Synthesis of trimethylenemethane by combination of methylene with allene at a diruthenium centre: X-ray structure of [Ru 2 (CO)(µ-CO){µ-η 1 ,η 3 -CH 2 C(CH 2 ) 2 }(η-C 5 H 5 ) 2 ]

Carbon–carbon bond formation is rapid when the µ-methylene complex [Ru2(CO)(MeCN)(µ-CH2)(µ-CO)(η-C5H5)2] is treated with allene at room temperature, affording the µ-trimethylenemethane complex [Ru2(CO)(µ-CO){µ-η1,η3-CH2C(CH2)2}(η-C5H5)2], structurally characterised by X-ray diffraction; the fluxionality and isomerisation of the complex, and its reactivity towards H+ and CO, are described.