M i l j a n i ć G r o u p M e e ti n g / L i t e r a t u r eU n i v e r s i t y o f H o u s t o n ▪ H o u s t o n , T X ▪ J a n u a r y 1 6 t h 2 0 0 9

Gary L loyd L im

ParacyclophenylenesCarbon Nanohoop Structures

Great Minds behind the Research

Carolyn BertozziPhD—University of California, Berkeley (1993)Predoc—Office of Naval Research (1988–1991)Diploma—Harvard University (1988)Professor at University of California, Berkeley

Jeffrey NeatonPostdoc—Rutgers University, Physics (2000–2003)

The Molecular Foundry, LBNL (2003–2005)PhD (Physics)—Cornell University (2000)Diploma—University of Minnesota (1995)Facility Director—Theory of Nanostructured Materials Facility

Joydeep Bhattacharjee—NCN Postdoc

Ramesh Jasti—University of California, Berkeley

Jasti, R.; Bhattacharjee, J.; Neaton, J.; Bertozzi, C. J. Am. Chem. Soc. 2008, 130, 17646.

California and Its Diversity

• Located on West Coast of the US

• 3rd largest state (163, 696 sq. mi.)

• Capital city is Sacramento

• Most populous state (36,756,666)

• Gross State Product of $1.812 trillion (2007)

• Climate varies from Mediterranean to subartic

• Well-known Universities in California:

University of California (10 campuses)

California Institute of Technology

Stanford University

Cycloparaphenylene Is a Synthetic Challenge

n

strained and distorted aromatic systems

Parekh, V. C.; Guha, P. C. J. Indian Chem. Soc. 1934, 11, 95.Jagedeesh, M. N.; Makuy, A.; Chandrasekhar, J. J. Mol. Model. 2000, 6, 226.

radially oriented p-orbitals

MeO OMe

I I

provides the curvature and rigiditynecessary for macrocyclization

3,6-syn-dimethoxy-cyclohexa-1,4-diene

Macrocylic precursors were prepared

MeO OMe

Bpin Bpin

MeO OMe

Bpin Bpin

MeO OMe

I I

Pd(PPh3)4, Cs2CO3

toluene/methanol (10:1), 80 oC

MeO

MeO OMe

m

OMe m = 2, 2% 3, 10% 5, 10%

Alonso, F.; Yus, M. Tetrahedron 1991, 47, 7471.Song, Z. Z.; Wong, H. N. C. J. Org. Chem. 1994, 59, 33.

MeO OMe

I I

I

I

1. i. nBuLi, THF, -78 oC ii. benzoquinone

2. i. NaH, THF, O oC ii. MeI, O oC to room temp.

i. nBuLi, THF, -78 oC

ii. isopropyl pinacol boronate (Bpin), -78 oC

34%

It is possible to convert cyclohexadiene moiety to aryl ring

MeO

.

e-

MeO

Lie-

Liu, H.-J.; Yip, J., Shia, K.-S. Tetrahedron Lett. 1997, 38, 2253.

MeO

MeO OMe

m

OMe

n

Li+-

THF, -78 oC

n = 5, 43% 8, 52% 14, 36%

.

What are the Properties of the Cycloparaphenylenes?

Nijegorodov, N. I.; Downey, W. S.; Danailov, M. B. Spectrochim. Acta, Part A 2000, 56, 783.

n

UV-Vis Absorption Spectra: lmax ≈ 340 nm

Fluorescence Spectra: as carbon nanohoop size decreases, the Stokes shift increases

Rings Are in a Staggered Configuration

Even-membered nanohoops, [12]- and [18] cycloparaphenylenes, have dihedral angles of 33o and 34o between two adjacent phenyl rings

Strain energies of 28 and 5 kcal mol−1 with diameters of 1.7 and 2.4 nm, respectively

Odd-membered nanohoop, [9] cycloparaphenylene, has varying dihedral angles of 18o, 30o, 31o and 34o around the carbon nanohoop

Strain energy of 47 kcal mol−1 with a diameter of 1.2 nm

Understanding its properties using Density Functional Theory

Eg = IP – EA – Ee-h IP = ionization potential

EA = electron affinity

Ee-h = electron-hole interaction energy

•IP – EA decreases as the number of phenyl rings increase

•Ee-h grows dramatically with the decreasing number of phenyl rings

Large Stokes shift observed is governed by the degree of structural relaxation in the optically excited state

Enhanced curvature leads to greater sp3 hybridization and increasingly asymmetric p-orbital

Cycloparaphenylenes Are Remarkable

1) Cycloparaphenylenes can be synthesized using a masked aromatic ring moiety

2) Cycloparaphenylenes are subunits of an armchair carbon nanotube

3) Possible route to extended carbon nanotubes using solution-phase chemistry

4) Preparation of carbon nanotubes of a specific chirality