8th and 9th group mixed metal clusters substituted with alkynes and their reactivity towards acids

Alkynes have proved to be very versatile ligands for carbonyl clusters since they can donate from 2 to 6 electrons to up to 4 metal atoms, giving rise to various coordination modes. The existing literature concerns mainly the tetranuclear homoand heterometallic clusters which show structural flexibility and can contain almost all the elements of the 6th, 7th, 8th, 9th and 10th groups of the periodic table. We decided to study the reactivity of tetrahedral mixed metal clusters (8th-9th group) with disubstituted mono- and di-alkynes. [Fe2Ir2(CO)12]2- reacts with diphenylacetylene in refluxing CH3CN loosing 2 COs and giving [Fe2Ir2(CO)10(PhCCPh)]2- whose structure consists of a metal butterfly arrangement surmounted by the alkyne; the C-C bond is parallel to the Ir-Ir hinge. The dropwise addition of H2SO4 to a dark red CH2Cl2 solution of this compound leads to the neutral species [FeIr2(CO)9(PhCCPh)], that can be crystallized from hexane at low temperature. X-ray analysis showed that the formal loss of a Fe(CO) fragment leaves the μ3-η2 || alkyne’s coordination mode unchanged; considering the two carbon atoms as a part of the cage, the new cluster can be described as a pseudo square pyramid. [CoRu3(CO)11(PhCCCCPh)]- is synthesized heating a CH3CN solution of [CoRu3(CO)13]- and 1,4-diphenylbutadiyne at 80°C for 4h; only one of the C-C triple bonds coordinates in the dihedral angle of the metallic butterfly, parallel to the Ru-Ru hinge. Again, the titration of a CH2Cl2 solution of the cluster with H2SO4 promotes the limited demolition of the molecule, but X-ray diffraction revealed also the partial hydrogenation of the former di-alkynic chain: the persisting μ3- coordination of the C1=C2 bond is enforced by a Ru2-C3 σ bond, whereas the PhC4H group doesn’t bind to the metal triangle. So the cluster’s molecular formula is [CoRu2(CO)9(PhCCCC(H)Ph)]. Cyclovoltammetric studies will ascertain if the electrochemical oxidation products are the same obtained in this chemical way.