Butadiene reacts with rhodium trichloride in methanol to give a crotyl, butadiene-bridged, chloro-bridged complex, [C4H7RhCl2(C4H6)RhCl2C4H7]. The complex reacts with pyridine to give [RhCl2(1-methylallyl)(py)2] and with cyclopentadienylthallium to give [RhCl(1-methylallyl)(C5H5)], both with evolution of butadiene. The complex [C4H7RhCl2(C4H6)RhCl2(C4H7)] is also formed by the oxidative addition of 1-methyallyl chloride to [RhCl(C4H6)2] or by treating [Rh2Cl2(C2H4)4] successively with 1-methylallyl chloride then with butadiene; this method was also used to synthesise the corresponding allyl and 2-methylallyl complexes, [Rh2Cl4(all)2(C4H6)](all = allyl or 2-methylallyl). An allyl alcohol complex [Rh2Cl4(Allyl)2(C3H5OH)2] has also been prepared. N.m.r. and infrared data are given.