Zusammenfassung
Niobocene ditelluride complexes [(tBuC(5)H(4))(2)Nb(Te-2)H] (1) and [(C5Me5)(2)Nb(Te2H)] (2) are useful starting materials for the synthesis of heterometallic telluride complexes and clusters. The presence of free electron pairs, the propensity for Te-Te bond cleavage and the ability to eliminate Te ligands allow stepwise formation of polyhedral structures in reactions with binary transition ...
Zusammenfassung
Niobocene ditelluride complexes [(tBuC(5)H(4))(2)Nb(Te-2)H] (1) and [(C5Me5)(2)Nb(Te2H)] (2) are useful starting materials for the synthesis of heterometallic telluride complexes and clusters. The presence of free electron pairs, the propensity for Te-Te bond cleavage and the ability to eliminate Te ligands allow stepwise formation of polyhedral structures in reactions with binary transition metal carbonyl complexes or reactive organometallic fragments. Among the products are the first examples of organometallic derivatives of the elusive [MTe4](2-) ion. Ligand cross-transfer (CO versus Te) from one metal center to the other and subsequent charge separation lead to the formation of anionic metal telluride clusters and cationic carbonylniobocene species. The latter play a decisive role in tuning the electronic properties of the cluster units. Whereas the 17-electron fragment (tBuC(5)H(4))(2)Nb(CO) is directly anchored at the cluster cores by Te bridges, the 18-electron cation [Cp* Nb-2(CO)(2)](+) (Cp* = C5Me5) formed in situ is able to stabilize large and differently charged cluster anions. This is particularly the case in cobalt telluride cluster chemistry which is characterized by hexacapped cubic Co@Co-8 or heptacapped pentagonal-prismatic Co@Co-10 polyhedra. These compounds exhibit pronounced electron-sponge behavior, and crystallographic studies of differently charged clusters allow a correlation of different cluster charges and bond parameters important for understanding electronic structures. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
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