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Synthesis of a New LigandN,N’-trans-bis-(tert -butyl)-9,10-dihydro-9,10-ethano-
anthracene-11,12-dimethanamine
Yap Woon Teck
under the direction ofProf. Christopher C. Cummins and John-Paul F. Cherry
Department of ChemistryMassachusetts Institute of Technology
Research Science InstituteAugust 7, 1999
Abstract
The main aim of the project is to synthesize a new ligand with the distinct proper-
ties of being sufficiently bulky to form stable amido complexes that do not readily react
with the metal alkyldiene catalyst. Despite its bulkiness, it still has to be applicable to
a variety of metals by routes analogous to those usually employed for synthesizing metal
dialkylamides of both the transition and main-group metals[1]. We attempted to synthe-
size the new ligand, N,N’-bis-trans-(tert-butyl)-9,10-dihydro-9,10-ethano-anthracene-11,12-
dimethanamine (bTAA), was synthesized from the reaction of tert-butylamine with trans-11-
,12-bis-(toluene-4-sulfonyloxymethyl)-9,10-dihydro-9,10-ethano-anthracene (Refer to Figure
3). The product was characterized by means of spectroscopy, including: 1H and 13C nuclear
magnetic resonance (NMR) as well as Fourier Transformation-Infrared (FT-IR).
1 Introduction
There was much research in the synthesis, study and characterization of metallic and semi-
conducting nanoclusters at the beginning of this decade[2]-[30]. The ultimate aim was to
synthesize semiconductor clusters of a predictable and desired size such that the structure
and properties from the electronic perspective are intermediate between those of an atom
or molecule and those of the bulk material[1]. These clusters are interesting from both the
theoretical and experimental standpoints[20]-[33]. Theoretically, the clusters would have
unprecedented optical and electronic properties which could be greatly utilized in the opti-
coelectronic industry[34], [35]. Experimentally, the synthesis of the clusters is challenging,
since a sample would have to be nearly monodisperse before the phenomenal characteristics
of a given size cluster can be observed[1].
Various methods of synthesizing the nanoclusters such as using zeolites, colloids and
inverse micelles, have been developed [7]-[13]. In 1991, Cummins et al. synthesized the lig-
ands, trans-2,3-bis(tert-butylamidomethyl)norborn-5-ene (bTAN) and trans-2,3-bis[(trimet-
hylsilyl)amidomethyl]norborn-5-ene (bSAN) with the purpose of preparing metal-containing
monomers that can be polymerized by living ring-opening metathesis polymerization to form
clusters (Refer to Figure 1) [1], [29], [36]. Ring-opening metathesis polymerizaton provides a
convenient and elegant route to produce the nanoclusters that had been greatly researched
upon.
In follow-up studies by Cummins et al., metals such as Sn, Pb and Zn had been attached
to the new ligands. The clusters had remarkable potential to be polymerized to form the
nanoclusters that had initially provided the impetus for the research. However, the reac-
tivity and electron-richness of the double bond in the norborn-5-ene cyclopentadienyl (Cp)
ring makes the new ligands highly susceptible to electrophilic attack. Moreover, both the
Sn(bTAN) and Pb(bTAN) complexes (Refer to Figure 1) are relatively unstable, believed by
Cummins et al. to be due to the amides in bTAN being strong electron donors, thus placing
1
too much electron density on Sn(II) and Pb(II) and leading to the ultimate reduction of the
metals[36].
N,N’-trans-bis-(tert-butyl)-9,10-dihydro-9,10-ethano-anthracene-11,12-dimethanamine
(bTAA) was conceived of with the intention of synthesizing a new ligand that retains the
desirable properties of bTAN. Comparing bTAA with bTAN, the former retains the desirable
properties of being bulky enough to form stable amido complexes that do not readily attack
the metal alkyldiene catalyst due to steric hindrance. In fact, bTAA is even bulkier than
bTAN, due to the replacement of the norborn-5-ene Cp ring with the bulkier anthracene ring.
