Matrix isolation investigation of the photochemical reaction of methyl-substituted benzenes with CrCl2O2

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of toluene, m-, o-, and p-xylene, mesitylene, and hexamethylbenzene with CrCl2O2. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of lambda > 300 nm. The irradiation was shown to lead to oxygen atom transfer, forming complexes between methylcyclohexadienone derivatives and CrCl2O. With the xylenes and mesitylene, di- and trimethylphenols, complexed to CrCl2O, were also observed, respectively. This latter result arises from C-H bond activation and oxygen atom insertion into a C-H bond. The identification of the complexes was further supported by isotopic labeling (2H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level. Product distributions were rationalized by an analysis of the electron density distribution.     

Matrix isolation investigation of the photochemical reaction of benzene with CrCl2O2 and OVCl3

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of benzene with CrCl(2)O(2) and OVCl(3). While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of lambda > 300 nm. Wavelength dependence studies determined that light of lambda < 590 nm led to reaction and oxygen atom transfer, forming an eta(1)-complex between 2,4-cyclohexadienone and CrCl(2)O. The identification of the complex was further supported by isotopic labeling ((13)C and (2)H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level. Merged-jet experiments in which thermal reactions are examined were also conducted, at temperatures as high as 150 degrees C. No products were observed.     

Matrix isolation and theoretical study of the reaction of substituted phosphines with CrCl2O2

The reactions between CrO2Cl2 and a series of substituted phosphines have been investigated using matrix isolation infrared spectroscopy. For all of the phosphines except PF3, twin jet co-deposition of the two reagents into argon matrices at 14 K initially led to the formation of weak bands due to the corresponding phosphine oxide. For all of the phosphines, subsequent irradiation with light of lambda > 300 nm led to the growth of a number of intense new bands that have been assigned to the phosphine oxide complexed to CrCl2O, following an oxygen atom transfer reaction. Gas-phase, merged jet reactions prior to matrix deposition led to a significant yield of the uncomplexed phosphine oxide. Theoretical calculations at the B3LYP/6-311++g(d,2p) level were carried out in support of the experimental work, to support product band assignments and clarify the nature of the molecular complexes.     

Matrix isolation study of the photochemical reaction of cyclohexane and cyclohexene with CrCl2O2

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of cyclohexane and cyclohexene with CrCl₂O₂. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of λ > 300 nm. The irradiation was shown to lead to oxygen atom transfer, forming complexes between cyclic alcohol derivatives and CrCl₂O, although complexes between ring expansion products and CrCl₂O could not be ruled out. This latter result could arise from C-C bond activation and oxygen atom insertion into a C-C bond. For the cyclohexene system, the cyclohexanone-CrCl₂O complex was also observed. The identification of the complexes was further supported by isotopic labeling (²H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level.     

Infrared matrix isolation study of the thermal and photochemical reactions of ozone with dimethylcadmium

The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to explore the reaction of (CH(3))(2)Cd with O(3) over a range of time scales and upon irradiation. During twin jet deposition, multiple novel product species were observed along with several stable "late" products. Following annealing of these matrices to 35 K, absorptions due to two novel product species increased in intensity. In addition, new bands appeared, indicating the formation of an additional product. Subsequent UV irradiation destroyed several of the initial products and produced a new photoproduct. On the basis of (18)O and (16,18)O spectroscopic data and theoretical calculations, the novel intermediates H(3)COCdCH(3), H(3)CCdCH(2)OH, H(3)COCdOOCH(3), and H(3)CCdCHO were identified. Merged jet deposition led to a number of stable "late" products, including H(2)CO, CH(3)OH, and C(2)H(6), identifications that were confirmed by (18)O substitution. Mechanistic inferences for this reaction are discussed.     

Matrix isolation study of the thermal and photochemical reaction of OVCl3 and CrCl2O2 with cycloalkylamines

The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to identify and characterize the initial and secondary products in the thermal and photochemical reactions of OVCl₃ and CrCl₂O₂ with cyclopropyl-, cyclobutyl- and cyclopentylamine. Initial twin jet deposition led to the formation of two new species, the 1:1 molecular complex and the secondary HCl elimination product (e.g. Cl₂V(O)N(H)C₃H₅), as well as free HCl. Overall, the yield decreased with the size of the cycloalkyl ring, to the point with cyclopentylamine, the yield was extremely low and no firm conclusions could be reached. The complexes appear to be moderately strongly bound, leading to shifts to certain vibrational modes of both the acid and base subunits. Bands due to the complexes were destroyed by near-UV irradiation and led an increase in the intensity of the bands due to the HCl elimination product, as well as cage-paired HCl. Theoretical calculations were used to aid in product identification and band assignments.     

