Reaction of FeRu(CO) 6( iPr-Pyca) ( 5) with the alkynes RCCC(O)OMe (RC(O)OMe (a); RH (b)) leads to the formation of FeRu(CO) 5( iPr-Pyca)(μ-η 1,η 3-MeOC(O)CC(R)C(O)) (RC(O)OMe ( 6a); RH ( 6b)). In the case of the monosubstituted alkyne HCCC(O)OMe ( b) the CC coupling reaction between the alkyne and the carbonyl ligand proved to be highly regioselective. However, in contrast to literature reports, the CC coupling exclusively takes place at the unsubstituted alkyne C atom, which indicates that substituent effects are dominant. An X-ray single crystal structure of complex 6a has been determined. Red crystals of 6a are monoclinic, space group P2 1/n, Z = 4, with unit cell dimensions a = 9.277(2), b = 20.112(4), c = 15.964(2) Å and β = 99.267(15)°. The structure refinement converged to R = 0.040 for 4123 observed reflections. Thermal conversion of the complexes 6a, b leads to the formation of FeRu(CO) 5(C 5H 4N-2-CHNC(Me) 2)(μ,η 2-RCCHR′) (RR′C(O)OMe ( 7a); RH, R′C(O)OMe ( 7b); RC(O)OMe, R′H (7b′)) in which, as a result of H migration of the isopropyl H atom from the iPr-Pyca ligand to the alkyne, a μ,η 2-vinyl fragment is present which is σ-bonded to Ru and η 2-bonded to Fe. The former imine C atom is σ-bonded to the Fe centre. The conversion of 6b leads to an unseparable mixture of the complexes 7b and 7b′ suggesting that during the H migration reaction the alkyne C atoms may change their positions and are both capable of abstracting a proton from the iPr-Pyca ligand. Given the fact that the formation of 7b is strongly favoured over the formation of 7b′ substituent effects appear to be important in determining the product distribution of the H migration reaction.