The reaction between [Rh(μ-Cl)(η 4-C 8H 12)] 2 and Tl[C 5(CO 2Me) 5] gave Rh(η 4-C 8H 12)[η 5-C 5(CO 2Me) 5] ( 3), which with PPh 2(CH 2) 2PPh 2 (dppe) gave [Rh(dppe)(η 4-C 8H 12)][C 5(CO 2Me) 5]. The complex Rh(azb) 2[C 5(CO 2Me) 5] ( 6; azb = C 6H 4N 2Ph) was obtained from [Rh(μ-Cl)(azb) 2] 2 and Tl[C 5(CO 2Me) 5]. Crystallographic characterisation of 3 and 6 showed that in the former, the C 5(CO 2Me) 5 group is attached via the ring carbons, whereas in 6, the ligand chelates the metal via two ester CO groups. Reactions of Tl[C 5(CO 2Me) 5] with MCl(CO)(PPh 3) 2 in MeCN gave [M(NCMe)(CO)(PPh 3) 2][C 5(CO 2Me) 5] ( 7, M = Rh; 8, M = Ir), in which the MeCN ligand is converted into (probably) acetic acid during recrystallisation, as shown by structural studies of the isomorphous Rh and Ir salts, 11 and 12. The [C 5(CO 2Me) 5] − anion is hydrogen-bonded to this acetic acid ligand. Crystal data: 3, triclinic, space group P 1 , a 18.591(3), b 14.053(4), c 10.395(3) Å, α 75.15(2), β 72.13(2), γ 81.38(2)°, Z = 4; 6, monoclinic, space group P2 1/ n, a 23.897(5), b 9.900(1), c 15.828(3) Å, β 99.56(2)°, Z = 4; 11, triclinic, space group P 1 , a 21.695(7), b 13.669(7), c 9.319(3) Å, α 103.15(3), β 95.39(3), γ 98.20(3)°, Z = 2; 12, triclinic, space group P 1 , a 21.685(2), b 13.615(2), c 9.306(2) Å, α 103.34(2), β 95.28(2), γ 98.31(1)°, Z = 2. For the four structure determinations, 6343, 5024, 3785 and 5462 observed data with I π 3σ( I) were refined to R 0.043 ( 3, 0.042 ( 6), 0.064 ( 11) and 0.057 ( 12), respectively.