Investigation of polymerisation and metathesis reactions: Part XIII : Heterogeneous bimetallic metathesis catalysts by reactions of differently substituted Fischer-type tungsten carbene complexes with reduced Phillips catalyst

Abstract

The reactions of reduced Phillips catalyst, a polymerisation catalyst for 1-alkenes, with differently substituted Fischer-type tungsten carbene complexes (CO) 5W = CR 1R 2 (R 1 = Ph, Tol, CH 3; R 2 = Ph, OCH 3), which are metathesis catalysts with poor activity, yield bimetallic heterogeneous compounds by the loss of one CO ligand. Diffuse reflectance FT-IR spectroscopy of the heterogeneous compounds shows a strong shift of the v-CO absorptions to higher wavenumbers, probably caused by a chromium-tungsten bond. The catalytic activity of these surface compounds was tested with 1-octene. All were found to be very active metathesis catalysts, and no polymerisation of 1-octene was observed. These results indicate that the polymerisation activity of the reduced Phillips catalyst was lost, whilst the metathesis activity of the carbene complexes was enhanced by activation with the reduced Phillips catalyst. The surface chromium atoms act as activating species for the carbene complex fragments. The influence of the carbene substituents on the metathesis reaction is not significant, with the exception of the methyl substituent of (CO) 5W = C(OCH 3)CH 3. The acidic protons of this methyl substituent are thought to give rise to further interaction with a Si—O—Cr or Si—O—Si group. The new bimetallic, heterogeneous metathesis catalysts are stable at 20 °C and can be stored without loss of activity for some months.