Underlying Mechanisms of Reductive Amination on Pd-Catalysts: The Unique Role of Hydroxyl Group in Generating Sterically Hindered Amine

Abstract

Pd nanospecies supported on porous g-C3N4 nanosheets were prepared for efficient reductive amination reactions. The structures of the catalysts were characterized via FTIR, XRD, XPS, SEM, TEM, and TG analysis, and the mechanisms were investigated using in situ ATR–FTIR spectroscopic analysis complemented by theoretical calculation. It transpired that the valence state of the Pd is not the dominating factor; rather, the hydroxyl group of the Pd(OH)2 cluster is crucial. Thus, by passing protons between different molecules, the hydroxyl group facilitates both the generation of the imine intermediate and the reduction of the C=N unit. As a result, the sterically hindered amines can be obtained at high selectivity (>90%) at room temperature.

Reductive amination of phenol over Pd-based catalysts: elucidating the role of the support and metal nanoparticle size

“…The species involved in this cycle and reported in Table 2 were identified via gas chromatography coupled to mass spectrometry, and their analytical standards were used for quantification (see ESI_2.xls and ESI_3.xls†). Despite several authors having proposed the hemi-aminal as an intermediary for these reactions, it is very reactive and unstable under the reaction conditions used here; thus, it was not detected by GC-MS. 15,73–76…”

“…The species involved in this cycle and reported in Table 2 were identified via gas chromatography coupled to mass spectrometry, and their analytical standards were used for quantification (see ESI_2.xls and ESI_3.xls †). Despite several authors having proposed the hemi-aminal as an intermediary for these reactions, it is very reactive and unstable under the reaction conditions used here; thus, it was not detected by GC-MS. 15,[73][74][75][76] Finally, time-dependent compositional profiles were used to analyze the presented reaction pathway using the first-and second-rank Delplot approach. 77 The initial rates of cyclohexylamine and phenol conversion (r 0 i , mmol h −1 mmol −1 Pd) were obtained via polynomial regression and differentiation of the C i vs. time curves (Fig.…”

Catalytic Continuous Reductive Amination with Hydrogen in Flow Reactors

“…Support can provide acidic or alkaline sites and affect the morphology, metal particle size, dispersion, and electronic state of the catalyst. [61][62][63] The synergistic effect between supports and Yingying Li is currently a research assistant at the Department of Chemical Engineering, Tsinghua University. She graduated from Beijing Technology and Business University with a master's degree in chemical engineering.…”

“…Support can provide acidic or alkaline sites and affect the morphology, metal particle size, dispersion, and electronic state of the catalyst [61–63] . The synergistic effect between supports and metals can further improve the reaction performance.…”

Bimetallic Pt–Pd catalysts supported on TiO2 for enhanced photocatalytic N-alkylation of amines with alcohols: the synergistic effect

“…However, when a benzene ring bearing a halogen group such as Cl or Br, the yield of the aimed product decreased and 30-40% dehalogenation product was observed, indicating that this catalyst was also suitable for photocatalytic dehalogenation of organic halides. 26,43 Besides, for a relatively tough taskthe synthesis of steric hindered amines such as DIPEA (3l) and its analogues, 63,64 the current method is also efficient.…”