Moreover, the replacement of the norborn-5-ene Cp ring (which contains the carbon-carbon
double bond) with the inert benzene rings of the anthracene makes the new complex less
susceptible to electrophilic attack by electrophiles. bTAA should also be able to retain the
characteristic of being a versatile ligand, applicable to a variety of metals by routes analogous
to those usually employed for synthesizing metal dialkylamides of both transition and main-
group metals. As in bTAN, the tert-butyl groups in bTAA would not only have an important
steric effect but would also give the metal complexes that form later, the desirable property
of solubility in hydrocarbon solvents, allowing solution-cast films to be prepared[36]. This
also aids in the crystallization of the complexes, allowing X-ray diffraction to be utilized
for determining the structure of the complexes. One of the most desirable properties that
bTAA has over bTAN is that bTAA has a bulky anthracene base which is extremely rich
in electrons. Hence, upon coordination to the metal atoms, bTAA may produce a new
organometallic complex which would have unprecedented, interesting properties which can
be further explored. This is especially true for the metal atoms, as there may be a shift in
the electron density towards the metal atoms, thus imparting new chemical and electronic
properties to the metal concerned (Refer to Figure 2 for structures of bTAN, bSAN and
bTAA).
Here we attempt to develop a better ligand, bTAA, via the reaction of anthracene with
dimethyl fumarate (Refer to Figure 3).
2
NN
Pb(bTAN)
Pb
NN
Sn
Sn(bTAN)
NN
Sn
ClCl
Sn(bTAN)Cl2
NN
ZnPh
PhZn
(ZnPh)2(bTAN)
Figure 1: Diagram showing Metal Complexes of bTAN; Pb(bTAN) and Sn(bTAN) are un-stable due to too much electron density on the Pb and Sn atoms; (ZnPh)2(bTAN) andSn(bTAN)Cl2 are stabilized by the presence of the phenyl groups and chlorine atoms
3
NH
NHNH
SiMe3
HN
Me3Si
HN
bTAN bSAN
bTAA
NH
Figure 2: Diagram showing the structures of trans-2,3-bis(tert-butylamidomethyl)norborn-5-ene (bTAN), trans-2,3-bis[(trimethylsilyl)amidomethyl]norborn-5-ene (bSAN), and N,N’-tr-ans-bis-(tert-butyl)-9,10-dihydro-9,10-ethano-anthracene-11,12-dimethanamine (bTAA); InbSAN, the tert-butyl groups in bTAN are replaced by the trimethylsilane groups; In bTAA,the norborn-5-ene base is replaced by the anthracene base
4
O
O
O
O
C
H3CO
O
COCH3
O
TsO
+ CH3
HN
dioxane
NH
OTs
2x TsCl/Pyridine
2x tBuNH2/DMF110oC
2x LiAlH4
OH
OH
H3C
110oC
anthracene
dimethyl fumarate
trans-9,10-dihydro-9,10-ethano-anth
racene-dicarboxylic
acid-(11.12)-dimethyl ester (1)
trans-11,12-bis-hydroxymethyl-9,10-dihydro-9,10-ethano-anthracene
(2)
trans-11,12-bis-(toluene-4-sulfonyl
oxymethyl)-9,10-dihydro-9,10-ethan
o-anthracene (3)
N,N'-trans-bis-(tert-butyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanamine
(4)
Figure 3: Reaction mechanism for the synthesis of N,N’-trans-bis-(tert-butyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanamine, illustrating how 4 is obtained from the initialreaction of anthracene with dimethyl fumarate
5
2 Materials and Methods
All experiments were done under a nitrogen atmosphere in a Vacuum Atmospheres drybox
or by using standard Schlënk techniques, unless otherwise stated. Reagent grade diethyl
ether and tetrahydrofuran (THF) were distilled from purple sodium benzophenone ketyl
under nitrogen. All dioxane, pyridine and dimethyl formamide were used as bought. 13C
and 1H NMR data are referenced with C6D6 at 128.39 parts per million (ppm) and 7.16
ppm, respectively; pyridine-d6 was referenced at 8.74 ppm. All NMR spectra were recorded
in benzene-d6, on the Varian Mercury-300 spectrometer unless otherwise noted. Infrared
spectra were recorded on a Bio-Rad 135 Series FTIR spectrometer.
