenation of the diaminoethane/propane backbone for the pentacoordinate [Fe(IV) (O)(L)](2+) cations. DFT calculations on [Fe(IV) (O)(bpmen)] ions showed that the experimentally observed preference for oxidative N-dealkylation versus dehydrogenation of the diaminoethane linker for the hexa- and pentacoordinate ions, respectively, is dictated by the proximity of the target C?H bond to the oxoiron(IV) moiety and the reactive spin state. Therefore, there must be a difference in ligand topology between the two ions. More importantly, despite the constraints on the geometries of the TS that prohibit the usual upright σ trajectory and prevent optimal σ(CH) -σ*?z?2 overlap, all the reactions still proceed preferentially on the quintet (S=2) state surface, which increases the number of exchange interactions in the d block of iron and leads thereby to exchange enhanced reactivity (EER). As such, EER is responsible for the dominance of the S=2 reactions for both hexa- and pentacoordinate complexes.     

Reactions of 2-(α-Haloalkyl)thiiranes with nucleophilic reagents: V. Reactions of 2-(α-Chloroalkyl)thiiranes with organolithium compounds

2-(α-Haloalkyl)thiiranes reacted with methyl-, butyl-, and phenyllithium to give the corresponding allyl sulfides. The reactions of diastereoisomeric erythro- and threo-2-(1-chloroethyl)thiiranes with phenyllithium were stereospecific, and they afforded (E)- and (Z)-1-phenylsulfanylbut-2-enes, respectively. 3-Chloromethyl-2,2-dimethylthiirane and phenyllithium gave rise to a mixture of 3-methyl-3-phenylsulfanylbut-1-ene and 3-methyl-1-phenylsulfanylbut-2-ene. The reactions of 2-chloromethylthiiranes with phenyllithium and methyllithium in the presence of a catalytic amount of copper(I) iodide (10 mol %) led to the formation of substituted thiiranes as the major products. Mechanisms of the observed transformations are discussed.     

Reactions of titanium(IV) isopropoxide with aliphatic and aromatic hydroxy esters,part I. 5-, 6-, 7- and 8-coordinate titanium(IV) complexes

Summary Reactions of titanium(IV) isopropoxide with ethyl 1-hydroxycyclohexylacetate, ethyl 2-hydroxy-2-arylpropionate, ethyl 2-hydroxy-2-arylbutyrate and ethyl 2-hydroxy-2-arylhydrocinnamate have been studied in dry benzene in different molar ratios under strictly anhydrous conditions. The Ti(OPr-i)₄-_nL_n type compounds, where L = hydroxy ester and n = 1 to 4, have been isolated and characterised by elemental analysis, molecular weight, i.r. and n.m.r. spectral studies. These products may be distilled unchanged under reduced pressure.Reprints of this are not available.