Endohedral Mixed Aggregates: Sodium Alkoxide Cages with Organic or Inorganic Central Anions and Variable Hull

Abstract

Alkali metal alkoxides are widely used in chemistry due to their Brønsted basic and nucleophilic properties. Potassium alkoxides assist alkyllithium in the metalation of hydrocarbons in Lochmann-Schlosser-bases. Both compounds form mixed aggregates, which enhance the thermal stability, solubility, and the basic reactivity of these mixtures. A very unusual spherical mixed alkoxy aggregate was discovered by Grützmacher et al., where a central dihydrogen phosphide anion is surrounded by a highly dynamic shell of thirteen sodium atoms and a hull of twelve tert-butoxide groups. This structural motif can be reproduced by a reaction of trimethylsilyl compounds of methane, halogens, or pseudo-halogens with excess sodium tert-butoxide. A nucleophilic substitution releases the corresponding anion, which is then encapsulated by the sodium alkoxide units. The compounds are soluble in hydrocarbon solvents, enabling studies of solutions by highresolution NMR spectroscopy and IR/Raman studies of the crystalline materials.

Cage-like manganesesilsesquioxanes: features of their synthesis, unique structure, and catalytic activity in oxidative amidations

“…It is known that variable encapsulation could cause different intriguing structural effects. 77 Remarkably, the same peculiarity for cage-like mixed-valent manganese complexes encapsulating any anions is realized in complex 4 , i.e. , the inner hydroxyl anion is linked only to the Mn III ions.…”

Size- and shape-adaptable mixed-alkoxide-aggregates: encapsulation of tetrafluoroborate and butadiynediide

“…These examples demonstrated that a range of smaller and larger, linear, or planar anionic units can be accommodated in the surrounding cationic [Na 13 (O t Bu) 12 + ] environment. The lower threshold in this molecular construction has already been determined: fluoride 8 and hydroxide 7 prefer arrangements reduced by two NaO t Bu units: Na 11 (O t Bu) 10 X (X = OH or F).…”

“…These values are close to those of the compounds CH 3 @1 and Br@1 . 8 The respective central anions CH 3 − and Br − are considerably smaller than BF 4 − , but the overall molecular size of BF 4 @1 is almost the same. This is contrary to the trend observed for other central anions and the size of their corresponding alkoxide hull.…”

“…This was demonstrated by a lithium alkoxide/potassium oxide mixed aggregate 5 [(K-tmeda) 2 (LiO t Bu) 8 O] (tmeda = N , N ′-tetramethylethylenediamine) or a potassium antimonate [K 4 Sb(O t Bu) 8 O]. 6 Other anions, such as hydroxide 7 or fluoride, 8 have also been reported as guests in homo-metallic mixed aggregates (Na 11 (O t Bu) 10 X, X = OH or F). A very unusual mixed aggregate based on sodium tert -butoxide [NaO t Bu] was reported by Grützmacher and co-workers.…”

“…In the middle of this arrangement and balancing the charge is situated a dihydrogenphosphide anion [PH 2 − ], resulting in the overall formula [Na 13 (O t Bu) 12 (PH 2 )]. While this compound is the product of a reaction of NaPH 2 with an excess of NaO t Bu, an alternative method was developed to release a range of central anions by nucleophilic attack of excess NaO t Bu on suitable trimethylsilyl compounds 8 (Scheme 1). To emphasise the endohedral position of the central anion, we chose a designation that is customary in describing endohedral fullerenes: X@Na 13 (O t Bu) 12 or X@1 .…”