Unusual Rearrangement of Modified PNP Ligand based Ru Complexes Relevant to Alcohol Dehydrogenation Catalysis

We report the synthesis of ‘hangman-type’ PNP pincer ligands and their associated Ru complexes. Upon deprotonation, the complexes undergo sp²-sp³ C-C bond cleavage and subsequent C-C formation processes to form a new, one carbon unit longer backbone motif. Unlike the starting geometry, the products are completely inactive in alcohol dehydrogenation catalysis. DFT and mechanistic studies suggest an intramolecular isomerization process via a spyrocycle cyclopropane intermediate, dependent upon arm pyridine coordination and ligand sterics.