Efficient C(sp3)–H alkylation of fluorene and bisindolylmethane synthesis catalysed by a PNN-Ni complex using alcohols

Abstract

This manuscript describes the C-alkylation of 9H-fluorene and the synthesis of bis(indolyl)methane derivatives catalysed by the nickel complex [(NiCl){(P^tBu₂)N(H)N-κ³-P,N,N}]OTf (hereafter referred to as Ni2). This efficient protocol offers several advantages, including low catalyst loading, and mild reaction conditions. It also offers a broad substrate scope (encompassing aliphatic, aromatic, and secondary alcohols), high functional group compatibility, and excellent chemoselectivity. The approach also enables post-functionalization of C-alkylated fluorenes and has been successfully applied to the synthesis of medicinally relevant indole derivatives to explore its potential applications. Mechanistic insights were obtained through control experiments. The results suggest that the reaction proceeds via metal–ligand cooperation within the catalytic cycle, and the formation of a nickel hydride intermediate was further confirmed by NMR and HRMS analysis.