Matrix isolation study of the reactions of CrO2Cl2 with a series of silanes

The reactions between CrO2Cl2 and a series of silanes have been investigated using matrix isolation infrared spectroscopy. Twin-jet codeposition of the two reagents into argon matrices at 14 K followed by irradiation with light of lambda > 300 nm led to the growth of a number of new bands. These have been assigned to the appropriate silanol species formed by oxygen insertion into the Si-H bond, strongly complexed to CrCl2O. The structures and vibrational frequencies of these complexes have been characterized by high-level theoretical calculations. These calculations also support the relative preference for the insertion reaction compared to other possible pathways. Merged-jet codeposition of SiH2Cl2 with CrO2Cl2 at 200 degrees C also led to the formation of the free silanol, HSiCl2OH.     

Infrared matrix isolation study of the thermal and photochemical reactions of ozone with dimethylzinc

The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to explore the reaction of (CH3)2Zn with O3 over a range of time scales. Upon twin jet deposition, an initial cage pair complex was observed, along with formation of the novel H3COZnCH3 species. Subsequent UV irradiation destroyed the complex and greatly increased the yield of H3COZnCH3. An extensive set of bands were seen for this molecule, and (18)O spectroscopic data were obtained as well. The identification of this species was supported by theoretical calculations at the B3LYP/6-311++g(d,2p) level. Merged jet deposition led to a very different set of products, including H2CO, CH3OH and C2H6, identifications that were confirmed by (18)O substitution. In addition, a new variable length concentric deposition technique was developed to permit study of the time scales between twin (relatively short) and merged (relatively longer) reaction times. Mechanistic inferences for this reaction are discussed.     

Vibrational and thermal studies of the complexes (NH4)[VO(O2)2(phen)].2H2O and (NH4)[V(O2)3(phen)].2H2O

The infrared spectra of the oxodiperoxo and triperoxo complexes, (NH4)[VO(O2)2(phen)].2H2O and (NH4)[V(O2)3(phen)].2H2O have been recorded and the observed bands are assigned on the basis of Cs symmetry. Thermogravimetric (TG) and differential thermal analysis (DTA) measurements on these two complexes were also carried out. A detailed mechanism for the mode of thermal decomposition of the two complexes has been given and supported by infrared spectral measurements on the thermal decomposition products. The data obtained agree quite well with the expected structure and indicate that the final thermal decomposition product of these two complexes is V2O5.     

挂式-四氢双环戊二烯热裂解产物分布研究

研究了常压下, 温度为450～650 ℃, 停留时间为15.44～4.03 s条件下的JP-10 (挂式-四氢双环戊二烯)热裂解产物分布. 在相对较长的停留时间下, JP-10热裂解转化率对温度很敏感. 热裂解主要产物为甲烷、乙烯、丙烯、丁烯、丁二烯、环戊二烯、苯、甲苯、苯乙烯、环戊烯的乙烯基取代物及C5, C6异构体(戊二烯、环戊烯的甲基取代物、环己烯、己二烯和环戊二烯甲基取代物), 其中, C1～C4、环戊二烯、苯、甲苯、乙烯基取代环戊烯为初始产物.     

Infrared matrix isolation study of the oxidation of H2S by CrCl2O2

The thermal and photochemical reactions between CrO2Cl2 and H2S have been investigated using matrix isolation infrared spectroscopy. Twin-jet co-deposition of the two reagents into argon matrices at 14 K followed by irradiation with light of lambda > 300 nm led to the growth of a number of new bands. These have been assigned to the HSOH-CrCl2O complex, and to SO2. These assignments were supported by deuterium isotopic substitution and high level density functional calculations. Merged-jet deposition with the reaction zone at temperatures above 125 degrees C led to substantial yields of SO2 and HCl, as well as the complex of HCl with excess parent H2S. The evidence suggests that the thermal and photochemical reactions may follow different pathways.     

Lewis acid mediated reactions of 1-cyclopropyl-2-arylethanones with allenic esters: a facile synthetic protocol for the preparation of dihydrofuro[2,3-h]chromen-2-one derivatives

TMSOTf-mediated reactions of 1-cyclopropyl-2-arylethanones with allenic esters afford a novel method for the synthesis of dihydrofuro[2,3-h]chromen-2-one derivatives in moderate to good yields. This process is a sequential reaction involving a nucleophilic ring-opening reaction of the cyclopropane by H(2)O, two intermolecular aldol-type reactions and one intramolecular aldol-type reaction, a cyclic transesterification, dehydration, and aromatization mediated by Lewis acid.     

