Complexation of Titana‐ and Zirconadihydrofuran Metallacycles with Organoaluminium Compounds and Catalytic Activity of the Resulting Complexes in Polymerization of ϵ‐Caprolactone

Abstract

AbstractThe interaction of the titanadihydrofuran metallacycles Cp2Ti[η2‐C(SiMe3)=C(Ph)‐C(Me)2O] (1) and Cp2Ti[η2‐C(SiMe3)= C(Ph)‐CH(Ph)O] (2) with iBu2AlH in n‐hexane at 20°C yields 1 : 1 complexes Cp2Ti[η2‐C(SiMe3)=C(Ph)‐C(Me)2O](iBu2AlH) (4) and Cp2Ti[η2‐C(SiMe3)=C(Ph)‐CH(Ph)O](iBu2AlH) (5) respectively. According to X‐ray diffraction data, the iBu2AlH molecule in 4 is coordinated by its aluminium centre with the oxygen atom whereas the hydride hydrogen atom of the iBu2AlH forms a bridge with the titanium. As a result of the complexation with iBu2AlH, the Ti−O and Ti‐C(SiMe3) bonds of the starting 1 are strongly elongated. An analogous 1 : 1 adduct (11) is formed in the interaction of iBu2AlH with the zirconadihydrofuran derivative Cp2Zr[η2‐C(SiMe3)=C(SiMe3)‐C(Me)2O] (3). Like the Ti−O and Ti‐C(SiMe3) bonds in 1, the Zr−O and Zr‐C(SiMe3) bonds in 3 are considerably elongated as a result of the coordination with iBu2AlH. The reaction of 1 with EtAlCl2 gives a complex, Cp2Ti[η2‐C(SiMe3)=C(Ph)‐C(Me)2O](EtAlCl2) (8), in which the organoaluminium compound is also coordinated by its aluminium centre with the oxygen atom. This leads to a strong elongation of the Ti−O bond. The C−O bond of the metallacycle in 8 is noticeably elongated as well but the Ti‐C(SiMe3) bond length even somewhat shortens. Complexes 4, 5, 8 and 11 are capable of catalysing ring‐opening polymerization of ϵ‐caprolactone. The highest activity is exhibited by complexes 4 and 5.