Effects of halides and related ligands on reactions of carbonylruthenium complexes (Ru-0-Ru-II)

While the primary motivation of fundamental studies on carbonylhalotriruthe nium complexes was to understand the promoter effect of halides on certain ruthenium-based catalytic systems of industrial relevance, such complexes h ave gained significance in their own right due to their remarkable ability to provide low-activation energy pathways for the coordination of organic s ubstrates. Limitations inherent to the fragility of these prototypes led to the design and development of a related family of more sophisticated deriv atives where an aminopyridyl group serves as an alternate hemilabile ancill ary ligand. Studies of their reactivity have revealed the possibility of ac hieving a number of stoichiometric or moderately catalytic "cluster-mediate d" transformations of organic substrates under very mild conditions. Yet, t he viability of these systems is still limited to a narrow low-energy domai n. By contrast, halotriruthenium derivatives are still seen to function as catalyst precursors under the actual conditions of certain catalytic reacti ons where they act as sources of ruthenium(II) halide complexes that become the active components of the system. The second part of the review focuses on novel aspects of their fascinating chemistry.