Elimination Of HX Research Articles

Facile transformation of benzyl ethers, alcohols, amides and amines to substituted indans

The elimination of HX from ArMe 2 CX (X = OH, OMe, NHCOMe, NH 2 ) in sulfuric acid–liquid hydrocarbon leads easily to indan formation.

HX elimination from Ir(H)2X(PBu2tPh)2 promoted by CO coordination: assessment of X ligand influence

The coordinatively unsaturated complexes Ir(H)2X(PBu2tPh)2 [X=Cl, Br, I, N3, NCNSiMe3, NHC(O)CH3, OC(O)CF3, OSO2CF3, OC(O)CH3, SPh, OPh, F] all react within the mixing time in arene solvents to bind carbon monoxide. Subsequent reactivity of these CO adducts reductively to eliminate HX is dependent on the magnitude of the inherent destabilization caused by filled-filled repulsions between the ligand pπ orbitals and metal dπ orbitals. This destabilization is not sufficient to promote the loss of HX when X=Cl, Br, I, N3, NCNSiMe3, NHC(O)CH3 or OC(O)CF3. When X=OC(O)CH3 or SPh, metastable CO adducts are formed that ultimately lose HX. The complexes containing OPh or F quickly lose HX upon reaction with CO. The unusual iridium(I) complexes IrH(CO)2(PBu2tPh) and IrH(CO)(PBu2tPh)2 have been characterized by multinuclear NMR and IR spectroscopy. The reaction of Ir(H)2(F)(PBu2tPh)2 with CO in a glass vessel yields crystalline [Ir(H)2(CO)2(PBu2tPh)2][SiF5] and [Ir(CO)2(PBu2tPh)2][SiF5]·C6D6, both characterized by X-ray diffraction. The latter, although approximately square planar, has a C–Ir–C angle of only 162.7°. Crystallographic data (Pc at -165 °C) for [Ir(H)2(CO)2(PBu2tPh)2][SiF5], a=8.293(2), b=12.462(5), c=16.333(7) A, β=98.21(2)° with Z=2. Crystallographic data (P21/n at -172 °C) for [Ir(CO)2(PBu2tPh)2][SiF5]·C6D6, a=13.041(7), b=12.998(5), c=22.553(13) A, β=97.50(2)° with Z=4.

Speculations on new mechanisms for Heck reactions

A mechanism for the olefination reaction is proposed, involving PdII/PdIV, in which a key step is reversible nucleophilic attack on the PdII-coordinated olefin to give an electron-rich σ-alkyl- or, with carbonate, a chelated σ-dialkyl-complex, which then oxidatively adds the organic halide e.g. ArX. Loss of nucleophile, migration of Ar from PdIV to coordinated olefin, β-hydrogen elimination and loss of HX then gives the product of olefination and regenerates the PdII catalyst.

Theoretical Study on Unimolecular Reactions of Acetyl Cyanide and Acetyl Isocyanide

The potential energy surfaces of acetyl cyanide and its functional isomer acetyl isocyanide in their electronic ground state have been investigated using ab initio molecular orbital MP2(FU)/6-311G** and QCISD(T)/6-311G** calculations. The molecular eliminations of CH3COX (X = CN,NC) to CH3X + CO, HX + CH2CO, and CH2 + HCOX, the unimolecular rearrangements to CH3C−OX and CH3O−CX carbenes, 1,3-hydrogen migration to CH2C(OH)X, 1,3-methyl migration to CH3NCCO, and radical decompositions to X• + CH3CO and CH3• + COX have been examined. Also the secondary decomposition processes of COCN and CONC radicals in their ground states and the secondary elimination of HX from CH2C(OH)X have been investigated. Cyanide−isocyanide isomerization is found to be the predominant channel in the unimolecular reactions of acetyl cyanide. Despite being exothermic, the decomposition of acetyl cyanide into CH3CN + CO is found to be kinetically unfavorable. Decomposition into HCN + CH2CO, the reverse reaction of CH3COCN synthesis, is...

