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21.
Temprado M McDonough JE Mendiratta A Tsai YC Fortman GC Cummins CC Rybak-Akimova EV Hoff CD 《Inorganic chemistry》2008,47(20):9380-9389
Synthetic studies are reported that show that the reaction of either H2SnR2 (R = Ph, n-Bu) or HMo(CO)3(Cp) (1-H, Cp = eta(5)-C5H5) with Mo(N[t-Bu]Ar)3 (2, Ar = 3,5-C6H3Me2) produce HMo(N[t-Bu]Ar)3 (2-H). The benzonitrile adduct (PhCN)Mo(N[t-Bu]Ar)3 (2-NCPh) reacts rapidly with H2SnR2 or 1-H to produce the ketimide complex (Ph(H)C=N)Mo(N[t-Bu]Ar)3 (2-NC(H)Ph). The X-ray crystal structures of both 2-H and 2-NC(H)Ph are reported. The enthalpy of reaction of 1-H and 2 in toluene solution has been measured by solution calorimetry (DeltaH = -13.1 +/- 0.7 kcal mol(-1)) and used to estimate the Mo-H bond dissociation enthalpy (BDE) in 2-H as 62 kcal mol(-1). The enthalpy of reaction of 1-H and 2-NCPh in toluene solution was determined calorimetrically as DeltaH = -35.1 +/- 2.1 kcal mol(-1). This value combined with the enthalpy of hydrogenation of [Mo(CO)3(Cp)]2 (1(2)) gives an estimated value of 90 kcal mol(-1) for the BDE of the ketimide C-H of 2-NC(H)Ph. These data led to the prediction that formation of 2-NC(H)Ph via nitrile insertion into 2-H would be exothermic by approximately 36 kcal mol(-1), and this reaction was observed experimentally. Stopped flow kinetic studies of the rapid reaction of 1-H with 2-NCPh yielded DeltaH(double dagger) = 11.9 +/- 0.4 kcal mol(-1), DeltaS(double dagger) = -2.7 +/- 1.2 cal K(-1) mol(-1). Corresponding studies with DMo(CO)3(Cp) (1-D) showed a normal kinetic isotope effect with kH/kD approximately 1.6, DeltaH(double dagger) = 13.1 +/- 0.4 kcal mol(-1) and DeltaS(double dagger) = 1.1 +/- 1.6 cal K(-1) mol(-1). Spectroscopic studies of the much slower reaction of 1-H and 2 yielding 2-H and 1/2 1(2) showed generation of variable amounts of a complex proposed to be (Ar[t-Bu]N)3Mo-Mo(CO)3(Cp) (1-2). Complex 1-2 can also be formed in small equilibrium amounts by direct reaction of excess 2 and 1(2). The presence of 1-2 complicates the kinetic picture; however, in the presence of excess 2, the second-order rate constant for H atom transfer from 1-H has been measured: 0.09 +/- 0.01 M(-1) s(-1) at 1.3 degrees C and 0.26 +/- 0.04 M(-1) s(-1) at 17 degrees C. Study of the rate of reaction of 1-D yielded kH/kD = 1.00 +/- 0.05 consistent with an early transition state in which formation of the adduct (Ar[t-Bu]N)3Mo...HMo(CO)3(Cp) is rate limiting. 相似文献
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袁勤勤 杨正 李仁忠 Wesley J. Transue 李志鹏 江凌 Niranjan Govin Christopher C. Cummins 王学斌 《化学物理学报》2018,31(4):463-470
Gaseous dibenzo-7-phosphanorbornadiene P-sulfide anions APS-(A=C14H10 or anthracene) were generated via electrospray ionization, and characterized by magnetic-bottle photoelectron spectroscopy, velocity-map imaging (VMI) photoelectron spectroscopy, and quantum chemical calculations. The electron affinity (EA) and spin-orbit (SO) splitting of the APS· radical are determined from the photoelectron spectra and Franck-Condon factor simulations to be EA=(2.62±0.05) eV and SO splitting=(43±7) meV. VMI photoelectron images show strong and sharp peaks near the detachment threshold with an identical electron kinetic energy (eKE) of 17.9 meV at three different detachment wavelengths, which are therefore assigned to autodetachment from dipole-bound anion states. The B3LYP/6-31++G(d,p) calculations indicate APS· has a dipole moment of 3.31 Debye, large enough to support a dipole-bound electron. 相似文献
24.
Diuranium μ-η(6),η(6)-arene complexes supported by ketimide ligands were synthesized and characterized. Disodium or dipotassium salts of the formula M(2)(μ-η(6),η(6)-arene)[U(NC(t)BuMes)(3)](2) (M = Na or K, Mes = 2,4,6-C(6)H(2)Me(3)) and monopotassium salts of the formula K(μ-η(6),η(6)-arene)[U(NC(t)BuMes)(3)](2) (arene = naphthalene, biphenyl, trans-stilbene, or p-terphenyl) were both observed. Two different salts of the monoanionic, toluene-bridged complexes are also described. Density functional theory calculations have been employed to illuminate the electronic structure of the μ-η(6),η(6)-arene diuranium complexes and to facilitate the comparison with related transition-metal systems, in particular (μ-η(6),η(6)-C(6)H(6))[VCp](2). It was found that the μ-η(6),η(6)-arene diuranium complexes were isolobal with (μ-η(6),η(6)-C(6)H(6))[VCp](2) and that the principal arene-binding interaction was a pair of δ bonds (total of 4e) involving both metals and the arene lowest unoccupied molecular orbital. Reactivity studies have been carried out with the mono- and dianionic μ-η(6),η(6)-arene diuranium complexes, revealing contrasting modes of redox chemistry as a function of the system's state of charge. 相似文献
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Brillouin and Raman scattering studies of salol from room temperature to within 5 mK of the melting transition at Tm = 40.97°C are reported. Changes in the Brillouin shifts and linewidths were accurately determined by nonlinear least-squares fitting and deconvolution. A marked increase in the deconvoluted Brillouin linewidth (~400%) and a gradual softening (~20%) of the transverse acoustic modes were observed very close to Tm. The increase of the Brillouin linewidths was analyzed by a simple dislocation model assuming the hypersonic attenuation to be proportional to the concentration of thermally generated defects near Tm. The defect formation energy ED(T) was computed from the temperature-dependent linewidth data, and was found to decrease significantly (~60%) near Tm, suggesting a cooperative effect producing a catastrophic growth of defects which brings about melting by destroying the long range order of the crystal. The conclusion that melting is mediated by a sudden growth of defect concentration near Tm was further strengthened by Raman scattering experiments in which 13 new Raman modes appeared close to Tm. These new modes are believed to be defect activated through breaking of the local symmetry of the crystal. A slight softening of the Raman modes (~5%) was observed close to the melting point. 相似文献
26.
Comparing Classes of Finite Structures 总被引:3,自引:0,他引:3
We compare classes of structures using the notion of a computable embedding, which is a partial order on the classes of structures. Our attention is mainly, but not exclusively, focused on classes of finite structures. Also, a number of problems are formulated. 相似文献
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