Baran Group Meeting
02/15/06
Platonic Hydrocarbons
Ryan Shenvi
Background
The knowledge at which geometry aims is knowledge of the eternal, and
not of aught perishing and transient . . . My noble friend, geometry will
draw the soul towards truth, and create the spirit of philosophy, and
raise up that which is now unhappily allowed to fall down. . . Nothing
should be more sternly laid down than that the inhabitants of your fair
city by all means learn geometry.
Platonic hydrocarbons are the corresponding carbogens, where each vertex is a carbon,
each edge a bond, and each face a ring.
–Plato (ca. 427-347 BC)
“The Republic,” ca. 370 BC
en arch hn o logoz kai o logoz hn proz ton qeon kai qeon hn o
logoz In the beginning was the word (logos) and the word was with
God and the word was God.
–St. John, (ca. 10 AD-100 AD)
“The Gospel of John,” ca. 96 AD
• Not all platonic solids translate to platonic hydrocarbons; limited by carbon valence,
bonding angles, and strain. Octahedrane and icosahedrane have not been prepared,
nor has unsubstituted tetrahedrane.
• However, numerous inorganic molecules adopt these geometries:
What are the 'platonic hydrocarbons'?
Platonic Solids:
• Regular solids, regular polyhedra: convex polyhedra whose faces are equivalent,
convex regular polygons.
• Discovered 'first' by the neolithic Scots, ca. 1300-1400 BC.
C2B10H12
carboranes
• Described mathematically by Theaetetus (417 BC-369 BC), who proved the existance
of 5 and only 5 regular solids; included in Euclid's Elements, Book X.
Polyhedron
Tetrahedron
Hexahedron
Octahedron
Dodecahedron
Icosahedron
Faces
4
6
8
12
20
Edges
6
12
12
30
30
Vertices
4
8
6
20
12
Symmetry Group
Td
Oh
geometric duals
Oh
Ih
Ih geometric duals
• Included in Plato's Timaeus as part of his 'theory of everything,' which assigned the
regular geometry of the solids to each of the elements: earth, water, air, fire, and ether
(an element of order or logic added to the original elements described by Emedocles
of Agrigentum, 495-435 BC).
• In 1852, Schläfli proved the existance of exactly six regular polyhedra in four dimensions and three in all higher dimensions (some may be familiar with the hypercube,
or tesseract, of A Wrinkle in Time fame).
[Zr6Cl18]3–
• Tetrahedrane and cubane have been called "super s-aromatic and super s-antiaromatic,
respectively:
Cyclopropane exhibits strong s-aromaticity as evidenced by its 1. large diamgnetic susceptibility and anisotropy, 2. upfield shifts of attached protons, 3. shielding of protons
above its ring and 4. a stabilization of 11.3 kcal/mol (compare 33.2 kcal/mol for benzene).
Cyclobutane exhibits strong s-antiaromaticity: 1. similarity to cyclopropane's strain (27.5
vs. 26.5 kcal/mol), 2. abnormally low diamagnetic susceptibility, 3. deshielded 1H and
13C shifts.
Planar cyclopropane, cyclobutane, tetrahedrane, and cubane dissected nucleus-independent
chemical shift grids. Red and green points denote positive and negative NICS values, respectively
Baran Group Meeting
02/15/06
Platonic Hydrocarbons
Ryan Shenvi
Dodecahedrane
DODECAHEDRANE
O
CO2Me
Considerations:
• tandem bond-forming events
require proper alignment
• severe entropic disadvantage
in dimerization events
• new bonds must form on the
endo face
O
Late-stage reactions must
all be able to take place from
the exo-face.
KOH (aq.), MeOH;
I2, NaHCO3
(94%)
O
O
c) Zn/Cu, MeOH
(78%)
I
O
CO2Me
CO2Me
Ph
heat, high pressure,
irradiation, transition
metals . . .
MeO2C
O
O
CO2Me
H2, Pd/C, EtOAc
(100%)
O
(C10H10) + (C10H10)
(C15) + (C5)
(C16) + (C4)
Eaton et al,
JACS, 1972, 1014.
FAILED
Paquette et al,
JACS, 1978, 1600.
FAILED
O
MeO2C
H
HCl, MeOH
OH OH
Li/ NH3, BOMCl
Cl
F
I 2, TH
C
°
–80
H
CO2Me
+
MeO2C
H
H
a) hn
b) TsOH
c) HN=NH
OPh
a) hn
CO2Me
OPh
CO2Me
(i-Bu)2AlH
b) Li/ NH3
c) H3O+
MeO2C
PCC
H
H
H
H
H
H
CO2Me
+
CO2Me
CO2Me
(15-20%) 1 : 1
H
H
H
O
CHO
H
CO2Me
+
CO2Me
CO2Me
CO2Me
CO2Me
O
(48%)
CHO
H
Na
CO2Me
CO2Me
O
950
°C
CO2Me
OPh
Cl
(62%)
SUCCESS!