A mild and selective dehydrohalogenating agent

A discriminating reagent has been discovered which effects E2 elimination of HX from relatively reactive substrates. Readily prepared from lead( II) oxide and lithium bromide hydrate, this compound is a hydrated lithium dibromoplumbite.

A High-Level Computational Study on the Thermochemistry of Vinyl and Formyl Halides: Heats of Formation, Dissociation Energies, and Stabilization Energies

The heats of formation, ΔHf 298, of vinyl and formyl halides calculated using G2 theory are −145.9 (CH2CHF), 21.8 (CH2CHCl), 79.6 (CH2CHBr), 147.1 (CH2CHI), −393.7 (HFCO), −192.7 (HClCO), −133.9 (HBrCO), and −66.2 kJ mol-1 (HICO), which agree with the available experimental data. While the covalent radii of sp3 and sp2 hybridized carbons are 0.762 and 0.735 Å, respectively, at the MP2/6-31G(d) level, the C−X bond lengths in formyl bromide and iodide are 0.016 and 0.045 Å, respectively, longer when compared with those in methyl bromide and iodide. However, the C−F bond in formyl fluoride is 0.040 Å shorter than the C−F bond in methyl fluoride. The C−X bond dissociation energies (DC-X) for vinyl, formyl, and methyl halides show good linear correlations with the Mulliken and Pauling electronegativites of the halogens. The DC-X values for formyl bromide and iodide are smaller than those calculated for methyl bromide and iodide. The stabilization energies (SE) yielding estimates of the stabilization of the CC and CO double bonds by halogens decrease from X = F to X = I and show reasonable linear correlations with the Mulliken and Pauling electronegativities of the halogens. While the DC-X energies for formyl halides are smaller than those for vinyl halides, the SE(formyl) values are larger than the corresponding SE(vinyl). The elimination of HX from formyl halides is exothermic, in contrast to the endothermic elimination of HX from vinyl halides.

Mass-Spectrometric Study on Ion-Molecule Reactions of CF3+with PhX (X = F, Cl, Br, I) at Near-Thermal Energies

Abstract The branching ratios of product ions for the reactions of CF3+ with PhX (X = F, Cl, Br, I) have been determined by using an ion-beam apparatus. The main reaction channels are electrophilic addition to a benzene ring, followed by HF and HX elimination, and X− abstraction reaction leading to phenyl cation. Charge transfer reaction leading to the parent cation was found only for PhI with the lowest ionization potential. Semi-empirical MNDO calculations of heats of formation of various intermediates and products were carried out to explore possible reaction mechanisms.

Magnesium Methyl Carbonate-Activated Alkylation of Methyl Ketones with an ω-Halo Nitrile, Esters, and Amides

Terminally substituted, extended-chain derivatives of the 2-dibenzofuranyl methyl ketone 6 and its phenylethyl analogue 12 were readily obtained by converting the ketones to magnesium chelates of their β-carboxylated enolates with magnesium methyl carbonate (MMC, methyl methoxymagnesium carbonate, Stiles's reagent), followed by alkylation in situ with ω-halo compounds, X(CH2)nY where X = Br and Y = CO2Me, CN, CONMe2, CON(i-Pr)2, CON(CH2)4, or CON(CH2)5 for n = 1; X = Br or I, and Y = CO2Me for n = 2; and X = Br and Y = CO2Me for n = 3. Dimethylcarbamoyl chloride (n = 0) gave products derived from MMC and the solvent, N,N-dimethylformamide. The order of reactivity of the halides was α > β > γ and β-I > β-Br. β-Bromo amides were found to be unsuitable reactants. Lower reaction temperatures favored alkylation over competing elimination of HX from methyl β-halopropionate. No self-condensation products of the ketones were observed; however, bis-alkylation and monomethylation products were formed when reaction ...

