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

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-CBH)-7,8-nido-CBH] 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-RuCBH)-3-(p-cymene)-3,1,2-closo-RuCBH] (3α) and β-[1-(8'-2'-(p-cymene)-2',1',8'-closo-RuCBH)-3-(p-cymene)-3,1,2-closo-RuCBH] (3β) in which the primed cage has undergone a spontaneous 3',1',2' to 2',1',8'-RuCB isomerisation. Analogous cobaltacarboranes α-[1-(8'-2'-Cp-2',1',8'-closo-CoCBH)-3-Cp-3,1,2-closo-CoCBH] (4α) and β-[1-(8'-2'-Cp-2',1',8'-closo-CoCBH)-3-Cp-3,1,2-closo-CoCBH] (4β) are formed by metalation with CoCl/NaCp followed by oxidation, along with a small amount of the unique species [8-(8'-2'-Cp-2',1',8'-closo-CoCBH)-2-Cp-2,1,8-closo-CoCBH] (5) if the source of the tetraanion is [HNMe][7-(7'-7',8'-nido-CBH)-7,8-nido-CBH]. Two-electron reduction and subsequent reoxidation of 4α and 4β afford species indistinguishable from 5. The reaction between [Tl][1-(1'-3',1',2'-closo-TlCBH)-3,1,2-closo-TlCBH] and [CoCpI(CO)] leads to the isolation of a further isomer of (CpCoCBH), rac-[1-(1'-3'-Cp-3',1',2'-closo-CoCBH)-3-Cp-3,1,2-closo-CoCBH] (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-CBH)-7,8-nido-CBH] tetraanion, whilst reduction-oxidation of 6 again results in a product indistinguishable from 5.