Li+ -induced sigma-bond metathesis: aryl for methyl exchange on boron in a methylated monocarbadodecaborate anion.

At 190 degrees C, formal sigma-bond metathesis between the B-CH3 bond in position 12 of the lithium monocarbadodecaborate derivative 1a and the C-Si(CH3)3 bond in p-bromophenyltrimethylsilane occurs and produces Si(CH3)4 and a salt of the arylated carborate anion 2, whose X-ray structure has been determined. The reaction requires the presence of active Li+ cations and does not occur with the cesium salt 1b or when 12-crown-4 is added to 1a. Possible mechanisms are briefly discussed.