Ionic nucleophilic substitution in halobenzene-NH 3 complexes: the entrance channel

Nucleophilic substitution reactions have been studied in halobenzene cations with ammonia. In ionic 1-1 complexes, three behaviours can be observed, depending on the nature of the halogen atom X (F, Cl, Br or I): (i) no reactivity, (ii) X elimination: XBz +NH 3 → BzNH 3 + + X, (iii) HX elimination: XBz +NH 3 → BzNH 2 + + HX. We propose a reactive potential energy surface in which the two eliminations proceed through the same entrance channel: the formation of an addition σ complex after a barrier crossing. This should be the key point for interpreting the ensemble of previous results. The reaction time for this barrier crossing has been estimated using the RRK formalism, giving a set of consistent barriers for σ complex formation in each halogenated compound studied from a comparison of modeling and experimental results.

Sequential Iron(I)-Mediated Homologization of Olefins by Methanol and Methyl Halides in the Gas Phase

The gas-phase chemistry of simple Fe(olefin)+ complexes with CH3X (X = OH, F, Cl, Br, I) has been studied by Fourier-transform ion cyclotron resonance mass spectrometry. C−C bond formation between the alkene and CH3X occurs via initial insertion of Fe+ into the C−X bond, followed by a migratory insertion of the olefin into the iron−carbon bond of (X)Fe(CH3)+. This step constitutes a gas-phase analog of the initial stage in the Ziegler−Natta type C−C bond formation; a combination of subsequent β-H shift and reductive elimination of HX completes the reaction. In the case of Fe(propene)+ a remarkable regioselectivity is observed in that the addition results in the exclusive formation of an unbranched Fe(butene)+ complex. Starting from Fe(ethene)+, up to two consecutive methylations occur using CH3OH as a reactant; with methyl halides the number of methylations varies from 2 (for X = I) to 4 (for X = F). For alkyl halides RX bearing a β-hydrogen, Fe+-mediated dehydrohalogenation of RX competes efficiently wit...

Why are B ions stable species in peptide spectra?

Protonated amino acids and derivatives RCH(NH2)C(+O)X · H(+) (X = OH, NH2, OCH3) do not form stable acylium ions on loss of HX, but rather the acylium ion eliminates CO to form the immonium ion RCH = NH 2 (+) . By contrast, protonated dipeptide derivatives H2NCH(R)C(+O)NHCH(R')C(+O)X · H(+) [X = OH, OCH3, NH2, NHCH(R″)COOH] form stable B2 ions by elimination of HX. These B2 ions fragment on the metastable ion time scale by elimination of CO with substantial kinetic energy release (T 1/2 = 0.3-0.5 eV). Similarly, protonated N-acetyl amino acid derivatives CH3C(+O)NHCH(R')C(+O)X · H(+) [X = OH, OCH3, NH2, NHCH(R″)COOH] form stable B ions by loss of HX. These B ions also fragment unimolecularly by loss of CO with T 1/2 values of ∼ 0.5 eV. These large kinetic energy releases indicate that a stable configuration of the B ions fragments by way of activation to a reacting configuration that is higher in energy than the products, and some of the fragmentation exothermicity of the final step is partitioned into kinetic energy of the separating fragments. We conclude that the stable configuration is a protonated oxazolone, which is formed by interaction of the developing charge (as HX is lost) with the N-terminus carbonyl group and that the reacting configuration is the acyclic acylium ion. This conclusion is supported by the similar fragmentation behavior of protonated 2-phenyl-5-oxazolone and the B ion derived by loss of H-Gly-OH from protonated C6H5C(+O)-Gly-Gly-OH. In addition, ab initio calculations on the simplest B ion, nominally HC(+O)NHCH2CO(+), show that the lowest energy structure is the protonated oxazolone. The acyclic acylium isomer is 1.49 eV higher in energy than the protonated oxazolone and 0.88 eV higher in energy than the fragmentation products, HC(+O)N(+)H = CH2 + CO, which is consistent with the kinetic energy releases measured.

