The radiolysis of mixtures of carbon dioxide and hydrogen

The self-radiolysis of CO₂ in excess tritium (³H₂) has been studied at pressures of 0.1 to 1.0 atm, temperatures of ?80° to +100°C, and in the presence of added H₂O, He, or Ar. The primary products of decomposition are CO and ³H₂O. Secondary products are C³H₄, C₂³H₄, and a white polymer. The rates of disappearance of CO₂ and formation of products and G-;values were measured. The disappearance of CO₂ initially obeys first-order kinetics, then slows down with time at a rate depending upon the initial pressure of ³H₂. The initial rates are proportional to pressures of CO₂ and ³H₂. They are independent of temperature, decreased by addition of H₂O vapor, and increased by addition of He or Ar. The proposed mechanism of decomposition of CO₂ and formation of products involves ionization of CO₂ followed by dissociative recombination forming CO and O. Then the O reacts with a hydrogen-containing species forming OH and H₂O, and a back reaction forms CO₂ from CO and OH.     

Palladium and platinum catalyzed hydroselenation of alkynes: SeH vs SeSe addition to CC bond

A mechanistic study of the hydroselenation of alkynes catalyzed by Pd(PPh₃)₄ and Pt(PPh₃)₄ has shown that the palladium complex gives products of both SeH and SeSe bond addition to the triple bond of alkynes, while the platinum complex selectively catalyzes SeH bond addition. The key intermediate of PhSeH addition to the metal center, namely Pt(H)(SePh)(PPh₃)₂, was detected by ¹H-NMR spectroscopy. The analogous palladium complex rapidly decomposes with evolution of molecular hydrogen. A convenient method was developed for the preparation of Markovnikov hydroselenation products H₂CC(SePh)R, and the scope of this reaction was investigated. The first X-ray structure of the Markovnikov product H₂CC(SePh)CH₂N⁺HMe₂·HOOCCOO⁻ is reported.     

Nucleophilic Addition Reactions of Tricarbonyl [η5−1-(Phenylsulfonyl)cyclohexadienyl]iron(I) Complex

Hydride abstraction of tricarbonyl[η⁴-1-(phenylsulfonyl)-1,3-cyclohexadiene]iron(0) complex 2 with Ph₃C⁺PF₆^? regiospecifically provided the title compound 3 in excellent yield. Cationic complex 3 could react with a variety of nucleophiles in good yields. Soft nucleophiles prefer to attack at the C-5 position, whereas hard nucleophiles such as methyllithium and the enolate of ethyl acetate gave the C-5 as well as the C-2 addition products. Some synthetic applications of the addition products were also studied.     

Evidence for Internal Ion Pair Formation upon Insertion of Reactive Alkene in the Zirconium–Carbon Bond of the cp2Zr(μ-C4h6)b(c6f5)3 Metallocene-Boron-Betaine Ziegler Catalyst System

Treatment of the (butadiene)ML₂ complexes 1 [ML₂ = Cp₂Zr ( a ), Cp₂Hf ( b ), and (.-C₅H₄CH₃)₂Zr ( c )] with B(C₆F₅)₃ gives the 1:1 addition products (CH₂CHCHCH₂–B(C₆F₅_₃)ML₂ ( 3a – c ). At –40°C the betaine complex 3a inserts one equivalent of methylenecyclopropane to give the regioisomeric insertion products 5a and 6a in a 60:40 ratio. These products exhibit the cyclopropylidene moiety in the α- and β-positions, respectively, relative to zirconium. The corresponding hafnocene complexes 5b and 6b are obtained in a 70:30 ratio starting from 3b . The reaction of 3 ( a – c ) with allene gives a single insertion product ( 7a – c ) in each case where the exo-methylene group is in the α-position to the metal center ([2,1]-insertion). The complexes 5 – 7 are chiral. They all exhibit a pronounced ·-interaction of the internal –C⁴H=C⁵H⁻ double bond of the s̀-ligand chain with the metal center in addition to a metallocene/–C⁶H₂–[B] ion pair interaction. The relative contributions of the cationic metallocene end of the dipolar complexes 5 – 7 are quite dependent on the steric and electronic properties of the respective metallocene units involved. This is revealed by a comparison to typical ¹³C-NMR parameters of the complexes 5 – 7 with a pair of suitable model complexes, namely the ethylene insertion product 4 into the betaine system 3a and its THF adduct 4 .THF.     

