On thermolysis of (CO)5MC(OEt)SiPh3 (M = W, Mo, Cr) in the solid state or in solution three different decomposition pathways are observed, which are unusual for Fischer-typecarbenecomplexes: fragmentation of the complex to give triphenylsilane, ethylene and M(CO)6, formation of ethyl(triphenylsilyl)ketone and decomposition to give ethyltriphenylsilane and M(CO)6. The proportions of reactants which