2.1 Synthesis of trans-9,10-dihydro-9,10-ethano-anthracene-dica-
rboxylic acid-(11.12)-dimethyl ester (1):
Anthracene (20.00g, 112 mmol) and dimethyl fumarate (24.26g, 168 mmol) were dissolved in
anhydrous dioxane (100mL) in a 250mL round-bottom flask, and refluxed at a temperature
of 110◦C for 72 hours, whereby the solution turned dark brown. The solution was dried
in vacuo, yielding a pale brown, powdery solid which was subsequently dissolved in hot
methanol (100mL, 65◦C), forming a dark brown solution which was filtered to remove any
insoluble impurities. The dark brown filtrate was cooled, giving cream-coloured crystals of
1 which were filtered and dried in vacuo. Yield: 22.08g (61.0%)
O
O
O
O
C
H3CO
O
C OCH3
O
110oC
trans-9,10-dihydro-9,10-ethano-anthracene-dicarboxylic acid-(11.12)-dimethyl ester (1)
CH3dioxaneH3C
anthracene
+dimethyl fumarate
Figure 4: Diels-Alder1 reaction of anthracene with dimethyl fumarate to yield 1
6
O
O
O
O
CH3H3C
Figure 5: Diagram showing electron pushing in the Diels-Alder reaction of anthracene withdimethyl fumarate to yield 1
2.2 Synthesis of trans-11,12-bis-hydroxymethyl-9,10-dihydro-9,1-
0-ethano-anthracene (2):
A 1L-3 neck flask was equipped with a 250mL dropping funnel (right neck), a reflux condenser
with N2-inlet atop (centre neck), a stopper on the left neck and a magnetic stirbar. Under
N2 atmosphere in the drybox, dry diethyl ether (300mL) was added to the flask, followed by
lithium tetrahydridoaluminate [LAH] (5.34g, 141 mmol). The reaction mixture was taken
out of the box and cooled to 0◦C and flushed with N2. The resultant dark yellow solution
from the dissolution (under N2 pressure) of 1 (21.68g, 67.3 mmol) in a mixture of diethyl
ether and THF (200mL; 2:3) was added to the dropping funnel. A dropwise addition, which
required 20 minutes, was commenced. After stirring for 18 hours, the resultant greenish-grey
reaction mixture, which had been allowed to warm up to room temperature, was quenched by
chilling to 0◦C. The reaction mixture was then worked up by carefully adding, sequentially,
H2O (5.34g), 15% NaOH (5.34g) and H2O (16.02g), producing a white, powdery precipitate
which was filtered off and washed with extra ether (2 x 100mL) and THF (2 x 100mL). The
combined ether and THF filtrates were dried (MgSO4) and excess solvent was removed in
1Refer to Appendix A for further explanation on Diels-Alder reactions
7
vacuo to yield 2 as a white, powdery solid. Yield: 13.40g (71.8%)
C
H3CO
O
C OCH3
O
H
AlH
H
HLi +[ ]
-+
OH
OH
lithium tetrahydridoaluminate
2trans-11,12-bis-hydroxymethyl-9,10-dihydro-9,10-ethano-anthracene (2)
trans-9,10-dihydro-9,10-ethano-anthracene-dicarboxylic acid-(11.12)-dimethyl ester (1)
Figure 6: Reduction of 1 with LiAlH4 to yield 2
2.3 Synthesis of trans-11,12-bis-(toluene-4-sulfonyloxymethyl)-9-
,10-dihydro-9,10-ethano-anthracene (3):
2 (13.40g, 50.3 mmol) was dissolved in pyridine (100mL) in a 1L round-bottom flask and
chilled to 0◦C while stirring. p-Toluenesulfonyl chloride [tosyl chloride] (23.02g, 121 mmol)
was added in portions over 6 minutes. After 30 minutes, the pyridine•HCl precipitate beganto appear. After 24 hours, during which the reaction mixture was allowed to warm up to
room temperature (25◦C), water (500mL) was added while stirring. Diethyl ether (300mL)
was added and the white precipitate, which would not go into the diethyl ether, was filtered
off. The organic layer of the reaction mixture (i.e., the ether/pyridine mixture) was removed
and dried in vacuo, producing a yellow powder, which was washed with diethyl ether until
it yielded a white powder of 3. Yield: 21.86g (75.6%)