Syntheses of polyfluoroalkyl aryl ether

The reactions of methoxyphenol and dihydroxybenzene with hexafluoropropene were studied. Eight new compounds 2-9 were separated from the reaction mixture of catechol and hexafluoropropene. The formation of these products was explained through nucleophilic attack of the aryloxy anion on hexafluoropropene, followed by elimination and addition (Scheme 1). However, the reaction of resorcinol and hydroquinone with C₃F₄ only gave the simple addition products 10 and addition-elimination products Z, E-11, 12. All new compounds were characterized by ¹H and ¹⁹F NMR, IR, MS and elemental analyses. The ¹⁹F NMR of seven membered ring compounds 4 and 5 were discussed in detail.     

Determination of237Np in environmental samples using inductively coupled plasma mass spectrometry

Ammonium uranates (AU) obtained by the addition of aqueous NH₄ OH to a solution of UO₂ (NO₃)₂ or the equilibrium reaction of UO₃ · 2H₂ O with the vapour over concentrated NH₄ OH have been studied by X-ray diffraction (XRD) analysis, diffuse reflectance Fourier transform infrared spectrometry (DR-FTIR) and chemical analysis. Ammonia can be present as either NH₃ or NH ₄ ⁺ . For precipitates obtained at a pH of 3.7, ammonia in the form of NH₃ is predominant. For ammonium uranate obtained by reaction over concentrated NH₄OH, most of the ammonia is bonded as NH ₄ ⁺ . The reaction mechanism and structures of the products are also discussed.     

Computational study on the mechanism for the gas‐phase reaction of dimethyl disulfide with OH

The mechanisms for the reaction of CH₃SSCH₃ with OH radical are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) level of theory. Five channels have been obtained and six transition state structures have been located for the title reaction. The initial association between CH₃SSCH₃ and OH, which forms two low‐energy adducts named as CH₃S(OH)SCH₃ (IM1 and IM2), is confirmed to be a barrierless process, The S? S bond rupture and H? S bond formation of IM1 lead to the products P1(CH₃SH + CH₃SO) with a barrier height of 40.00 kJ mol^?1. The reaction energy of Path 1 is ?74.04 kJ mol^?1. P1 is the most abundant in view of both thermodynamics and dynamics. In addition, IMs can lead to the products P2 (CH₃S + CH₃SOH), P3 (H₂O + CH₂S + CH₃S), P4 (CH₃ + CH₃SSOH), and P5 (CH₄ + CH₃SSO) by addition‐elimination or hydrogen abstraction mechanism. All products are thermodynamically favorable except for P4 (CH₃ + CH₃SSOH). The reaction energies of Path 2, Path 3, Path 4, and Path 5 are ?28.42, ?46.90, 28.03, and ?89.47 kJ mol^?1, respectively. Path 5 is the least favorable channel despite its largest exothermicity (?89.47 kJ mol^?1) because this process must undergo two barriers of TS5 (109.0 kJ mol^?1) and TS6 (25.49 kJ mol^?1). Hopefully, the results presented in this study may provide helpful information on deep insight into the reaction mechanism. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Unprecedented and Effective Synthesis of Thiazolines from Perfluoro-3-isothiocyanato-2-methyl-2-pentene and Certain P-Nucleofuges

The reactions of perfluoro-3-isothiocyanato-2-methyl-2-pentene with PPh₃ and P(NEt₂)₃ in the presence of NaBF₄, KI, and NaBPh4 form phosphonium salts with the heterocyclic substituent (4E)-5,5-bis(trifluoromethyl)-4-(tetrafluoroethylidene)-4,5-dihydro-1,3-thiazol-2-yl, instead of involving desulfurization and formation of P-F-containing products. The reaction with tris(pentafluorophenyl)phosphine fails. The reactions with P(OEt)₃ in the presence of ClSiMe₃ or (CH₃O)₂POSiMe₃ yield diethyl or dimethyl [(4E)-5,5-bis(trifluoromethyl)-4-(tetrafluoroethylidene)-4,5-dihydro-1,3-thiazol-2-yl]phosphonates and no intramolecular alkylation products. The ¹H, ¹³C, ¹⁹F, and ³¹P spectra are presented, and the reaction pathways are discussed. Potential mechanisms of the biological and catalytic activity of the reaction products are considered.     

