Zur Reaktivität isomerer Heterodinuclearer Fischer-Carben-Komplexe mit Titanaoxetan- und Titanaoxolenteilstrukturen — Cycloreversions- und Insertionsreaktionen

Studies on the Reactivity of Isomeric Heterodinuclear Fischer-Carbene Complexes exhibiting a Titanaoxetan or Titanaoxolen Substructure – Cycloreversion and Insertion Reactions The reactivity of isomeric four- and five-membered carbene complexes Cp*₂ 3 and Cp*₂ 4 [ML_n: Cr(CO)₅ ( a ); W(CO)₅ ( b ); Cp*: C₅(CH₃)₅] has been investigated. A cycloreversion reaction, unusual for common metallaoxetanes, is found to dominate the chemical behaviour of 3 . The generation of vinylidene fragment [Cp*₂Ti?C?CH₂] 2 as an intermediate is proved either by trapping with ethylene and isocyanate or by protonation of the α-carbon atom. On the other hand no cycloreversion is observed for the titanaoxolene carbene complexes 4 . Ringenlargement is found by the reaction of 3 and 4 with isonitriles under formation of iminoacyl complexes. Accordingly 2,6-dimethylphenylisonitrile reacts with 3 b forming Cp*₂ 12 [Ar: 2,6-(CH₃)₂? C₆H₃]. A reversible insertion of cyclohexylisonitrile in 4a leads to isolation of the six-membered metallacycle Cp*₂ 16 (Cy: C₆H₁₁).