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Synthesis and Characterization of novel Porphyrin--Dyads and Cyclomalonate- linked Trisfullerene

Synthese und Charakterisierung von neuartigen Porphyrin-Fulleren Dyaden und Cyclomalonat- verknüpften Trisfulleren

Der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg

zur

Erlangung des Doktorgrades Dr. rer. nat.

vorgelegt von

Maximilian Popp

aus Nürnberg

Als Dissertation genehmigt von der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)

Tag der mündlichen Prüfung: 11.01.2019

Vorsitzender des Promotionsorgans: Prof. Dr. Georg Kreimer

Gutachter: Prof. Dr. Andreas Hirsch

Prof. Dr. Jürgen Schatz

Mein besonderer Dank gilt meinem Doktorvater Prof. Dr. Andreas Hirsch für die Bereitstellung des interessanten und herausfordernden Themas, seine Förderung und fachliche Unterstützung und das Interesse am Fortgang dieser Arbeit.

Die vorliegende Arbeit entstand in der Zeit von Mai 2014 bis April 2018 am Lehrstuhl für Organische Chemie II des Departments Chemie und Pharmazie der Friedrich- Alexander-Universität Erlangen-Nürnberg (FAU).

meinen Eltern

Chemistry begins in the stars. The stars are the source of the chemical elements, which are the building blocks of matter and the core of our subject. Peter Atkins

Abbreviations, Acronyms and Symbols

List of Abbreviations, Acronyms and Herein Used Symbols

ACN/MeCN acetonitrile

AcO/OAc acetyl-

APPI atmospheric pressure photoionization

Ar aryl

Boc t-butoxycarbonyl

calc. calculated

conc. concentrated

COSY correlation

CS2 carbon disulfide

CuAAC (I)-catalyzed -azide

d day(s)

DBU 1,8-diazabicyclo[5.4.0]undec-7-ene

DCC N,N’-dicyclohexylcarbodiimide

DDQ 2,3-dichloro-5,6-dicyano-p-benzoquinone

DIBAL-H diisobutylaluminium hydride

DIPEA N,N-diisopropylethylamine

DMA 9,10–dimethylanthracene

DMAP 4-dimethylaminopyridine

DMF N,N-dimethylformamide

DMSO dimethyl sulfoxide

equiv./eq. equivalent

ESI electrospray ionization

Et ethyl

Et2O/OEt2 diethyl ether

EtOAc ethyl acetate

EtOH

exp. expected

h hour(s)

I

Abbreviations, Acronyms and Symbols

HPLC high performance liquid

HRMS/HiRes high resolution

Hz Hertz hν photonic/light energy

IR infrared (spectroscopy)

IUPAC International Union of Pure Appl. Chem.

J coupling constant

LDI laser desorption/ionization

LiALH/LAH lithium aluminium hydride m meta m milli

M molar m/z mass to charge ratio

MALDI matrix assisted laser desorption ionization

Me methyl

MeOH methanol

MS mass spectrometry n normal- n-BuLi n-butyllithium

NMR nuclear magnetic resonance o ortho- oDCB o-dichlorobenzene p para-

Ph phenyl ppm parts per million p-TSA p-toluenesulfonic acid p-TSCl p-toluenesulfonyl chloride quant. quantitative

RBF round bottom flask

Rf retention factor

II

Abbreviations, Acronyms and Symbols rt room temperature

SN nucleophilic substitution t tert; tertiary tBDMS t-butyldimethylsilyl

TEA triethylamin

TFA trifluoroacetic acid

TGA thermal gravimetric analysis

THF tetrahydrofuran

TLC thin layer chromatography

TMS trimethylsilyl

TOF time of flight

TPP tetraphenylporphyrin

UV/Vis ultraviolet/visible (spectroscopy)

δ chemical shift

ε extinction coefficient

λ wavelength

III

Table of Contents

Table of Contents

1 Introduction ...... 1 1.1 History of the Fullerene...... 1 1.1.1 Geometric Solids in Organic ...... 1 1.1.2 Discovering the Fullerene ...... 2 1.1.3 The Structure of ...... 3 1.2 Functionalization of Fullerenes ...... 5 1.2.1 Exohedral Functionalization of Fullerenes ...... 5 1.2.2 Multiple Exohedral Functionalization ...... 8 1.2.3 Cyclomalonate as Building Block in ...... 10 1.2.4 as Powerful Tool for Fullerene Functionalization ...... 14 1.3 Applications of Fullerene Compounds ...... 19 1.3.1 Bioactive Fullerene Derivatives ...... 19 1.3.2 Photoactive Fullerene Derivatives ...... 24 2 Proposal ...... 28 3 Results and Discussion ...... 31 3.1 Novel Fullerene-Porphyrin Hybrids ...... 31 3.1.1 Monopropargyl-Substituted Cyclo-[2]-Hexylmalonate ...... 31 3.1.2 Dipropargyl-Substituted Cyclo-[2]-Hexylmalonate ...... 43 3.1.3 Alkylation of Cyclo-[2]-Hexylmalonate with Longer Alkyne-Chains ...... 49 3.1.4 Synthesis of Fullerene Monoadducts ...... 61 3.1.5 Formation of Cyclo-[2]-Malonate-Linked Porphyrin-Fullerene Dyads ...... 67 3.2 Novel Cyclo-[n]-Bridged Fullerene-Trimer ...... 71 3.2.1 Synthesis of Fullerene Trimer from Diethyl Pentakisadduct ...... 71 3.2.2 Attempted Synthesis of Fullerene Trimer with Terminal ...... 77 3.3 Synthesis of Alkyne-Functionalized Fullerene Monoadducts as Dyes for the formation aaaaaaof Hierarchical Structures on ...... 81 3.4 Fullerene Diamino Monoadduct as Bidentate for the Coordination to a aaaaaaMetalloporphyrin-Dimer...... 89 4 Summary ...... 98 5 Zusammenfassung ...... 103 6 Experimental Section ...... 108

IV

Table of Contents

6.1 General Information ...... 108 6.2 General Remarks ...... 110 6.2.1 Synthesis According to Literature ...... 110 6.2.2 Synthesis of Literature Known Compounds ...... 111 6.3 Synthetic Procedure and Spectroscopic Data...... 117 6.3.1 Synthesis of Precursors for Covalently Bound Porphyrins ...... 117 6.3.2 Synthesis of Propargyl Substituted Cyclo-[2]-Malonate and its Precursors ...... 119 6.3.3 Synthesis of Fullerene Monoadducts with Propargyl Substituted Cyclo-[2]- aaaaaaaMalonate ...... 127 6.3.4 Synthesis of Novel Clicked Porphyrin-Fullerene Dyad...... 129 6.3.5 Synthesis of Cyclo-[2]-Malonate, Substituted with Heptynyl Chains ...... 130 6.3.6 Synthesis of Novel Fullerene Trimer Bridged by Cyclo-[3]-Malonate ...... 133 6.3.7 Synthesis of Alkyne-Functionalized Fullerene Monoadduct ...... 135 6.3.8 Synthesis of Fullerene Amino-Monoadducts ...... 137 7 References ...... 143 8 Appendix ...... 153

V

Introduction

1 Introduction

1.1 History of the Fullerene

1.1.1 Geometric Solids in

Organic chemistry deals with the synthesis of carbon based . By connecting carbon with each other, very complex structures are accessible. Long chains or branched systems form a huge variety of compounds, of which topological defined solids being a special case. The most obvious representative is probably diamond, since it is the most famous natural occurring carbon allotrope. In diamonds all carbon atoms are tetrahedrally bound in a covalent network lattice, resulting in a face centered cubic crystal structure. The smallest unit in its lattice is called – derived from the Greek adamantinos meaning invincible[1] – a highly symmetrical and rigid ring system where all carbon valences are saturated with H- [2] [3] [4] atoms, resulting in a C10H16 formula. Schleyer further improved the synthesis in 1962.

Another group of regular cage molecules are the platonic hydrocarbons, matching the structure of the platonic polyhedral. Only three of the five existing are accessible from carbon scaffold (Figure 1).[5] The formation of octahedrane is highly unlikely. The angle would cause instability. Furthermore there are not any bonds left for hydrogen atoms, making it an C6 carbon allotrope.[6] Icosahedrane would require pentavalent carbon, thus is ruled out as well. The smallest Platonic hydrocarbon is tetrahedrane, which synthesis remains elusive so far, but should in principle be possible.[7] Many derivatives have been synthesized successfully, the first was tetra-tert-butyltetrahedrane,[8] Cubane, a highly strained [9] consists, as the name predicts, of 8 C-atoms in cubic form. In 1964 Eaton and Cole[10] were able to synthesize this octahedral symmetrical compound for the first time. The last Platonic hydrocarbon is dodecahedrane. It has an icosahedral symmetry and was first synthesized in 1982,[11] the being later improved by the group of Prinzbach.[12] With increasing number of carbon atoms, the molecular shape resembles more and more a sphere.

Figure 1: Structure of Platonic hydrocarbons tetrahedrane, cubane and dodecahedrane. [8-11]

1

Introduction

Moving from Platonic to Archimedean polyhedra, this trend continues. Polyhedra are built from regular polygons, but in Archimedean solids multiple types of polygons are used, whereas Platonic polyhedra are formed with only one type. Not all Archimedean polyhedral can be used as model for hydrocarbon compounds, for the same reasons as the Platonic solids. One of the seven examples is of greater interest. Schultz first described truncated icosahedrane as theoretical polyhedron with 60 carbon atoms at the vertices. He expected the formula to be [5] C60H60. At the time he could not anticipate, how close he got to predicting the structure of a new carbon allotrope.

1.1.2 Discovering the Fullerene

In the following year Jones proposed hollow carbon cages. They would be made from graphene sheets that are folded into a sphere by defects in the sheet.[13] Later he realized that the defects have to be pentagons.[14] In 1970 Osawa found the structure of corannulene to be a subset of a football. He suggested a spherical molecule build in the same hexagon/pentagon pattern should be stable[15] and might be aromatic (Figure 2).[16] In the following years Hückel calculations of the π-electrons in such a molecule were carried out by Gal`pern,[17] Davidson[18] and later by [19] Haymet. The total synthesis of a C60 sphere was attempted in the early 1980’s by the synthetic organic Orville Chapman,[20] but he did not succeed.

Figure 2: Structure of corannulene and truncated icosahedron C60.

Several groups in the early 1980’s examined carbon clusters by a laser vaporization supersonic beam source and an associated probe. Kaldor and coworkers [21] were the first to find clusters of up to 190 atoms. Surprisingly clusters of more than 30 atoms were always even-numbered. They also observed a more intense peak for 60 carbon atoms, the first spectroscopic hint for the existence of [60]fullerene. Similar results were obtained by the group of Brown[22] with [23] cluster . It was Curl, Kroto and Smalley who examined the preeminence of C60 in detail. They found it to be the most abundant and therefore the most stable form and realized carbon forms these clusters spontaneously by itself. Without knowledge of the theoretical work that had been done on this molecule, they supposed it to be a closed and highly symmetrical carbon cage structure and proposed the form of a truncated icosahedron. The name they gave the molecule, (buckminster)fullerene stems from the geodesic domes of R. Buckminster Fuller, which inspired them during their search for the molecular structure.