TsOSH3C
O
O
Cl
p-toluenesulfonyl chloride
OH
OHOTs[[+2
trans-11,12-bis-hydroxymethyl-9,10-dihydro-9,10-ethano-anthracene (2)
trans-11,12-bis-(toluene-4-sulfonyloxymethyl)-9,10-dihydro-9,10-ethano-anthracene (3)
Figure 7: Reaction of 2 with p-toluenesulfonyl chloride to yield 3
8
2.4 Synthesis of N,N’-trans-bis(tert-butyl)-9,10-dihydro-9,10-et-
hanoanthracene-11,12-dimethanamine (4):
3 (11.54g, 20.1 mmol) was dissolved in dimethyl formamide [DMF] (88.07g) in a 250mL thick-
walled glass vessel, producing a colourless solution. Upon addition of excess tert-butylamine
(36.72g, 502 mmol), the reaction mixture turned pale yellow. The glass vessel was tightly
closed with a Teflon stopcock and was then immersed in a 110◦C bath. The reaction mixture
was stirred magnetically and maintained at 110◦ for 22.5 hours. A white sublimate appeared
at the top of the vessel. The sublimate was shaken back into the reaction mixture and
redissolved. The resultant, homogeneous, intense bright yellow solution was cooled to 25◦C
and poured into a 1L separatory funnel containing 1.33 M NaOH (250mL) and the resulting
mixture was extracted with 30-65 petroleum ether (3 x 200mL). The combined petroleum
ether extracts were dried with MgSO4 and all the solvent was removed in vacuo, forming a
yellowish-white powder. The powder was redissolved in diethyl ether and 4 was recrystallized
from the resultant bright yellow solution, to yield a white, microcrystalline powder. Yield:
2.13g (28.2%)
TsOCH3
NCH3
H3C
H
H
HN[tert-butylamine
+OTs [
xsNH
110oC
DMF
trans-11,12-bis-(toluene-4-sulfonyloxymethyl)-9,10-dihydro-9,10-ethano-anthracene (3)
N,N'-trans-bis-(tert-butyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanamine (4)
Figure 8: Reaction of 3 with tert-butylamine to yield 4
9
3 Results and Data
The product obtained had only a single melting point of 193◦C. The Fourier-Transformation
Infrared (FT-IR) spectrum of the product that was obtained from the reaction of 3 and
tert-butylamine showed that there was no detectable N-H stretching around the region of
3300-3500 cm−1 (Refer to Appendix D). From this, it was evident that the product did not
contain any hydrogen atoms which were directly bonded to the nitrogen atoms.
Moreover, the product, 4, showed no apparent reaction with butyllithium, an extremely
strong deprotonating reagent. This is corroborated by the fact that the 1H NMR spectra
taken before and after the reaction of 4 with butyllithium were exactly the same and that
there was no detectable difference in the intensity of any peaks. This showed that 4 had not
been deprotonated by the butyllithium (See Appendix E and F). There was no reason why
4 should not be deprotonated, unless there was no hydrogen to begin with.
Hence it was deduced and inferred that the desired ligand, N,N’-trans-bis-(tert-butyl)-
9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanamine had not been produced. There-
fore, a new structure of the product, 5, that the resulted from the reaction of 3 with tert-
butylamine was proposed (Refer to Figure 9) :
N
Figure 9: Proposed Structure of the Product, 5 Obtained from the Reaction of 3 withtert-butylamine
10
N
A
B
CD
F
GH
I
E
Figure 10: Structure for 1H NMR analysis
With reference to the structure in Figure 10 and Appendix B, it can be deduced that,
1H NMR (C6D6) δ 7.182, 7.030, 7.010, 6.891, 6.961, 6.941 are due to the hydrogens at
positions A, B, C and D; 4.072 is due to the hydrogens at E; 2.303, 2.280, 2.273 are due to
the hydrogens at F; 1.616, 1.599, 1.584 are due to the hydrogens at G; 2.773 is due to the
hydrogens at H and 0.859 are due to the hydrogens at I.
