Studies of the mechanisms of organometallic reactions will be continued. Concerted organometallic reactions will be examined in which elementary steps that would otherwise generate high energy intermediates with vacant coordination sites combine with steps that consume vacant coordination sites. The stereochemistry of addition of hydrogen chloride to rhenium carbene complexes and the rearrangements of the alkyl chloro rhenium products will be carefully studied. The synthesis and reactions of unusual metal-metal double-bonded compounds will will be explored. Studies of hydrocarbyl bridged diiron compounds, which have proven useful in carbon-carbon bond-forming processes, will be continued. The mechanism of an unusual photochemical dehydrogenation of a m-alkylidene diiron complex will receive special attention. %%% In this project in the Inorganic, Bioinorganic, and Organo- metallic Program of the Chemistry Division, Dr. Charles Casey of the University of Wisconsin, Madison, will continue studies of the mechanisms of organometallic reactions. These studies will have application to homogeneous catalysis and the synthesis of new and useful compounds.