An experimental solution to the 'missing hydrogens' question surrounding the macropolyhedral 19-vertex boron hydride monoanion [B _(19)H_(22)]~-, a simplification of its synthesis, and its use as an intermediate in the first example of syn -B_(18)H _(22) to anti -B_(18)H_(22) isomer conversion

摘要

The macropolyhedral [B_(19)H_(22)]~- monoanion 1 and the dianion [B_(19)H_(21)]~(2-) 2 are synthesized in consistent 86-92% yields by the reaction of [PSH]~+[syn-B _(18)H_(21)]- with BH_3(SMe_2) in 1,2-Cl_2C_2H_4 at 72 °C. [PS is an abbreviation for Proton Sponge, 1,8-bis-(dimethylamino)naphthalene. PSH is its protonated derivative.] The molecular structures of 1 and 2 were elucidated as their [PS{BH_2}]~+ and [PS{BH_2}]_2~+ salts 1a and 2a by single-crystal X-ray diffraction studies, in which all atoms were located, and supported by mass spectrometric analyses together with calculations of the cluster molecular geometries (ab ignitio and/or DFT) and of ~(11)B chemical shifts based on GIAO-DFT shielding tensors. Acidification of dianion 2 with CF_3COOH in acetonitrile, H_2SO_4 in dichloromethane, or aqueous HCl results in the clean formation of the monoanion [B_(19)H_(22)]~- 1. Conversely, shaking a concentrated acetonitrile solution of 1 in 0.5 M aqueous NaOH cleanly yields the [B_(19)H_(21)]~(2-) dianion 2. Reaction of a dichloromethane solution of 1 with a 36% aqueous solution of HCHO in the presence of H_2SO_4 quantitatively converts 1 at room temperature to a 1:1 mixture of the syn- and anti-isomers of B _(18)H_(22). This cluster dismantling process is the first example of a syn- to anti-B_(18)H_(22) isomer conversion.