Metal Segregation in Bimetallic Co-Pd Carbide Carbonyl Clusters: Synthesis, Structure, Reactivity and Electrochemistry of [H6-nCo20Pd16C4(CO)48]n-(n=3-6)

Nanometric CoPd bimetallic [H6-nCo20Pd16C4(CO)(48)](n-) (n=3-6) tetracarbide carbonyl clusters have been prepared by redox condensation of [Co6C(CO)(15)](2-) with [PdCl2(Et2S)(2)]. The crystal structures of both the dihydride tetra-anion and monohydride penta-anion have been determined as their [NEt4](4)[H2Co20Pd16C4(CO)(48)]4CH(3)COCH(3) and [NMe3(CH2Ph)][NMe4](4)[HCo20Pd16C4(CO)(48)]5CH(3)COCH(3) salts, respectively. The two species are isostructural and their structures display a perfect segregation of the two metals. They are composed of a cubic close-packed (ccp) Pd-16 core stabilised on its surface by four {Co5C(CO)(12)} organometallic fragments. Their polyhydride nature has been corroborated by the study of their reactions with acids and bases, and confirmed by electrochemical studies. In addition, the reactions of [H2Co20Pd16C4(CO)(48)](4-) with Na/naphthalene and PPh3/CO allowed the isolation of other lower nuclearity homoleptic and heteroleptic clusters, that is, [H6-nCo16Pd2C3(CO)(28)](n-) (n=5, 6), [Co4Pd2C(CO)(11)(PPh3)(2)], [Co2Pd5C(CO)(8)(PPh3)(5)], and [Co4Pd4C2(PPh3)(4)(CO)(10)Cl](-). [H6-nCo16Pd2C3(CO)(28)](n-) (n=5, 6) represent the first homoleptic metal-carbonyl clusters containing three interstitial carbide atoms.