N
1
2
3 4
5
6
11
11117
9
8
10
Figure 11: Structure for 13C NMR analysis
With reference to the structure in Figure 11 and Appendix C, it can be deduced that, 13C
NMR (C6D6) δ 152.141, 140.358, 126.971, 126.067, 125.991, 121.697 are due to the carbons
at positions 1, 2, 3, 4, 5 and 6; 53.506 is due to the carbon at 7; 52.607 is due to the carbons
at 8; 46.713 is due to the carbons at 9; 46.317 is due to the carbons at 46.317 and 26.958 is
due to the carbons at 11.
11
4 Discussion
4.1 Reasons For The Failure to Produce bTAA via the Reaction
of 3 with tert-butylamine
There are several reasons why the attempt to form N,N’-trans-bis(tert-butyl)-9,10-dihydr-
o-9,10-ethanoanthracene-11,12-dimethanamine from the reaction of 3 with tert-butylamine
failed and resulted in the formation of the new organic molecule 5 (Refer to Figure 9).
Firstly, comparing the desired ligand, bTAA, with bTAN, we observe that bTAA has an
anthracene base compared to the norborn-5-ene Cp ring of bTAN. Sterically, the 2 benzene
rings of the anthracene base surrounding the bridge may actually “push” the tert-butyl group
upwards when one molecule of tert-butylamine reacts with 3. The nitrogen is now closer to
the tosylate group and 5 is more likely to be formed.
In addition, intramolecular electron transfer may take place, resulting in the formation of
a covalent bond between the nitrogen atom and the carbon atom, thus producing a closed-
ring cyclic compound, 5.
Furthermore, the anthracene base may actually cause a strain in the C-N bond of 4,
as the N-C-N bond angle in 4 is rather small, as the bond length of N-C and C-N in 4
are relatively short. Thus, the tert-butyl group is again forced upwards, resulting in the
formation of 5.
Finally, looking at the proposed reaction mechanism for the formation of 5 from the
reaction of 3 with tert-butylamine (Refer to Figure 12), we notice that initially the tosylate
group detaches from 3, to be replaced by the tert-butylamine group. Simultaneously, the
tert-butylamine group loses a hydrogen atom, which combines with the tosylate group to
form the alcohol. As the second tosylate group detaches from 3, one of two reactions can
occur:
1. The nitrogen atom that is already attached to 3 could lose another hydrogen atom
12
and form a pentagonal, closed ring with the carbon atom on the opposite side. At the
same time, another equivalent of the alcohol is formed.
2. A new tert-butylamine molecule could collide with the carbon atom (which is on the
opposite side from the nitrogen atom), with the correct collision geometry to form the
desired ligand, 4.
Comparing the two scenarios, it would be much easier for the attached nitrogen atom
to rotate about the carbon atom, and form a closed ring with the other carbon atom. The
intramolecular transfer in this case would also be much more rapid than the collision and
reaction of another tert-butylamine with the molecule. Moreover, the strain in the N-C bond
(as mentioned above), may actually facilitate the forming of the closed ring.
Therefore, 5 is formed.
4.2 Alternative Pathways to Obtain the Desired Ligand, N,N’-tra-
ns-bis-(tert-butyl)-9,10-dihydro-9,10-ethanoanthracene-11,12
-dimethanamine
From Figure 13 and 14, the pathway might be successful in producing the desired ligand
bTAA, as the formation of the dicarbonyl from the reaction with tert-butylamine is actually
analogous to another reaction that is found to be successful in literature. In literature,
the tert-butylamine was replaced by ortho-tert-butylaniline. Moreover, the reduction of the
dicarbonyl with lithium tetrahydridoaluminate is a very standard method of removing the
carbonyl groups. An additional advantage is that the nitrogen and carbon atoms would have
absolutely no opportunity to form a closed ring as the oxygen atom in the carbonyl group
would sterically hinder the formation of the closed ring. Thus, 5 is less likely to be formed.
