Heterogeneous Ni Catalysts for N-Alkylation of Amines with Alcohols

Abstract

Nickel nanoparticles loaded onto various supports (Ni/ MO x ) have been prepared and studied for the N-alkylation of amines with alcohols. Among the catalysts, Ni/θ-Al 2 O 3 prepared by in situ H 2reduction of NiO/θ-Al 2 O 3 shows the highest activity, and it acts as reusable heterogeneous catalyst for the alkylation of anilines and aliphatic amines with various alcohols (benzyl and aliphatic alcohols) under additive free conditions. Primary amines are converted into secondary amines and secondary amines into tertiary amines. For the reaction of aniline with an aliphatic alcohol the catalyst shows higher turnover number (TON) than precious metal-based state-of-the-art catalysts. Mechanistic studies suggest that the reaction proceeds through a hydrogen-borrowing mechanism. The activity of Ni catalysts depends on the nature of support materials; acid−base bifunctional supports give higher activity than basic or acidic supports, indicating that acid−base sites on supports are necessary. The presence of basic (pyridine) or acidic (acetic acid) additive in the solution decreased the activity of Ni/θ-Al 2 O 3 , which suggests the cooperation of the acid− base site of θ-Al 2 O 3 . For a series of Ni/θ-Al 2 O 3 catalysts with different particle size, the turnover frequency (TOF) per surface Ni increases with decreasing Ni mean particle size, indicating that low-coordinated Ni species and/or metal−support interface are active sites. From these results, we propose that the active site for this reaction is metal−support interface, where low-coordinated Ni 0 atoms are adjacent to the acid−base sites of alumina.

Ligand‐free Iron(II)‐Catalyzed N‐Alkylation of Hindered Secondary Arylamines with Non‐activated Secondary and Primary Alcohols via a Carbocationic Pathway

“…[11,12] For example, Zeng, [13] Shimizu, [14] Saito, [15] Feringa [16] and other groups [17] reported metal catalyzed mono-N-alkylation of primary amines with alcohols by a borrowing hydrogen transfer (BHT) methodology. Noteworthy, highly abundant and bio-relevant homogeneous transition metal catalysts such as Fe, Co and Mn which were used in the mono alkylation of primary amines with primary as well as secondary alcohols.…”

‘‘Hydrogen-Free’’ Hydrogenation of Nitrobenzene Over Cu/SiO2 Via Coupling with 2-Butanol Dehydrogenation

“…Nagaraja et al[10] and Sawadjoon et al[56] reached a similar conclusion in their analysis of the gas phase coupling of cyclohexanol dehydrogenation with furfural hydrogenation (T = 453-523 K, P = 1 atm) over Cu-MgO-Cr 2 O 3 and liquid phase coupling of alcohol hydrogenolysis with formic acid as hydrogen donor (T = 353 K, P = 1 atm) over Pd/carbon, respectively. Moreover, there is evidence in the literature for the formation of transitory metal-H (Cu-H[57], Ru-H[58], Ag-H[59] and Ni-H[60]) species (via interaction with hydrogen abstracted from alcohols) that can serve as a source of reactive hydrogen. In this study, the abstracted hydrogen associated with copper (Cu-H) must participate in the nitrobenzene hydrogenation step.…”

N–Alkylation of Amines Catalyzed by a Ruthenium–Pincer Complex in the Presence of in situ Generated Sodium Alkoxide

“…However, recent years have witnessed a surge in the development of catalytic systems based on inexpensive metals[5c] such as Cu, Mn,[5a], [5b], Fe, Ni and Co.[13a], Emphasis has also been laid on using heterogeneous catalytic N ‐alkylation systems based on Pd,[12b], [14a], Au,[12a] Ag, W, Cu and Ni , . It is noteworthy that ruthenium‐based N ‐alkylation systems have enjoyed great success and have been reported with several types such as [RuX 2 (PPh 3 ) 3 ] (X = Cl,, [15e], [15r], [15s], [15t] Br[15f]), [RuH 2 (PPh 3 ) 4 ],[15e] [RuHCl(PPh 3 ) 3 ],[15f] Ru–Phosphine complexes,[15d], [15f], [15g], [15h], [15i], [15m], [15n], [15o], [15p], [15x] Ru‐cyclopentadienyl complexes, Ru–amine complexes,[15j], [15u] Ru– N ‐Heterocyclic complexes[15d], [15k] and even ruthenium–pincer complexes.…”