Paquette, L. A.; Ternansky, R. J.; Balogh, D. W. JACS, 1982, 104, 4502
Ni
(83%)
first non-meso
intermediate
O
O
O
b) P4O10, MsOH
O
CO2Me
H
(77%)
O CO2Me
NaBH4,
MeOH
(81%)
S
Ph
a) H2O2, MeOH
CO2Me
Woodward et al,
JACS, 1964, 3162.
FAILED
CO2Me
a) NaOH, MeOH
O
I b) H2SO4, Na2Cr2O7
a) KOH, EtOH
Pd/ C
b) hn
c) TsOH
d)HN=NH
250 °C
Baran Group Meeting
02/15/06
Prinzbach et al. Angew. Chem. Int. Ed. Engl. 1994, 2239.
O
Cl
Cl
Cl
Cl
Cl
Cl
O
S
Cl
O
Cl
Cl
A
Cl
Cl
Cl
TETRAHEDRANE
• Numerous attmpts towards its synthesis . . .
O
S Cl
Cl
Cl
[–SO2]
Cl
Cl Cl
Cl
D
Cl
H
Cl
Cl
Cl
Cl
D
Li, t-BuOH
c) Pd/C, 250 °C
(35%)
(95%)
Cl
O
O
O
H
TsLiN
O
• High-energy diradical-like intermediate can rapidly convert to its lower energy lumomer.
Cl
nearly equal energies
of activation
Cl H H
Cl
Cl
Cl
HOMO-LUMO crossing
through diradical bicyclobutane
Cl
Cl
hn
'bonding' interaction
between 'radicals,
and s-conjugation
~126
O
O
O
O
O
O Cu2O, bipy., H2O
E
~22
PhH, D
~32 (kcal/
mol)
a) B2H6•THF,
quinoline, 150 °C (73%)
b) NaOH, H2O2
c) CrO3, Me2CO
O
MeO2C
N
O
" . . . leaving as the only consolation the knowledge of how not to make tetrahedrane."
-Henning Hopf
• High-energy diradical-like intermediate can rapidly convert to its lower energy lumomer.
Cl
Cl
a) A, D
b) Li, t-BuOH
N
H
•
O
O
H2 transfer
NLiTs
Cl
Cl H
H
Cl
Cl
Cl
Cl
isodrin
(30%)
Platonic Hydrocarbons
Ryan Shenvi
Dodecahedrane
CO2Me
hn
O
N2
N2
O
MeOH
(95%)
a) HCO2Me, NaH
O
b) TsN3, Et3N
(83%)
'anti-bonding' interaction
between 'radicals and
through space interaction
with central bond
~94
Schematic representation of the MERP (minimum energy reaction path) for conversion of
tetrahedrane to cyclobutadiene.
• However, tetrahedrane (Estr= 126-140 kcal/mol) can be stabilized by 'corset effect.'
a) OH–
(76%) b) Pb(OAc)4, I2
CCl4, hn
c) Na-K, THF; t-BuOH
any movement away tetrahdral geometry increases tert-butyl
steric interactions, imparting kinetic stability
t-Bu
E
Pt/Re/Al2O3/H2
t-Bu
t-Bu
t-Bu
H
'black box'
DHf°
64.4
(Estr) (115.0)
Pagodane: 14 pots
24% overeall (90%/step)
250 °C
(3 - 8%)
– 42.2 kcal/mol
(–46.1)
H
22.2
(68.9)
H
H
decomposition
products
Rxn Coordinate
• Originally proposed and utilized by G. Maier et al in the first synthesis of a tetrahedrane
Maier, G. et al Angew. Chem. Int. Ed. Engl., 1978, 520.
Baran Group Meeting
02/15/06
Platonic Hydrocarbons
Ryan Shenvi
Platonic Hydrocarbons
Cubane (Hexahedrane)
t-Bu
O
t-Bu
t-Bu
t-Bu
hn
O
+
t-Bu
t-Bu
H
Eaton, P. E. et al. JACS 1964, 962.
Eaton, P. E. et al. JACS 1964, 3157.
H
O
hn
O
O
t-Bu
O
O
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
t-BuLi, DME
t-Bu
t-Bu
O
13C
t-Bu
t-Bu
Br
O
12%
8:3 t-hexane/
pentane
(Rigisolve)
–196 °C
(35%)
50% KOH (aq.) (30%)
130 °C,
cyclosilane
DHf = 144-159 kcal/mol
(calculated)
1H NMR: d = 4
t-Bu
t-Bu
hn (300 nm),
rt
t-Bu
t-BuO2
O
CO2H
2. t-BuO2H, HO C
2
Py.
