Metallatome in der Synthese von Metallclustern, II¹⁾ Reaktionen von substituierten Cyclopentadienen und Nickelocen mit Nickel‐ und Eisenatomen

Metal Atoms in the Synthesis of Metal Clusters, II 1) . – Reactions of Substituted Cyclopentadienes and Nickelocene with Nickel and Iron Atoms By vaporizing nickel atoms into solutions of tert ‐butyl‐substituted cyclopentadienes in methylcyclohexane mononuclear sandwich compounds ( 1, 4 , and 6 as main products) as well as tri‐ and tetranuclear clusters are prepared. With mono‐ and di‐ tert ‐butyl‐substituted cyclopentadienes as ligands the new clusters 2 and 5 are obtained. In the reaction with 1,2,4‐tri‐ tert ‐butylcyclopentadiene 6 is the only observed product. Hindered rotation around the metal‐ligand bond vector is observed for 4 even at room temperature. When treating 1 with nickel atoms cluster 2 is formed, indicating some importance of 1 during the formation of 2 in the above reaction. Clusters 2 and 5 contain hydrido ligands, which could be identified in the case of tris(1,3‐di‐ tert ‐butyl‐η 5 ‐cyclopentadienyl)trinickel dihydride ( 5 ) by a single crystal structure determination as μ 3 ‐H bridges. A tetrahedral structure is found for the cluster 2 by X‐ray crystallography. With the aid of MS, IR, magnetic measurements, and cyclovoltammetric investigations 2 is identified as a mixture of 2a and 2b bearing one or three bridging hydrogens, respectively. In general 2a, 2b , and 5 show a rich redox chemistry with reversible redox couples between –2 and +2. Reaction of iron atoms, nickelocene, and mesitylene in methylcyclohexane at −120°C leads unexpectedly to cluster 3 , tetrakis(η 5 ‐cyclopentadienyl)tetranickel trihydride and a not yet identified (η 5 ‐cyclopentadienyl)mesityleneiron complex. Possible formation routes for 1 – 6 are discussed.