2

Introduction

In 1990 the first report of the production of [60]fullerene in macroscopic scale by Krätschmer et al.[24] led to an explosive growth of fullerene science. X-ray diffraction studies, IR analysis[25], as well as 13C-NMR[26] confirmed the postulated structure. Now being available in large quantities, fullerenes were widely investigated. Up to this day, thousands of publications cover topics from physical properties, chemical reactivity to potential applications.

1.1.3 The Structure of Fullerenes

Fullerenes are spherical closed carbon cluster of 2(10+M) carbon atoms. Following Eulers theorem,[27] 12 pentagons are necessary to form a closed shell structure with M hexagons, just as Jones and Osawa[13-16] predicted. In the case of icosahedral [60]fullerene, the football shape is made of 12 pentagons and M=(60/2)-10=20 hexagons. The next larger fullerene, C70, can be imagined as C60 with the northern hemisphere separated from the southern and rotated by 1/10. By adding a ring of 10 carbon atoms connecting the spheres, the egg-shaped fullerene is obtained.[28]

Stable structures are formed, if no pentagons are annulated.[29] Abutting pentagons involve eight antiaromatic conjugated π-electron circuits around the ring, which is destabilizing. Furthermore it would increase the curvature and raise the already high strain energy. Based on Barth and Lawton’s work on corannulene,[30] the Isolated Pentagon Rule (IPR) was proposed: all pentagons must be completely surrounded by hexagons to form a cage with optimum [31] stability. C60 is in fact the first carbon cluster to obey this rule. Only one single signal at 13 143.2 ppm is observed in the C-NMR spectrum of pristine C60 in deuterated , proving [32] that all 60 carbon atoms are identical. The spherical shape of C60 introduces large strain energy, making it the least thermodynamical stable fullerene. Meanwhile, the strain energy, estimated to be about 8 kcal mol-1 per carbon, is equally distributed over the entire sphere, [33] because of said molecules ball-shape and its Ih-symmetry. The curvature of the cluster also results in a pyramidalization of the carbon atom orbitals. Only in planar situations (for example in graphene sheets), the pure p character of π orbitals is possible. Therefore, the deviation from planarity causes rehybridization of the sp2 σ and the p π-orbitals, moving from sp2 to sp2.278 in the fullerene framework.[34] Due to the rehybridization, low-lying π*-orbitals have considerable s character, making C60 a fairly electronegative molecule. The electrophilicity is demonstrated by the efficiency of electrochemical and chemical reductions as well as addition reactions with a large variety of nucleophiles.[35]

[36] There are 12500 possible Kekulé-structures for C60, out of which one is dominant (Figure 3). In it, double bond character is found for all bonds at the [6,6]-ring junctions, while the single bonds are all at [6,5]-ring junctions. In 13C-NMR experiments, two bond lengths were measured.[37] The shorter bonds (1.38 Å) are the junctions of the hexagons, the bonds in the pentagonal rings are slightly longer (1.45 Å). This alternation implies that C60 is not aromatic in the classical sense.

3

Introduction

A diameter of 710 pm was investigated by NMR-measurements. The inner cavity is almost 4 Å in diameter, enough to hold any element of the , leading to a large variety of endohedral fullerenes.[28a, 38]

Figure 3: Lowest energy Kekulé structure of C60.

Since their discovery, there is an ongoing debate, whether or not fullerenes have to be considered aromatic,[39] caused by controversial and regularly changing definitions of .[40] An analogy to benzene and other planar aromatics is implied by the structure of the carbon cage, leading Kroto et al. to the conclusion that fullerenes’ inner and outer surfaces would be covered by a “sea of π-electrons”.[23] Contrary to planar aromatic systems, the characteristical substitution reactions are not possible for fullerenes. Even though reactivity cannot be taken as criteria for aromaticity, C60 acts chemically like an electron deficient olefin, with only addition reactions taking place on the surface. The occurrence of paramagnetic – for antiaromatic molecules – and diamagnetic – for aromatic molecules – ring currents is an indicator for the aromaticity of molecules. In theoretical calculations of C60, Haddon found strong paramagnetic ring currents in the pentagons and weak diamagnetic ring currents in the hexagons.[41] The paramagnetic currents in the twelve pentagons are large enough that the diamagnetic currents in the twenty six-membered rings are almost exactly cancelled. This lead [33b] to the conclusion that C60 is “ambiguously aromatic”.

The Hückel rule describes the aromaticity of annulenes and heteroannulenes, after which annulenes with 4n+2 electrons are aromatic, whereas those with 4n electrons are antiaromatic. However this rule cannot be applied in polycyclic rings, where the benzoid rings are fused by four- or five-membered rings. For the spherical polycyclic π-system fullerene, another count rule had to be found. Hence, Hirsch et al.[42] proposed a rule to determine the aromaticity of three–dimensional polycyclic systems. Molecules with 2(n+1)2 π–electrons feature . Here the charge is distributed over the entire sphere, and fully occupied π–shells. 10+ Therefore, closed shell systems like the hypothetical tenfold cation C60 show spherical aromaticity, while C60 with 60 π–electrons is non–aromatic.

4

Introduction

1.2 Functionalization of Fullerenes

1.2.1 Exohedral Functionalization of Fullerenes

With fullerenes available in macroscopic scale, it was not long until the first investigations of their chemistry began. Most of the work on fullerene functionalization was done on C60. The reason is the availability in reasonable amounts of [60]fullerene compared to the higher carbon clusters and its perfect symmetry. Furthermore, the compounds in this work are all based on

C60. Therefore only selected C60 functionalization methods will be described. They are confined to exohedral functionalization by addition reaction, the most important and widespread chemical transformation for fullerenes. Other examples – like endohedral functionalization, metal fullerides, and open cage fullerenes – are omitted due to the limitations of this work. First attempts of hydrogenation,[43] functionalization with osmium tetraoxide[44] and alkylation with methyl iodide,[45] proved fullerenes to be a promising tool in the pursuit of [46] new and unusual types of organic molecules. Metals were successfully attached to C60 in reactions with organometallic reagents.[47] This gave the first hints, that the reaction chemistry of C-C double bonds in fullerenes was similar to that of electron-poor arenes and .[48]

Five rules of reactivity were postulated by Hirsch,[35] based on the knowledge about structural and physical properties of C60:

i. In neutral C60 the h shell is incompletely filled, resulting in a distortion corresponding to

the only internal freedom that the C60 molecule has without breaking the Ih symmetry. This is the bond length alternation between [6,6]-and [5,6]-bonds. Since in the occupied states (HOMOs), bonding interactions are predominantly located at the [6,6]-sites and the antibonding interactions (nodes) at the [5,6]-sites, a contraction of the [6,6]-bonds

causes an energy lowering. Hence, the lowest energy VB structure of neutral C60 contains only [6,6]-double bonds and [5,6]-single bonds.

ii. The regiochemistry of additions to C60 is driven by the maintenance of the MO structure and the minimization of energetically unfavorable [5,6]-double bonds.

iii. The spherical shape causes a pyramidalization of the C atoms and, therefore, a large amount of strain energy. Addition chemistry is driven by the strain relief introduced by the formation of almost strain-free sp3-C atoms. At a certain degree of addition this strain relief mechanism has to compete with new strainintroducing processes such as the increasing introduction of eclipsing interactions and the formation of planar cyclohexane substructures.

iv. Due to the s character of the π-orbitals, caused by the pyramidalization and the

resulting repulsion of valence electron pairs (rehybridization), C60 is a comparatively

5

Introduction

electronegative molecule that is easily accessible for reductions and for the addition of nucleophiles.

v. Due to the pyramidalization of the C atoms and the rigid cage structure of C60 the outer convex surface is very reactive towards addition reactions but at the same time the inner concave surface is inert (chemical Faraday cage). This allows the encapsulation, observation and tuning of the wavefunction of extremely reactive species that otherwise would immediately form covalent bonds with the outer surface.

Since the beginning in the early 90’s a large variety of chemical transformations has been investigated,[49] including addition[50] of alkyl radicals[51] and perfluoroalkyl radicals.[52] Moreover reactive species like superoxide or hydroxide radicals[53] and centered radicals.[54] Furthermore halogenation by reaction with chlorine,[55] [56] and fluorine,[57] as well as metal fluorides[58] and noble gas fluorides,[59] was observed. Another type of functionalization is of organo lithium organyls and Grignard reagents,[60] amines,[61] hydroxides,[62] alkoxides,[63] cyanides,[64] phosphonium ylids[65] or nucleophiles.[66]. Oxygenation via UV irradiation,[67] heating in the presence of oxygen[68] or reaction with oxiranes[69] is also possible. Last, cycloaddition of the [4+2] Diels-Alder-type with dienes[70] and [3+2] dipolar cycloaddition with azides,[71] diazomethanes[72] or diazoacetat.[73] Furthermore [2+2]cycloaddition of benzyne[74] and ketenes[75] as well as [2+1] cycloaddition of [60a] and nitrenes,[76] are well documented fullerene transformation reactions.

Due to their importance in the use of fullerene functionalization, two very prominent reactions must be emphasized. The is a very versatile cycloaddition. In general C60 reacts with highly reactive ylides in situ in a [3+2] dipolar cycloaddition.[77] The ylide is formed by the reaction of an amino acid, e.g. sarcosine, and an aldehyde. These precursors can be bound to a variety of functional groups, thus allowing the introduction of all kinds of structural motifs on the fullerene core. The second reaction will be discussed in more detail, because of its pertinence for this work. Nucleophilic cyclopropanation is one of the most common fullerene functionalization methods and named after its discoverer Carsten Bingel.[78] In the Bingel- reaction bromomalonates and C60 form methanofullerenes in the presence of a base, here NaH (Scheme 1). The α-halo-CH-acidic malonate is deprotonated and a is formed, which reacts with the electron deficient fullerene [6,6]-double bond.[79] The halogen on the malonate is then substituted by the new carbanion located on the fullerene and methano fullerene 1 is obtained through intramolecular ring closure.

6

Introduction

[78] Scheme 1: Cyclopropanation of bromomalonate with C60 under Bingel conditions.

