Electron paramagnetic resonance studies of some supported organometallic catalysts

Abstract

E.p.r. spectroscopy has been used to study catalysts obtained by supporting the following complexes on high surface area silica: Mo₂(CH₃CO₂)₄, M₂[CH₂Si(CH₃)₃]₆(M = Mo or W), W(CO)₆, W(CH₃)₆, Cr(CO)₆, Cr[CH₂C(CH₃)₃]₄. The supported molybdenum complexes activated at sufficiently high temperatures give rise to e.p.r. signals identical to those observed previously from silica supported Mo(CO)₆ and MoO₃ catalysts, due to Mo^V in square pyramidal co-ordination, and O^–₂ formed by interaction of O₂ with tetrahedrally coordinated Mo^V. The supported tungsten complexes give only an O^–₂ signal on exposure to O₂. The spectrum of adsorbed CH₃ radicals is detected during decomposition of supported W(CH₃)₆. The supported chromium complexes activated in vacuo and exposed to O₂ give Cr^V signals identical to those observed from silica supported CrO₃. The catalytic implications of these observations are discussed.