The formation of carbon-oxygen bond upon addition of O-nucleophiles to unsaturated molecules is very attractive as it represents an atom economical strategy to prepare a variety of saturated compounds from olefins and vinylic derivatives from alkynes. Group 8 metals, especially ruthenium have provided an important contribution in this field. We report here on iron- and ruthenium-catalyzed addition of nucleophiles to unsaturated systems. As additions to alkenes are still scarce with these metals and the use of iron catalysts is limited, the main part of the chapter is dedicated to addition of carbamates, carboxylic acids, alcohols and water to triple bonds with ruthenium catalysts.
