Structural rearrangements induced by acid–base reactions in metal carbonyl clusters: the case of [H_(3?n)Co_(15)Pd_9C_3(CO)_(38)]~(n?) (n = 0–3)?

摘要

The new bimetallic [HCo_(15)Pd_9C_3(CO)_(38)]~(2?) tri-carbide carbonyl cluster has been obtained from the reaction of [H_2Co_20Pd_(16)C_4(CO)_(48)]~(4?) with an excess of acid in CH_2Cl_2 solution. The mono-hydride di-anion can be reversibly protonated and deprotonated by means of acid–base reactions leading to closely related [H_(3?n)Co_(15)Pd_9C_3(CO)_(38)]~(n?) (n = 0–3) clusters. The crystal structures of the three anionic and the neutral clusters have been determined as their H_3Co_(15)Pd_9C_3(CO)_(38)·2thf, [NEt_4][H_2Co_(15)Pd_9C_3(CO)_(38)]·0.5C_6H_(14), [NMe_3(CH_2Ph)]_2[HCo_(15)Pd_9C_3(CO)_(38)]·C_6H_(14) and [NEt_4]_3[Co_(15)Pd_9C_3(CO)_(38)]·thf salts. They are composed of a Pd9(μ_3-CO)_2 core stabilised by three Co_5C(CO)_(12) organometallic fragments. The poly-hydride nature of these clusters has been indirectly inferred via chemical, electrochemical and magnetic measurements. Besides, cyclic voltammetry shows that the [H_(3?n)Co_(15)Pd_9C_3(CO)_(38)]~(n?) (n = 1–3) anions are multivalent, since they undergo two or three reversible oxidations. SQUID measurements of [HCo_(15)Pd_9C_3(CO)_(38)]~(2?) indicate that this even electron cluster is paramagnetic with two unpaired electrons, giving further support to its hydride nature. Finally, structural studies show that the Pd_9 core of [H_(3?)nCo_(15)Pd_9C_3(CO)_(38)]~(n?) (n = 0,1) is a tri-capped octahedron, which becomes a tri-capped trigonal prism in the more charged [H_(3?n)Co_(15)Pd_9C_3(CO)_(38)]~(n?) (n = 2,3) anions. Such a significant structural rearrangement of the metal core of a large carbonyl cluster upon protonation–deprotonation reactions is unprecedented in cluster chemistry, and suggests that interstitial hydrides may have relevant stereochemical effects even in large carbonyl clusters.