Cyclobis(paraquat‐p‐phenylene). A Tetracationic Multipurpose Receptor

Abstract

-90°C). When the temperature was near -60°C. quenching of the solution in water and standard workup afforded crude reaction products in ca. 90Yo yield (GC). Purification (recrystallization or column chromatography) gave pure products.[9] Only the Markownikoff regioisomer 9 (by GC and I3C NMR analyses) was fund to be present in yields of 69%-91% after quenching in water.Academic Press, Orlando, FL, USA 1984, Chapter 5, p. 341. Chem. 88 (1976 Cyclobis(paraquat-p-phenylene). A Tetracationic Multipurpose ReceptorBy Barbara Odell, Mark V. Reddington, Alexandra M. Z . Slawin, Neil Spencer, J. Fraser Stoddart,* and David J . WilliamsRecently, we reported''] on cyclophane-like molecular receptors, such as bisparaphenylene-34-crown-10 1, which contains n-electron-rich hydroquinone units for face-to-face complexation ( Fig. 1) with paraquat 2, a n-electron-deficient dication. These observations led us to propose that it might be possible to reverse constitutionally the roles of the receptor and the substrate and so bind a n-electronrich diphenol ether, such as 1,4-dimethoxybenzene 3a, inside a tetracationic molecular receptor (Fig. 1). Such a receptor is the tetracation cyclobis(paraquat-p-phenylene) 4 which incorporates two n-electron-deficient paraquat residues connected in a phane-like manner by means of two para-phenylene groups.[21 Here, we describe (i) the synthesis of 4 as its tetrakis(hexafluorophosphate) 4 . 4 PF,, (ii) its X-ray structural characterization as the acetonitrile solvate 4 . 4 PF6.3 MeCN, (iii) the UV and 'H-NMR spectroscopic evidence for 1 : 1 complex formation (a) between 4 . 4 PF6 and 1,2-, 1,3-, and 1,4-dimethoxybenzene 3a/3b/ 3c in acetonitrile (CD,CN) and (b) between 4 . 4 C I and 1,4-dihydroxybenzene 6 in water (D20)J3' and (iv) the results of molecular and semiempirical quantum mechanical calculations on 4 and on 4 . 2 MeCN.[ Fig. 1 Schematic representation of the basis for the proposal that the cyclobis(paraquat-p-phenylene) 4 should act as a tetracationic receptor for 1,4-dimethoxybenzene 3a.The procedure (cf. Ref.[2]) employed for the preparation of 4 -4 P F 6 starting from the bis(pyridinium) salt 5 and 1,4-bis(bromomethyl)benzene is outlined in Scheme 1. (Fig. 2, top) that 4 adopts a rigid centrosymmetric rectangular box-like conformation with the two paraquat units forming the longer sides and the two para-xylylene residues, the shorter ones. There is a 19" twist angle between the two pyridinium rings of each paraquat unit: in addition, there are deformations of both the paraquat and para-xylylene components producing a bowing of the sides of the cyclophane. Thus, the strain within the molecule is relieved by out-of-plane bending of the six aromatic rings and is distributed throughout the macrocycle with the maximum deviations associated with the exocyclic C-CH2 bonds emanating from the para-phenylene residues: these bonds subtend an angle of 14" with respect to each other whilst the two Ne-CH, bonds associated with the paraquat units subtend an angle of 23 O . There is also a con...

Dynamic donor–acceptor [2]catenanes

“…A cursory glance at the structure (24) of CBPQT 4ϩ suggests a facile nucleophilic attack on the benzylic methylene groups that should displace ( Fig. 2A) the positively charged bipyridinium group as a good nucleofuge or leaving group, aided and abetted by the considerable relief of ring strain (Fig.…”

“…These deformations are the most obvious in the bending of the exocyclic C-CH 2 and N ϩ -CH2 bonds emanating from the p-phenylene and bipyridinium residues: these bonds are at angles of 14°and 23°relative to each other (see ref. 24). The strain in the ring system is coupled with the inherently higher reactivity of benzylic position and with the nucleofugality of the bipyridinium to render the CBPQT 4؉ ring reactive toward nucleophilic substitution.…”

Electrochromic materials using mechanically interlocked molecules

“…[ [13][14][15] we have been developing in recent years in the shape of two-station [2]catenanes [16][17][18][19] are usually composed of the π-electron deficient tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT 4+ ) [20][21][22][23], and another π-electron rich ring, encompassing multiple binding sites (stations) for the CBPQT 4+ ring-for instance, tetrathiafulvalene (TTF) [24][25][26], 1,5-dioxynaphthalene (DNP) [27][28][29] and benzidine (BZ) [30,31], etc. When the π-electron deficient CBPQT 4+ ring resides on a π-electron rich binding site, the compound exhibits the color on account of charge-transfer (CT) between the CBPQT 4+ ring and the binding site [20][21][22][23][24][25][26][27][28][29][30][31].…”

“…When the π-electron deficient CBPQT 4+ ring resides on a π-electron rich binding site, the compound exhibits the color on account of charge-transfer (CT) between the CBPQT 4+ ring and the binding site [20][21][22][23][24][25][26][27][28][29][30][31]. In the case of the two-station [2]catenanes, we have designed an electrochemically controllable one, where the CBPQT 4+ ring resides preferentially at one or another binding sites in the ground and electrochemically oxidized states, respectively.…”

Tuneable pseudorotaxane formation between a biotin–avidin bioconjugate and CBPQT4+

“…7 The tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT 4+ , 1) has emerged as an important host molecule for electron-rich guests. 8 This is primarily due to: the ability to synthesize this cyclophane in reasonable quantities; 9 its ability to have its recognition properties tuned by redox processes; 10 its ability to form complexes in both organic and aqueous media 11 and its formation of guest-specific coloured complexes that conveniently allows guest exchange reactions to be monitored using UV-Vis spectroscopy. 12 Here, we report a biotinylated naphthalene derivative 2 that has the propensity to bind to avidin strongly.…”