The “Borrowing Hydrogen Strategy” by Supported Ruthenium Hydroxide Catalysts: Synthetic Scope of Symmetrically and Unsymmetrically Substituted Amines

Abstract

The N-alkylation of ammonia (or its surrogates, such as urea, NH(4)HCO(3), and (NH(4))(2)CO(3)) and amines with alcohols, including primary and secondary alcohols, was efficiently promoted under anaerobic conditions by the easily prepared and inexpensive supported ruthenium hydroxide catalyst Ru(OH)(x)/TiO(2). Various types of symmetrically and unsymmetrically substituted "tertiary" amines could be synthesized by the N-alkylation of ammonia (or its surrogates) and amines with "primary" alcohols. On the other hand, the N-alkylation of ammonia surrogates (i.e., urea and NH(4)HCO(3)) with "secondary" alcohols selectively produced the corresponding symmetrically substituted "secondary" amines, even in the presence of excess amounts of alcohols, which is likely due to the steric hindrance of the secondary alcohols and/or secondary amines produced. Under aerobic conditions, nitriles could be synthesized directly from alcohols and ammonia surrogates. The observed catalysis for the present N-alkylation reactions was intrinsically heterogeneous, and the retrieved catalyst could be reused without any significant loss of catalytic performance. The present catalytic transformation would proceed through consecutive N-alkylation reactions, in which alcohols act as alkylating reagents. On the basis of deuterium-labeling experiments, the formation of the ruthenium dihydride species is suggested during the N-alkylation reactions.

Catalysis in flow: Au-catalysed alkylation of amines by alcohols

“…[7][8][9] In terms of practicality, heterogeneous catalysts are much more attractive, as they can be easily separated from the product stream. In this regard, Ru(OH) x /TiO 2 was found to have the widest applicability, including the preparation of highly substituted amines from 55 urea, 10,11 and the alkylation of (hetero)aromatic amines. 12 The scope of first-row transition metal catalysts (Cu, Fe) appears to be limited to certain substrates, such as activated benzyl alcohols or aromatic amines.…”

Important Industrial Procedures Revisited in Flow: Very Efficient Oxidation and N-Alkylation Reactions with High Atom-Economy

“…The above "borrowing hydrogen" strategy was also applied with inexpensive supported ruthenium hydroxide catalyst Ru (OH) x /TiO 2 [25]. N-alkylation of ammonia and amines with alcohols, including primary and secondary alcohols, was carried out.…”

Supported Metal Hydroxides as Efficient Heterogeneous Catalysts for Green Functional Group Transformations

“…Besides the above-mentioned transformations, we have successfully developed several functional group transformations using hydroxide-based heterogeneous catalysts; for example, oxygenation and aromatization of alkylarenes 58) , oxidative homocoupling of 2-naphthols and substituted phenols 59) , N-alkylation of amines and NH3 using alcohols as the alkylation reagents 60), 61) , self-condensation of primary amines to secondary amines 62) , rearrangement of aldoximes to primary amides 63), 64) , and dehydration of aldoximes to nitriles 65) . Our hydroxide-based strategy demonstrated here has high generality and applications especially in the fields of catalytic chemistry and synthetic organic chemistry.…”