The malonate precursors, required for this addition reaction, are readily synthesized by esterification of alcohols with the selected malonates. However, in the original protocol brominated malonate had been used as nucleophile. Since the preparation of monobrominated malonates is quite tedious, later works prefered in situ halogenation with elemental [80] [81] and CBr4. Another improvement over the original protocol was the use of the organic non- nucleophilic base DBU, instead of NaH, facilitating the workup procedure .[82]

According to the rules of reactivity mentioned earlier, the nucleophilic or radical attack only happens at [6,6]-double bonds. Furthermore, the formation of [5,6]-double bonds is avoided, due to the unfavorable increase of strain energy. Therefore the regiochemistry of methanofullerenes is simplified. Only two of the possible four isomers (Figure 4) can be isolated – the [5,6]-opened a and the [6,6]-closed c.[72c]

Figure 4: The four theoretical monoadduct isomers.[72c]

7

Introduction

1.2.2 Multiple Exohedral Functionalization

With the technique for exohedral functionalization at hand, the next step was the synthesis of polyadducts with defined three-dimensional structure. The fullerenes spherical shape and its multitude of possible binding sites, allow for it being used as a structure–determining tecton. A plethora of interesting architectures with highly symmetrical and stereochemically defined addition patterns is feasible, with possible applications in material[83] or biological research.[84]

Nine different binding sites are available for the second attack at a [6,6]-double bond of a C60 monoadduct (Figure 5). Therefore, nine different regioisomers can theoretically be obtained for two different addends. Only eight regioisomeric bisadducts must be considered for identical addends.[85] In order to distinguish the different isomers, a simple nomenclature was introduced by Hirsch.[86] The [60]fullerene is divided in two hemispheres. Now the isomers can be named in regards of the relative positional relationship of [6,6]-bonds. The attack of a second addend can take place on the same hemisphere as the first addition (cis) or on the opposite one (trans) or equatorial (e). In order to discern the three cis and four trans [6,6]-double bonds from each other, a number is assigned to each, indicating its distance to the poles. Two regioisomers are principally possible from attacks at the equatorial sites (e’ and e’’). However, for identical addends, addition in these positions leads to the same product – as mentioned above.

Figure 5: Denotation for [6,6]-bisadducts in relationship to the first addend A1.

Unfortunately, this nomenclature is not suitable for higher adducts nor [5,6]-addition patterns. Hence, Hirsch introduced a general algorithm,[87] based on a numbering scheme of the C atoms of a given fullerene in a spiral fashion, devised by Taylor.[88] A Schlegel diagram is used to depict the spherical C60 in a two-dimensional plane. Some fullerenes – for example the bisadducts cis–

3 (C2–symmetry) and trans–2 (C2) or the trisadducts trans–3, trans–3, trans–3 (D3) and e,e,e

(C3) – have an inherent chiral addition pattern. Even when symmetrical, achiral addends are used, the mirror images of the two isomers cannot be brought to superposition. Diederich proposed configural descriptors fC and fA to unambiguously describe the absolute configuration of an adduct and so distinguish the two enantiomers (Figure 6).[89] This procedure utilizes the fact, that the numbering schemes in Schlegel diagrams are chiral themselves, 8

Introduction despite the inherently achirality of fullerenes. The diagram is numbered in a way, which leads to the lowest set of locants. The handedness of the numbering scheme is determined and indicated by a descriptor – fC for fullerene clockwise or fA for fullerene anticlockwise.

f f [89] Figure 6: Configural descriptors C and A in a Schlegel diagram of inherently chiral C60 adducts.

[60]Fullerene adducts with multiple addends are widely investigated, finding applications for [90] example in supramolecular materials. An example is the formation of C60 with an octahedral addition pattern.[91] By using a reversible template activation fairly high yields are obtained for fullerene hexakisadducts. In a first step, an excess of 9,10–dimethylanthracene (DMA) is added to a solution of [60]fullerene. In contrast to the addition of malonates, the Diels–Alder reaction is reversible at room temperature. Higher DMA-adducts are formed, by increasing the amount of DMA, to shift the equilibrium towards higher addition products.[92] An incomplete octahedral addition pattern predominates at equilibrium.

This allows for an irreversible addition by an added malonate. DMA is successive replaced in [82] situ until the Th–symmetrical hexakisadduct with irreversible addends is achieved. Another method for the synthesis of a variety of hexakisadducts does not use DMA but an increased [93] excess of CBr4.

Unfortunately, for lower adducts, regioselective synthesis is quite challenging. Isomeric mixtures are obtained which afford a tedious chromatographic separation and lower the yields significantly.[94] To overcome this problem, Diederich and co-workers[95] proposed the regioselective addition of multiple addends to C60 by tether-directed remote functionalization – an adaptation of a similar strategy developed by Breslow (Scheme 2).[96] A defined spacer connects two or more functional groups – in the case of Bingel-functionalization malonates are used. The second addition reaction only takes place after the first addend was bound to the C60

9

Introduction core. Therefore, the addition site of the second addend is predetermined by conformational preferences and steric constraints of the tether. The tether is ideally designed in such manner as to only enable the successive intramolecular reaction taking place at one specific position. Almost all bisadducts – cis-1 is sterically impossible – are accessible through this functionalization concept by choosing the appropriate tethered bismalonate system.[97]

Scheme 2: Scheme for the tether directed remote functionalization for C60 bisadducts.

1.2.3 Cyclomalonate as Building Block in Fullerene Chemistry

Despite the successful application of malonates for the tethered remote functionalization of fullerenes, this method has some disadvantages. A complex, multistep synthesis is necessary to obtain tethered addends. The yields of the functionalization reactions are low.[98] Higher adducts – with exceptions[98-99] – are almost impossible to synthesize. Furthermore, the tethers have to be specifically designed for each addition pattern. There is no building block, which enables a fast and reliable access to the whole variety of fullerene multiaddends.

Most of the previous examples used tethers with addends in a preformed and rigid structure. This was done for the purpose of selectivity. By using more flexible linker systems, such as alkyl chains, several positions for the second addend become available, thus causing the isomeric mixture, the method was designed to prevent in the first place. This problem can be avoided by the formation of macrocyclic rings, reducing the flexibility of the spacer. Many examples for synthetic macrocyclic di-and tetralactones can be found in literature.[100] Several different spacer moieties are used to bridge the two ester in the macrocycle, including ethyleneglycol,[101] oligoether[102] and o-bis(bromomethyl)benzene.[103]

The simplest linker chain is an alkyl chain. Such macrocycle, containing alkyl spacer and two or more malonates have the ability to bind to C60 in multiple places. These systems, developed by Hirsch and co-workers[104] exhibit all the desired characteristics, missing in previous examples – facile synthesis of the addends, high and regioselectivity for the addition to [60]fullerene and facile adaptation to a wide range of addition patterns. By varying the spacer length, the 10

Introduction selectivity can be adjusted, making this a very versatile method. Since the IUPAC nomenclature is not convenient, these compounds are called “cyclo-[n]-alkylmalonates”, with the number in brackets representing the number of repetition units.[105] In this way, regioselectivity is not based on steric preorganization but the minimization of unequal strain in the alkyl chains.[106] As a consequence, the symmetry of the addition pattern is determined by the alkyl chains used as spacer. In macrocycles with alkyl chains of identical length, only adducts with rotational symmetry – C2 for bisadducts and C3 for trisadducts – are formed. Other regioisomers are not accessible through this method, because they would introduce strain, caused by different distances between the ester functions. On the other hand, in the case of mixed macrocycles only Cs-symmetrical adducts are formed, for the same reason explained above. Several bis-, tris and even tetrakisadducts have been synthesized with these macrocyclic systems(Figure 7).[107]

Figure 7: Examples of bis-, tris- and tetrakisadducts obtained through tether-directed remote functionalization. [107]

By adding one or several addends to the fullerene cage, its Ih symmetry is reduced. To every addition pattern of the resulting adducts a subgroup of the cyclic and dihedral point group can be allocated. Some of them, e.g. the D3, C1, C2 and C3 point groups, are chiral, so every addition pattern belonging to these point groups is inherently chiral[80, 108]. The synthesis of such inherently chiral adducts is widely researched,[85-86, 109] and enantiomerically pure adducts are of great interest, for example as building blocks in chiral macromolecular architectures.[110] One approach is the stepwise nucleophilic cyclopropanation to the desired inherently chiral adduct, followed by separation of its racemic mixture with preparative chromatography on a chiral

11

Introduction column.[111] Another way to obtain enantiomerically pure [60]fullerene adducts is the utilization of chiral tethered systems. For that purpose, an optically active spacer is used to connect the reactive malonate groups. Examples include the use of isopropylidene ketal[80, 112] and the Tröger base.[113] Most of the chiral tethered systems use the open-chain motif of two or more malonates connected by a rigid spacer. As shown earlier, the cyclo-malonate approach is superior to that of rigid tethered systems, for its greater adaptation potential and simpler synthesis. Unfortunately the addition of cyclo-[n]-malonates leds to a racemic mixture of C60 adducts with an inherently chiral addition pattern. Therefore, new chiral cyclo-malonate tether had to be developed to synthesize enantiomerically pure adducts. One such example is the preparation of the pure enantiomers of a [60]fullerene trisadduct with an e,e,e-addition pattern.[114]

Scheme 3: Preparation of cyclo-[n]-octylmalonate from malonyl chloride and octane diol with pyridine. 12

Introduction

Preparation of cyclo-[n]-malonates can be done in several ways. The simplest is a one-pot condensation depicted in Scheme 3. Up to nine diol repeat units can be detected in the crude mixture by FAB MS analysis. The most desired products – the monomeric, dimeric and trimeric malonate macrocycles – are admittedly the most abundant. Since cyclo-[2]-alkylmalonates are of the most interest for many projects done on this topic, different approaches for the synthesis of said compounds were investigated. Multi-step synthesis is one possibility to improve the yield of dimeric macrocycle formation. One way is to use an excess of malonic acid instead of equimolar amount of malonyl dichloride (Scheme 4). A high dilution is necessary as well, to prevent the formation of cyclic and polymeric side products. In this way, a malonate dimer, linked by the alkyl chain, is formed primarily and can be isolated. The formation of macrocycles with an uneven number of repetition units in the second step is prevented, reducing the number of possible byproducts by half. Problematic is the separation of alkyl linked malonic acid derivative by , due to its two free carbonic acid functionalities, causing a high polarity. An improvement is the utilization of methyl malonyl chloride instead of malonic acid. It has the advantage, that separation after the first step and working with high dilutions are not necessary. This method requires, however, an additional step of ester hydrolysis.

Scheme 4: Selective preparation of cyclo-[2]-malonate from malonic acid and diol under Steglich

conditions.

The yield limiting step in all previous described synthesis methods is the intramolecular esterification of the diol and malonyl dichloride. Since it is a statistic reaction, higher macrocycles than the desired cyclo-[2]-malonate are formed as well, reducing the overall yield. In order to overcome this problem, a metal template could be introduced to hold the reactive groups in proper position[115] for the formation of the bismalonate. Similar to the preparation of several crown-ethers, the metal could coordinate to oxygen in the diol and the malonate. Unfortunately, the limited number of donors in both precursors might not be enough for the metal to coordinate to. This problem is solved by the exchange of alkyl chains for polyether linker, resulting in a crown- ether-like macrocycle. Zhou et al.[116] were the first to utilize this concept. By exchanging the alkyl chain for triethylene glycol, they were able to apply solid- liquid phase-transfer- (PTC) conditions and KF as template to prepare mono-, bis- and

13

Introduction trismalonates with polyether linkers. The yields for the templated cyclization were in fact improved, compared to those in the absence of PTC conditions. Another example for the successful use of templating ions in the synthesis of polyether-malonate macrocycles was done by the group of Chronakis,[117] investigating amphiphilic [3,3]-hexakisadducts – consisting of cyclo-[3]-octylmalonate in one sphere of the fullerene core and cyclo-monomalonates bearing a 1,2-diol moiety as hydrophilic head on the other. They were interested in the effect of structural change of the addends on the aggregation behavior. Therefore, two ethylene units were exchanged for oxygen. The additional oxygen donor in the diol enabled them to double the overall yield of the malonates step-wise preparation by using Na+/K+ as templating for the cyclization step.

