Functionalization of the macropolyhedral borate anion cluster [B22H22]2−: isolation and characterization of the OH and OEt derivatives

Preparation and characterization of the first derivatives of the fused macropolyhedral anion [B22H22]2− are reported. The species [B22H21OH]2− (1) and [B22H21OEt]2− (2) are obtained from workup of the products of the reaction between HgBr2 and [NBzlEt3]2[B22H22]; a cluster involving the conjoining of a closo-B12 icosahedron with a nido-B10 cluster. Washing the products with ethanol followed by thin-layer chromatography allows the isolation of 1 and 2, reproducibly, in yields of 27 and 20%, respectively. The species were characterized by NMR spectroscopy, elemental analysis and X-ray diffraction studies. The crystal structure determinations of the two species identify novel features. Apparently the influence of the O atoms in the ions [B22H21OH]2− and [B22H21OEt]2− results in the lengthening of what was a gunwale BB connection adjacent to the junction of the two cages such that the distances are 2.180 and 2.230 Å, respectively. These latter are longer than the corresponding distance in the parent species [B22H22]2−, which is 2.09 Å; quite long for a normal BB distance. Thus it is assumed that these B atoms, in 1 and 2, one of which bears the substituent, are not bonded to each other.