Synthesis and characterization of synthetically useful salts of the weakly-coordinating dianion [B12Cl12]2-

The closo-dodecahydrododecaborate [NEt3H](2)[B12H12] has been prepared on a lab scale by an improved synthesis from cheap and readily available starting materials Na[BH4] and I-2 in diglyme ( diethylene glycol dimethyl ether). Subsequent chlorination with elemental chlorine in aqueous solution at normal pressure yielded the per-chlorinated weakly coordinating [B12Cl12](2-) anion. By simple metathesis reaction a variety of useful salts [cation](2)[B12Cl12] (cation = [NEt3H](+), [NBu4](+), Li+, Na+, K+, Cs+) is available. These salts are useful starting materials, which have the potential to open up the chemistry of [B12Cl12](2-) as a weakly coordinating dianion. Exemplarily, they were used in further reactions to prepare [NO](2)[B12Cl12], [PPN](2)[B12Cl12], and [CPh3](2)[B12Cl12]. The crystal structures of Cs-2[B12Cl12]center dot SO2, [CPh3](2)[B12Cl12]center dot 2C(2)H(4)Cl(2), and [CPh3](2)[B12Cl12]center dot 2SO(2) and preliminary crystal structures of [NO](2)[B12Cl12] center dot SO2 and [PPN](2)[B12Cl12]center dot CH2Cl2 were determined. The crystal structure of the SO2 solvate Cs2[ B12Cl12] center dot SO2 is related to the crystal structure of solvent free Cs-2[ B12Cl12]. [ CPh3] (2)[ B12Cl12] center dot 2C(2)H(4)Cl(2) and [CPh3](2)[ B12Cl12]center dot 2SO(2) have very similar structures in the solid state. In both cases the [ CPh3](+) cations form only very weak contacts to the [ B12Cl12](2-) anion and SO2 or C2H4Cl2 solvent molecules respectively. The averaged experimental B-B (178.7 pm) and B-Cl (178.9 pm) bond lengths within [ B12Cl12](2-) are essentially unchanged in all determined structures and are reproduced well by PBE0/TZVPP quantum chemical calculations (B-B 178.6 pm, B-Cl 179.3 pm). All results indicate that [B12Cl12](2-) is a readily accessible weakly-coordinating dianion.