Much Ado About Nothing:Much Ado About Nothing:The Platonic Solids andThe Platonic Solids andHydrocarbon ChemistryHydrocarbon Chemistry

Chris GallifordChris Galliford

20th January 200420th January 2004

Introduction - The Platonic SolidsIntroduction - The Platonic Solids

www.sbu.ac.uk/water/ platonic.html

•According to Plato, the matter surrounding us and out of which we are made is composed of four elements: fire, earth, water and air. •A fifth element also exists, not part of the physical world, but provides the basis for the construction of the ”heavenly matter”, or ”ether”, and is responsible for the ”beautiful order” of the universe.

•These five elements are assigned characteristic regular polyhedra - the tetrahedron (fire), the cube (earth), the octahedron (water), the icosahedron (air) and the pentagonal dodecahedron (ether).•These platonic solids are both pleasing aesthetically, and when considered as a hydrocarbon framework, provide interesting synthetic challenges.

TetrahedraneTetrahedrane

•Tetrahedrane is the only platonic hydrocarbon which has not yet been prepared in unsubstituted form.•126-140 kcal/mol calculated strain energy, kinetically and thermodynamically highly unstable.

Tetra-Tetra-terttert-Butyl -Butyl TetrahedraneTetrahedrane

•The stability of tetra-tert-butyltetrahedrane compared to tetrahedrane is attributed to the ”corset effect”.•Intramolecular repulsion between the four tert-butyl groups is at a minimum when their mutual distance is at a maximum. This condition is satisfied by the symmetry of a tetrahedron

G. Maier & S. Pfriem Angew. Chem. Int. Ed. Engl. (1978), 17, 520

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

SiR3

CubaneCubane

Cubane, C8H8 was first synthesized by Eaton and Cole in 1964.

Octa- and other polynitrocubane derivatives Have attracted considerable military interest, The non-shock sensitive ONC is reported to be 30% more explosive than it’s nearest non-nuclear alternative!

P.E. Eaton & T.W. Cole J. Am. Chem. Soc., (1964), 86, 962-964.P.E. Eaton & T.W. Cole ibid., (1964), 86, 3157-3158.P.E. Eaton et al.Propellants, Explosives and Pyrotechnics, (2002), 27, 1-6.P.E. Eaton et al. Angew. Chemie. Int. Ed. Engl.,(2000), 39, 401-404.

Cubane Cubane - First Synthesis by Eaton- First Synthesis by Eatonand Coleand Cole

Br

O

OBr

Br

OBr

OO

Br

Br

OO

O

Br

O

O

HO2C

Br

O

Br

O

O

CO2H

t-BuO3CBr

O

O

1. (CH2OH)2/H+

2. HCl(aq)(85% combined)

hν(95%)

10% KOH(aq)(95%)

1. SOCl22. t-BuO3H(95% combined)

cumene 152 oC(55%)

75% H2SO4(aq)(30%)

25% KOH(aq)(55%)

1. SOCl22. t-BuO3H(95% combined)3. diisopropylbenzene 100 oC (30%)

Cubane Cubane - An Alternative Synthesis- An Alternative Synthesisby Pettitby Pettit

R. Pettit, L. Watts & J. C. J. Am. Chem. Soc., (1966), 88, 1328-1329.

Fe(CO)3

O

O

Br

BrCe(IV)

O

O

Br

Br

O

O

Br

Br

CO2H

CO2H

hν

80% 90%

aq. KOH90%

SOCl2 followed byt-BuOOH, then Δ

DodecahedraneDodecahedrane

L.A. Paquette; D.W. Balogh & J.F. Blont J. Am. Chem. Soc., (1981), 103, 228-230.L.A. Paquette; G.G. Christophe; D.W. Balogh, D. Kountz, R. Usha Science (1981), 211, 575.L.A. Paquette; D.W. Balogh J. Am. Chem. Soc., (1982), 104, 774-783.L.A. Paquette; G.G. Christoph & D.W. Balogh, P.Engel, R. Usha ibid, (1982), 104, 784-7.

