The reaction of potassium salt of 7,9-dicarba-nido-undecaborate anion K7,9-C2B9H12 (meta-nido-carborane) with mercury(II) chloride was studied under various conditions. It was shown that, in contrast to the 7,8-dicarba-nido-undecaborate anion, the reaction in a mixture of benzene and acetonitrile proceeds non-selectively and leads to a complex mixture of products, from which, after column chromatography on silica gel, a derivative with a condensed diboroxazole ring 2,11-(μ-OC(Me)=NH–O,N)-7,9-nido-C2B9H10 (the main product) and 6,8-dicarba-arachno-nonaborane were isolated. The using of excess of HgCl2 allows one to avoid the formation of 6,8-arachno-C2B7H13, but leads to the formation of a difficult-to-separate impurity of the chloro derivative 4-Cl-2,11-(μ-OC(Me)=NH–O,N)-7,9-nido-C2B9H9. It was shown that 6,8-dicarba-arachno-nonaborane (6,8-arachno-C2B7H13) can be selectively obtained by the reaction of K7,9-C2B9H12 with HgCl2 in hydrochloric acid.
Bogdanova et al. (Thu,) studied this question.