Metal-Metal Multiple Bonds in Organometallic Compounds. I. (Di-ie/-/-butylacetylene)hexacarbonyldiiron and -dicobalt

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pentadienyl moieties and transamination, are often plagued by ligand redistribution reactions and concurrent formation of Cp3U(NR2). Cp3U(NEt2) also forms when Cp2U(NEt2)2 is further reacted with cyclopentadiene. Thermal stability also appears to favor the tricyclopentadienyl derivatives since attempted sublimation of some of the products produced Cp3U(NR2)-type compounds. It is clear that steric factors are of utmost importance in this area of chemistry. The combination of two cyclopentadienyl groups and two amide moieties is sometimes sufficient to saturate the coordination sphere of uranium(IV) and stabilize the so formed Cp2UX2 species. However, given a chance, even those species rearrange or react to give the more favored Cp3U containing complexes.Cp2U[NC4Me3(COOEt)]2 appears to be an exception. In this case, the postulated interaction between oxygen of the carboxylate functionality and uranium may account for the added stability. Indeed, as will be seen in the following papers, replacement of the amido gropus by potentially bidentate ligands results in the synthesis of relatively stable Cp2UX2 (X = R2NCS2, R2NCOS, R2NC02, RC02, RCOS) compounds.Acknowledgment. This work was supported at LBL by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. W-7405-Eng-48, and at Alberta by the Natural Sciences and Engineering Research Council and the University of Alberta. A.L.A. also thanks the NSERC for a postgraduate fellowship.

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