Search Results for "nanohoop"

Nanohoop of linked napthlylene groups

Itami continues to design novel macrocycles containing aromatic rings (see this post). This latest paper reports the synthesis of the first nanohoops containing naphthylenes, namely [9]cyclo-1,4-naphthylene 1.1 Since the macrocycle contains an odd number of naphthylene units, the lowest energy conformation is of C2 symmetry with one of the naphthylene rings in the plane of the macrocycle. (See Figure 1 for the B3LYP/6-31G(d) optimized structure). This conformation gives rise to 27 peaks in the proton NMR, and while the value of the computed chemical shifts differ from the experimental ones by about 0.5 to 1 ppm, their relative ordering is in very nice agreement.

1

2

Figure 1. B3LYP/6-31G(d) optimized geometries of 1 and the racemization transition state 2.

Itami also notes that 1 is chiral and computed the barrier for racemization of 19.9 kcal mol-1¸ through the transition state 2, also shown in Figure 1. This racemization process is compared with the racemization of 1,1’-binaphthyl.

References

(1) Yagi, A.; Segawa, Y.; Itami, K., "Synthesis and Properties of [9]Cyclo-1,4-naphthylene: A π-Extended Carbon Nanoring," J. Am. Chem. Soc. 2012, 134, 2962-2965, DOI: 10.1021/ja300001g

InChIs

1: InChI=1/C90H54/c1-2-20-56-55(19-1)73-37-38-74(56)76-41-42-78(60-24-6-5-23-59(60)76)80-45-46-82(64-28-10-9-27-63(64)80)84-49-50-86(68-32-14-13-31-67(68)84)88-53-54-90(72-36-18-17-35-71(72)88)89-52-51-87(69-33-15-16-34-70(69)89)85-48-47-83(65-29-11-12-30-66(65)85)81-44-43-79(61-25-7-8-26-2(61)81)77-40-39-75(73)57-21-3-4-22-58(57)77/h1-54H/b75-73-,76-74-,79-77-,80-78-,83-81-,84-82-,87-85-,88-86-,90-89-
InChIKey=WUFIQFYLEOBLMY-YNQZQJAJBX

nanohoops Steven Bachrach 27 Mar 2012 No Comments

Chiral Nanohoops

Single-walled carbon nanotubes (SWNT) can be thought of as built from component macrocycles, often called nanohoops. So, for example, cycloparaphenylenes like 1 can be the thought of as the precursor (at least in principle) of armchair SWNTs. To create chiral SWNTs, Itami1 has suggested that cycloparaphenylene-naphthalene (2) and other acene substituted macrocycles would serve as appropriate precursors.


1


2

Itami has synthesized 2 (having 13 phenyl groups and one naphthyl group) and also examined the ring strain energy and racemization energy of a series of these types of compounds at B3LYP/6-31G(d). As might be expected, based on studies of the cycloparaphenylenes themselves,2,3 ring strain energy decreases with increasing size of the macrocycle. So, for example, the macrocycle with one naphthyl group and 5 phenyl rings has a strain energy of 90 kcal mol-1, but the strain is reduced to 40 kcal mol-1 with 13 phenyl rings.

The macrocycle 2 and related structures are chiral, existing in P and M forms. The racemization involves first rotation of the naphthyl group, as shown in Figure 1, with a barrier of about 8 kcal mol-1. The direct product has the opposite stereochemistry but is not in the lowest energy conformation. Rotations of some phenyl groups remains to occur, but these rotations are expected to have a barrier less than that for the rotation of the naphthyl group, based on the previous study of cycloparaphenylenes. Again, the racemization barrier decreases with the size of the macrocycle.

(P)-2

2-TS

(M)-2’

Figure 1. B3LYP/6-31G(d) optimized structures along the racemization pathway of 2.

References

(1) Omachi, H.; Segawa, Y.; Itami, K., "Synthesis and Racemization Process of Chiral Carbon Nanorings: A Step toward the Chemical Synthesis of Chiral Carbon Nanotubes," Org. Lett., 2011, 13, 2480-2483, DOI: 10.1021/ol200730m

(2) Segawa, Y.; Omachi, H.; Itami, K., "Theoretical Studies on the Structures and Strain Energies of Cycloparaphenylenes," Org. Lett., 2010, 12, 2262-2265, DOI: 10.1021/ol1006168

(3) Bachrach, S. M.; Stuck, D., "DFT Study of Cycloparaphenylenes and Heteroatom-Substituted Nanohoops," J. Org. Chem., 2010, 75, 6595-6604, DOI: 10.1021/jo101371m

InChIs

2: InChI=1/C88H58/c1-2-60-4-3-59(1)61-5-9-63(10-6-61)65-13-17-67(18-14-65)69-21-25-71(26-22-69)73-29-33-75(34-30-73)77-37-41-79(42-38-77)81-45-49-83(50-46-81)85-53-55-88-58-86(54-56-87(88)57-85)84-51-47-82(48-52-84)80-43-39-78(40-44-80)76-35-31-74(32-36-76)72-27-23-70(24-28-72)68-19-15-66(16-20-68)64-11-7-62(60)8-12-64/h1-58H/b61-59-,62-60-,65-63-,66-64-,69-67-,70-68-,73-71-,74-72-,77-75-,78-76-,81-79-,82-80-,85-83-,86-84+
InChIKey=VXOGKWSXPGSUSO-ZMOMEJFTBU

nanohoops Steven Bachrach 31 May 2011 9 Comments

Nanobelt

The synthesis of components of nanostructures (like fullerenes and nanotubes) has dramatically matured over the past few years. I have blogged about nanohoops before, and this post presents the recent work of the Itami group in preparing the nanobelt 1.1