13
OTsCH3
NCH3
CH3
H
H
NH CH3S
O
O
OH
NH
N
CH3S
O
O
-OH+
CH3S
O
O
OH
N
OTs
+
+
+OTs
+
+ +
+
+-
CH3S
O
O
-O
Figure 12: Proposed Reaction Mechanism for the Formation of 5 from 3 and tert-butylamine,whereby the pentagonal closed-ring forms, instead of the desired 4
14
+ OO
OH
O
H
C
HO
O
COH
O
C
Cl
O
CCl
O
C
HN
O
CNH
O
HN
NH
dioxane
110oC
SOCl2
xs tBuNH2-HCl
LiAlH4
Figure 13: Alternative Reaction Pathway 1 to Obtain the Desired Ligand, via the reactionof anthracene with fumaric acid
15
Cl
O
Cl
O
C
Cl
O
CCl
O
C
HN
O
CNH
O
HNLiAlH4
RNH2
NH
+
dioxane
110oC
Figure 14: Alternative Reaction Pathway 2 to Obtain the Desired Ligand, via the reactionof anthracene with fumaryl chloride
16
Cl
O
Cl
O
CH3
NCH3
CH3
H
H
NH
O
HN
O
NHHN
HN
+
LiAlH4
NH
Figure 15: Alternative Reaction Pathway 3 to Obtain the Desired Ligand, via the reactionof fumaryl chloride with tert-butylamine
17
Cl
O
Cl
O
CH3
NCH3
CH3
H
H
NH
O
HN
O
HN
C
HN
O
CNH
O
+
LiAlH4 NH
Figure 16: Alternative Reaction Pathway 4 to Obtain the Desired Ligand, via the reactionof fumaryl chloride with tert-butylamine
18
4.3 Yields
Comparing our yields of between 60% to 76% to those found in literature, and especially
analogous reactions by Cummins et al., they were significantly lower by about 5% to 10%.
This may be due to the fact that the analogous reactions done by Cummins et. al. in-
volved molecules containing norborn-5-ene rings as the base whereas ours have an anthracene
base in place of the Cp ring. Sterically, the anthracene base is bulkier and may actually cause
our molecule to be less reactive, kinetically, and hence the yields are lower.
The second reason is that we did not optimize the conditions for the reactions, whereas
those found in literature were optimized results. Hence, our yields are comparatively lower.
4.4 Applications of the Ligand
Potential applications for the ligand are few, mainly to synthesize new metal clusters or
complexes that may be of interest. The metal complexes themselves, may hold the key
to obtaining catalysts which can be used for polymerization reactions or the synthesis of
complex organic molecules, just to name a few. In addition, they may prove to be more
efficient and economical than those catalysts currently in use in many industrial processes.
This area of research is still awaiting further investigation.
4.5 Future Studies
Upon successful synthesis of the ligand, bTAA, several experiments can be done to produce
the desired versatile metal complexes which would then form the basis of further experimen-
tation and investigation. Some of these future studies are illustrated in Figure 17, where M
= Cr, Mo and MCl3 = CrCl3(THF)3, CrCl3, MoCl3(THF)3.
19
LiHN
NH N
NLi
Li
N
N
M
Cl
N
Li
N
N
MN
N
N
MNa+
NN
M
+ -2
MCl3
---
+
Na
Na ++
Figure 17: Future Reactions To Be Studied Upon Successful Synthesis of 4, where M =Cr, Mo; The addition of Na could reduce the metal complex to form a univalent anion orremove the chloride from the metal; Reaction with Li[N(tBuAr)] could form a metal-nitrogencomplex
20
5 Conclusion
From our unsuccessful attempts to synthesize N,N’-trans-bis(tert-butyl)-9,10-dihydro-9,10-
ethanoanthracene-11,12-dimethanamine, it can be seen that the reaction of 3 with tert-
butylamine is not a viable method of synthesizing the desired ligand.
The product which we have obtained (Refer to Figure 9) still remains to be further puri-
fied and characterized by elemental analysis. Its exact structure has yet to be characterized
by X-ray crystallography, which we are still investigating. Its chemical and physical proper-
ties e.g. crystal packing are yet largely unknown and thus remains to be further explored.
The proposed pathways for synthesizing N,N’-trans-bis(tert-butyl)-9,10-dihydro-9,10-et-
hanoanthracene-11,12-dimethanamine (Refer to Figure 13 and 14) are still under investi-
gation. Further experimentation has to be carried out to determine the versatility of the
desired ligand to be applied to various transition and main-group metals, its exact chemi-
cal properties, whether its theoretical advantages over bTAN are existent, and its practical
flaws.
