Synthesis of a Strained Spherical Carbon Nanocage by Regioselective Alkyne Cyclotrimerization

Abstract

The smallest spherical carbon nanocage so far, [2.2.2]carbon nanocage,h as been synthesized by the cationic rhodium(I)/H 8 -binap complex-catalyzed regioselective intermolecular cyclotrimerization of ac is-1-ethynyl-4-arylcyclohexadiene derivative followed by the triple Suzuki-Miyaura cross-couplings with 1,3,5-triborylbenzene and reductive aromatization. This cage molecule is highly strained, and its ring strain is between those of [6] and [5]cycloparaphenylenes.A significant red-shift of an emission maximum was observed, compared with that of known[ 4.4.4]carbon nanocage.T he sequential cyclotrimerizations of ac is-1,4-diethynylcyclohexadiene derivative with the same rhodium(I) catalyst followed by reductive aromatization failed to afford[ 1.1.1]carbon nanocage;i nstead, a b-graph-shaped cage molecule was generated. Figure 3. Energy diagrams of the frontier MOs of [4.4.4] and [2.2.2]carbonn anocages E (ref. [9b]) and 1 (left and middle, respectively). Two-way arrows represent HOMO-LUMO gaps. H = HOMO, L = LUMO. Pictorial representations of the frontier MOs of 1 (right). Scheme 2. Attempted synthesis of [1.1.1]carbon nanocage, which affords b-graph-shaped cage 12.T BAF = tetrabutylammonium fluoride.

A Fourfold Gold(I)−Aryl Macrocycle with Hyperbolic Geometry and its Reductive Elimination to a Carbon Nanoring Host

“…Other applications in a variety of research areas, such as sensing or imaging, have also been investigated [25–27] . Existing synthetic methodologies of ring or belt formation have been applied to extend the possible molecular shapes in the areas of macrocycles, [28] belts, [7–9, 29–31] lemniscates, [26, 32, 33] and cages [34–36] . Larger cyclic nanorings, such as molecular phenine nanotubes, [37–39] cyclo[ n ]porphyrins, [40] or cyclo[ n ]hexabenzocoronenes [41] were constructed from extended molecular subunits as building blocks in a macrocyclization strategy.…”

Ein vierfacher Gold(I)−Aryl‐Makrozyklus mit hyperbolischer Geometrie und dessen reduktive Eliminierung zu einem Kohlenstoffnanoring‐Wirt

“… [25–27] . Beschriebene präparative Methoden für CPPs wurden dazu benutzt die bekannten Strukturen im Bereich der Makrozyklen [28] um neue molekulare Gürtel, [7–9, 29–31] Schleifen (Lemniskate) [26, 32, 33] und Käfige zu erweitern [34–36] . Größere Nanoringe, wie etwa die Phenin‐Nanoröhren, [37–39] Cyclo[ n ]porphyrine [40] oder Cyclo[ n ]hexabenzocoronene [41] wurden aus großen molekularen Bausteinen in verschiedenen Makrozyklisierungen hergestellt.…”

Cycloparaphenylenesvia[2+2+2] cycloaddition

“…For example, they applied the cationic [Rh(H 8 -BINAP)] catalyst 26 to synthesize the appealing nanocage (Scheme 1). 32 First, they prepared the key building block 14 , which was also utilized in the syntheses of other bent aromatic systems. A cyclotrimerization of the terminal alkyne 14 liberated a C 3 -symmetric squid like compound 13 , which was then converted to the strain-reduced cage via a threefold Suzuki coupling.…”

“…Within this route the [2+2+2] CA is Scheme 1 Retrosynthetic perspective of Tanaka's nanocage. 32 This journal is © The Royal Society of Chemistry 2022 incorporated at a rather late stage of the synthesis rendering this approach feasible for a versatile functionalization. However, as the macrocyclization is performed in advance, there is no flexibility in size.…”