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

The interaction of the titanadihydrofuran metallacycles Cp 2 Ti[η 2 ‐C(SiMe 3 )=C(Ph)‐C(Me) 2 O] ( 1 ) and Cp 2 Ti[η 2 ‐C(SiMe 3 )= C(Ph)‐CH(Ph)O] ( 2 ) with i Bu 2 AlH in n ‐hexane at 20°C yields 1 : 1 complexes Cp 2 Ti[η 2 ‐C(SiMe 3 )=C(Ph)‐C(Me) 2 O]( i Bu 2 AlH) ( 4 ) and Cp 2 Ti[η 2 ‐C(SiMe 3 )=C(Ph)‐CH(Ph)O]( i Bu 2 AlH) ( 5 ) respectively. According to X‐ray diffraction data, the i Bu 2 AlH molecule in 4 is coordinated by its aluminium centre with the oxygen atom whereas the hydride hydrogen atom of the i Bu 2 AlH forms a bridge with the titanium. As a result of the complexation with i Bu 2 AlH, the Ti−O and Ti‐C(SiMe 3 ) bonds of the starting 1 are strongly elongated. An analogous 1 : 1 adduct ( 11 ) is formed in the interaction of i Bu 2 AlH with the zirconadihydrofuran derivative Cp 2 Zr[η 2 ‐C(SiMe 3 )=C(SiMe 3 )‐C(Me) 2 O] ( 3 ). Like the Ti−O and Ti‐C(SiMe 3 ) bonds in 1 , the Zr−O and Zr‐C(SiMe 3 ) bonds in 3 are considerably elongated as a result of the coordination with i Bu 2 AlH. The reaction of 1 with EtAlCl 2 gives a complex, Cp 2 Ti[η 2 ‐C(SiMe 3 )=C(Ph)‐C(Me) 2 O](EtAlCl 2 ) ( 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(SiMe 3 ) 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 .