62248-92-4Relevant academic research and scientific papers
Cooperative Multifunctional Catalysts for Nitrone Synthesis: Platinum Nanoclusters in Amine-Functionalized Metal–Organic Frameworks
Li, Xinle,Zhang, Biying,Tang, Linlin,Goh, Tian Wei,Qi, Shuyan,Volkov, Alexander,Pei, Yuchen,Qi, Zhiyuan,Tsung, Chia-Kuang,Stanley, Levi,Huang, Wenyu
supporting information, p. 16371 - 16375 (2017/11/28)
Nitrones are key intermediates in organic synthesis and the pharmaceutical industry. The heterogeneous synthesis of nitrones with multifunctional catalysts is extremely attractive but rarely explored. Herein, we report ultrasmall platinum nanoclusters (PtNCs) encapsulated in amine-functionalized Zr metal–organic framework (MOF), UiO-66-NH2 (Pt@UiO-66-NH2) as a multifunctional catalyst in the one-pot tandem synthesis of nitrones. By virtue of the cooperative interplay among the selective hydrogenation activity provided by the ultrasmall PtNCs and Lewis acidity/basicity/nanoconfinement endowed by UiO-66-NH2, Pt@UiO-66-NH2 exhibits remarkable activity and selectivity, in comparison to Pt/carbon, Pt@UiO-66, and Pd@UiO-66-NH2. Pt@UiO-66-NH2 also outperforms Pt nanoparticles supported on the external surface of the same MOF (Pt/UiO-66-NH2). To our knowledge, this work demonstrates the first examples of one-pot synthesis of nitrones using recyclable multifunctional heterogeneous catalysts.
Kinetics of Reversible Thiolate Ion Addition to Substituted β-Nitrostyrenes in Water. Radicaloid Transition State or Principle of Nonperfect Synchronization?
Bernasconi, Claude F.,Schuck, David F.
, p. 2365 - 2373 (2007/10/02)
The kinetics of reversible nucleophilic thiolate ion (RS- with R = n-Bu, HOCH2CH2, MeO2CCH2CH2 and MeO2CCH2) addition to Z-substituted β-nitrostyrenes (Z = 4-Me2N, 4-MeO, 4-MeS, 4-Me, H, 3-Cl, 4-Cl, 3-CN, 4-CN, and 3-NO2), to form ArCH(RS)CH=NO2-, have been measured in water at 20 deg C.Rate constants in the forward (k1) and reverse direction (k-1) and equilibrium constants (K1) correlate reasonably well with Hammett ?-constants for the non-?-donor substituents but show deviations for the ?-donors 4-Me2N, 4-MeO, and 4-MeS.These deviations are negativefor K1 but positive for k1 and k-1; the positive deviations for the ?-donor substituents are also observed when plotting log k1 vs log K1 (Broensted plots).The negative deviations of K1 are a consequence of resonance stabilization of the olefin.The positive deviations are attributed to a transition-state stabilization stemming from a preorganization created by the ?-donor which leads to a better delocalization of the negative charge into the nitro group.An alternative interpretation of the rate acceleration in terms of a radicaloid transition state (Gross, Z.; Hoz, S.J.Am.Chem.Soc. 1988, 110, 7489) cannot be ruled out but is shown to be less attractive and unnecessary.Broensted parameters such as βnuc, βeq, βnnuc, and βnlg, and intrinsic rate constants (k0 = k1 = k-1 when K1 = 1) were determined from the dependence on the RS- basicity for β-nitrostyrene and 3-cyano-β-nitrostyrene. βeq is low (0.5), indicating that the carbon basicity of RS- is less sensitive to electronic effects in R than its proton basicity. βnuc (βnnuc) is very low, suggesting a transition state withvery little C-S bond formation.The low βnnuc (0.22) contrasts with a large αnnuc = d log k1/d log K1 = 0.74 (variation of Z), indicating a large transition-state imbalance (αnnuc - βnnuc), as previously observed in the reaction of RS- with α-nitrostilbenes.The intrinsic rate constant (log k0 = 3.5) is also similar to that for the reaction of RS- with α-nitrostilbenes and significantly higher than for the reaction of amines with β-nitrostyrenes.Most of these features can, at least in part, be attributed to the soft acid-soft base interactions of RS- with the nitroolefins.Rate constants for carbon protonation of several of the ArCH(RS)CH=NO2- adducts by acetic acid (kHAp were also determined.They display the unusual, but for nitronate ions typical, acceleration when Ar and/or R is made more electron withdrawing.