1

The synthesis is accomplished through a series of Wittig reactions with an aryl-aryl coupling to stitch together the final rings. The molecule is characterized by NMR and x-ray crystallography. The authors have also computed the structure of 1 at B3LYP/6-31G(d), shown in Figure 1. The computed C-C distances match up very well with the experimental distances. The strain energy of 1, presumably estimated by Reaction 1,2 is computed to be about 119 kcal mol-1.

1

Figure 1. B3LYP/6-31G(d) optimized structure of 1.

Rxn 1

NICS(0) values were obtained at B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d); the rings along the middle of the belt have values of -7.44ppm and are indicative of normal aromatic 6-member rings, while the other rings have values of -2.00ppm. This suggests the dominant resonance structure shown below:

References

1) Povie, G.; Segawa, Y.; Nishihara, T.; Miyauchi, Y.; Itami, K., "Synthesis of a carbon nanobelt." Science 2017, 356, 172-175, DOI: 10.1126/science.aam8158.

2) Segawa, Y.; Yagi, A.; Ito, H.; Itami, K., "A Theoretical Study on the Strain Energy of Carbon Nanobelts." Org. Letters 2016, 18, 1430-1433, DOI: 10.1021/acs.orglett.6b00365.

InChIs:

1: InChI=1S/C48H24/c1-2-26-14-40-28-5-6-31-20-44-32(19-42(31)40)9-10-34-24-48-36(23-46(34)44)12-11-35-21-45-33(22-47(35)48)8-7-30-17-41-29(18-43(30)45)4-3-27-15-37(39(26)16-28)25(1)13-38(27)41/h1-24H
InChIKey=KJWRWEMHJRCQKK-UHFFFAOYSA-N

Aromaticity &nanohoops Steven Bachrach 22 May 2017 No Comments

Host-guest complexes

Grimme and coworkers have a featured article on computing host-guest complexes in a recent ChemComm.1 They review the techniques his group has pioneered, particularly dispersion corrections for DFT and ways to treat the thermodynamics in moving from electronic energy to free energy. they briefly review some studies done by other groups. They conclude with a new study of eight different host guest complexes, three of which are shown in Figure 1.

1

2

3

Figure 1. TPSS-D3(BJ)/def2-TZVP optimized structures of 1-3.

These eight host-guest complexes are fairly large systems, and the computational method employed means some fairly long computations. Geometries were optimized at TPSS-D3(BJ)/def2-TZVP, then single point energy determined at PW6B95-D3(BJ)/def2-QZVP. Solvent was included using COSMO-RS. The curcurbituril complex 2 includes a counterion (chloride) along with the guest adamantan-1-aminium. Overall agreement of the computed free energy of binding with the experimental values was very good, except for 3 and the related complex having a larger nanohoop around the fullerene. The error is due to problems in treating the solvent effect, which remains an area of real computational need.

An interesting result uncovered is that the binding energy due to dispersion is greater than the non-dispersion energy for all of these complexes, including the examples that are charged or where hydrogen bonding may be playing a role in the bonding. This points to the absolute necessity of including a dispersion correction when treating a host-guest complex with DFT.

As an aside, you’ll note one of the reasons I was interested in this paper: 3 is closely related to the structure that graces the cover of the second edition of my book.

References

(1) Antony, J.; Sure, R.; Grimme, S. "Using dispersion-corrected density functional theory to understand supramolecular binding thermodynamics," Chem. Commun. 2015, 51, 1764-1774, DOI: 10.1039/C4CC06722C.

Grimme &host-guest Steven Bachrach 12 May 2015 1 Comment

Fantastic host-guest complex

Check out this an incredibly cool host guest complex: the [10]-cycloparaphenylene ([10]CPP) hoop encapsulating C60!1

(Be sure to click on this image to bring up the 3-D interactive structure – as with all structures in my blog!)

1H and 13C NMR and fluorescence quenching spectrometry clearly indicate that this complex is formed when [10]CPP is mixed with C60 in toluene. In fact, when C60 is mixed with a mixture of nanohoops ranging from 8 to 12 phenyl ring, only the [10]CPP hoop complexes with the fullerene. The experimental binding energy is between 38 and 59 kJ mol-1.

M06-2x/6-31G* computations give the structure shown above. The computed binding energy is 173 kJ mol-1, but the computations do not include solvent. So this overestimation might be somewhat due to the difference in gas phase vs. solution complexation.

(Check out this post for other interesting nanohoops.)

References

(1) Iwamoto, T.; Watanabe, Y.; Sadahiro, T.; Haino, T.; Yamago, S., "Size-Selective Encapsulation of C60 by [10]Cycloparaphenylene: Formation of the Shortest Fullerene-Peapod," Angew. Chem. Int. Ed., 2011, 50, 8342-8344, DOI: 10.1002/anie.201102302

nanohoops Steven Bachrach 13 Sep 2011 2 Comments