Benzimidazolin-2-ylidene N-heterocyclic carbene complexes of ruthenium as a simple catalyst for the N-alkylation of amines using alcohols and diols

Abstract

Simple non-chelating ruthenium benzimidazolin-2-ylidene complexes as efficient N-alkylation catalysts using alcohols and diols following a hydrogen borrowing strategy.

Towards a general ruthenium-catalyzed hydrogenation of secondary and tertiary amides to amines

“…Although numerous ruthenium-based catalytic systems have been developed to date which promote the atom-economical and environmentally benign alkylation of amines with alcohols (water is the only by-product), the present system is quite different. 20 , 21 In fact, the results of our control experiments, the recently reported Ru–Triphos catalyzed amination of alcohols with ammonia 22 and the methylation of aromatic amines with formic acid as the sole carbon and hydrogen source 23 add to the toolbox of useful synthetic transformation promoted by the Ru–Triphos system for the synthesis of amines, which includes their methylation with H 2 and CO 2 ( ref. 24 ) and alkylation with carboxylic acids and hydrogen.…”

Ruthenium(II)‐(Arene)‐N‐Heterocyclic Carbene Complexes: Efficient and Selective Catalysts for the N‐Alkylation of Aromatic Amines with Alcohols

“…The ruthenium complex [RuCl 2 ( p ‐cymene){ N , N′ ‐bis(mesityl)imidazolylidene}] featuring aryl substituents directly connected to the nitrogen atoms of the carbene is known to catalyze the formation of amides from alcohols and primary aliphatic amines including aniline at a lower extend, in the presence of 15 mol‐% of t BuOK . Recently, ruthenium complexes such as [ N , N ‐bis(benzyl)benzimidazolylidene]‐ and [ N , N ‐bis(isopropyl)benzimidazolylidene]‐RuCl 2 ( p ‐cymene) equipped with N ‐alkyl or/and N ‐benzyl NHC ligands with no chelating or hemilabile group on the NHC have revealed good catalytic properties for the alkylation of anilines with various alcohols under neat conditions at 130 °C with 5 mol‐% catalyst loading without additional base . The presence of the functionalized benzyl and alkyl group in our NHC precursors does not seem to be essential in terms of reactivity, but contributes to promote the formation of amines rather than imines or amides.…”

“…The catalytic products N ‐benzylaniline ( 3aa ),[34c] N ‐( p ‐isopropylbenzyl)aniline ( 3ab ),[18w], [34c] N ‐(4‐methoxybenzyl)aniline ( 3ac ),[32c], [18v] N ‐(3,7‐dimethyloct‐6‐en‐1‐yl)aniline ( 3ad ),[24c], [34c] N ‐(benzyl)‐ p ‐methylaniline ( 4aa ),34c N ‐( p ‐isopropylbenzyl)‐ p ‐methylaniline ( 4ab ),[18x], [34c] N ‐(3,7‐dimethyloct‐6‐en‐1‐yl)‐ p ‐methylaniline ( 4ac ),[34c] N ‐(benzyl)‐2,4‐dimethylaniline ( 5aa ),[34c] N ‐(4‐methoxybenzyl)‐2,4‐dimethylaniline ( 5ab ),[34c] N ‐(benzyl)‐2‐aminopyridine ( 6aa ),[18v], [34c] N ‐( p ‐isopropylbenzyl)‐2‐aminopyridine ( 6ab )[34c] and N ‐(hexan‐1‐yl)‐2‐aminopyridine ( 6ac )[34c] are known in the literature. For the 1 H NMR and 13 C NMR spectrums of the all catalytic products see SI, pp.…”

“…Valerga reported the N ‐alkylation of both aromatic and non‐aromatic amines using ruthenium(II)‐picolyl‐NHC complex as a catalyst . Recently, Huynh and Seayad have reported the N ‐alkylation of amines with alcohols and diols using [RuCl 2 ( p ‐cymene)(NHC)] complex . More recently, our research group [RuCl 2 (arene)(NHC)] complexes (Figure , A ) have also been used for the formation of tertiary amines from cyclic secondary amines and primary benzylic alcohols (or aldehydes).…”

Synthesis and Structures of Arene Ruthenium (II)–NHC Complexes: Efficient Catalytic α‐alkylation of ketones via Hydrogen Auto Transfer Reaction

“…Further, complexes 2c and 2d exhibit similar geometry with slight changes in bond angles and bond lengths. The structural data of all the complexes are coincide with the formerly reported arene ruthenium (II)‐NHC complexes …”