A tetraanionic molecular square containing four pentacovalent siliconates is produced in high yield by the condensation of phenyltriethoxysilane and spirocatechol 1. A single isomer, meso 2, is produced from this diastereoselective condensation reaction. The steps leading up to the formation of meso-2 are not known, but the reaction appears to be driven by the insolubility of the tetrakistriethylammonium salt 2a. The tetraanionic macrocycle is a stable salt that undergoes ion-exchange reactions. An ion pair composed of the tetraanionic siliconate macrocycle and cyclobis(paraquat-p-phenylene) tetracation (2e) has been synthesized by ion exchange. Following complete assignment of all proton resonances in this 4 × 4 complex, the solution conformation was analyzed by an intermolecular double pulsed field gradient spin−echo (DPFGSE) NOE study. These results, aided by a molecular mechanics modeling study, have led to a proposed dynamic solution structure that features the cyclic bisparaquat tetracation selectively intercalating around a phenyl ring of the C 2 face of the macrocyclic tetraanion which in turn is engulfed by the interior of the tetraanion (Figure ). This novel host−host complexation calls attention to the conformational flexibility of the macrocyclic tetrasiliconates and, in all probability, all macrocycles be they charged or neutral.

Considerable information is available regarding penta-and hexaeoordinale silicon, both as reaction intermediates in organosilicon transformations' and as structurally interesting stable compounds.2We have been involved in the synthesis of linear polymers and more highly condensed network materials that contain pentaand hexacoordinate silicon as an integral component of the polymer main chain.3-5 The polysiliconate materials were prepared by condensation of organotriethoxysilyl derivatives with biscatechols (eq 1).m With the use of angular biscatechols such as spirocatechol l.6 the opportunity arises for formation of macrocyclic siliconates. In this communication, we report the synthesis and characterization of the first example of a macrocyclic tetrasiliconate. a tetraanion containing four pentacovalent silicons.Macrocycle 2a was prepared by condensation of spirocatechol 1 and an equimolar amount of phenyltriethoxysilane in refluxing THF using 3 equiv of triethylamine as base (eq 2). A white precipitate formed within 48 h in 80% yield. The salt was washed with excess THF and dried in vacuo.

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The versatile cyclopropene synthon 1 -bromo-2-chlorocyclopropene has been used to synthesize new di-and tricycloproparenes. Treatment of these cycloproparenes with silver ion in chloroform leads to rapid oligomerization via carbocation intermediates to give materials in which the aromatic systems are connected by six-membered rings. The ladder polymer formed by treating the linearly fused dicyclopropanaphthalene with silver ion in chloroform has been characterized by solid state nuclear magnetic resonance spectroscopy.The manufacture and manipulation of structures at the molecular level have been recognized as important goals for more than thirty years (1). The synthesis of linear rigid molecules composed primarily of six-membered rings (molecular lines) is of interest in this regard. Miller and his co-workers have prepared short molecular lines composed of polyacenequinone units via repetitive Diels-Alder reactions (2,3). The Diels-Alder reaction has also been identified as a route to other novel belts or collars (4-9). In this manuscript we summarize our recent work on the synthesis of six-membered rings using cycloproparenes (10) as starting materials.The reaction is exemplified below using the simplest cycloproparene, benzocyclopropene 1. Other examples in which benzocyclopropenes have been dimerized by silver ion in chloroform to yield dimers connected by six-membered rings are presented in Table 1.