Synthesis and Nucleophilic Addition Reactions of Tricarbonyl[η5‐2‐(phenylthio)hexadienyl]iron Hexafluorophosphate

3‐Phenylthio‐3‐sulfolene ( 1 ) was readily converted to a C‐5 substituted product 2 , which upon thermolysis and complexation with Fe₂(CO)₉ gave (η⁴‐diene)iron complexes 3a and 3b . Treatment of 3a and 3b with aq. HPF₆ and Ac₂O provided the title compound 5 , which reacted regio‐ and stereospecifically with some nucleophiles to give the addition products 3b and 7 .     

Structural study of C,N‐chelated monoorganotin(IV) halides

Three monoorganotin(IV) compounds of general formula L^CNSnX₃, where L^CN is a 2‐(dimethylaminomethyl)phenyl‐ group and X = Cl ( 1 ), Br ( 2 ) and I ( 3 ), were prepared and characterized using XRD and NMR techniques. Compound 1 reacts with moisture producing [(L^CN)₂HSnCl₂]⁺ [L^CNSnCl₄]^?. Compound 3 decomposes to (L^CN)₂SnI₂, SnI₂ and I₂ when heated. Compound 2 was reacted with NH₄F yielding an equilibrium of fluorine‐containing species. The major products were [L^CNSnF₅]^2? and [(L^CNSnF₃)₂(µ²‐F)₂]^2? (4a). When compound 2 was reacted with another fluorinating agent, L^CN(n‐Bu)₂SnF, an oligomeric product, [L^CNSnF₂(µ²‐F)₂]_n, was observed. Further addition of NH₄F led to subsequent formation of 4a. The structure of fluorinated products was investigated by ¹H, ¹⁹F and ¹¹⁹Sn NMR spectroscopy. Copyright © 2006 John Wiley & Sons, Ltd.     

Ion-molecule reactions and collision-activated dissociation of C4H 4 +. isomers: A case study in the use of the MS3 capabilities of a pentaquadrupole mass spectrometer

Isomeric C₄H ₄ ^+. radical cations vinylacetylene (a), butatriene (b), methylene cyclopropene (c), and the nonaromatic cyclobutadiene (d), generated, respectively, from the neutral precursors 3-butyn-1-ol (1), 1,4-dichloro-2-butyne (2), benzene (3), and 7,8-benzotricyclo [4.2.2.0^2,5]deca-3,7,9-triene (4), undergo diagnostically different ion-molecule reactions with allene, isoprene, furan, and thiophene. It is speculated that adducts are generated by [2 + 2] cycloadditions with the first reagent and [4 + 2] Dials-Alder cycloadditions with isoprene, furan, and thiophene. The initially formed cycloaddition adducts fragment rapidly, isomerize, or undergo further addition of neutral reagent to yield a complex set of products. With a pentaquadrupole mass spectrometer, MS³ experiments that employ three stages of ion mass analysis are used to help elucidate the ion-molecule reactions and to distinguish the isomeric C⁴H ₄ ^+. ions. Among these experiments, the reaction intermediate spectrum reveals the nature of the intermediates connecting the reactant to a selected product while the sequential product spectrum provides mechanistic and structural information on the adducts and other ion-molecule products. The unique combination of ion-molecule reactions with collision-activated dissociation employed here provides valuable information on the chemistry of ionized cyclobutadiene, including its proclivity to undergo [2 + 2] and [4 + 2] cyc1oadditions.     

