Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen XXVIII. Cycloaddition von heterokumulenen an oxorhenium-halbsandwich-komplexe: Synthese neuartiger metallacyclen

The dinuclear oxorhenium complex (η⁵-C₅Me₅)Re₂O₄ reacts with diphenylketene to give, via formal [2 + 2]-cycloaddition at the (hypothetical) fragment (η⁵-C₅Me₅)ReO₂, the novel, four-membered metallacyclic compound (η⁵-C₅Me₅)Re(O)(η²-O₂CCR₂) (R = C₆H₅). Cleavage of the dinuclear Re₂O₂ core with addition of the heterocumulene to a ReO group is also observed when phenyl isocyanate is used instead of diphenyl ketene. In this case, the cyclic derivative (η⁵-C₅Me₅)Re(O)(η²-OCONR) (R = C₆H₅) containing a O,N-coordinated ligand in the four-membered structure has been formed. In contrast, the mononuclear half-sandwich complex (η⁵-C₅Me₅ReO₃ reacts with diphenylketene according to a formal [3 + 2]-cycloaddition at a ReO₂ core to give the five-membered metallacycle (η⁵-C₅Me₅)Re(O)(η²-O₂COCR₂) (R = C₆H₅). The three cycloaddition products have been structurally characterized by means of X-ray diffraction techniques.