A Ru(II)-catalyzed efficient and selective N-alkylation of amines by C1–C10 aliphatic alcohols is reported. The catalyst [Ru(L1a)(PPh3)Cl2] (1a) bearing a tridentate redox-active azo-aromatic pincer, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (L 1a ) is air-stable, easy to prepare, and showed wide functional group tolerance requiring only 1.0 mol % (for N-methylation and N-ethylation) and 0.1 mol % of catalyst loading for N-alkylation with C3–C10 alcohols. A wide array of N-methylated, N-ethylated, and N-alkylated amines were prepared in moderate to good yields via direct coupling of amines and alcohols. 1a efficiently catalyzes the N-alkylation of diamines selectively. It is even suitable for synthesizing N-alkylated diamines using (aliphatic) diols producing the tumor-active drug molecule MSX-122 in moderate yield. 1a showed excellent chemo-selectivity during the N-alkylation using oleyl alcohol and monoterpenoid β-citronellol. Control experiments and mechanistic investigations revealed that the 1a-catalyzed N-alkylation reactions proceed via a borrowing hydrogen transfer pathway where the hydrogen removed from the alcohol during the dehydrogenation step is stored in the ligand backbone of 1a, which in the subsequent steps transferred to the in situ formed imine intermediate to produce the N-alkylated amines.

Herein we report a cobalt‐catalyzed sustainable approach for C‐N cross‐coupling reaction between amines and alcohols. Using a well‐defined Co‐catalyst 1a bearing 2‐(phenyldiazenyl)‐1,10‐phenanthroline ligand, various N‐alkylated amines were synthesized in good yields. 1a efficiently alkylates diamines producing N, N'‐dialkylated amines in good yields and showed excellent chemoselectivity when oleyl alcohol and β‐citronellol, containing internal carbon‐carbon double bond were used as alkylating agents. 1a is equally compatible with synthesizing N‐heterocycles via dehydrogenative coupling of amines and alcohols. 1H‐indole was synthesized via an intramolecular dehydrogenative N‐alkylation reaction, and various substituted quinolines were synthesized by coupling of (2‐aminophenyl)methanol and secondary alcohols. A few control reactions and spectroscopic experiments were conducted to illuminate the plausible reaction mechanism, indicating that the 1a‐catalyzed N‐alkylation proceeds through the borrowing hydrogen pathway. The coordinated arylazo ligand participates actively throughout the reaction; the hydrogen eliminated during dehydrogenation of alcohols was set aside in the ligand backbone and subsequently gets transferred in the reductive amination step to imine intermediates yielding N‐alkylated amines. On the other hand, 1a‐catalyzed quinoline synthesis proceeds through dehydrogenation followed by successive C‐C and C‐N coupling steps forming H2O2 as a by‐product under air.