CE/ES-MS ANALYSIS ON MACROCYCLIC SCHIFF BASES DERIVED FROM A SODIUM TEMPLATE CYCLOCONDENSATION OF 2,6-DIFORMYL-4-METHYLPHENOL WITH ALKYLDIAMINES

Abstract

The template reaction of sodium 2,6-diformyl-4-methylphenolate with alkyl diamines H₂NRNH₂ [R = (CH₂)_n, n = 4, 5, 6] led to the production of macrocyclic Schiff bases which were characterized by elemental analyses, IR and proton NMR spectra. Positive ion fast atom bombardment (FAB) and electron spray ionization (ES) mass spectroscopic investigations on the above products showed the presence of a [3 ± 3] (H₃L³) cyclocondensation mode in addition to the common [2 ± 2] (H₂L²) mode. The product in a typical reaction was analysed by capillary electrophoresis (CE) coupled to a mass spectrometer (MS) via an electrospray (ES) ionization interface, confirming the independent formation of both tetraimine and hexaimine macrocycles as a mixture of Na₂L² and Na₃L³.     

Kinetics of the reactions of the IO radical with dimethyl sulfide,methanethiol, ethylene,and propylene

The reactions of IO radicals with CH₃SCH₃, CH₃SH, C₂H₄, and C₃H₆ have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH₃SCH₃ → products (1): k₁ = (1.5 ± 0.2) × 10^?14; IO + CH₃SH → products (2): k₂ = (6.6 ± 1.3) × 10^?16; IO + C₂H₄ →products (3): k₃ < 2 × 10^?16; IO + C₃H₆ → products (4): k₄ < 2 × 10^?16 (units are cm³ molecule^?1 s^?1). CH₃S(O)CH₃ and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k₁ compared to our previous determination is discussed.     

Rhodium catalyzed hydroacylation of ethylene with 4-pentenals. reactions of 4-hexenal-1-d

A catalyst derived from 2,4-pentanedionatobis(ethylene)rhodium(I), I, promoted the addition of 4-pentenal to ethylene. The reaction was accompanied by the formation of double bond migration products derived from the 4-pentenal reactant and from the 6-hepten-3-one primary product. Compound I accomplished the addition of 4-hexenal to ethylene to afford high yields of 6-octen-3-one. The fate of the aldehyde hydrogen in this transformation has been determined in experiments employing 4-hexenal-1-d as reactant. Treatment of 4-hexenal-1-d with I in CHCl₃ and CDCl₃ afforded 6-octen-3-one possessing >50% d_o molecules while the isotopic composition of recovered unexpended 4-hexenal remained >96% d₁. 6-Octen-3-one products with isotopic compositions of >66% d_o were afforded when ethylene was introduced to reaction mixtures. The location of deuterium in 6-octen-3-one, derived from treatment of 4-hexenal-1-d with I in the absence of added C₂H₄, was determined to be distributed at C-1 and C-2 and at the CC bond by analysis of the ¹H and ²H NMR spectra. Unexpended ethylene was recovered and was found to contain a substantial amount of deuterium. Mechanistic implications of these results are discussed.     

Catalyzed hydroboration of nitrostyrenes and 4-vinylaniline: a mild and selective route to aniline derivatives containing boronate esters

Transition metal catalyzed reactions of catecholborane (HBcat; cat = 1,2-O₂C₆H₄) with β-nitrostyrene and 3-nitrostyrene lead to products derived from competing hydrogenation and hydroboration of the alkene unit along with reduction of the nitro group. Hydroboration of 4-vinylaniline gave regioselective formation of either the branched or the linear organoboronate ester depending upon the catalyst precursors (i.e., RhCl(PPh₃)₃ or Rh(acac)(dppe) vs [Cp^∗IrCl₂]₂) used to facilitate this reaction. Hydroboration products were converted to air-stable primary amines by addition of pinacol.     

Intramolecularly Stabilised Group 10 Metal Stannyl and Stannylene Complexes: Multi‐pathway Synthesis and Observation of Platinum‐to‐Tin Alkyl Transfer