6 Acknowledgments
The author would like to thank Mr. John-Paul F. Cherry for his kind guidance and assistance
during the entire course of the research internship and the writing of the research paper.
He wishes also to thank Professor Christopher C. Cummins of the Chemistry Department,
Massachusetts Institute of Technology, for his invaluable advice and inception of the research
topic.
He also desires to extend his thanks to the Cummins Research Group and anyone who
has helped out in one way of another.
The author thanks Mr. Eric Ford, Miss Deborah C. Yeh, Mr. Daniel Kaganovich and
Miss Aimee Crago for their advice and constructive criticisms during the writing of the paper
and for looking through the manuscripts.
21
Finally, he wishes to express his gratitude to the Center for Excellence in Education
and the Research Science Institute for providing this priceless opportunity for the scientific
challenges and the social experiences.
22
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[12] Steigerwald, M. L.; Alivisatos, A. P.; Gibson, J. M.; Harris, T. D.; Kortan, R.; MullerA. J.; Thayer, A. M.; Duncan T. M.; Douglas, D. C.; Brus, L. E.; J. Am. Chem. Soc.1988, 110, 3046.
[13] Thomas, J .K.; Lianos, P.; Chem. Phys. Lett. 1986, 125, 299.
[14] Wang, Y.; Suna, A.; Mahler, W.; Kasowski, R.; J. Chem. Phys. 1987, 87, 7315.
[15] Mahler, W.; Inorg. Chem. 1988, 27, 435.
[16] Brennan, J. G.; Siegrist, T.; Carroll, P. J.; Stuczynski, S. M.; Brus, L. E.; Steigerwald,M. L.; J. Am. Chem. Soc. 1989, 111, 4141.
[17] Olshavsky, M. A.; Goldstein, A. N.; Alivisatos, A. P.; J. Am. Chem. Soc. 1990, 112,9438.
[18] Brennan, J. G.; Siegrist, T.; Carroll, P. J.; Stuczynski, S. M.; Reynders, P.; Brus L. E.;Steigerwald, M. L.; Chem. Mater. 1990, 2, 403.
[19] Stuczynski S. M.; Brenna, J. G.; Steigerwald, M. L.; Inorg. Chem. 1989, 28, 4431.
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23
[22] Brus, L. E.; J. Chem. Phys. 1984, 80, 4403.
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[26] Rossetti, R.; Nakahara, S.; Brus, L. E.; J. Chem. Phys. 1983, 79, 1086.
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24
A Brief Explanation of Diels-Alder Reactions
Diels-Alder reactions are basically 1,4-cycloaddition reactions of dienes, which were devel-
oped by two German chemists, Otto Diels and Kurt Alder, in 1928. Diels-Alder reactions
have great versatility and much synthetic utility and are especially useful in organic synthesis
of compounds, as they can often form larger molecules that are cyclic and hence can be used
precursor reactions that lead to more interesting ones.
Essentially, a Diels-Alder reaction is one that takes place between a conjugated diene
(which is a 4π-electron system) and a dienophile, a compound containing a double bond
(which is a 2π-electron system). The product of a Diels-Alder reaction is known as an
adduct.
The simplest case of a Diels-Alder reaction is that, which takes placed between 1,3-
butadiene and ethene, where the former is the conjugated diene and the latter is the
dienophile. The reaction is carried out at 200◦C under high pressures to yield hexene as
the adduct. Typical yields are about 20%.
200oC+
Figure 18: Diels-Alder reaction of 1,3-butadiene (diene) and ethene (dienophile) to formhexene
With respect to the reaction of dimethyl fumarate and anthracene, the conjugated diene
is the anthracene whereas the dienophile is the dimethyl fumarate. Trans-9,10-dihydro-9,10-
ethano-anthracene-dicarboxylic acid-(11.12)-dimethyl ester is produced as the adduct, with
yields typical ranging from 60% to 75%.