Nowadays, the applications for cyclo-[n]-alkylmalonates are not limited to tether-directed addition on C60. They have become a versatile building block for fullerene chemistry. As mentioned earlier,[117] cyclic addends can be used to introduce functionalities to the fullerene core. Most malonate addends found in literature are opened-structure malonates substituted with flexible alkyl chains. In contrast, macrocyclic malonates are quite rigid, the macrocyclic structure restricting their flexibility. This effect is often utilized for the synthesis of Th- [118] symmetrical hexakisadducts of C60. Cyclo-[2]-malonate is also used as linker between two fullerenes.[119]An impressive example was prepared in the group of Hirsch.[93a] Mixed [5:1]hexakisadducts bearing one cyclo-malonate were cyclopropanated to a fullerene core, resulting in a novel heptafullerene. This procedure also allowed the synthesis of a Janus dumbbell, containing both anionic and cationic termini.

1.2.4 Click Chemistry as Powerful Tool for Fullerene Functionalization

Previous chapters covered the regio- and stereoselective functionalization of fullerenes with one or multiple addends. These allow the easy preparation of fullerene derivatives with improved physical properties – e.g. solubility, biological activity or electronic behavior. Unfortunately, the synthesis of structurally more complicated addends is generally complex, low yielding and requires tedious purification.[120] This limits the accessibility of fullerene derivatives, rendering the approach unpractical. Furthermore, the preparation of different malonates for each derivative would be necessary.[121] Therefore, an alternative strategy has to be found. Nevertheless, post-functionalization is not very common.[122] Due to the chemical reactivity of the fullerene subunit, further chemical transformation of fullerene derivatives is limited. Some attempts were made to transform [60]fullerene derivatives into sophisticated molecular structures by using reaction types like esterification,[123] amidification[124] and condensation.[125] A problem poses the limited scope of the reactions, because not all functional groups are tolerated. A better alternative would be the formation of simpler addends bearing terminal groups that allow the post-functionalization of its C60 derivative with different kinds of functional groups.[126] 14

Introduction

Furthermore, to obtain functionalized derivatives in good yields, an extremely efficient reaction is required. Click chemistry comes to mind, as an appealing tool for the post- functionalization of fullerene derivatives[93b] under these requirements.[127]

The term “click” chemistry was coined by Sharpless,[128] when presenting new synthetic strategies for drug discovery, following one rule: “All searches must be restricted to molecules that are easy to make”. Thus, the aim was to generate new substances by combining small units with heteroatom links. A set of stringent criteria were defined, that a reaction must fulfill to be counted as “click” reaction. It must be modular, wide in scope and stereospecific (but not necessarily enantioselective). The reaction must give high yields, work under simple reaction conditions and with readily available starting materials and reagents. Isolation of the product must be nonchromatographic. No solvents or a solvent that is either benign (like water) or easily removed must be used. Since its proposal in 2001, the “click” chemistry approach had a significant impact on synthetic chemistry, with applications in biology,[129] material science[130] and drug discovery.[131]

The most famous example of click-reactions[132] is the 1,3-dipolar Huisgen alkyne-azide cycloaddition. Here, triazoles are formed by the reaction of azides with alkynes. Kinetic factors allow aliphatic azides to remain nearly chemically invisible until presented with a good dipolarophile, although azide decomposition is thermodynamically favored. The slow cycloaddition is a direct effect of said kinetic stability of alkynes and azides. As a result, the reaction usually requires long reaction times and elevated temperatures. A mixture of 1,4- and 1,5-regioisomer is obtained with the original version of the Huisgen 1,3-dipolar cycloaddition.[133] The investigation of the selective formation of only one regioisomer brought no usable results.[134] The Cu(I)-catalyzed variant of the 1,3-dipolar cycloaddition of azides and alkynes were presented by Sharpless[135] and Meldal[136] independently. The copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) has many advantages over the original procedure. The reaction works at room temperature in all solvents, the exclusion of oxygen and water is not necessary. Almost full conversion and regioselectivity towards the 1,4-isomer are achieved with the copper-catalyst, making this reaction a prime example for “click” chemistry. In fact, “click chemistry” is often used as synonym for the Cu(I)-catalyzed 1,3-dipolar cycloaddition. Commonly, Cu(SO)4*5 H2O and sodium ascorbate as reducing agent are used to generate Cu(I) in situ. Mixtures of water and organic solvents are used as solvents. A stepwise mechanism was proposed. The catalytic cycle (Scheme 5) starts with the formation of Cu(I) acetylide. In the first step a π-complex between the copper dimer 1 and the alkyne is formed. The terminal hydrogen is removed to give the copper acetylide 2. This is normally achieved without the addition of a base in aqueous solution, due to the copper π-coordination lowering the pKa of the alkyne hydrogen up to nine orders of magnitude. A base, such as 2,6-lutidine or N,N’- diisopropylethylamine (DIPEA), must be added, when a non-basic solvent, such as acetonitrile, is used. As with the Sonogashira coupling[137], internal alkynes do not react under these conditions.[138] Despite large efforts, the nature of the copper acetylide complex is not

15

Introduction completely resolved. A change between mono-, di- and polymeric complexes is indicated by the different reaction orders found in dependence on the copper concentration. The two-copper species 3 has an important role, as one copper is complexed to the acetylene unit, while the other can activate the azide. Although the subsequent cyclization has only been explored for monomeric copper species, a similar process can be proposed for dimeric copper complexes.[139] Metallocycle 4 is generated by the nucleophilic attack of the acetylide carbon on the complexated azide,[140] followed by the transformation to the triazole 5. In the end the catalyst is regenerated and the product obtained through protonation of the triazole-copper derivative 6 and dissociation of the product.

Scheme 5: Mechanism of copper(I)-catalyzed alkyne-azide cycloaddition.

While CuAAC is apparently a highly efficient and versatile reaction, it has not been used for fullerene functionalization in the early years. Isobe was the first to present a fullerene derivative with terminal azide moieties to be used in CuAAC.[141] The problem was, that in [71a, principle, organic azide may undergo [3+2]cycloaddition to the [6,6]double-bonds of C60 142]as opposed to the desired “click” reaction. However this reaction usually requires elevated temperatures.[143] With the copper-mediated Huisgen 1,3-dipolar cycloaddition of azides and alkynes being carried out at room temperature, the reaction of C60 with azides should not significantly compete with the cycloaddition leading to the desired 1,2,3-triazole derivatives. Still, it was not clear, whether CuAAC reactions were compatible with fullerenes. The group of Nierengarten[120b, 144] and others[145] performed systematic investigations into the possibility of using “click” chemistry for the functionalization of [60]fullerene derivatives. Using Bingel-type fullerene derivatives with terminal alkyne groups (Scheme 6), it was demonstrated, that under CuAAC conditions and optimized concentration – using highly soluble building blocks like 2 – the reactivity of the fullerene moiety with the organic azide was negligible. In contrast, when using poorly soluble compounds (4) and the cycloaddition of azides to the C60 core is more

16

Introduction distinct. The reactivity is further reduced, when fullerene bisadducts are used (6). This is in accordance with the well-known fact, that the reactivity of the fullerene unit decreases, when the number of substituents increases.[97d]

Scheme 6: 1,2,3-Triazole-formation under CuAAC-conditions with different alkyne precursor 2,4,6. [144b]

When using terminal azide moieties instead of alkynes, the stability of the fullerene derivatives becomes problematic. This is caused by intermolecular cycloaddition reactions between the azides and C60. Again, this effect is less severe for fullerene multiadducts. The stability of the fullerene azide derivatives can be increased by choosing the right addend.[123a, 146] Encapsulation of the fullerene sphere in a cyclic addend surrounded by two 3,5- didodecylbenzyl ester moieties prevents the unwanted side reaction through sterical hindrance.

Fullerene hexakisadducts with 12 terminal alkyne or azide groups were also investigated.[93b, 120b, 126] The advantage over the standard one-step approach is the comparatively simple synthesis of the precursors. They enable the functionalization of C60 with 12 fairly complex building blocks. Both alkyne and azide bearing hexakisadducts were prepared, the azide compound having the same stability issues as described above. Still, mixed [5:1] fullerene 17

Introduction hexakisadducts with both alkyne and azide functional groups were synthesized successfully. Using a TMS-protected alkyne unit, the corresponding azide/alkyne building blocks could be clicked to the fullerene in two successive CuAAC reactions. The copper-catalyzed 1,3 cycloaddition also allows the synthesis of compounds, that are hardly accessible from [147] corresponding malonates and C60. By reacting a fullerene hexakisadduct 8 bearing 12 terminal alkyne groups with dendritic azides, fullerodendrimers were obtained in very good yields. In fact, the first-generation dendritic C60 hexakisadduct was prepared in 17-fold higher yield than a comparable, literature known compound.[148] Besides, the second-generation derivative obtained via CuAAC reactions, is almost impossible to prepare from C60 and the corresponding malonate (Figure 8).

Figure 8: Fullerodendrimer 8 from fullerene hexakisadduct bearing 12 terminal alyne units and 12 Gn- azides (n = 0,1, or 2).[120b]

Another interesting application for copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition reaction is the formation of all carbon , comprising fullerenes and carbon nanotubes (CNT) or graphene oxide (GO). Their remarkable electronic properties make them an interesting topic in the field of material science.[149] Unfortunately, such hybrid materials are quite problematic to synthesize, due to the low solubility of the starting materials. Moreover most functionalization reactions of CNT and GO are not compatible with fullerene derivatives, because of its limiting chemical reactivity. However, it was demonstrated, that by grafting fullerene-azide under CuAAC conditions to nanomaterial, pre-functionalized with terminal alkynes, hybrid [150] can be obtained.

18

Introduction

1.3 Applications of Fullerene Compounds

Due to the combination of three-dimensionality with unique photoelectric and electrochemical properties, fullerene derivatives offer a huge potential as nanostructures in different areas of research, e.g. material science, , organic electronics or . The constant interest in this carbon sphere over the last decades resulted in the synthesis of many astonishing and aesthetically pleasing architectures with all kinds of properties. Functionalized [60]fullerene in the form of [6,6]phenyl-C61-butyric acid methyl ester (PCBM) is investigated as electron acceptor material in organic bulk-heterojunction solar [151] cells. C60-derivatives will, in the years to come, certainly find their way out of the laboratory into everyday life. The following will give a short overview about two examples of the manifold fields; applications of fullerenes are currently investigated in. Due to the scope of this thesis, the overview cannot be comprehensive, and will focus on those examples, which are interesting and relevant for the fullerene architectures that have been synthesized in this work.