Reaction of [PdClMe(P^N)₂] with SnCl₂ followed by Cl‐abstraction leads to apparent Pd?C bond activation, resulting in methylstannylene species trans‐[PdCl{(P^N)₂SnClMe}][BF₄] (P^N=diaryl phosphino‐N‐heterocycle). In contrast, reaction of Pt analogues with SnCl₂ leads to Pt?Cl bond activation, resulting in methylplatinum species trans‐[PtMe{(P^N)₂SnCl₂}][BF₄]. Over time, they isomerise to methylstannylene species, indicating that both kinetic and thermodynamic products can be isolated for Pt, whereas for Pd only methylstannylene complexes are isolated. Oxidative addition of RSnCl₃ (R=Me, Bu, Ph) to M⁰ precursors (M=Pd or Pt) in the presence of P^N ligands results in diphosphinostannylene pincer complexes trans‐[MCl{(P^N)₂SnCl(R)}][SnCl₄R], which are structurally similar to the products from SnCl₂ insertion. This showed that addition of RSnCl₃ to M⁰ results in formal Sn?Cl bond oxidative addition. A probable pathway of activation of the tin reagents and formation of different products is proposed and the relevancy of the findings for Pd and Pt catalysed processes that use SnCl₂ as a co‐catalyst is discussed.     

Rate Coefficients of the Reactions of CN and NCO with O2 and NO2 at 296 K

The rate coefficients of the reactions of CN and NCO radicals with O₂ and NO₂ at 296 K: (1) CN + O₂ → products; (2) CN + NO₂ → products; (3) NCO + O₂ → products and (4) NCO + NO₂ → products have been measured with the laser photolysis-laser induced fluorescence technique. We obtained k₁ = (2.1 ± 0.3) × 10^?11 and k₂ = (7.2 ± 1.0) × 10^?11 cm³ molecule^?t s^?1 which agree well with published results. As no reaction was observed between NCO and O₂ at 297 K, an upper limit of k₃ < 4 × 10^?17 cm³ molecule^?1 S^?1 was estimated. The reaction of NCO with NO₂ has not been investigated previously. We measured k₄ = (2.2 ± 0.3) × 10^?11 cm³ molecule^?1 s^?1 at 296 K.     

The reaction of trimethylchlorosilane with phenyltelluromagnesium bromide in tetrahydrofuran: Characterisation of the products by 29Si and 125Te NMR spectroscopy

The products of the reaction of Me₃SiCl with PhTeMgBr in THF have been identified with the aid of high resolution ²⁹Si and ¹²⁹Te NMR spectroscopy. In addition to the expected product Me₂SiTePh (40%), the symmetrical telluride (Me₃Si)₂Te (10%) and the ether Me₃SiO(CH₂)₄TePh (45%) are also formed. The latter results from ring-opening of the solvent THF by Me₃SiCl followed by reaction of the product with PhTeMgBr.     

Reaction of an “Invisible” Frustrated N/B Lewis Pair with Dihydrogen

D ‐(+)‐Camphor forms the enamine 2 with piperidine. Compound 2 adds HB(C₆F₅)₂ at the enamine carbon atom C3 to form a Lewis acid/Lewis base adduct (exo‐/endo‐isomers of 3 ). Exposure of 3 to dihydrogen (2.5 bar, room temperature) leads to heterolytic splitting of H₂ to form the H⁺/H^? addition products ( 4 , two diastereoisomers) of the “invisible” frustrated Lewis pairs ( 5 , two diastereoisomers) that were apparently generated in situ by enamine hydroboration under equilibrium conditions.     

Building C(sp3) Molecular Complexity on 2,2′-Bipyridine and 1,10-Phenanthroline in Rhenium Tricarbonyl Complexes

The reactions of [Re(N-N)(CO)₃(PMe₃)]OTf (N-N=2,2′-bipyridine, bipy; 1,10-phenanthroline, phen) compounds with tBuLi and with LiHBEt₃ have been explored. Addition to the N-N chelate took place with different site-selectivity depending on both chelate and nucleophile. Thus, with tBuLi, an unprecedented addition to C5 of bipy, a regiochemistry not accessible for free bipy, was obtained, whereas coordinated phen underwent tBuLi addition to C2 and C4. Remarkably, when LiHBEt₃ reacted with [Re(bipy)(CO)₃(PMe₃)]OTf, hydride addition to the 4 and 6 positions of bipy triggered an intermolecular cyclodimerization of two dearomatized pyridyl rings. In contrast, hydride addition to the phen analog resulted in partial reduction of one pyridine ring. The resulting neutral Re^I products showed a varied reactivity with HOTf and with MeOTf to yield cationic complexes. These strategies rendered access to Re^I complexes containing bipy- and phen-derived chelates with several C(sp³) centers.