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Umsetzungen der Komplexe [(OC)5M(THF)], M = Cr, Mo, mit dem Alkylarylstannylen RR′Sn:, R = 2,4,6‐tBu3C6H2, R′ = CH2C(CH3)2‐3,5‐tBu2C6H2, ergibt die donorfreien Stannylenkomplexe [(OC)5CrSnRR′] (6) und [(OC)5MoSnRR′] (8). Die Röntgenstrukturanalysen der isotypen Verbindungen 6 und 8 zeigen das Vorliegen planar umgebener dreifach koordinierter Zinnatome mit spitzen CSnC‐Winkeln von 91,2° (6) und 91,3° (8) an.

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Treatment of [Fe,(CO) Reports on unambiguously characterized transitionmetal stannylene complexes containing a tricoordinated tin atom are still scarce [2]. This is particularly apparent for complexes of the lighter transition metals with stannylenes that do not experience inter-or intramolecular stabilization from the free electron pairs of donor atoms"']. Thus, in the case of iron and nickel for example, the heterosubstituted iron-stannylene complex lr3] and the homoleptic, heterosubstituted nickel complex 2L41 were prepared and their structures elucidated.We recently prepared compound 3 as an example of a diarylstannylene lacking stabilization by donor atoms [5]. Although compound 3 is stable in the solid state, it undergoes irreversible rearrangement in solution to furnish the alkylarylstannylene 4, the formation of which was demonstrated indirectly by means of trapping reactions and preparation of the isotypic complexes [(OC)5M=SnRR'] where M = Cr, Mo, WL6,' 1. Large M-Sn bond lengths and small C -Sn--C bond angles are characteristic of these complexes and indicate that compound 4 behaves mainly as a o-donor in such compounds while its x-acceptor properties are only weakly effective. The different positions that a ligand can occupy in a trigonal bipyramid serve as a criterion for the evaluation of its donor or acceptor properties [s]. Hence, we attempted to prepare an iron complex of the type 1 and now report on the formation and structure of the stannylene complex 5 .