Synthesis, characterization, and electronic structure of diimine complexes of chromium

We have prepared and structurally characterized several complexes of chromium coordinated by diimine (or 1,4-diazadiene) ligands, that is, Ar-N=C(R)-(R)C=N-Ar (RL(Ar)) (where Ar = 2,6-diisopropylphenyl ("iPr") or 2,6-dimethylphenyl ("Me") and R = H or Me). The reaction of CrCl2 with HLiPr gave dinuclear [(HLiPr)Cr]2(mu-Cl)3(Cl)(THF) when isolated from Et2O; in THF solution, however, the product exists as mononuclear (HLiPr)CrCl2(THF)2. Two isostructural derivatives, (MeLMe)CrCl2(THF)2 and (HL(Me))CrCl2(THF)2, have also been prepared. Furthermore, the bis-ligand complex, (HLiPr)2Cr, has been prepared along with its reduction product, Li(THF)4[(HLiPr)2Cr]. We have also synthesized the tetracarbonyl complex, (HLiPr)Cr(CO)4, by addition of HLiPr to Cr(CO)4(NCCH3)2. The structure and variable temperature magnetic susceptibility of the previously reported Cr halide dimer, [(HLiPr)Cr(mu-Cl)]2, is also discussed in detail. All of the diimine complexes have been characterized structurally, spectroscopically, and magnetically, and their electronic structures are discussed with the aid of density-functional theory calculations.     

Experimental and theoretical studies of charge transfer and deuterium ion transfer between D2O+ and C2H4

The charge transfer and deuterium ion transfer reactions between D(2)O(+) and C(2)H(4) have been studied using the crossed beam technique at relative collision energies below one electron volt and by density functional theory (DFT) calculations. Both direct and rearrangement charge transfer processes are observed, forming C(2)H(4) (+) and C(2)H(3)D(+), respectively. Independent of collision energy, deuterium ion transfer accounts for approximately 20% of the reactive collisions. Between 22 and 36 % of charge transfer collisions occur with rearrangement. In both charge transfer processes, comparison of the internal energy distributions of products with the photoelectron spectrum of C(2)H(4) shows that Franck-Condon factors determine energy disposal in these channels. DFT calculations provide evidence for transient intermediates that undergo H/D migration with rearrangement, but with minimal modification of the product energy distributions determined by long range electron transfer. The cross section for charge transfer with rearrangement is approximately 10(3) larger than predicted from the Rice-Ramsperger-Kassel-Marcus isomerization rate in transient complexes, suggesting a nonstatistical mechanism for H/D exchange. DFT calculations suggest that reactive trajectories for deuterium ion transfer follow a pathway in which a deuterium atom from D(2)O(+) approaches the pi-cloud of ethylene along the perpendicular bisector of the C-C bond. The product kinetic energy distributions exhibit structure consistent with vibrational motion of the D-atom in the bridged C(2)H(4)D(+) product perpendicular to the C-C bond. The reaction quantitatively transforms the reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the deuterium ion is transferred in a configuration in which both the breaking and the forming bonds are extended.     

Reactions of early lanthanide metal atoms (Nd, Sm, Eu) with water molecules. A matrix isolation infrared spectroscopic and theoretical study

The reactions of early lanthanide metal atoms Nd, Sm, and Eu with water molecules have been investigated using matrix isolation infrared spectroscopy and density functional calculations. The reaction intermediates and products were identified on the basis of isotopic labeled experiments and density functional frequency calculations. The ground state metal atoms react with water to form the M(H2O) and M(H2O)(2) complexes spontaneously on annealing (M = Nd, Sm, Eu). The M(H2O) complexes isomerize to the inserted HMOH molecules under red light irradiation, which further decompose to give the metal monoxides upon UV light irradiation. The Nd(H2O)(2) complex decomposes to form the trivalent HNd(OH)(2) molecule, while the Sm(H2O)(2) and Eu(H2O)(2) complexes rearrange to the divalent Sm(OH)(2) and Eu(OH)(2) molecules under red light irradiation.     

