Utilizing this fact, the CO insertion reaction could also be exploited to trap the rapidly formed syn product 2-Pr,Ph generated in the reaction of 1 with PhCC n Pr. Addition of CO to in situ generated 2-Pr,Ph results in an immediate colour change and yellow crystals of the product could be obtained by recrystallization from hexane. Here too, a characteristic doublet for the acyl carbon could be located in the C{ 1 H} spectrum of the product (δ C = 287.4 ppm; 2 J CP = 65 Hz), and X-ray crystallography confirmed connectivity as the analogous five-membered metallocycle 4-Pr,Ph (Figure ). Moreover, this derivatization corroborates NMR evidence that the product formed by insertion of 1-phenyl-1-pentyne into 1 is indeed 2-Pr,Ph, featuring the alkyl and aluminium fragments bound to the same alkenic carbon centre. In conclusion, we report the first examples of insertion of an alkyne into a hetero-metallic M-M' bond, producing (aluminyl-alkenyl)copper compounds which possess differential reactivity at the two derived M-C functions. This system allows control over the nature of the product formed: kinetic control gives access to syn isomers with high selectivity, while the corresponding anti products can be obtained under more forcing conditions. Moreover, the use of short reaction times allows near-exclusive regio-control to be exerted over the insertion of mixed aryl/alkyl substituted alkynes. Longer reaction times generate mixtures of regio-isomers, with independent experiments showing that the initial insertion process is chemically reversible, such that one alkyne substrate is capable of displacing another. Stereo-chemically syn systems can be selectively derivatized by reaction with CO, leading to the formation of the first structurally characterized examples of copper acyl compounds -aided by the cooperative reactivity of the proximal aluminium centre. Finally, metallocycles such as 4-Et can be hydrolysed cleanly to free the organic fragment, with the α,β unsaturated aldehyde product (in this case (E)-2-ethylpent-2-enal) being formed via the net hydroformylation of an alkyne through the controlled action of an unsymmetrical bimetallic reagent.