Metal–Ligand Cooperative Nitrile Activation Triggered by a Catalytic Amount of Weak Base

Abstract

Nitriles are common functional groups in chemical building blocks, yet their direct conversion into diverse functional groups typically requires forcing conditions due to the thermodynamic stability of the C≡N bond. Activation of nitriles through metal–ligand cooperativity (MLC) has emerged as a powerful strategy and typically involves the use of strong bases to generate a reactive complex featuring a dearomatized pincer ligand. Herein, we report a mononuclear ruthenium platform supported by a 1,8-naphthyridine-based PNNP ligand that enables nitrile activation via MLC using only catalytic amounts of the weak base triethylamine. Combined experimental and computational mechanistic studies reveal a mechanism proceeding via an initial endergonic ligand deprotonation that is followed by nitrile coordination, intramolecular nucleophilic attack and reprotonation of the resulting ketimido nitrogen by the conjugate acid of the base. In addition, we show that bimetallic analogues undergo two concurrent metal–ligand cooperative activation events of two acetonitrile molecules to form diastereomeric bis-ketimine complexes.