Synthesis and Structures of π-Extended [n]Cyclo-para-phenylenes (n = 12, 16, 20) Containing n/2 Nitrogen Atoms

Abstract

[n]Cyclo-para-phenylene congeners of n = 12, 16, 20 with n/2 nitrogen atoms were synthesized via Pt-mediated one-pot macrocyclization reactions. The reaction allowed diversification of participating arylene numbers to afford a series of nanohoop molecules. Spectroscopic analyses in solution showed arylene rotations, and crystallographic analyses in crystals revealed an interesting packing motif. The nanohoop molecules were interwoven by the alkyl substituents in a thread-in-bead manner to form nanoporous packing structures in the crystal.is an interesting class of compounds.1 The [n]CPP macrocycles with para-linked phenylene units result in a unique hoop-shaped molecular structure possessing aromatic panels stood in parallel with the cylindrical axis of the molecule in the crystalline solid state. 13 Because of increasing interest in the structures of [n]CPP, a wide range of structural variations has quickly been accumulated within the past few years.4 Driven by our own curiosity, 3,5 we started utilizing large polycyclic aromatic hydrocarbons to design and synthesize belt-persistent macrocycles 5 and demonstrated that the tubular structures provided unique nanosized spaces to accommodate various guests. 6 In this Letter, we report π-extended, nitrogen-embedded [n]CPP congeners. The synthesis relied on the unexpected, favorable effects of an azaaromatic panel on Pt-mediated macrocyclization reactions.1c,5a We found that macrocyclization was effective in the presence of multiple (n/2) coordinating nitrogen atoms, and the number of participating units was randomized. 7,8 The nitrogen atoms also served as a probe for the dynamic behaviors to reveal rapid rotations of the arylene panels. Crystallographic analysis of one of the nitrogen-embedded congeners revealed that we may design porous organic crystals by utilizing the large hoop-shaped structure in combination with interwoven packing structures.The Pt-mediated macrocyclization reaction of arylene panels comprising one pyrenylene 2k,9 and two phenylene units was first examined for π-extension but failed to afford the desired macrocycles. 5 We synthesized a basic pyrenylene unit 2 with two borylated phenylene groups from brominated precursor 1 and subjected it to a macrocyclization reaction with [PtCl 2 (cod)] (Scheme 1a). Unexpectedly, we could not detect any macrocyclic Pt-complexes by MS analysis of the crude mixture. As an assignable species, we detected only an L-shaped biarylated Pt-complex.As an alternative arylene motif, we next introduced diazapyrenylene by adopting a synthetic strategy developed by one of the authors.10 A concise synthesis route for bromophenylated 1,8-diazapyrene 3 allowed us to introduce two nitrogen atoms and two hexyl substituents in the precursor unit for macrocyclization (Scheme 1b). Thus, after transforming 3 into a borylated synthetic intermediate 4 via Miyaura borylation with 30 mol % of [Pd(dppf)Cl 2 ]¢CH 2 Cl 2 (dppf: 1,1¤-bis(diphenylphosphino)ferrocene), we examined the platinum-mediated macrocyclization. Previous reactio...

An Obtuse‐angled Corner Unit for Fluctuating Carbon Nanohoops

“…We next describe the crystal structure of 5‐mer 4 . To the best of our knowledge, this is the largest CPP hydrocarbon structure that has been unequivocally determined by X‐ray crystallography . As shown in Figure a, the aromatized structure was found to be an oval‐shaped ring.…”

“…We next describe the crystal structureo f5 -mer 4.T ot he best of our knowledge,t his is the largestC PP hydrocarbon structure that has been unequivocally determined by X-ray crystallography. [26] As shown in Figure 3a,t he aromatized structure was found to be an oval-shaped ring. Upon aromatization from 3 to 4,t he directing anglesw ere widened by 408 to 1628 on average,w hich originated from the completiono ft he sp 2hybridized carbon networks in ah oop-shaped structure.…”

Conjugated Nanohoops Incorporating Donor, Acceptor, Hetero‐ or Polycyclic Aromatics

“…32 [76] 344 7.3 10 4 427 0.80 --27 [46] 345 2.8 10 4 541 0.11 -À2.39 [c,e] 28 [46] 349 9.2 10 4 544 0.13 -À2.32 [c,e] 29 [46] 353 1.1 10 4 542 --À2.39 [c,e] 30 [47] 342 5.5 10 4 --0.67 [d,f ] À2.18 [f ] 33 [77] 345 1.2 10 5 ----34 [65] 327 5. [71] 27-29, [46] 30, [47] 32, [76] 33, [77] [n]31, [78] and 34. [79] nitrogen atoms from 340 nm ([n]CPPs) to 353 nm (29).…”

“…In 2016, the groups of Chiba and Isobe incorporated 1,8diazapyrene units into [n]CPPs to obtain nanohoops [n]31 (n = 3-5). [78] While preliminary studies using a 2,7-diphenylpyrene unit in a Pt-mediated coupling reaction (Scheme 1 c) of boronic esters did not furnish any macrocycles, the introduction of nitrogen atoms into the structure allowed for the synthesis of [n]31. The nanohoops showed simple NMR spectra due to the fast conformational fluctuation of their structures, even at À60 8C.…”

Stereoisomerism, crystal structures, and dynamics of belt-shaped cyclonaphthylenes

“…1), and the atropisomerism uniquely originated from restricted sp 2 -sp 2 rotations due to macrocyclic ring strain (12). However, the experimental relationship between the structure and dynamics of the arylene rotations in the nanohoops remains unclear (13)(14)(15)(16) and will add novel insight to biaryl atropisomerism with structural and historical importance (17)(18)(19)(20). We herein report our first attempt to reveal the structure-dynamics relationship in belt-shaped nanohoop molecules via the synthesis of a series of [n]cyclo-amphi-naphthylenes ([n]CaNAP, n = 6-11; Fig.…”