Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)

Abstract

Examples of singly-metallated derivatives of 1,1′-bis(o-carborane) have been prepared and spectroscopically and structurally characterised. Metallation of [7-(1′-1′,2′-closo-C₂B₁₀H₁₁)-7,8-nido-C₂B₉H₁₀]²⁻ with a {Ru(p-cymene)}²⁺ fragment affords both the unisomerised species [1-(1′-1′,2′-closo-C₂B₁₀H₁₁)-3-(p-cymene)-3,1,2-closo-RuC₂B₉H₁₀] (2) and the isomerised [8-(1′-1′,2′-closo-C₂B₁₀H₁₁)-2-(p-cymene)-2,1,8-closo-RuC₂B₉H₁₀] (3), and 2 is easily transformed into 3 with mild heating. Metallation with a preformed {CoCp}²⁺ fragment also affords a 3,1,2-MC₂B₉-1′,2′-C₂B₁₀ product [1-(1′-1′,2′-closo-C₂B₁₀H₁₁)-3-Cp-3,1,2-closo-CoC₂B₉H₁₀] (4), but if CoCl₂/NaCp is used followed by oxidation the result is the 2,1,8-CoC₂B₉-1′,2′-C₂B₁₀ species [8-(1′-1′,2′-closo-C₂B₁₀H₁₁)-2-Cp-2,1,8-closo-CoC₂B₉H₁₀] (5). Compound 4 does not convert into 5 in refluxing toluene, but does do so if it is reduced and then reoxidised, perhaps highlighting the importance of the basicity of the metal fragment in the isomerisation of metallacarboranes. A computational study of 1,1′-bis(o-carborane) is in excellent agreement with a recently-determined precise crystallographic study and establishes that the {1′,2′-closo-C₂B₁₀H₁₁} fragment is electron-withdrawing compared to H.