Synthesis and characterization of novel metallocarborane triple-decker complexes

Abstract

The syntheses of two novel triple-decker complexes are described where the [C₂B₉H₁₁]^2– dianion is utilized for the first time as a terminal ligand. The sandwich anion [Co(C₅H₅)(C₃B₂MeEt₄)]^–(C₃B₂MeEt₄= 1,3,4,5-tetraethyl-1H-2,3-dihydro-2-methyl-1,3-diborol-2-yl) reacts with the [C₂B₉H₁₁]^2– dianion and bis(pentane-2,4-dionato)nickel(II) to give the symmetrical tetradecker complex [Ni{(C₃B₂MeEt₄)-Co(C₅H₅)}₂] and the two unsymmetrical triple-decker complexes [(C₅H₅)Co(C₃B₂MeEt₄)Ni(C₂B₉H₁₁)] and [(C₅H₅)Co(C₃B₂MeEt₄)Co(C₂B₉H₁₁)]. The molecular structures of the three complexes were established from elemental analyses and ¹H and ¹¹B-{¹H} NMR and mass spectroscopic studies. In addition, the single-crystal X-ray analyses of the unsymmetrical ones were performed. Both complexes crystallize in the orthorhombic space group P2₁2₁2₁(no. 19) with cell dimensions: for CoNi, a= 10.077(4), b= 13.880(1), c= 18.318(2); for CoCo, a= 9.973(3), b= 13.885(3), c= 18.280(5)Å. The CoCo triple-decker was also synthesised in higher yield from the reaction of the [Co(C₅H₅)(C₃B₂MeEt₄)]^– anion with the [C₂B₉H₁₁]^2– dianion and cobalt(II) chloride. The redox properties of the triple-decker complexes were studied by cyclic voltammetry.