Chromium Catalyzed Sustainable C-C and C-N Bond Formation: C-Alkylation and Friedländer Quinoline Synthesis Using Alcohols

A phosphine-based novel pincer chromium (II) catalyst CrCl2(PONNH) (Cr-1) is reported. The complex exhibited promising catalytic performance in C-C and C-N bond formation by borrowing hydrogen methodology. The Cr-1 catalyzed α-alkylation of ketones using primary alcohols as alkyl surrogates in the presence of catalytic amount of base. The catalyst was also found to perform β-alkylation of secondary alcohols with primary alcohols. In addition, dehydrogenative annulation of 2-aminobenzyl alcohols with ketones to form quinolines was also achieved using Cr-1. Supported by the mechanistic investigation, a plausible mechanism based on metal-ligand cooperation is proposed. The reactions are redox-neutral, atom efficient, producing water as the only by-product, thus contributing towards the sustainable development.