文摘
The use of water as a reagent in redox-driven reactions is advantageous because it is abundant and environmentally compatible. The conversion of water to dioxygen in photosynthesis illustrates one example, in which a redox-inactive CaII ion and four manganese ions are required for function. In this report we describe the stepwise formation of two new heterobimetallic complexes containing CoII/III and CaII ions and either hydroxo or aquo ligands. The preparation of a four-coordinate CoII synthon was achieved with the tripodal ligand, N,N鈥?N鈥?[2,2鈥?2鈥?nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido, [MST]3鈥?/sup>. Water binds to [CoIIMST]鈭?/sup> to form the five-coordinate [CoIIMST(OH2)]鈭?/sup> complex that was used to prepare the CoII/CaII complex [CoIIMST(渭-OH2)CaII15-crown-5(OH2)]+ ([CoII(渭-OH2)CaIIOH2]+). [CoII(渭-OH2)CaOH2]+ contained two aquo ligands, one bonded to the CaII ion and one bridging between the two metal ions, and thus represents an unusual example of a heterobimetallic complex containing two aquo ligands spanning different metal ions. Both aquo ligands formed intramolecular hydrogen bonds with the [MST]3鈥?/sup> ligand. [CoIIMST(OH2)]鈭?/sup> was oxidized to form [CoIIIMST(OH2)] that was further converted to [CoIIIMST(渭-OH)CaII15-crown-5]+ ([CoIII(渭-OH)CaII]+) in the presence of base and CaIIOTf2/15-crown-5. [CoIII(渭-OH)CaII]+ was also synthesized from the oxidation of [CoIIMST]鈭?/sup> with iodosylbenzene (PhIO) in the presence of CaIIOTf2/15-crown-5. Allowing [CoIII(渭-OH)CaII]+ to react with diphenylhydrazine afforded [CoII(渭-OH2)CaIIOH2]+ and azobenzene. Additionally, the characterization of [CoIII(渭-OH)CaII]+ provides another formulation for the previously reported CoIV鈥搊xo complex, [(TMG3tren)CoIV(渭-O)ScIII(OTf)3]2+ to one that instead could contain a CoIII鈥揙H unit.