Half-Sandwich Iridium Complexes with Hydrazone Ligands: Synthesis and Catalytic Activity in <i>N</i>-Alkylation of Anilines or Nitroarenes with Alcohols via Hydrogen Autotransfer

Abstract

Here, we synthesize a series of hydrazone-based <i>N</i>,<i>O</i>-chelate half-sandwich iridium complexes through a facile route. All air-stable iridium complexes show high catalytic activity in <i>N</i>-alkylation of a broad scope of aniline derivatives and alcohols with liberating water as the sole byproduct. This reaction provides a smooth route to synthesize diverse monoalkylated amines in good to excellent yields at moderate temperature with a low catalyst loading. Moreover, the challenging <i>N</i>-alkylation process using nitroarene substrates as coupling partners is also carried out in this catalytic system. The mechanistic study shows that the present iridium catalysis process proceeds through a hydrogen borrowing mechanism. All iridium(III) complexes <b>1</b>-<b>4</b> are characterized by infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis.