Metal-ligand cooperative activation of nitriles by a ruthenium complex with a de-aromatized PNN pincer ligandElectronic supplementary information (ESI) available. CCDC 1481313. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt02478e

The pincer complex (PNN)RuH(CO), with a de-aromatized pyridine in the ligand backbone, is shown to react with nitriles in a metal-ligand cooperative manner. This leads to the formation of a series of complexes with new Ru-N(nitrile) and C(ligand)-C(nitrile) bonds. The initial nitrile cycloaddition products, the ketimido complexes 3 , have a Brønsted basic (nitrile-derived) Ru-N fragment. This is able to deprotonate a CH 2 side-arm of the pincer ligand to give ketimine complexes ( 4 ) with a de-aromatized pyridine backbone. Alternatively, the presence of a CH 2 group adjacent to the nitrile functionality can lead to tautomerization to an enamido complex ( 5 ). Variable-temperature NMR studies and DFT calculations provide insight in the relative stability of these compounds and highlight the importance of their facile interconversion in the context of subsequent nitrile transformations. Metal-ligand cooperative activation of nitriles by a de-aromatized Ru pincer complex leads to equilibrium mixtures (tautomers) as a result of ligand deprotonation by the Brønsted basic Ru-ketimido moiety.