In Diels-Alder reactions, two new σ bonds are formed at the expense of two π bonds of
the diene and the dienophile. Since σ bonds are generally stronger than π bonds, formation
25
O
O
O
O
C
H3CO
O
C OCH3
O
110oC
trans-9,10-dihydro-9,10-ethano-anthracene-dicarboxylic acid-(11.12)-dimethyl ester (1)
CH3dioxaneH3C
anthracene
+dimethyl fumarate
Figure 19: Diels-Alder reaction of anthracene (diene) with dimethyl fumarate (dienophile)to yield 1 (adduct)
of the adduct is usually energetically favoured. However, most Diels-Alder reactions are
reversible.
Diels-Alder reactions are highly stereospecific. This is shown by the following observed
phenomena.
1. The reaction is a syn2 addition of the dienophile to the diene and the configuration of
the dienophile is retained in the product.
2. Out of necessity, the diene must react in the s-cis conformation rather than the s-trans.
3. Diels-Alder reactions primarily occur in an endo3 rather than exo4 fashion when the
reaction is kinetically controlled.
As a result, the following phenomena are observed:
1. A trans dienophile gives a trans adduct; a cis dienophile gives a cis adduct. Two
examples that illustrate this fact is the reaction between dimethyl maleate (a cis-
dienophile) and 1,3-butadiene (a diene) and that between dimethyl fumarate (a trans-
dienophile) and 1,3-butadiene (a diene).
2A syn addition reaction is one that places parts of the adding reagent on the same side/face of thereactant
3An organic group that is on the same side as the longest bridge of bridged rings is said to be endo4A group that is anti to the longest bridge is said to be exo
26
H
H COCH3
COCH3
O
OH
COCH3
HCOCH3
O
O
+
Dimethyl maleate(a cis-dienophile)
1,3-butadiene(a diene)
Dimethyl 4-cyclohexene-cis-1,2-dicarboxylate
Figure 20: Reaction of a cis dienophile giving a cis adduct
H
H3COC H
COCH3
O
HCOCH3
O
1,3-butadiene(a diene)
Dimethyl 4-cyclohexene-trans-1,2-dicarboxylate
+
Dimethyl fumarate(a trans-dienophile)
O
COCH3
OH
Figure 21: Reaction of a trans dienophile giving a trans adduct
27
2. Reactions in the s-trans conformation would, if it occurred, produce a six-membered
ring with a highly-strained trans double bond. Hence, this course of the Diels-Alder
reaction has never been observed.
s-cis Conformation s-trans ConformationFigure 22: Diagram show cis and trans conformations of 1,3 butadiene
O
RX
C
O
R
+
Figure 23: Diagram showing why Diels-Alder reactions does not take place for the transform of the diene
28
B 1H NMR Spectrogram of 4 in deuterated benzene
(C6D6)
ppm
12
34
56
7
6.961
6.981
7.010
7.030
7.160
7.182
6.941
4.072
2.773
2.280
2.303
2.273
1.616
1.599
1.584
0.859
7.19
1.86
2.00
2.25
2.40
12.28
29
C 13C NMR Spectrogram of 4 in deuterated benzene
(C6D6)
ppm
20
40
60
80
100
120
140
160
180
200
220
240239.071
152.141
128.708
140.358
128.390
128.067
126.971
126.067
125.991
121.697
46.713
52.607
53.504
46.317
26.958
23.241
14.818
30
D Fourier-Transformation Infrared Spectrum of 4 in
deuterated benzene (C6D6)
1000
2000
3000
4000
-25
-20
-15
-10-505
Tranmittance
Wav
enum
ber
(cm
-1)
31
E 1H NMR Spectrogram of 4 before Reaction with
Butyllithium in deuterated benzene (C6D6)
ppm
12
34
56
7
6.961
6.981
7.010
7.030
7.160
7.182
6.941
4.072
2.773
2.280
2.303
2.273
1.616
1.599
1.584
0.859
7.19
1.86
2.00
2.25
2.40
12.28
32
F 1H NMR Spectrogram of 4 After Reaction with B-
utyllithium in deuterated benzene (C6D6)
ppm
12
34
56
7
6.961
6.981
7.010
7.030
7.160
7.182
6.941
4.072
2.773
2.280
2.303
2.273
1.616
1.599
1.584
0.859
7.19
1.86
2.00
2.25
2.40
12.28
33
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