Polymetallated 4‐tert‐Butylcalix[4]arene Complexes of Sodium and Potassium Stabilized by Crown Ethers: Syntheses, Structures and Activation of Carbon Dioxide

Abstract

4‐tert‐Butylcalix[4]arene and 18‐crown‐6 react with NaH in THF to form the complex [(18‐crown‐6)(THF)Na4(4‐tert‐butylcalix[4]arene‐4H)]2·3THF (1). Analogously, the reaction with 4‐tert‐butyltetrathiacalix[4]arene in DMF results in the formation of [(18‐crown‐6)Na(dmf)1.5]2[(4‐tert‐butyltetrathiacalix[4]arene‐4H)2Na6(dmf)2] (2) The X‐ray analysis of 1 shows an Na6O6 skeleton consisting of two fused open heterocubanes. Two Na+ ions are encapsulated in the cavities of the calix[4]arene units. Additionally, two peripheral Na+ ions, each surrounded by a crown ether and one THF ligand, are connected to the central Na6O6 skeleton by one bridging oxygen of the calix[4]arene. In contrast, 2 contains the highly symmetrical anion [(4‐tert‐butyltetrathiacalix[4]arene‐4H)2Na6(dmf)2]2− and crown‐ether‐stabilized cations. While 1 shows a dynamic process in solution above 40 °C, the structure of the highly symmetrical compound 2 remains stable at higher temperatures. The solid‐state structure of the potassium complex [(dibenzo‐18‐crown‐6)K4(4‐tert‐butylcalix[4]arene‐4H)(THF)3]2·4THF (4) is similar to 1; however, the calix[4]arene units in the open heterocubane structure of 4 are shifted less than half a diameter to one another than in the sodium complex 1. According to the 1H NMR spectra complex 3a, containing 18‐crown‐6, has a very similar structure to the related complex 4. Both 1 and 4 absorb carbon dioxide in THF and are active CO2‐transfer reagents towards 2‐fluoropropiophenone; complex 2 is much less active. This clearly demonstrates the subtle influence of the structure of the alkali metal complexes on the CO2 reactivity in these types of compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Calixarenes as platforms for the construction of multimetallic complexes

“…7 where each calixarene has a metal in the cavity with KÁ Á Áp interactions to two opposite aromatic rings [20]. A related dibenzo-18-crown-6 derivate has each ÔK(THF) 3 Õ replaced by ÔK(dibenzo-18-crown-6)(THF)Õ, with these alkali metal centres attached only to one phenolate O-centre [21]. A similar sodium analogue has each ÔK(THF) 3 Õ replaced by ÔNa(18-crown-6)(THF)Õ [21].…”

The chain-like polynuclear coordination compounds (ZnBr2)n(18-crown-6)2 (n = 4, 6, 8, 10) and [Zn5Br9][N(Tf2)]

“…17 . 18,19 For the title compound, the coordination of Zn 2+ is best described as a distorted pentagonal bipyramid (Fig. 2).…”

Alkali-Metalated Forms of Thiacalix[4]arenes

“…Surprisingly little is known about alkali metal salts of thiacalix[4]arenes. Harrowfield et al described partially deprotonated thiacalixarene complexes of the metals lithium to cesium 10a. They succeeded in determining the crystal structures of complexes of the alkali metal ions with, in the case of Li, the dianion and, in the cases of Na to Cs, the monoanion of p - tert -butyltetrathiacalix[4]arene.…”