1.3.1 Bioactive Fullerene Derivatives

1.3.1.1 Fullerenes in Medicinal Chemistry

Fullerenes, with their three-dimensional nature and unique electronic properties, have become interesting research targets for the formation of biologically active molecules. The biggest problem for the application of fullerene derivatives in biological systems is their lack of solubility in aqueous solution. Therefore, a central aspect of research in this field was the development of efficient strategies to obtain biocompatible fullerenes.[152] To overcome the fullerenes natural repulsion for water, different methods were tested. Among the most common – besides encapsulation[60a, 153] and suspension[154] – is the introduction of solubilizing groups through chemical functionalization. By covalently attaching hydrophilic groups to the [155] C60 core, the fullerene derivatives are easily dissolved in water (Figure 9). Problematic, still, is the monoadducts’ tendency to form clusters in aqueous solutions. Here, the hydrophobic carbon spheres stick to each other with the hydrophilic chains surrounding the aggregate.[156] This effect can be avoided by multiple functionalization, with bisadducts apparently being enough to reduce the problem of clustering.[157] Better still are fullerene hexakisadducts, because of the peculiar spherical distribution of substituents around the C60 core, resulting in high solubility without the risk of aggregation.[158]

Fullerene derivatives are investigated for many different possible applications in medicinal chemistry.[159] They exhibit competitive inhibition of HIV-1 protease (HIVP) (Figure 10). A quasi-spherical hydrophobic cavity with a diameter of about 10 Å can be found on HIVP’s active site. Friedman[84, 160] was the first to demonstrate, through molecular modeling and experiments, that the hydrophobic site is able to accommodate [60]fullerene, which then is able to inhibit the catalytic activity of HIVP.

19

Introduction

Figure 9: Water-soluble dendro[60]fullerene 9.[155]

Cationic fullerene derivatives can be used as gene vectors.[161] It’s worth pointing out, that the fullerene derivatives’ cytotoxicity is negligible. It appears to be essential, that the

functionalized C60 has the appropriate balance between hydrophobicity and hydrophilicity. Otherwise fullerene-DNA nanostructures, that are capable of crossing the cell membrane and releasing the DNA, are not formed.[162] Derivatives, obtained from fullerene hexakisadducts via CuAAC post-functionalization, demonstrated remarkable gene-delivery capabilities.[163] Polyplexes from DNA and dendronized polycationic fullerenes exhibit the same efficiency as commercially available systems. Typically, the efficiency of dendritic vectors is directly correlated to the number of generations.[164] In contrast however, the gene-delivery capability is already at optimum for the second-generation compound of fullerene vectors.

Figure 10: Fullerene derivatives with the ability to inhibit the HIV-1 protease.[160]

Fullerenes, with their extended π-conjugation, absorb visible light and have a high triplet yield. 10 11 12 They are able to generate reactive oxygen species upon illumination, what makes them a possible candidate as photosensitizer (PS) in photodynamic therapy (PDT) to treat multiple diseases, for example cancer.[165] The PS is administered to a lesion. After accumulation, the lesion is irradiated with visible or near infrared light in the presence of oxygen, leading to the generation of cytotoxic oxygen species, which causes cell death and tissue destruction.[166]

20

Introduction

1.3.1.2 Glycofullerenes

Another example of bioactive fullerene derivatives developed in the last two decades is glycofullerenes. These C60 derivatives, substituted with sugar residues, are of particular interest.[167] Besides acting as solubilizing groups, the intrinsic biological properties of the sugar residues also provide additional appealing features to the conjugate.[168] The first synthesis of glycofullerenes was reported by Vasella and Diederich.[169] They reacted a nucleophilic glycosylidene precursor with C60, to introduce protected carbohydrates into the carbon cage. Since then, several other glycofullerenes have been synthesized (Figure 11). One [170] method is to use reactive sugar derivatives for the direct functionalization of C60. For the others, fullerene derivatives bearing suitable functional groups are prepared. In the last step, complementary saccharides bind to these functional groups to form the conjugates.[171]

[169-171b] Figure 11: Some literature known examples of glycofullerenes.

As mentioned before, the most important requirement for the biological activity of a compound is water solubility. This, unfortunately, is limited for glycofullerenes with one or two sugar residues. Therefore, the number of sugar moieties on the carbon cage has to be increased. The group of Nakamura[141, 172] developed a methodology, yielding a highly water-soluble glycofullerene with five azido-carbohydrate moieties clicked to a pentaalkynylated C60 core under CuAAC conditions. In another approach, Hirsch and co-workers[173] reported the formation of mono-and bisglycodendron fullerene adducts with six sugar subunits in the periphery. All previously mentioned, glycofullerenes are amphiphilic. A large part of the outer architecture of the molecule is occupied by the hydrophobic fullerene subunit, which causes aggregation and reduces the solubility.[168] To overcome this problem, one can take advantage of the unique globular structure of the fullerene hexakisadduct. A direct functionalization of

C60 with six sugar residues bearing malonates, however, is not suitable. This method would require the use of protection groups on the hydroxyl functions of the carbohydrates and the synthesis of new malonate building blocks for every sugar subunit.

21

Introduction

A better approach is to obtain glycol hexakis fullerenes through post-functionalization with easily accessible building blocks via CuAAC. In this way, fullerene “sugar balls” were obtained, with 12 or more functional groups on their periphery in a unique globular and multivalent topology.[121]

The investigated biological applications for glycofullerenes are similar to other fullerene derivatives, mentioned in the last chapter. So, glycoconjugates are able to generate reactive oxygen species to selectively degrade HIVP.[174] This is due to the high affinity of the protein for fullerene derivatives. Another example, exploiting the phototoxicity of glycofullerenes, lies in the potential use as a photosensitizer in PDT.[175] In most examples reported in literature, the sugar subunit is used as solubilizing agent. But some make use of carbohydrate-protein interactions, vital to a large variety of biological processes.[176] The proteins involved in these biomolecular interactions are called lectins. Intensive investigations have been made on the design of high affinity for such proteins. Blocking or influencing some essential biological processes might be possible with these synthetically obtained molecules.[177] Colonization and bacterial adhesion to host cells comes to mind as typical example. It is the first step in bacterial infection[178], and might be prevented or even reversed by anti-adhesive agents, prepared from glycofullerenes, interfering with the recognition process between host cell and pathogen. High-affinity ligands block the bacteria’s lectin binding site.[179] A multivalent presentation of carbo-hydrates is necessary for this purpose. Sugar balls, with their high local concentration of sugars around the C60 core fulfill this requirement perfectly. In fact, binding studies on different lectins[180] demonstrated high binding affinities.

Likewise, interactions between cellular receptors and glycoconjugates present on the surface of pathogens play a major role in the early stage of certain infections. Several viruses, like HIV and Ebola, depend on these interactions to enter and infect the cells.[181] Therefore, novel ligands, that bind with high affinity to these receptors, effectively blocking the receptor at the early stage of infection and inhibiting the entry of pathogens, are essential. Here too, glycofullerenes demonstrate interesting antiviral activity. The group of Martin[182] used “click” chemistry to synthesize fullerene hexakisadducts, bearing up to 36 sugar moieties. In an Ebola pseudotyped infection model, they effectively inhibited the viral infection. It is notably, that the combination of multivalency with the right ligand accessibility and flexibility is of eminent importance for the affinity of the binding process. Recently, the same group[183] reported the synthesis of a tridecafullerene, decorated with 120 peripheral carbohydrate subunits, the so called “superball” (Figure 12). Despite their size and molecular complexity, the synthesis is straightforward and affords the final compound in good yield. As before, copper-catalyzed 1,3 dipolar cycloaddition is used to graft 12 [5:1]fullerene hexakisadducts with a terminal azide group onto a fullerene hexakisadduct, bearing 12 terminal alkyne units. Three different “superballs” were prepared, varying in chain length and carbohydrate.

22

Introduction

As expected, the galactose derivative was not able to inhibit the infection, since the investigated receptor is selective for mannose. On the other hand, both compounds with mannose-based residues showed very strong antiviral activity.

Figure 12: Giant globular multivalent glycofullerene 16 as potent inhibitor in a model of Ebola virus infection.[183]

23

Introduction

1.3.2 Photoactive Fullerene Derivatives

Fullerene C60 is a redox active chromophore. According to theoretical calculations, it exhibits a

LUMO comparatively low in energy that is triply degenerate. This is the reason why C60 acts like an electronegative molecule, readily accepting up to six electrons in solution.[43, 184] In electron-transfer processes [60]fullerene demonstrates a very remarkable property. It accelerates the photoinduced charge separation and slows down the charge recombination in the dark.[184c, 185] The explanation for such unique photophysical properties can be found in the combination of the symmetry of the C60 π-system and the pyramidal nature of the fullerene constituent carbon atoms.[186] Furthermore, the reorganization energy (λ) of the fullerene is smaller compared to other acceptor molecules.[187] A wide variety of donor-acceptor systems – such as molecular dyads, triads, tetrads and pentads, connected by covalent or supramolecular bonds – have been designed, with these unique electrochemical and photophysical properties as motivation.[188] Suitable electron donors for the electron transfer to fullerenes include porphyrins, phthalocyanines, tetrathiafulvalenes, ferrocenes and other metallocenes, amines and π–conjugated oligomers and dendrimers.[189] Due to the interesting optical and electronic properties, the investigation of donor-linked organofullerenes is a promising field. Such compounds are the basis for molecular devices,[190] for the preparation of systems exhibiting nonlinear optical properties[191] and for the design of artificial photosynthetic systems.[192]

Porphyrins are frequently used as electron donor in such donor-acceptor conjugates. They are easily synthesized, chemically stable, and most importantly, porphyrins exhibit excellent light absorption properties.[193] Furthermore, the molecules can be reversibly oxidized.[194] In a porphyrin-fullerene hybrid, both their internal structure and solvent neighbourhood are only slightly affected by addition or removal of electrons, due to their rigid scaffolds, large size and strong conjugation.[195] Owing to the efficient photogeneration of long lived charge-separated states by photoinduced electron transfer, these conjugate systems are of particular interest for photovoltaic devices. The solar energy conversion efficiencies of such hybrid compounds are [196] very promising. Since the first reported preparation of a C60–linked porphyrin by Gust et al. (17),[197] a great number of covalently linked dyads (Figure 13), triads and multichromophoric arrays have been synthesized in different geometries, including cyclophane (20)[198] and pacman systems (18).[199] Dendritic molecules, featuring an array of peripheral porphyrins grafted onto a fullerene core, have been reported as well.[200] Other examples in which the fullerene is linked to the β-pyrrole position[201] or through the benzene ring at the ortho position [202] exhibit a more rigid geometry. Furthermore various wire-like molecular spacers have been used as linker between donor and acceptor (19).[203] A better understanding of the intercomponent excited state interactions in these porphyrin-fullerene hybrids could be gained through systematic changes of the relative distance and orientation of the two partners as well as of the solvent polarity.[204]

24

Introduction

[197-199, 203] Figure 13: Different types of covalently bound porphyrin-fullerene dyads.

