Formation of Binuclear Zigzag Hexapentaene Titanium Complexes via a Titanacumulene [Ti=C=C=CH2 ] Intermediate.

The reaction of bis(η5 :η1 -pentafulvene)titanium complexes with an allylidenephosphorylide Ph3 P=C(H)- C(H)=CH2 leads to binuclear zigzag hexapentaene titanium complexes (Ti2a, Ti2b). The formation of the central C6 H4 unit can be described as a spontaneous double C-H bond activation process, leading to an R3 P=C=C=CH2 intermediate, as a synthon for a titanabutatriene fragment [(CpR )2 Ti=C=C=CH2 ] (R: 2-adamantyl, CH(p-tol)2 ). In a subsequent dimerization Ti2a and Ti2b are formed, proofed by single-crystal X-ray diffraction and NMR measurements. The reaction sequence is confirmed by DFT calculations.