Selective <i>C</i>- and <i>N</i>‑Methylation of Secondary\nAlcohols and Nitroaromatics with\nMethanol Catalyzed by a New Ru(II)-Azo Complex

Using MeOH as the methylating agent, selective methylation\nof secondary\nalcohols and nitroaromatics is achieved using a newly prepared Ru(II)-catalyst <b>1a</b> of a tridentate azo-aromatic ligand. Two new organometallic\nRu(II)-complexes [Ru(Cp)(PPh<sub>3</sub>)(<b>L</b><sup><b>a</b></sup>)]Cl (<b>1a</b>) and [Ru(Cp)(PPh<sub>3</sub>)(<b>L</b><sup><b>b</b></sup>)]Cl (<b>1b</b>) of tridentate\nredox-active ligands 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline\n(<b>L</b><sup><b>a</b></sup>) and 2-(phenyldiazenyl)-1,10-phenanthroline\n(<b>L</b><sup><b>b</b></sup>) were prepared and characterized\nby different spectroscopic methods. <b>1a</b> and <b>1b</b> demonstrated good catalytic activity in the methylation of a diverse\narray of 1-aryl ethanols and nitroarenes. <b>1a</b> showed encouraging\ncatalytic efficiency with various naturally occurring steroids, including\n4-cholestene-3-one, progesterone, estrone, and β-sitosterol,\nhighlighting its capability to modify natural product scaffolds. Mechanistic\nstudies revealed that <b>1a</b>-catalyzed methylation reactions\nadvance through a hydrogen borrowing pathway involving cooperative\nparticipation of both Ru(II) and the aryl azo scaffold.