(prepared by Fluorochem
in CA, and EniChem
Synthesis in Milan on a
multi-kilogram scale)
O
t-Bu
t-Bu
Br
+
Fe(CO)3
Br
Br
O
hn, PhH
CAN
O
(90%)
Br
O
Br
O
O
Br
O
hn
CO2Me
e–
aromatic 6p
cyclobutadiene
t-Bu
TMS
TMS
TMS
CpCo(CO)2
TMS
Co
TMS
2Li
Li, THF, rt
TMS
TMS
R = Me, H (2.85 ppm)
BrCH2CH2Br,
THF
(85%)
TMS
TMS
TMS
TMS
TMS
TMS
Sekiguchi, A. et al. JACS, 2003, 12684.
NC
b) SOCl2, D
(90%)
CN
HO2C O
a) CH2Cl2, (COCl)2;
THF, NH3, –78 °C
N(i-Pr)2
NC
TMS
TMS
TMS
pentane,
–100 °C
(50%)
CN
TMS
CO2
(90%)
N(i-Pr)2
NC
CN
(77%) a) BrMgTMP, THF,
–78 °C; CO2
(100%) b) KOH (aq), EtOH, D
HO2C O
TMS
O
BrMgTMP, THF,
–78 °C;
hn (254 nm),
MeLi, THF, rt
(67%)
TMS
N(i-Pr)2
CO2H
a) CH2Cl2, (COCl)2;
(99%)
THF, NH3, –78 °C
b) CHCl3, DMF, TMEDA (77%)
SOCl2, –10 °C
Eaton et al. JACS, 1993, 10202
NC O
N(i-Pr)2
–78 °C; CO2 NC
(85%)
TMS
R
Me2SO4,
C6D6, rt
OR
N(i-Pr)2
TMS
2–
O
Mg(TMP)2,
THF
NC
MeO2C
TMS
TMS
O2t-Bu
R. Pettit and co-workers JACS 1966, 1328.
hn
t-Bu
Li
100 °C
t-Bu
t-Bu
t-Bu
C6D6,
rt
1. SOCl2
diisopropylbenzene
t-Bu
t-Bu •
+
Br
Br
O
H
O
t-Bu
O
t-Bu
6N KOH, 2d t-Bu
(80%)
O
hn (254 nm),
t-Bu
O
t-Bu
NMR: d = 32.26, 28.33, 10.20
mp = 135 °C
t-Bu
t-Bu
t-Bu
Br
O
Br2, CCl4;
–10 °C to rt
2d
(22%)
O
hn, MeOH, HCl
3. Et3N
(40%)
O
O
+
t-Bu
TMS
1. NBS
2. Br2/ Br–
HO2C
HO2C
N(i-Pr)2
CO2H
LAH, THF, D;
Ac2O,
(89%)
AcO
AcO
OAc
N(i-Pr)2
OAc
DMDO, Me2CO;
SOCl2; Barton's
NaNHPT, DMAP;
t-BuSH, hn,
PhH (72%)
AcO
OAc
AcO
OAc
Baran Group Meeting
02/15/06
AcO
OAc
AcO
OAc
Cubane
10% NaOH (aq.)
KMnO4
HO2C
(85%)
HO2C
SOCl2, MeCN;
CH2Cl2, TMSN3;
CO2H
CO2H
CHCl3, D; DMDO,
Me2CO, H2O
(30%)
NO2
O2 N
O2N
NO2
4 equiv. NHMDS,
THF/MeTHF –78 °C;
N2O4, –130 °C, (74%)
i-pentane;
H+, Et2O
O2N
O2N
O2N
O2N
NO2
NO2
NO2
NO2
O3
(45-55%)
DHf = 81-144 kcal/mol
density ~ 1,9-2.2 g/cm
'leads to calculated detonation velocities
and pressures much higher than
that of TNT, 15-30% greater than HMX
and perhaps even better than CL-20,
the most powerful nonnuclear explosive
known.'
O2 N
O2N
O2N
O2N
NO2
NO
LHMDS, CH2Cl2
NO2
NO2
–78 °C
Me
O2 N
N
O2N
NO2
NO2
TNT
NO2
NO2
O2N
O2N
O2N
NO2
N
N
O2 N
NO2
H
O2N
O2N
NO2
N
O2N
N
N
NO2
HMX
NO2 N
N N
N
NO2
CL-20
NO2
Platonic Hydrocarbons
Ryan Shenvi