Crosslinking in halogen containing novolac electron beam negative resists

AbstractHalogenophenol novolac (HPN)‐based negative resists exhibit excellent sensitivity and pattern resolution properties. The HPNs act as synergists for crosslinking with other irradiation labile compounds such as naphthoquinone diazide and bisazide vs. hydrogen halide (HX) elimination reaction, resulting in additional crosslinking, probably by aryl radical recombination and/or addition. We describe a new resist formulation based on HPN binder and melamine crosslinker (Cymel 303). In this case the irradiation induced HX elimination additionally catalyzes the melamine crosslinking.

Solid-state cyclometallation of the 1-methyl-2,4′-bipyridinium complexes of palladium II and platinum II

The complexes [M(2,4′-bpyMe)X3] · nH 2O (M = Pd, Pt; X = Cl, Br; 2,4′-bpyMe = 1-methyl-2,4′-bipyridinium, n = 0, 1, 2) cyclometallate with elimination of HX to give [M(2,4′bpyMe-H)X 2] in the solid state on heating or upon microwave irradiation. Thermal analysis (TGA, DTA, DSC) in conjunction with infrared spectroscope indicates that these complexes cyclometallate in the temperature range 160–260°C. The ease of cyclometallation is Pd > Pt and Cl > Br. The time of cyclometallation with microwave irradiation depends on the mode of irradiation.

Osmiumkomplexe vom Halbsandwichtyp mit Oximen, Iminen und Azavinylidenen als Liganden

Osmium Complexes of the Half‐Sandwich Type with Oximes, Imines, and Azavinylidenes as LigandAzavinylideneosmium complexes of the general composition [(arene)Os(NCRR)(L)]X (L = PMe3, PMetBu2, PiPr3) have been prepared by two methods. The first one uses the hydrido compound [C6H6OsHI(PMetBu2)] (2) and oximes HONCRR as starting materials and proceeds via the oxime complexes [C6H6OsH{N(OH)CRR}(PMetBu2)]PF6 (10, 11) as intermediates. They react with Al2O3 with elimination of water to give the final products 6–9. The second method starts with the dichloro‐ or diiodoosmium(II) compounds [(arene)OxX2(PR3)] (14, 16, 19, 21; arene = C6H6, 1,3,5‐Me3C6H3i R = Me, iPr) which upon treatment with HN = CPh2 or imine derivatives XNC(R)Ph (X = Li, SiMe3) afford the azavinylidene complexes 13b, 18, 23, 33. In the reactions with HNCPh2, the corresponding imine complexes [(arene)OsX(NHCPh2)‐(PR3)]X (15, 17, 20, 22) are formed as the primary products. Whereas nucleophilic addition of H– and CH3— to the N=C carbon atom of [C6H6Os(NCPh2)(PMetBu2)]+ (6) gives the imidoosmium(II) compounds [C6H6Os(NCRPh2)(PMetBu2)] (24, 25), the reaction of [C6H6Os(NCPh2)(PiPr3)]PF6 (13 b) with LiAlH(OtBu)3 yields the hydrido(imino) derivative [C6H6OsH(NHCPh2)(PiPr3)]PF6 (26). The bis(azido) complex [C6H6Os(N3)2(PiPr3)] (27), which is prepared either from 13 b or [C6H6OsI2(PiPr3)] (14) and NaN3, undergoes a [3 + 2] cycloaddition reaction with C2(CO2Me)2. Two isomeric (triazole)osmium compounds 28, 29 have been isolated. Treatment of [C6H6Os(NCRPh)(PiPr3)]PF6 with HX (X = O2CCF3) leads to addition of the acid to the OsN bond and, for R = Ph (13 b), by subsequent elimination of HX to the formation of a five‐membered metallaheterocycle 31. The X‐ray structural analysis of [C6H6Os(NCPh2)(PMetBu2)]PF6 (6) reveals an allene‐like arrangement of the ligands and substituents around the OsNC unit.