•The first dodecahedrane ever prepared was 1,16- dimethyl dodecahedrane in 19 steps in 1982 by Paquette and co-workers.

•Paquette reported the synthesis of the parent hydrocarbon by a similar route shortly afterwards.

Dodecahedrane Dodecahedrane - First Synthesis- First Synthesisby Paquetteby Paquette

Ni

H

H

Na2950 oC I2, THF-78 oC

ε

ε

ε

ε

CO2CH3H3CO2C

Δ

εε

ε

ε

CO2CH3

CO2CH3

20% optimized yieldfor whole sequence

Completing the Carbon FrameworkCompleting the Carbon Framework

CO2CH3

CO2CH3

CO2CH3

CO2CH3 OO

OO

II

CO2CH3

CO2CH3

II

OHOH

CO2CH3

CO2CH3O

O

1. Na2Cr2O7/H+ (92%)2. Zn/Cu, CH3OH (78%)

SPh2

(77%)CO2CH3

CO2CH3

O

O

O

O

CO2CH3

CO2CH3

O

O

O

O

H2O2, CH3OH (quantitiative)

KOH(aq)/MeOHthen I2 NaHCO3

(94%)

NaOH/MeOH(quantitative)

Closure of the Closure of the Dodecahedrane Dodecahedrane CageCage

CO2CH3

CO2CH3

O

O

O

O

CO2CH3

CO2CH3

P4O10, MeSO3H(83%)

H2, Pd/C EtOAc (quantitative)

CO2CH3

CO2CH3

O

O

O

O

O O

OO

CO2CH3

CO2CH3

Cl

ClO

CO2CH3PhOH2C

NaBH4, MeOH (81%)

HCl, MeOH(62%)

1. Li, NH3 2. PhOCH2Cl(48% combined)

Closure of the Closure of the Dodecahedrane Dodecahedrane CageCage

CO2CH3PhOH2C CHOPhOH2C

CH2OHHO

CHOOO

H H

O

CO2CH3PhOH2C

1. hν2. TsOH3. N2H2

DIBAl-H

1. hν2. Li, NH3

3. H3O+

PCCKOH, EtOH (37%)

1. hν2. TsOH

N2H2 H2 Pd/C, 250 oC(50%)

Dodecahedrane Dodecahedrane CC2020HH2020 Isomers Isomers

There are many C20H20 isomers, including various multi-bridged cyclophanes, dimers of C10 structures (e.g.basketene dimer) and other saturated polycyclic systems.

Interconversion of these hydrocarbons by thermally or photochemicallymediated isomerization reactions has been the basis for severalattempted syntheses of hydrocarbon structures.

Prinzbach and co-workers were able to demonstrate analternative route to dodecahedrane, via thethermodynamically controlled isomerization of anotherC20H20 hydrocarbon, pagodane.

PagodanePagodane

W. D. Fessner; B. Murty; J. Worth; D. Hunkler; H. Fritz & H. Prinzbach Angew. Chem. Intl, Ed. Engl., (1987), 26, 452-454.

•ca. 40 kcal/mol higher heat of formation than dodecahedrane.•Readily isomerized to dodecahedrane by Pt/Re on Al2O3.

Building the Reflection of aBuilding the Reflection of aPagodaPagoda

OO

OO

O

hνO

O

OΔ

OO O

Cu2O, bypyridyl, H2O

1. B2H6/THF, quinoline 150 oC2. NaOH, H2O2

3. CrO3

(91% combined)

Completion of the CarbonCompletion of the CarbonFrameworkFramework

O

ONN

NN

CO2CH3

H3CO2CI I

1. HCO2CH3/NaH2. p-TsN3/NEt3 rt(82% combined)

MeOH hν, rt(95%)

Pb(OAc)4, I2, CCl4, hν(80%)

Na-K, THF, then t-BuOH(quantitative)

O

O