Asymmetric [3+2] Photocycloadditions of Cyclopropanes with Alkenes or Alkynes through Visible‐Light Excitation of Catalyst‐Bound Substrates

The herein reported visible‐light‐activated catalytic asymmetric [3+2] photocycloadditions between cyclopropanes and alkenes or alkynes provide access to chiral cyclopentanes and cyclopentenes, respectively, in 63–99 % yields and with excellent enantioselectivities of up to >99 % ee. The reactions are catalyzed by a single bis‐cyclometalated chiral‐at‐metal rhodium complex (2–8 mol %) which after coordination to the cyclopropane generates the visible‐light‐absorbing complex, lowers the reduction potential of the cyclopropane, and provides the asymmetric induction and overall stereocontrol. Enabled by a mild single‐electron‐transfer reduction of directly photoexcited catalyst/substrate complexes, the presented transformations expand the scope of catalytic asymmetric photocycloadditions to simple mono‐acceptor‐substituted cyclopropanes affording previously inaccessible chiral cyclopentane and cyclopentene derivatives.     

环丙烷衍生物在D2O离子体系中的H/D交换反应

在D2O化学反应气条件下研究了环丙烷衍生物的H/D交换反应特性.发现了三种新的产物离子[M+1]+、[M+2]+和[M+3]+.应用碰撞诱导碎裂(CID)技术研究了这些离子的碎裂反应特性.实验结果表明三种新的产物离子是由反应物与试剂离子之间发生H/D交换反应生成的.并获得了环丙烷衍生物结构中活泼氢位置及其数量的信息.     

Characterization and reactivity of γ-Al_2O_3 supported Pd–Ni bimetallic nanocatalysts for selective hydrogenation of cyclopentadiene

Several g-Al2O3 supported Pd–Ni bimetallic nanocatalysts(Pd–Ni(x:y)/Al2O3; where x and y represent the mass ratio of Pd and Ni, respectively) were prepared by the impregnation method and used for selective hydrogenation of cyclopentadiene to cyclopentene. The Pd–Ni/Al2O3 samples were confirmed to generate Pd–Ni bimetallic nanoparticles by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The catalytic activity was assessed in view of the effects of different mass ratios of Pd and Ni, temperature, pressure, etc. Among all the samples, the Pd–Ni(1:1)/Al2O3(PN-1:1) catalyst showed extremely high catalytic ability. The conversion of cyclopentadiene and selectivity for cyclopentene can be simultaneously more than 90%.     

Reactions of late lanthanide metal atoms with water molecules: a matrix isolation infrared spectroscopic and theoretical study

The reactions of late lanthanide metal atoms (Gd-Lu) with water molecules have been investigated using matrix isolation infrared spectroscopy. The reaction intermediates and products were identified on the basis of isotopic substitution experiments and density functional theory calculations. All of the metal atoms except Lu react with water to form the M(H2O) complexes spontaneously upon annealing (M = Gd, Tb, Dy, Ho, Er, Tm, and Yb). The Dy(H2O) and Ho(H2O) complexes are able to coordinate a second water molecule to form the Dy(H2O)2 and Ho(H2O)2 complexes. The M(H2O) complexes isomerize to the inserted HMOH isomers under visible light irradiation, which further decompose to give the MO and/or HMO molecules upon UV light irradiation. The M(OH)2 molecules (M = Gd-Lu) were also produced. The results have been compared with our earlier work covering the early lanthanide metal atoms (Nd, Sm, Eu) to observe the existent trends for the lanthanide metal atom reactions.     

Intramolecular C-H activation reactions of molybdenacyclobutanes

Molybdenacyclobutane complexes can be prepared by reaction of Cp*Mo(NO)(=CHCMe3) (formed spontaneously by loss of neopentane from Cp*Mo(NO)(CH2CMe3)2 (1) under ambient conditions) with cyclic olefins, including cyclopentene, cycloheptene, and cyclooctene. The cyclopentene metallacyclobutane orients the metallacycle bridgehead protons cis to each other. A trans arrangement is observed for the cyclooctene congener, and both cis and trans orientations occur for the cycloheptene species. The reaction of 1 with cyclohexene initially forms a metallacyclobutane that then undergoes an allylic C-H activation to form an allyl-alkyl-coupled product with the concomitant loss of H2. The analogous allyl-alkyl structure is also observed as the thermodynamic product for the reactions of cycloheptene and cyclooctene with 1. The cyclooctene allyl-alkyl compound (5C) can be converted to an eta2-diene complex by heating with pyridine. Alternatively, heating of 5C in the presence of a variety of olefins displaces the diene ligand that can then be isolated in its unbound state.