Gas-phase reactions of iron(benzyne)+ [.eta.6-1,3-cyclohexadien-5-yne)iron(1+)] with simple alkyl halides

An an extension of work on M(benzyne){sup +} complexes (M = Fe, Fe{sub 2}, CoFe, Sc), here the authors report the primary and secondary reactions of Fe(benzyne){sup +} with CH{sub 3}F and the small alkyl halides, C{sub n}H{sub 2n+1}X (n = 1-3; X = Cl, Br, I). Reaction mechanisms are postulated based on the product ion structures which are determined by ion-molecule reactions and collision-induced dissociation. In general, The reactions are observed to proceed by an initial C-X or C-C insertion. If {beta}-hydrogens are present on the alkyl moiety, subsequent {beta}-H transfer and elimination of HX is observed. Secondary reactions generally involve dehydrohalogenation and halogen abstraction. One of the most interesting reactions is with CH{sub 3}I. Following C-I insertion, transfer of the CH{sub 3} group to the benzyne ligand results in an Fe(I)(tolyl){sup +} intermediate which competitively eliminates either FeI to generate C{sub 7}H{sub 7{sup +}} or I{sup {sm_bullet}} to generate FeC{sub 7}H{sub 7{sup +}}. Ion-molecule reactions indicate that the C{sub 7}H{sub 7{sup +}} has an o-tolyliron structure. For larger alkyl halides, however, the analogous reactions are not observed due to the availability of {beta}-hydrogens, which undergo facile transfer and elimination of HX as described above. Finally, the thermochemical implicationsmore » of these results are discussed.« less

Effect of alkali metal cationization on the collision‐induced decomposition of alkyl per‐O‐acetyl‐2‐deoxy‐2‐halo‐α‐O‐mannopyranosides

AbstractThe effect of alkali metal cationization on the collision‐induced decomposition of alkyl per‐O‐acetyl‐2‐deoxy‐2‐bromo‐and‐iodo‐α‐O‐mannopyranosides was studied. The bromo sugars gave fairly abundant MH+, whereas for the iodo sugars the MH+ ions were insignificant. However, both the bromo and the iodo derivatives gave abundant M + alkali metal ion complexes. In contrast to the behaviour of the MH+ ion, the [M + Li]+, [M + Na]+ and [M + K]+ ions of these compounds do not decompose by loss of the C(1) substituent. Elimination of AcOH is the preferred fragmentation pathway of [M + Cat]+. Elimination of HX occurs only after loss of AcOH and CH2CO from MH+, whereas [M + Cat]+ directly loses HX. The elimination of HX is more pronounced from [M + Na]+ and [M + K]+ than from [M + Li]+. Loss of AcOLi is an additional fragmentation route observed in the case of the decomposition of [M + Li]+ ion.

Vinylidene Transition Metal Complexes, XXII[1]. – Alkyne, Alkynyl(hydrido)1‐, Vinylidene‐, and Vinylvinylidene Complexes of Rhodium from OH‐, NH2‐, and Cl‐Functionalized Alkynes

AbstractThe reaction of [RhCl(PiPr3)2]n with γ1‐functionalized 1‐alkynes HCC‐CRR′X (XOH, OMe, Cl, NH2) at room temperature leads to the formation of either alkyne‐, alkynyl(hydrido)1‐, or vinylidenerhodium complexes. The alkyne and alkynyl‐(hydrido) derivatives rearrange thermally or in the presence of deactivated Al2O3 to the isomeric vinylidenerhodium compounds in almost quantitative yield. On treatment of the γ1‐functionalized vinylidenerhodium complexes trans‐[RhCl(CCH‐CRR′X)(PiPr3)2] with Al2O3 or traces of acids, elimination of HX occurs and (for RH, CH3; R′CH3; XOH, Cl, NH2) the (vinylvinylidene)rhodium compounds trans‐[RhCl(CCH‐CRCH2)(PiPr3)2] are formed. In contrast, the reaction of trans‐[RhCl(CCHCPh2OH)(PiPr3)2] with either Al2O3 or acid gives the allenylidene complex trans‐[RhCl(CCCPh2)(PiPr3)2]. The 1‐hexyne derivatives HCC[CH2]3CH2X (XOH, Cl) react with [RhCl(PiPr3)2]n to give alkyne‐, alkynyl(hydrido)1‐, and vinylidenerhodium compounds; attempts to form the cyclic vinylidene complex trans‐ by HX elimination from trans‐[RhCl(CCCH[CH2]3CH2X)(PiPr3)2] (XOH, Cl) failed. The half‐sandwich‐type (vinylvinylidene)rhodium compounds [C5H5Rh(CCH‐CRCH2)(PiPr3)] (RH, Me) are obtained from [RhH(CC‐CRCH2)Cl(py)(PiPr3)2] and NaC5H5.

