Pentacoordinate Siliconate Tetraanionic Molecular Squares. Synthesis, Structure, and Solution Conformation of a Novel Tetraanion−Tetracation Ion Pair

Abstract

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.

Chiral Polymers of Intrinsic Microporosity: Selective Membrane Permeation of Enantiomers

“…Porosity originates solely from the molecular structure,w hich is independent of processing history. Racemic 1 has also been used as abuilding block for siliconate tetraanionic molecular squares [21][22][23][24] and tetraanionic organoborate squares,aswell as for the synthesis of racemic PIMs. [18][19][20] All PIMs reported to date have been achiral, and all reported studies of materials incorporating 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI(1)) have utilized the racemic form.…”

Tetraanionic Organoborate Squares Glued Together by Cations To Generate Nanotubular Stacks

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5',6, hereafter LH 4 )

, which is easily obtained in racemic form, is an attractive building block for the construction of functional solids, because of its ready availability, its rigid angularity, and its chirality. [1] Although no X-ray crystallographic data are available, NMR spectroscopy indicates that a single diastereoisomer with C 2h symmetry containing the two L 4À enantiomers in equal numbers is selectively formed. [1] Although no X-ray crystallographic data are available, NMR spectroscopy indicates that a single diastereoisomer with C 2h symmetry containing the two L 4À enantiomers in equal numbers is selectively formed.

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“…[1] Although no X-ray crystallographic data are available, NMR spectroscopy indicates that a single diastereoisomer with C 2h symmetry containing the two L 4À enantiomers in equal numbers is selectively formed. Shea and co-workers have reported that reaction of LH 4 with phenyltriethoxysilane under basic conditions generates tetraanionic molecular squares of composition [(C 6 H 5 Si) 4 L 4 ] 4À , in which the silicon centers have five-coordinate environments that are probably close to square pyramidal with a square O 4 base defined by two L 4À units.…”

“…When the two locally chiral doubly chelated molybdenum centers in [(MoO 2 ) 2 L 2 ] 4À have the same absolute configuration, and when the two L 4À units are of the same chirality, a relatively strain-free 2:2 association is formed. [1] Preliminary synthetic and structural exploration indicates that many nitrogen bases, upon reaction with LH 4 and B(OMe) 3 , yield tetragonal crystalline products, in which either all squares in a column have the same chirality (given by Et 3 N, Me 3 N, Me 2 NCH 2 CH 2 NH 2 , Et 2 NCH 2 CH 2 OH, BzEt 2 N, and piperazine) or squares of opposite chirality alternate within a column (given by NH 2 (CH 2 ) n NH 2 (n = 2, 3, or 6), NH 3 , N 2 H 4 , Et 2 NOH, and triethylenetetramine). The two catechol groups are essentially coplanar in the case of [(C 6 H 5 Si) 4 L 4 ] 4À , thereby providing the O 4 base of a square pyramidal coordination environment, and are essentially orthogonal in the case of [B 4 L 4 ] 4À , forming a tetrahedral coordination environment.…”

“…Shea and co-workers have reported that reaction of LH 4 with phenyltriethoxysilane under basic conditions generates tetraanionic molecular squares of composition [(C 6 H 5 Si) 4 L 4 ] 4À , in which the silicon centers have five-coordinate environments that are probably close to square pyramidal with a square O 4 base defined by two L 4À units. [1] Although no X-ray crystallographic data are available, NMR spectroscopy indicates that a single diastereoisomer with C 2h symmetry containing the two L 4À enantiomers in equal numbers is selectively formed. Duhme and co-workers isolated Na 4 [(MoO 2 ) 2 L 2 ] from the reaction of LH 4 with sodium molybdate.…”