The specific aims of this project are (1) to discover what types of ditungsten and dimolybdenum Mu-hydrazido(4-) complexes can be prepared in which the metal is in its highest possible oxidation state; (2) to replace chloride or alkyl ligands in such complexes with thiolate ligands in an effort to come as close as possible to a sulfur coordination sphere related to that around molybdenum in nitrogenase; (3) to discover what factors determine whether hydrazine or ammonia is formed by a combination of protonation/reduction steps; (4) to design and study systems that will coordinate dinitrogen between two of the same or two different metals to give Mu-hydrazido(4-) complexes analogous to those previously prepared. We have recently shown that it is possible to make Mu-dinitrogen complexes by reducing a monopentamethylcyclopentadienyl complex of tungsten(V) under dinitrogen. This cyclopentadienyl system seems to be the most likely area to look for other dinitrogen complexes containing more relevant alkoxide or thiolate ligands bound to the metal. It also should be extendable to molybdenum. Both molybdenum and tungsten complexes of the type MX4 (X = alkoxide or thiolate) is another area ripe for exploration. A third area concerns the use of ligands that link two metals together at a distance that is appropriate (about 4.8A) for nitrogen to coordinate between the two metals. Ligands such as linked cyclopentadienyl ligands, dimethyl resorcinol, or dimethyl dithiaresorcinol are high on the list. The recent discovery of the especially high reactivity of phenoxide-substituted tungsten alkylidyne complexes toward the carbonyl group suggests that we will be able to prepare vinyltrialkoxytungsten dinitrogen complexes from alkylidyne complexes and azines. The synthetic studies will be complemented by electrochemical, x-ray structural, and Raman studies of the most relevant complexes.
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