Double deboronation and homometalation of 1,1′-bis(ortho-carborane)

Abstract

Double deboronation of 1,1′-bis(ortho-carborane) results in a mixture of racemic and meso diastereoisomers which are sources of the [7-(7′-7′,8′-nido-C₂B₉H₁₀)-7,8-nido-C₂B₉H₁₀]⁴⁻ tetraanion. Consistent with this, metalation of the mixture with {Ru(p-cymene)} affords the diastereoisomers α-[1-(8′-2′-(p-cymene)-2′,1′,8′-closo-RuC₂B₉H₁₀)-3-(p-cymene)-3,1,2-closo-RuC₂B₉H₁₀] (3α) and β-[1-(8′-2′-(p-cymene)-2′,1′,8′-closo-RuC₂B₉H₁₀)-3-(p-cymene)-3,1,2-closo-RuC₂B₉H₁₀] (3β) in which the primed cage has undergone a spontaneous 3′,1′,2′ to 2′,1′,8′-RuC₂B₉ isomerisation. Analogous cobaltacarboranes α-[1-(8′-2′-Cp-2′,1′,8′-closo-CoC₂B₉H₁₀)-3-Cp-3,1,2-closo-CoC₂B₉H₁₀] (4α) and β-[1-(8′-2′-Cp-2′,1′,8′-closo-CoC₂B₉H₁₀)-3-Cp-3,1,2-closo-CoC₂B₉H₁₀] (4β) are formed by metalation with CoCl₂/NaCp followed by oxidation, along with a small amount of the unique species [8-(8′-2′-Cp-2′,1′,8′-closo-CoC₂B₉H₁₀)-2-Cp-2,1,8-closo-CoC₂B₉H₁₀] (5) if the source of the tetraanion is [HNMe₃]₂[7-(7′-7′,8′-nido-C₂B₉H₁₁)-7,8-nido-C₂B₉H₁₁]. Two-electron reduction and subsequent reoxidation of 4α and 4β afford species indistinguishable from 5. The reaction between [Tl]₂[1-(1′-3′,1′,2′-closo-TlC₂B₉H₁₀)-3,1,2-closo-TlC₂B₉H₁₀] and [CoCpI₂(CO)] leads to the isolation of a further isomer of (CpCoC₂B₉H₁₁)₂, rac-[1-(1′-3′-Cp-3′,1′,2′-closo-CoC₂B₉H₁₀)-3-Cp-3,1,2-closo-CoC₂B₉H₁₀] (6), which displays intramolecular dihydrogen bonding. Thermolysis of 6 yields 4α, allowing a link to be established between the α and β forms of 3 and 4 and racemic and meso forms of the [7-(7′-7′,8′-nido-C₂B₉H₁₀)-7,8-nido-C₂B₉H₁₀]⁴⁻ tetraanion, whilst reduction–oxidation of 6 again results in a product indistinguishable from 5.