Synthesis of a Five-Membered Molecular Necklace: A 2+2 Approach

Abstract

Like with a string of pearls, four molecular "beads" are threaded on a molecular rectangle to form a molecular necklace. This rectangular species is synthesized from two L-shaped, preorganized pseudorotaxanes with two molecular beads each (cucurbituril, schematically symbolized by the barrels), held together by Cu ions [Eq. (1)].

Materials Based on Glycoluril

“…[5] In this structure, 2 2 cucurbituril units are threaded onto two bisammonium ªhalf-chainsº, which are connected by metal coordination (Fig. 1).…”

An Introduction to the Mechanical Bond

“…Over the years, our own group has fabricated molecular shuttles, 174 switches, 175 push-buttons, 176 trains, 177 elevators, 178 pistons, 179 muscles, 180 abacuses, 181 motors, 182 and valves. 183 Other groups have reported MIMs as molecular necklaces, [184][185][186] locks, 187 rotors, 188 chameleons, 189 and charm bracelets 190 -the list goes on and on. These types of molecular nanostructures, whose names and representations are deliberately evocative, are known 191,192 also as technomimetic molecules.…”

“…They include (in order of appearance) (i) slippage 309 (Section 3.1), which involves the passage of a ring over a size-complementary stopper that is sufficiently bulky to prevent deslipping, (ii) olefin metathesis 310 (Section 3.4), which involves a catalysttypically Grubbs' Ru alkylidene catalysts-scrambling the constituents of double bonds, (iii) disulfide exchange (Section 3.5.1), which involves the oxidative coupling of thiols and reductive cleavage of disulfides, (iv) kinetically labile metal-ligand bonds (Section 3.2)-a revolution led by Makoto Fujita,202 (v) reversible nucleophilic substitutions (Section 3.5.2), such competing S N 2 processes 312 in dynamic equilibrium, (vi) imine bonds 129,315 (Section 3.3.1) whose reversible nature facilitates the self-assembly of MIMs, (vii) boronic esters 313 (Section 3.3.3) formed reversibly from boronic acids and diols, and (viii) self-assembled monolayers 314 (SAMs) (Section 3.6). We emphasize here that thermodynamically controlled reactions-especially olefin metathesis, metal coordination, and imine bonding-have been indispensible in orchestrating the self-assembly of many of the most exotic, beautiful, and challenging topologies and architectures including molecular necklaces, 184,186,190,247,316,317 handcuff catenanes, 259 331 and very large discrete rigid-rod oligorotaxanes. 138,300 3.…”

Cucurbiturilas

“…Alguns grupos bloqueadores são complexos metálicos, que são ligados aos eixos dos rotaxanos, quando estes possuem pontos de coordenação [86][87][88][89][90][91][92][93][94] . É possível criar estruturas do tipo colar de pérolas [95][96][97] , montando polirotaxanos a partir de oligômeros de poliacrilamidas e poliestirenos, além de estruturas tridimensionais como dendrímeros 83,98,99 . Pelo seu tamanho menor, os CB [5] e CB [6] são os mais utilizados para este propósito, uma vez que os grupos bloqueadores podem ser menores do que seriam com anéis mais largos sendo, portanto, mais facilmente sintetizados 65 .…”