Although most research on porphyrin-fullerene conjugates was based on covalent chemistry, several examples of supramolecular ensembles involving both chromophores have been reported.[205] Many of these hybrids involve π–π-interactions[206] between donor and acceptor, particularly with porphyrin tweezers and cages (21).[207] However, the nature of this affinity is not fully understood and challenges the traditional belief that a curved guest requires curved hosts for effective complexation.[208] The reason probably lies, as crystallographic data suggests, in the attraction between the protic center of a free base porphyrin or the metal of a metalporphyrin and the higher electron density of a [6,6] double bond The role of the metal atom is not fully investigated yet.[205c, 209] Other supramolecular interactions involve metal−ligand bonds,[210] hydrogen bonds,[211] electrostatic interactions,[212] mechanical bonds,[213] or a combination of several of these interactions.[205c, 214] In contrast to covalently bound hybrids, supramolecular arrays involving conjugated multiporphyrin systems are rare in the literature (Figure 14).[205d, 215]

25

Introduction

Figure 14: Example for the supramolecular ensemble of porphyrin and fullerene.[207]

Among the numerous covalently linked porphyrin-fullerene conjugates, a few were synthesized using copper-catalyzed azide-alkyne cycloaddition.[216] Fazio et al.[217] were the first to report the application of CuAAC to form triazole-linked porphyrin-fullerene dyads. One reason for the use of aromatic triazoles as bridging unit is their ability to act as conjugative π-linker in intramolecular electron transfer processes.[218] Another advantage is the facile synthesis of clickable building blocks, allowing the preparation of more complex hybrid structures, which are difficult to obtain from direct functionalization. In this way, otherwise hardly obtainable hexakisadducts with 12 porphyrins in the periphery (Figure 15) can be prepared in good yields.[93b] The large number of chromophores causes a very strong absorption in the UV/Vis region. Meanwhile intramolecular π-π-interactions between porphyrins in the dendrimer structure can be observed as broadening of Soret and Q bands. In contrast to the aforementioned hybrid systems, this giant globular conjugate exhibits no photoinduced processes. Due to the hexafunctionalization of the fullerene core, the π- fullerene structure is extensively broken and photoinduced electron transfer becomes thermodynamically permitted. However, a monosubstituted guest can axially coordinate to the multi-topic receptor. A photoinduced electron transfer can be observed with a relatively long life-time for the charge-separated state. Furthermore, the multiporphyrin array can act as antenna, harvesting the absorbed light prior to the electron-transfer event. Such host-guest ensemble mimics all the primary events of the natural photosynthetic system.[205b]

26

Introduction

[93b] Figur e 15: Multimetalloporphyrin array constructed around a hexasubstituted fullerene core.

27

Aims

2 Proposal

Based on previous results of several predecessors in the field of fullerene and porphyrin chemistry, the primary aim of this thesis was the development of new porphyrins-fullerene dyads. In contrast to previous works, instead of open-chain malonates, cyclo-[2]-malonate, developed in our group, should be used as linker unit (Figure 16). Such compounds are unprecedented in literature and promise new and interesting properties. In contrast to open- chain malonates, cyclic malonates have a more rigid structure, which should result in conjugates with a defined structure. The reduced flexibility should also have a positive influence on a possible charge transfer system between the porphyrin and the fullerene core. Furthermore, the spatial arrangement should be conserved, when the malonate’s alkyl chain length is increased, therefore simply increasing the distance between fullerene and porphyrin, keeping the fixed geometry.

Figure 16: Concept for novel cyclomalonate-linked porphyrin-fullerene conjugates.

Since the addition chemistry of malonates to the fullerene is widely understood, the synthetic strategy should be focused on the development of a connection between the cyclo-[2]- malonate and the porphyrin. It is important to note, that only one side of the malonate can be affected by this, while the other must remain completely unaltered, allowing the reaction of said malonate with the C60 core in the Bingel-reaction in a later step of the synthesis. For that purpose cyclo-[2]-malonate should be prepared according to the literature procedure. In the next step several different methods should be investigated to achieve the bond between the malonate and one or two porphyrins. Finally these porphyrin-malonate building blocks should be used in the to obtain novel fullerene mono- and hexakisadducts carrying between one and up to twelve porphyrins in its periphery (Figure 17).

28

Aims

Figure 17: Concept for novel fullerene hexakisadduct with cyclomalonate-linked porphyrins conjugates.

In another part of this thesis a different aspect of fullerene-malonate chemistry should be examined. Cyclo-[n]-malonates of n>2 are typically obtained as side products of the synthesis of cyclo-[2]-malonate. Since dumbbell-shaped bisfullerenes, connected by a cyclo-[2]-bridge are already known, the synthesis of possible trigonal trimers and tetragonal tetramers from higher cyclomalonates should be investigated. For that purpose, cyclo-[3]- and cyclo-[4]-malonate should be prepared, followed by cyclopropanation with C60 and different fullerene pentakis adducts. This should lead to the formation of novel fullerene multimers, consisting of cyclo-[n]- malonate and n fullerenes (Figure 18).

Figure 18: Concept for novel fullerene multimers constructed from cyclomalonates.

29

Aims

In an additional project, three fullerene monoadducts should be prepared. The malonates should contain alkyl chains of varying lengths and a terminal alkyne (Figure 19). They should then be attached to Al2O3 nanoparticles. These particles should be functionalized with azide/alkyl derivatives of phosphonic acid in different ratios, allowing click reaction between the fullerene and the azide chains. The amount of fullerene that can be bound to the azide moieties is directly correlated to the ratio of azide/alkyl. The influence of the bound fullerene on the optical properties of the should be studied in regards to the amount of fullerene on the particles surface and in comparison to other dyes.

Figure 19: Fullerene monoadduct with terminal alkyne moiety.

For the last part of this thesis, two new fullerene monoadducts should be synthesized. Their respective malonates should contain either one or two amino pentyl chains (Figure 20). It should be used as ligand of a porphyrin dimer to investigate whether the diamino fullerene has the same effect on the turnability of the porphyrin dimer as a previously measured diaminoalkanes.. Furthermore the possibility of a novel electron-donor-acceptor system between the porphyrin and the fullerene should be investigated.

Figure 20: Amino-fullerene for the planarization of a porphyrin-dimer.

30

3 Results and Discussion

3.1 Novel Fullerene-Porphyrin Hybrids

The main goal of this work was to attach a porphyrin to cyclo-[2]-malonate, which in turn should be bound to C60 (Fig. 21). For that purpose, the synthesis of porphyrins, cyclo-[2]-malonate and its derivatives are shown in the following chapters. Different methods to obtain the bond between malonate and porphyrin should be investigated, as well as modifications to the number and length of this linker. In the end, fullerene monoadducts of the different malonate linker should be prepared, allowing the formation of different porphyrin-fullerene conjugates.

Figure 21: Scheme of the planned new porphyrin-fullerene dyade linked through substituted cyclo- [2]-hexylmalonate.

3.1.1 Monopropargyl-Substituted Cyclo-[2]-Hexylmalonate

The formation of a bond between the malonate and the porphyrin was attempted in several different ways. The most promising approach was by introducing an additional linker between the two functional parts. Several different options could be imagined to accomplish this bond. For this project the so called “click chemistry”,[135] a copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition was selected (see introduction). Therefore, a terminal alkyne group was necessary on one reactant, which was determined to be the malonate, and an azide functionality on the other, in this case the porphyrin. This allocation was done for practical reason, stemming from the synthetically approach and could have been turned, if the synthesis strategy would have been different.

The porphyrin was synthesized in a statistical synthesis, following a modified Lindsey- protocol[219] (Scheme 7). For this purpose the required 4-(bromomethyl)benzaldehyde 24 had to be synthesized according to literature[220] from 4-(bromomethyl)benzonitrile 23 by reduction with DIBAL-H in THF. The porphyrin was obtained by mixing 24 at room temperature with pyrrole 25 and 3,5-(dimethoxy)benzaldehyde 26 under atmosphere in a solvent mixture of CH2Cl2 and EtOH. Borontrifluoride etherate as acid catalyst was added to the mixture and stirred for one hour to form the cyclic porphyrinogen.

31

To convert the porphyrinogen to the porphyrin, the oxidant DDQ was added and the reaction mixture was further stirred for additional three hours. Due to the statistical approach the desired AB3- porphyrin 27 had to be separated from B4 and A2B2 byproducts by a series of column chromatography steps (SiO2) using CH2Cl2/MeOH (98:2) followed by /CH2Cl2 (7:3) as eluent.

Scheme 7: Reaction pathway to porphyrin 27: a) DIBAL-H, toluene, 0 °C, 1 h, 74 %; b) BF3OEt2, DDQ,

CH2Cl2/MeOH, N2, rt, 4 h, 11 %.

Subsequently the free-base porphyrin was metallated (Scheme 8). This was done by heating to reflux in the presence of an excess of ZnOAc for 4 hours to give Zn-porphyrin 28 in almost quantitative yields. The Zn-porphyrin was used to prevent acid-base side-reactions of the amino protons with solvents or reagents. Alternatively to zinc, could have been used as metal center as well. The advantage of zinc was that it could be removed under comparatively mild conditions. This would allow the insertion of other metals, to test their influence on the porphyrin-fullerene dyad.

Scheme 8: Metallization to obtain Zn-porphyrin 28: a) Zn(OAc)2, THF, rt, 4 h, 94 %.

32

β-pyrH

CDCl3

1 Figure 22: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 28. Solvent impurities are marked with an asterisk.

In Figure 22 the 1H-NMR spectrum of Zn-porphyrin 28 is presented. At around 8.96 ppm 6 of the 8 β-pyrollic protons appeared as multiplet. The remaining two protons were observed as doublet at 8.84 ppm with a coupling constant of 4.67 Hz. Two doublets for the aromatic protons resonated at 8.10 and 7.70 ppm, respectively, with 3J = 8.0 Hz. Aromatic protons in ortho-position gave a doublet of a doublet, that overlapped, resulting in one signal at 7.3 ppm with a coupling constant of 4J = 2.2 Hz. The H-atoms in para-position were found as doublet of a doublet at 6.77 ppm and 4J = 2.3 Hz. The H-atoms of the methylene unit between aromatic ring and bromide resonated as singlet at 4.78 ppm. At 3.84 ppm the signal of the methoxy-protons were detected as singlet.

33

Zn-porphyrin 28 was additionally characterized by 13C-NMR (see Figure 23). At 158.7 ppm, the signal of the aromatic carbon bound to oxygen was observed. The α-pyrollic carbon atoms resonated at 150.1, 150.0 and 150.0 ppm. Next, the signal for the carbon atoms of the phenyl- rings connected to the porphyrin frame were found at 144.6 ppm. Between 134.7 and 131.8 ppm, the β-pyrollic C-atoms together with the aromatic signals appeared. The meso- carbons resonated at 127.3 ppm. A signal at 113.8 ppm was assigned to the aromatic carbon- atoms in ortho-position, next to the signal for the para-position at 100.1 ppm. In the aliphatic region, the signals for the three different methoxy-carbons overlapped and appeared at 55.6 ppm. At 33.5 ppm the signal for the methylene-carbon between the phenyl-ring and bromide was observed.

