Hydricity Modulated Methylation of Indoles and Nitriles Using Methanol: Selective Synthesis of C3-Methylated Indoles, Bisindolylmethanes, and α-Methylated Nitriles

Abstract

The selective functionalization of indoles using methanol via borrowing hydrogen (BH) and interrupted borrowing hydrogen (I-BH) pathways offers a sustainable approach to access value-added molecules. Herein, the synthesis of a series of benzimidazole-functionalized cyclometalated (NC)-Ru(II) and (NN)-Ru(II) complexes and their application in the chemodivergent functionalization of indoles with methanol are reported, affording either C3-methylated indoles or bis(indolyl)methanes (BIMs). The product selectivity was governed by the hydricity of the Ru–H species, which was effectively tuned by ligand backbone modification. This varying catalytic behavior of these complexes under consideration toward the selective formation of different products was fairly understood by analyzing their electronic properties based on electrochemical and density functional theory studies. Additionally, the electron-rich (NC)-Ru complex facilitated the α-methylation of phenylacetonitrile under relatively mild conditions. Finally, an array of control experiments and the identification of different intermediates aided in establishing the proposed mechanism.