Expanding the reactivity of Rosenthal's reagent to cyclopropenes and allenes

The reactions of the Rosenthal reagent Cp₂Ti(η²-BTMSA) with cyclopropenes and allenes were systematically investigated. With cyclopropenes, selective 1,2-insertion into the Ti-C bond induces a ring expansion from three- to five-membered frameworks, affording titanacyclopentenes. These bicyclic complexes undergo rearrangement under mild conditions to generate highly reactive titanium carbene species, which subsequently participate in [2 + 2] cycloaddition reactions with alkynes (BTMSA and 1,2-diphenylacetylene), yielding titanacyclobutenes. In contrast, reactions with allenes proceed via ligand exchange of the alkyne ligand, giving titanacyclopentane derivatives. In addition to these transformations, the titanium complex was found to catalyze the isomerization of cyclotrideca-1,2-diene to cyclotrideca-1,3-diene. All isolated complexes were comprehensively characterized by NMR spectroscopy, and the solid-state structures of most species were identified by single-crystal X-ray diffraction.