Barrier Widths and Tunneling in the Four‐Centered Syn Elimination of H‐X from Ethyl‐X. The Role of Transition State Asymmetry

AbstractThe syn elimination of HX from CH3CH2X produces a C2H4‐HX complex, which is stabilized relative to ethylene and HX. The primary kinetic H/D isotope effects in the complex‐forming steps of such reactions have been examined ab initio for X = H, BH2, CH2, NH2, NH3+, OH, OH2+, F, Cl, and Br, using 3–21G, 3–21G(d), 6–31G(d), and MP2/6–31G(d)optimized structures and vibration frequencies. Four‐centered transition structures are found for all but X = H, BH2, and CH3; with BH2, no transition structure exists at MP2/6–31G(d); with H and CH3, the transition structures are three‐centered. In addition, although the syn mechanism has lower energy for X=H than the four‐centered Woodward‐Hoffman allowed anti mechanism, C‐H, C‐C, and H‐H bond breaking would be favored over either pathway. The semiclassical primary kinetic isotope effect increases systematically as the central atom of a neutral X is varied from left to right along a row, or down a column, of the periodic table. Concurrently, the X‐H‐C angle in the transition state increases. The increase in kH/kD as the X‐H‐C angle becomes more linear is the direction predicted by E.S. Lewis for hydride (deuteride) transfer, and by More O'Ferrall for hydron transfer. One‐dimensional corrections to these isotope effects predict significant quantum mechanical tunneling only in the cases of F and OH, for which the Bell and Eckart barriers are narrower than those obtained from intrinsic reaction coordinate (IRC) calculations. In contrast, for NH2, where tunneling seems unimportant, the Eckart barrier is wider than the IRC. A quantitative measure of barrier width is the imaginary frequency of the transition state. Tunneling occurs when this is large, when the barrier is large, and, most importantly, when the transition structure is symmetrical.

A b i n i t i o studies of dissociation pathways on the ground state potential energy surface for HFCO and HClCO

Reaction pathways for the decomposition of HFCO and HClCO on the ground state potential energy surface have been studied by using ab initio methods. Heats of reaction and barrier heights have been computed by using Mo/ller–Plesset perturbation theory. Spin projections have been applied to free radical dissociation pathways for annihilation of spin contamination. The favorable dissociation path predicted is molecular elimination of HX to yield CO. The substitution effects on decomposition pathways of HFCO and HClCO are also examined.

Dirhenium complexes derived from the ligand 2-mercaptoquinoline (2-mqH). Structure of [Re2Cl3(.mu.-dppm)2(2-mq)]PF6 (dppm = Ph2PCH2PPh2)

The triply bonded dirhenium complexes Re 2 X 4 (dppm) 2 (X=Cl,Br; dppm=Ph 2 PCH 2 PPh 2 ) react with 2-mercaptoquinoline (2-mqH) to afford the adducts Re 2 X 4 (dppm) 2 (2-mqH), in which the 2-mqH ligand (in its zwitterionic form) is probably bound in a monodentate fashion through its deprotonated thiol donor. These complexes undergo a reversible one-electron transfer to give [Re 2 X 4 (dppm) 2 (2-mqH)] + (isolable as their PF 6 − salts). This oxidation is followed by the slow elimination of HX to give paramagnetic [Re 2 X 3 (μ-dppm) 2 (2-mp)]PF 6 . A single-crystal X-ray structure determination of the chloride complex has been carried out at 20 o C. Crystal data are as follows: monoclinic space group P2 1 /c