N‑Alkylation and N,C-Dialkylation of Amines with Alcohols in the Presence of Ruthenium Catalysts with Chelating N‑Heterocyclic Carbene Ligands Zeynel Şahin, † Nevin Gü rbü z, † I ̇ smail O ̈ zdemir,* ,† Onur Şahin, ‡ Orhan Bü yü kgü ngö r, § Mathieu Achard, ∥ and Christian Bruneau ∥ † Catalysis Research and Application Center, Inö nü University, 44280 Malatya, Turkey ‡ Scientific and Technological Research Application and Research Center, Sinop University, 57010 Sinop, Turkey § Department of Physics, Ondokuz Mayıs University, 55139 Samsun, Turkey ∥ Universite ́ de Rennes 1, UMR6226: Institut des Sciences Chimiques de Rennes, Centre de Catalyse et Chimie Verte, 35042 Rennes, France *S Supporting Information ABSTRACT: A series of new benzimidazolium salts and ruthenium(II) complexes containing chelating N-heterocyclic carbenes (NHCs) functionalized with a benzylic group and an acetal group were prepared. All of the synthesized compounds were characterized by elemental analysis and NMR spectros- copy, and the molecular structures of 2c and 2d were determined by X-ray crystallography. All of the complexes were tested in the alkylation of cyclic amine derivatives with alcohols and showed excellent activity in this reaction. Cyclic amines were alkylated with primary and heteroaromatic alcohols. The Ru−NHC complexes also catalyzed N,C3- dialkylation of cyclic amines. ■ INTRODUCTION The first N-heterocyclic carbene (NHC) complexes were synthesized independently by O ̈ fele, Wanzlick, and Lappert in the early 1970s. 1 In 1991 Arduengo et al. 2 isolated free 1,3- bis(adamantyl)imidazolin-2-ylidene, which triggered the devel- opment of important studies related to these nucleophilic ligands. Because of their strong σ-donor ligand properties, NHCs were extensively introduced as phosphine substitutes in metal complexes for applications in catalytic reactions. 3 Since then, various aspects of the chemistry of NHC-based metal catalysts and catalysis have been extensively reviewed. 4−8 Amines are important building blocks that have found widespread applications for the synthesis of pharmaceuticals, agrochemicals, dyes, and polymers. 9,10 N-Alkylamines are obtained by the reaction of primary or secondary amines with alkyl halides in the presence of stoichiometric amounts of mineral bases or by reductive amination of aldehydes or ketones. 9b The generation of inorganic salts and the use of unstable and expensive carbonyl compounds constitute the main drawbacks of these procedures. Alternatively, in a greener approach, readily available alcohols have been used as alkylating agents using a catalytic “hydrogen borrowing” strategy (Scheme 1). 11 This process produces water as the only byproduct and hence offers a sustainable method for N-alkylation reactions. 11 Since the pioneering work of Guerbet, 12 in situ dehydrogen- ative activation of alcohols in the presence of alkoxide as a base has been extended to amines, alcohols, and alkanes with heterogeneous catalysts and more recently under homogeneous conditions. Alkylation of amines with alcohols proceeding via the hydrogen borrowing route using heterogeneous nickel catalysts has been known since 1932. 13 In 1981, Grigg and Watanabe independently reported homogeneous catalysts for the amination of alcohols using late-transition-metal cata- Special Issue: Mike Lappert Memorial Issue Received: October 27, 2014 Scheme 1. Hydrogen Borrowing Strategy for the Alkylation of Amines with Alcohols Article pubs.acs.org/Organometallics © XXXX American Chemical Society A DOI: 10.1021/om501066n Organometallics XXXX, XXX, XXX−XXX