synthesis of a new ligand trans-bis-(tert-butyl)-9,10-dihydro-9...

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)


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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[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.

[20] Brus, L. E.; J. Chem. Phys. 1983, 79, 5566.


23


[23] Rossetti, R.; Hull, R.; Gibson, J. M.; Brus, L. E.; J. Chem. Phys. 1985, 82, 552.

[24] Brus, L. E.; New. J. Chem. 1987, 11, 123.

[25] Steigerwald, M. L.; Brus, L. E.; Annu. Rev. Mater. Sci. 1989, 19, 471.

[26] Rossetti, R.; Nakahara, S.; Brus, L. E.; J. Chem. Phys. 1983, 79, 1086.

[27] Rossetti, R.; Hull, R.; Gibson, J. M.; Brus, L. E.; J. Chem. Phys. 1985, 83, 1406.

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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


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

synthesis of a new ligand trans-bis-(tert-butyl)-9,10-dihydro-9...

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