CDCl 3

aromatic

β-pyrH

α-pyrH

13 Figure 23: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 28. Solvent impurities are marked with an asterisk.

The absorption spectra of both free-base-porphyrin 27 and zinc-porphyrin 28 in CH2Cl2 are depicted in Figure 24. The Soret band maximum was observed at around 421 nm for both 27 and 28. Four Q-bands were observed for porphyrin 27, which is the expected result for free- base-porphyrins. They were found at 515, 548, 589 and 644 nm. In contrast to that the zinc- porphyrin 28 only showed two Q-bands, which appeared at 548 and 589 nm, respectively.

34

Figure 24: UV/Vis spectrum of free-base-porphyrin 27 and zinc-porphyrin 28 recorded in CH2Cl2.

In the next step the azide had to be introduced into Zn-porphyrin 28. It was important to use the metallated porphyrin instead of the free-base porphyrin. Otherwise, copper, which was used in a later step as catalyst for the click-reaction, could insert itself into the porphyrin center. This would have created a paramagnetic species, rendering characterization by NMR impossible. Bromide exchange for azide was achieved by stirring Zn-porphyrin 28 with sodium azide in DMF at 50 °C, resulting in azido-Zn-porphyrin 29 (Scheme 9).

Scheme 9: Synthesis procedure for azido-porphyrin 29: a) NaN3, DMF, 50 °C, 24 h, 95 %.

The successful exchange of bromide for azide was proven by mass spectrometry, where the expected difference between bromide and azide variety of m/z = 951 to 911 was found. The 1H- NMR of azido-porphyrin 29 was identical to that of its precursor in regards to its signals in general (Figure 25). It differed only in the shifts of the single signals. Again some small impurities are visible, probably due to an incomplete work-up. While the signals for the β- pyrollic protons were shifted highfield by 0.08 ppm, the doublets of the aromatic protons were

35

slightly shifted downfield. The same was true for the doublet of the doublet of the ortho- protons and the doublet of the doublet of the para-protons. The proton signal for the methylene-unit, again, was slightly shifted highfield, whereas the protons of the methoxy- group were shifted from 9.92 to 9.97 ppm.

28 29

β-pyrH CDCl3

1 Figure 25: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 29. Solvent impurities are marked with an asterisk.

Scheme 10: Synthetic procedure to cyclo-[2]-malonate 31: a) malonyl dichloride, pyridine, CH2Cl2, N2, rt, 4 d, 13 %.

Parallel to the formation of azido-porphyrin 29, the malonate building block was synthesized. In the first step the cyclo-[2]-hexylmalonate 31 was prepared according to a procedure developed in our group[104] and improved by Wasserthal[221](Scheme 10). Malonyl dichloride was reacted with 1,6-hexanediol 30 in the presence of pyridine in CH2Cl2 to give the desired cyclo-[2]-hexylmalonate in 13 % yield. Concentration of the reactants was kept very low, to favor the formation of cyclo-[2]-malonate over the other, higher malonates, which were formed

36

under these conditions as well, however in smaller quantities. The analytical data was identical to literature data.[222] During the course of this work, the protocol for the synthesis of cyclo-[2]- hexylmalonate was changed to the stepwise build-up described later in this thesis.

Scheme 11: Synthesis of monosubstituted cyclo-malonate 32: a) propargyl bromide, K2CO3, DMF, N2, rt, 2 d, 21 %.

The next step was the introduction of the alkyne function onto the cyclo-[2]-malonate. As shown above, the SN2 nucleophilic substitution worked fine for cyclo-[2]-hexylmalonate with

K2CO3 as base and was consequently used in the following synthesis. Propargylbromide was selected as alkylating reagent, for being comparatively short. This gave the advantage of keeping the distance between malonate and porphyrin reasonably small, which was important, since the main objective of this project was to bind porphyrin to C60 via a cyclomalonate linker. By increasing the chain length too much, this would not have been practical anymore, because it basically meant the introduction of another linker additionally to the intended bridging unit cyclo-[2]-hexylmalonate. Concurrently, the propargyl chain still allowed enough flexibility for the porphyrin, after the triazole ring had been formed in the click reaction step. This was important in later parts of this project. The formation of bissubstituted malonates, as shown in the next chapter, made it necessary for the porphyrins to be able to move out of the way, to prevent steric hindrance through the first porphyrin during the click-chemistry step of the second. For the alkylation (Scheme 11) cyclo-[2]-hexylmalonate 31 was reacted with propargylbromide in the presence of K2CO3 in DMF over two days. To prevent simultaneous alkylation on both sides of the malonate, the concentration was kept quite low and the alkyne was added slowly. Despite these precautions, side reactions happened, as the reaction control by TLC clearly demonstrated. Column chromatography of the crude product in CH2Cl2 (SiO2) was necessary to separate product 32 from starting material 31 and side-products. Due to their similar polarities, efficient separation required use of relatively dilute solutions of the product mixtures and a comparatively large volume of silica. Due to the side reactions the yield for the desired propargyl-substituted cyclo-[2]-malonate was only 21 %.

37

The introduction of propargyl on the α-carbon caused a decrease in symmetry in comparison to 1 the precursor 31, clearly visible in H-NMR (Figure 26). The protons of the CH2-group in α– position to oxygen 1 and 2 resulted in multiplets between 4.25 ppm and 4.03 ppm. The single α- proton 3 was observed as triplet at 3.55 ppm with a coupling constant of 3J = 7.7 Hz. At 3.34 ppm the singlet for the other two α-protons 4 was found. The H-atoms 5 showed a doublet of doublet with a chemical shift of 2.75 ppm and 4J = 2.7 and 3J = 5.0 Hz. The alkyne proton 6 appeared as triplet at 1.99 ppm with a coupling constant of 4J = 2.6 Hz. Two multiplets for the protons of the alkyl chain 7,8 displayed at 1.65 – 1.59 ppm and 1.37 – 1.32 ppm. Small impurities hint at the formation of bisalkylated species, which was not completely removed during purification.

1 Figure 26: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 32. H grease impurities are marked with an asterisk.

Figure 27 shows the 13C-NMR of compound 32. A splitting was seen for the signals of the carbonyl groups 1,2 at 168.8 ppm and 166.4 ppm, due to the two different environments. At

65.7 ppm and 65.4 ppm two signals were detected for the oxygen-bound CH2-groups 5 and 6. The substituted α-carbon atom 7 gave a signal at 51.1 ppm, while the methano carbon 8 on the other side was found at 42.2 ppm. Three additional signals for the propargyl 3,4 and 13 at 79 ppm, 77 ppm and 18 ppm further proved the successful alkylation. The methylene units 9- 12 of the alkyl chain only showed two signals instead of four, resonating between 28.5 ppm and 25.5 ppm. In MALDI-TOF the expected mass of 32 was found at m/z = 411.

38

CDCl3

9-12

13

13 Figure 27: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 32.

In another approach, an alternative halogen source for the cyclopropanation of the propargyl substituted malonate on [60]fullerene was tested. In the original publication by Bingel, brominated malonate was used for cyclopropanation with C60. Due to low yields, caused by the formation of dibromomalonates, and a tedious separation of the products, the preparation of brominated malonates is complex. Later Hirsch proposed an improvement by using CBr4 as in situ bromine source, thereby facilitating the reaction. In the case of cyclic malonates, however, this method is to the detriment of a controlled sequential addition. Due to scrambling of the Br atom between both malonate sites, the formation of asymmetric fullerene structures is not accessible through this method. Recently, Wasserthal et al.[221] demonstrated the use of chlorinated malonates in the Bingel reaction for the nucleophilic cyclopropanation of [6,6]– double bonds of [60]fullerene. By this method, halogen scrambling could be avoided and highly selective and sequential fullerenylations of bismalonates became accessible. Furthermore it was observed that the addition of a second chloride to the malonate did not occur on the side of the first chloride, but on the opposite side, despite the higher acidity of the proton neighbouring the chloride.

Therefore, this alternative approach was applied by using chlorinated cyclo-[2]-hexylmalonate as base for the substitution instead of 31. The assumption was that the chloride sterically hinders the addition of another substituent on the same carbon, allowing the controlled formation of alkylated cyclomalonate with an in-situ halogen source for the subsequent Bingel- reaction.

39

Scheme 12: Planned synthesis of 34: a) sulfuryl chloride, CHCl3, N2, reflux, 12 h, 54 %; b) propargyl

bromide, K2CO3, DMF, N2, rt, 2 d.

For this (Scheme 12), cyclo-[2]-hexylmalonate 31 in chloroform was heated to reflux with an equimolar amount of sulfuryl chloride for 12 hours.[223] The concentration of the mixture was very important, for a high dilution decreased the yield. Therefore the amount of solvent was kept as low as possible and a moderate yield of 54 % could be achieved. Separation of the desired compound 33 from the starting material and multiple chlorinated byproducts was done by column chromatography in CH2Cl2 on silica. As with the monoalkylated compound, the monochlorinated required the use of a comparatively dilute solution of the product mixture and a large volume of silica.

The 1H-NMR spectrum of 33 (Figure 28) showed a similar result to what has been shown for 32 (see pages 37). Due to the neighboring chlorine, the signal for the single acidic proton 1 was shifted downfield to 4.85 ppm. The other α-protons 4 appeared as singlet with double intensity at 3.33 ppm. The alkoxy protons were found as two multiplets between 4.31 ppm and 4.07 ppm in a 1:3 ratio. The methylene units showed two multiplets at 1.68 – 1.58 ppm and 1.39 – 1.30 ppm.

CH2Cl2

1 Figure 28: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 33.

40

Figure 29: Alkylation product of monochlorinated cyclo-[2]-malonate 35.

In the next step, the chlorinated malonate was reacted with propargyl bromide in the presence of K2CO3 in DMF. Unfortunately this time the desired product 34 could not be obtained. LDI- TOF analysis indeed exhibited the correct molecular ion peak at m/z = 445 nm, but 1H-NMR spectrum (Figure 30) clearly showed, that a different compound had been synthesized. Like above, the propargyl chain resulted in two new signals, a triplet with a chemical shift of 2.10 ppm for the terminal alkyne proton 5 and a coupling constant of 4J = 2.6 Hz and a doublet at 3.14 ppm with 4J = 2.6 Hz, corresponding to the methylene group 4. The signals for the methylene units bound to oxygen 1, 2 split, as expected, resulting in two multiplets at 4.26 – 4.17 ppm and 4.15 – 4.07 ppm. The two different substituents at the α-carbon had discriminable effects on the shifts of the acidic protons. There was no signal observed for the proton next to chlorine, found at 4.84 ppm in compound 33. One singlet signal 3 at 3.33 ppm was found, which corresponded to the two acidic protons at the unsubstituted α-carbon in 35. That meant that the substitution did in fact happen at the chlorinated carbon instead of the other side, resulting in molecule 35 (Figure 29) that shared the same composition hence the same mass, but highly differed in configuration to the desired target molecule 34.

1 Figure 30: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 35. H grease impurities are marked with an asterisk.

41

The attempted alkylation of the chlorinated malonate did not lead to the desired compound, despite the promising results of the bischlorination. The best explanation was found in the SN2 mechanism. Malonate acts as nucleophile to substitute bromide on the alkyne group. For that purpose the acidic α-proton was removed by a base to form the necessary carbanion. Due to its neighboring chlorine, the single proton became more acidic than the two on the opposite side. The electron withdrawing influence of the halide resulted in a simplified removal of the proton, causing a second alkylation on the already substituted malonate instead of the other side, as it was planned. No further attempts at improving the yield of the monoalkylated malonate were taken.

