Qizhen. Shi

Effect of substituents on amineN-oxides on the rates of O-atom transfer to metal carbonyls

Abstract The kinetics of CO substitution in Cr(CO)6 to afford Cr(CO)5PPh3 in the presence of different alkyl amine N-oxides, R3NO, and aryl amine N-oxides (p-X-C6H4)(CH3)2NO, are reported. Within each type of amine N-oxide. the rates of reaction increase with increasing basicity of the amine N-oxide. However, even at lower basicities, the aryl reagents react more rapidly than do the alkyl reagents. Competition experiments between py (pyridine) and P(n-Bu) for the coordinatively unsaturated intermediates “M(CO)5” show that the discrimination abilities increase in the order Cr

Origin of the exceptional reactivity of vanadium pentacarbonyl nitrosyl

Le complexe V (CO) 5 (NO) subit une substitution de CO par PMe 3 , PPh 3 , P (OMe) 3 et NEt 3 (L) pour donner V (CO) 4 L (NO). Etude de stabilite thermique

Kinetics and Mechanism of Co Substitution by Phosphites of Co4(CO)12

Abstract The otherwise very fast CO substitution of Co4(CO)12 by P(OMe)3 and P(OEt)3 in aprotic solvents, affording phosphite-monosubstituted products was retarded by the use of CHCI3 as solvent. This made it possible to investigate these reactions by conventional methods. Kinetic data were obtained by following changes in IR spectra during reaction. The rates show predominantly a ligand-dependent pathway, with the usual two-term rate law, rate = (k1 + k2 [P(OR)3])C4(CO)12. It is suggested that the rates are retarded in protonic solvents by decreasing the nucleophilicity of phosphites due to a hydrogen bonding interaction between the H atom of CHCI3 and the O atoms of the ligands.

Mechanism of Lewis base induced disproportionation of vanadium hexacarbonyl

Vanadium hexacarbonyl undergoes disproportionation in the presence of several bases (L)(pyridine, tetrahydrofuran, diethyl ether, and acetonitrile) according to a second order rate law k[V(CO)6][L]; Fourier transform i.r. spectroscopic analysis of the reaction for L = pyridine reveals the presence of an isocarbonyl intermediate [(OC)6VCOV(L)4OCV(CO)5]en route to the ultimate product [V(L)6][V(CO)6]2.

Kinetics and mechanism of CO substitution of [η5-CpFe(CO)3]PF6 with PPh3 in the presence of substituted pyridine N-oxide

Abstract The kinetics of substitution reactions of [ η -CpFe(CO) 3 ]PF 6 with PPh 3 in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH) 4 , 4-Ph, 3-Me, 2,3-(CH) 4 , 2,6-Me 2 , 2-Me), the reactions yeild the same product [ η 5 -CpFe(CO) 2 PPh 3 ]PF 6 , according to a second-order rate law that is first order in concentrations of [ η 5 -CpFe(CO) 3 ]PF 6 and of R-PyO but zero order in PPh 3 concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH ≠ = 13.4 ± 0.4 kcal mol −1 , ΔS ≠ = −19.1 ± 1.3 cal k −1 mol −1 for 4-PhPyO; ΔH ≠ = 12.3 ± 0.3 kcal mol −1 , ΔS ≠ = 24.7 ±1.0 cal K −1 mol −1 for 2-MePyO. For the various substituted pyridine N -oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N -oxide basicities, but decrease with increasing 17 O chemical shifts of the N -oxides. Electronic and steric factors contributing to the reactivity of pyridine N -oxides have been quantitatively assessed.

Chemical education in China: Lanzhou University

This article explains to the the reader the educational system in China with a special focus on chemistry education.