[RuCl(η5-3-phenylindenyl)(PPh3)2] (1) has been shown to be a highly active catalyst for the isomerisation of allylic alcohols to the corresponding ketones. A variety of substrates undergo the transformation, typically with 0.25-0.5 mol% of catalyst at room temperature, outperforming commonly-used complexes such as [RuCl(Cp)(PPh3) 2] and [RuCl(η5-indenyl)(PPh3) 2]. Mechanistic experiments and density functional theory have been employed to investigate the mechanism and understand the effect of catalyst structure on reactivity. These investigations suggest a oxo-π-allyl mechanism is in operation, avoiding intermediate ruthenium hydride complexes and leading to a characteristic 1,3-deuterium shift. Important mechanistic insights from DFT and experiments also allowed for the design of a protocol that expands the scope of the transformation to include primary allylic alcohols

We thank the ERC (Advanced Investigator Award ` FUNCAT' to SPN) and the EPSRC for funding. Umicore is thanked for gi. s of materials. SPN is a Royal Society Wolfson Merit Award holder. Melanja Smith and Dr Tomas Lebl are thanked for assistance with NMR spectroscopy facilities. Dr Cesar A. Urbina-Blanco is acknowledged for useful discussions. LC thanks the HPC team of Enea for using the ENEA-GRID and the HPC facilities CRESCO in Portici (Italy) for access to remarkable computational resources. AP thanks the Spanish MICINN for a Ramon y Cajal contract (RYC-2009-05226) and European Commission for a Career Integration Grant (CIG09-GA-2011-293900)