Strain‐Induced Double Carbon–Carbon Bond Activations of Cycloparaphenylenes by a Platinum Complex: Application to the Synthesis of Cyclic Diketones

Abstract

The carbon-carbon (CÀC) bond activation of [n]cycloparaphenylenes ([n]CPPs) by atransition-metal complex is herein reported. The Pt 0 complex Pt(PPh 3 ) 4 regioselectively cleaves two C À C s bonds of [5] CPP and [6]CPP to give cyclic dinuclear platinum complexes in high yields.Theoretical calculations reveal that the relief of ring strain drives the reaction. The cyclic complex was further transformed into acyclic diketone by using aCOinsertion reaction.Cycloparaphenylenes (CPPs;S cheme 1) have attracted immense scientific interest because of their fascinating structure,p hysical properties,a nd potential applications in materials science.T his interest originates from their nonplanar and conjugated structure corresponding to the shortest cyclic structural unit of an armchair carbon nanotube. [1] After the successful bottom-up organic synthesis of CPPs by Jasti and Bertozzi et al., [2] Itami et al., [3] and Yamago et al., [4] CPPs of various sizes, [5][6][7] and their derivatives, [8] are available,a nd their unique physical properties,s uch as size-dependent photophysical [9] and redox properties [7a, 10] and host-guest chemistry, [11] have been unveiled. In particular, recent achievements in the large-scale synthesis of CPPs by the groups Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/anie.201806591. Scheme 1. Possible reactions of [n]CPP with atransition-metal complex. Ma nd Ld enote metal and ligand, respectively. Scheme 2. The CÀCactivation of [n]CPPs and subsequent transformation.

Synthesis of Belt- and Möbius-Shaped Cycloparaphenylenes by Rhodium-Catalyzed Alkyne Cyclotrimerization

“…7 In 2017, Itami successfully applied this nickel(0)-mediated aryl−aryl coupling to the synthesis of CNBs, 8,9 but the yields were low presumably due to the strain-relieving reversible oxidative addition of the product carbon−carbon bonds to a nickel(0) complex (Figure 1c). 10 Very recently, Niao and Chi achieved the high-yielding CNB synthesis, in which the belt-forming Scholl reaction step is accompanied by either a small increase or even a decrease in strain energy. 11 For the Mobius-shaped molecules, several examples of the synthesis of Mobius-shaped π-conjugated rings, in which π components are linked by single πand/or σ-bonds, have been reported, but it is necessary to disturb the rotation of the ring around this σ-bond to keep the Mobius structure or prevent racemization.…”

“…Whereas, four sequential cyclotrimerizations of cyclic pentadecayne 2 afford triyne C in which the 1,4-diphenoxy-2-butyne moiety locates between two phenylacetylene moieties. The cyclotrimerization of C using a chiral rhodium(I) catalyst may proceed enantioselectively by twisting 180°to give enantioenriched Mobius-shaped [10]CPP (4) through strained rhodacycle D (Scheme 1c). 22 We investigated the synthesis of cyclic polyynes 1 and 2 by macroetherification of hydroquinone-derived diyne 5 with ditosyloxy monoyne 6.…”

Impact of Cyclic Strain on the Structural Relaxation Dynamics of Macrocyclic Thiophenes

“…Note that due to relatively large molecular size of C-NT NV with two kinds of bridges, vinylene and ethynylene ones, and the aforementioned significant structural distortions in large macrocycles, calculations and comparison of cyclic strain energies, which were widely described for cyclacenes and cycloparaphenylenes, were impractical for our macrocycles. 48,49 Along with initial anisotropy, the rates of TAA decays are also dependent on ring size. The smaller rings show slower decays despite their lower r 0 values, which is most obvious for data obtained from the highest energy excitation (Figures 2 and S4).…”

“…Note that due to relatively large molecular size of C- N T N V with two kinds of bridges, vinylene and ethynylene ones, and the aforementioned significant structural distortions in large macrocycles, calculations and comparison of cyclic strain energies, which were widely described for cyclacenes and cycloparaphenylenes, were impractical for our macrocycles. , …”

Strain Visualization for Strained Macrocycles

“…Macrocyclic strain is leveraged in chemical biology for bioorthogonal reactivity 1,2 and in polymer chemistry for ring opening metathesis. 3,4 Additionally, graphitic macrocycles, such as carbon nanohoops, 5 have enhanced solubility, 6 remarkable photophysical properties, 7,8 and reactivity [9][10][11][12] that all arise from strain. These attributes, and improvements in methods for their synthesis, [13][14][15][16] have caused a renewed interest in strained macrocyclic molecules.…”