Coupling reactions of alkynes with half-open titanocenes: Agostic (C–C) → Ti interactions in a tetra(alkyne) coupling product with the Ti(C5H5)(c-C8H11) fragment

The reaction of the half-open titanocene Ti(C5H5)(c-C8H11)(PMe3) (c-C8H11 = cyclooctadienyl) with four equivalents of PhC2SiMe3 has been found to lead to an unusual, very electron deficient coupling product, containing both metallacyclobutane and metallacyclobutene fragments. Structural studies of both complexes have been carried out, and for the latter reveal apparent (C–C) → Ti agostic interactions in both the metallacyclobutane and metallacyclobutene fragments.