Co-ordination of the acyl oxygen atom in a di-iron µ2-η2-(C,C)-ketenecomplex, Fp–CH2CO–Fp [Fp =(η5-C5H5)Fe(CO)2] to Lewis acidic organometallic centres produces cationic trinuclear µ3-η3-(C,C,O)-ketenecomplexes, the two metal components of which exchange with each other via an intramolecular process.