Reaction of [Ru(π-C4H7)2C8H12] with various phosphorus ligands gives soluble crystalline complexes of the type [Ru(π-C4H7)2L2][L = P(OMe)3, P(OEt)3, P(OCH2)3CMe, or P(OCH2)3CEt; or L2= Me2PCH2CH2PMe2]. The 1H n.m.r. spectra of these complexes showed that the π-allylic groups were asymmetrically bonded to ruthenium. The synthesis of [Ru(π-C3H5)2(CO)2] is reported and its 1H n.m.r. spectrum interpreted in terms of two equivalent π-allyl groups asymmetrically bonded to ruthenium. Variable-temperature n.m.r. studies show that, in addition to a syn–anti exchange at high temperatures, there is a rapid intramolecular rearrangement at room temperature, in which the CH2 groups of the π-allyl groups effectively exchange environments. This is rationalised on the basis of an intramolecular ‘twist’ mechanism.