Mercury(II) Complexes of the Carba-closo-dodecaboranyl Ligands [closo-1-CB₁₁X₁₁]²– (X = H, F, Cl, Br, I)

Salts of the mercury(II) complexes [Hg( closo -1-CB 11 X 11 ) 2 ] 2– (X = H ( 1 ), Cl ( 3 ), Br ( 4 )) and [PhHg( closo -1-CB 11 X 11 )] − (X = H ( 6 ), Cl ( 8 ), Br ( 9 ), I ( 10 )) were synthesized and characterized by multi-NMR spectroscopy, mass spectrometry, elemental analysis, and differential scanning calorimetry. Single crystals of Cs 2 1 ·2Et 2 O, Cs 2 3 ·MeCN, Cs 2 4 ·4Me 2 CO, Cs 9, and [Et 4 N] 6 ·0.5Me 2 CO were studied by X-ray diffraction, and the interpretation of the bond properties is supported by theoretical data. In contrast to the mercury atom of the previously published [Hg( closo -1-CB 11 F 11 ) 2 ] 2– ( 2 ), which coordinates either acetonitrile or water, the metal atom of the related dianionic complexes 1, 3, and 4 does not reveal any further coordination. According to results derived from DFT and ab initio calculations, this different behavior is reasoned in the case of 1 by a reduced Lewis acidity at mercury and in the case of 3 and 4 by the increased shielding of the central mercury atom as a result of the bulky halogenated carba- closo -dodecaboranyl ligands [ closo -1-CB 11 X 11 ] 2– (X = Cl, Br). The dianionic complex [Hg( closo -1-CB 11 I 11 ) 2 ] 2– ( 5 ) with the bulkiest carba- closo -dodecaboranyl ligand was generated via collision-induced dissociation and characterized by (−)-ESI mass spectrometry. The fragmentation pathways of the anionic complexes [Hg( closo -1-CB 11 X 11 ) 2 ] 2– (X = H, F, Cl, Br, I ( 1 – 5 )) and [PhHg( closo -1-CB 11 X 11 )] − (X = H, F, Cl, Br, I ( 6 – 10 )) were studied by (−)-ESI mass spectrometry.