With the alkyne building block 32 at hand, the next step would be the Bingel-reaction with C60 to form fullerene adducts. Nucleophilic cyclopropanation of one [6,6]-double bond led to the desired product, followed by click reaction with the azide bearing porphyrin (see page 66ff). For adducts higher than mono, unfortunately a problem had to be considered. With the alkyne chain binding to the sp3 α-carbon, there were two possible isomers. For the malonate itself or in a fullerene monoadduct, both isomers were superposable. But for adducts with two malonates or more this was obviously no longer the case (Figure 31). The propargyl chain on the malonate’s α-carbon atom can face in two directions. In the case of a bisadducts this results in the formation of two enatiomeric pairs, which are diastereomers towards each other. The number of diastereo isomers increases, going from bisadducts all the way to the hexakisadduct. Due to the nature of higher fullerene adducts, especially bis- and trisadducts, existing as multiple regioisomers with varying symmetries, a vast number of possible fullerene diastereo isomers could be imagined, making purification, even with HPLC, very complex and time- consuming.

Figure 31: Proposed fullerene hexakisadduct 36 with six alkyne moieties.

42

3.1.2 Dipropargyl-Substituted Cyclo-[2]-Hexylmalonate

To overcome the problem of diastereoisomerism and the resulting large number of isomers, a more symmetrical malonate was synthesized next. Here, two alkyne chains are attached to the α-carbon instead of just one. By this, only one malonate isomer would be formed, thus allowing the preparation of higher fullerene adducts without the problem of isomer separation. Unfortunately, as previous experiments have shown, though alkylation was possible on cyclo- [2]-malonate, no bissubstituted malonate was obtained in this way. However, comparable di- substituted malonic ester compounds found in literature[131b, 224] demonstrated the successful di-substitution of monomalonates. It was assumed that the problem was not due to the procedure, but the use of cyclic bismalonate. Therefore another strategy had to be designed to achieve the new building block 40 (Scheme 13).

Scheme 13: Synthesis strategy of alkyne functionalized cyclo-[2]-malonate 40: a) tBDMS-Cl, imidazole, THF, rt, 6 h, 68 %; b) malonyl dichloride, pyridine, CH2Cl2, N2, rt, 12 h, 64 %; c) propargyl bromide, K2CO3, DMF, N2, rt, 2 d, 63 %; d) BF3OEt2, CH2Cl2/MeCN 2:1, rt, 1 h, 99 %; e) malonyl dichloride, TEA, CH2Cl2, N2,,rt, 2 d, 58 %.

The new synthesis route was a stepwise-approach starting from smaller precursor. Instead of forming the cyclo-[2]-malonate first, followed by alkylation, now a malonic ester with two hydroxyhexyl groups was prepared. To prevent unwanted side-reactions – for example the formation of cyclo-[1]-malonates or malonate oligomers in the presence of malonyl chloride and pyridine – the terminal hydroxyl-group needed to be protected. In the next step the ester was bissubstituted with propargyl bromide.

43

Subsequent deprotection regained the reactivity of the terminal alcohols followed by the formation of cyclo-[2]-hexylmalonate through a second reaction with malonyl dichloride. Therefore, 1,6-hexanediol 30 was selectively monoprotected with tBDMS chloride following a literature known procedure,[225] yielding the mono-tBDMS-ether 36 in 68 %. This molecule is widely described in literature as synthetic tool, including in the total synthesis of natural compounds,[226] supramolecular assembly[227] or the formation of non-viral gene vectors.[228]

The protected hexanol was further esterified with malonyl dichloride and pyridine in CH2Cl2 to give 47 after purification by column chromatography (SiO2, CH2Cl2) in 64 % yield.

1 Figure 32: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 37.

The analytical data of 36 was in accordance with the literature.[229] In the 1H-NMR spectrum of 3 37 (Figure 32) the oxygen-bound CH2-atoms 1 resonated as triplet at 4.11 ppm with J = 6.7 Hz. The other methylene unit 2 in α-position to oxygen was found as triplet at 3.57 ppm with a coupling constant of 3J = 6.6 Hz. The acidic protons 3 gave a signal at 3.34 ppm. Between 1.64 ppm and 1.30 ppm the multiplets of the aliphatic protons 4, 5 and 6 appeared. At 0.86 ppm the singlet signal for the tert- 7 was detected. The methyl protons 8 appeared as singlet at 0.03 ppm.

Scheme 14: Alternative synthesis of cyclomalonate 31: a) BF3OEt2, CH2Cl2/MeCN 2:1, rt, 1 h, 99 %; b) malonyl dichloride, TEA, CH2Cl2, N2, rt, 2 d, 60 %. 44

In order to prove the concept of this stepwise cyclo-[2]-malonate formation, cyclo-[2]- hexylmalonate 31 should be synthesized following the new protocol (Scheme 14), from the open-chain bishydroxyhexyl malonate 41.[230] For that, the tBDMS-protection group of compound 37 was removed with BF3OEt3 in a mixture of CH2Cl2/MeCN at room temperature in one hour.[231] Purification was done by aqueous workup yielding the hydroxyl functionalized malonate 41 in quantitative yield. Subsequent cyclisation with malonyl chloride and TEA in dichloromethane gave the desired compound in 60% yield, which was still 26% over four steps, about twice as much compared to the standard one pot reaction (see page 35).

OH

1 Figure 33: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 41.

1 In Figure 33 the H-NMR spectrum of 41 is shown. The two different oxygen-bound CH2- groups 1 and 2 were found as triplets at 4.11 ppm with a coupling constant of 3J = 6.6 HZ and 3.61 ppm with 3J = 6.2 HZ. The acidic protons 3 appeared as singlet at 3.34 ppm. At 2.52 ppm a broad signal was observed for the terminal OH. The remaining alkyl chain protons 4-6 gave multiplets between 1.64 and 1.35 ppm. No signals were observed for the tBDMS-group. MALDI-TOF mass spectrometry further confirmed the successful deprotection by exhibiting the correct molecular ion peak at m/z = 304.

After proving the effectiveness of the new synthesis concept, the formation of bisalkylated cyclomalonate continued with the alkylation of protected malonate 37 towards the bisalkylated malonate 38. The reaction was carried out with propargyl bromide and K2CO3 in

DMF. Column chromatography (SiO2, CH2Cl2/ 6:4) provided the pure compound in 63 % yield. In the next step the malonate was deprotected, again using borontrifluoride etherate in a 2:1 mixture of CH2Cl2 and acetonitrile. After stirring for one hour and aqueous workup, the dihexanol malonylester 39 was obtained in nearly quantitative yield. Finally the desired cyclo-[2]-hexylmalonate 40 was prepared by reacting the hydroxyhexyl malonic ester with malonyl dichloride in CH2Cl2 for two days.

45

Both malonates were used in very low concentration. This was important to prevent the formation of mixed byproducts. After column chromatography (SiO2, CH2Cl2) to purify the compound, the cyclo-[2]-malonate was obtained in 58 % yield.

38 39

1 Figure 34: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 38/39.

In Figure 34 the 1H-NMR spectra of compound 38 and the deprotected derivative 39 are shown. In the case of 38, the signal for the protons 1 bound to the malonate’s oxygen moiety 3 appeared as triplet at 4.15 ppm with a coupling constant of J = 6.6 Hz. The CH2-group next to the ether functionality 2 resonated as triplet at 3.58 ppm with 3J = 6.49 Hz. At 2.99 the doublet of the propargyl’s methylene unit 3 was found with a coupling constant of 4J = 2.65 Hz. The alkyne proton 4 gave a triplet at 2.02 ppm with 4J = 2.62 Hz. The signals for the remaining protons in the alkyl chain were detected as three multiplets between 1.66 – 1.59 ppm for 5,

1.51 – 1.46 ppm for 6 and 1.36 – 1.31 ppm for the remaining two CH2-units 7. The protecting group displayed as two singlets at 0.88 ppm (8) and 0.03 ppm (9), respectively. The successful removal of the tBDMS-moiety in 39 was demonstrated by the lack of the two singlets in the aliphatic region. Besides that, a slight downfield shift was detected for the remaining proton signals in comparison to the precursor.

46

1 Figure 35: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 40. H grease impurities are marked with an asterisk, water impurities from CDCl3 are marked with a circle.

In the 1H-NMR spectrum of 40 (Figure 35) the alkoxy protons 1 resonated as multiplet at 4.10 – 4.18 ppm. The acidic protons 2 were observed as singlet with a chemical shift of 3.34 ppm. The propargyl group 3, 4 appeared as doublet at 2.96 ppm with a coupling constant of 4J = 2.7 Hz 4 and a triplet at 2.01 ppm with J = 2.7 Hz. The CH2-unit 5 in β–position to oxygen was detected as multiplet at around 1.63 ppm. Between 1.39 ppm and 1.31 ppm the multiplet of the remaining methylene groups 6 was found.

CDCl3

13 Figure 36: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 40.

Figure 36 shows the 13C-NMR spectrum of 40. Two signals were observed for carbonyl atoms 1, 2 at 168.6 ppm and 166.4 ppm. The propargyl moiety 3, 4 and 11 gave three signals at 78.4 ppm, 71.7 ppm and 22.6 ppm. The oxygen-bound carbon 5, 6 was observed at 65.9 ppm and 65.3 ppm. At 56.3 ppm the substituted α-carbon 7 gave a signal, the methano carbon 8 on the other side was detected at 42.2 ppm. The aliphatic carbon atoms 9 and 10 were found 47

between 28.5 ppm and 25.5 ppm. MALDI-TOF analysis showed a molecular ion peak at m/z = 471, corresponding with [M+Na]+. HiRes-APPI-MS exhibited the correct molecular composition at m/z = 449.2168 (calc. m/z = 449.2168)

With this new synthetic approach at hand, not only was it possible to obtain the desired bisalkylated building block 40, but also this method demonstrated a new way for the formation of cyclo-[2]-malonates. The disadvantage of multiple step build-up compared to the one-pot synthesis was compensated by the possibility to form unsymmetrical bismalonates in a more controlled fashion. As before, the synthesis of mixed cyclo-[2]-malonates had been possible but rather unpractical, because of its statistical approach. Now it was possible to get only the desired unsymmetrical malonate as sole product. In addition compounds that were so far not obtainable by previous methods were now accessible.

48

3.1.3 Alkylation of Cyclo-[2]-Hexylmalonate with Longer Alkyne-Chains

After the successful synthesis of cyclo-[2]-malonate building blocks carrying two propargyl groups, the procedure should be used to form a malonate linker, with prolonged alkyl substituents. The consequential fullerene adducts could have been applied in a supramolecular context. Nierengarten and Coworkers[205b] reported of a self-assembled fullerene-porphyrin ensemble, with a photoinduced electron transfer between porphyrin and fullerene. In this supramolecular photosynthetic model, a pyrrolidinofullerene-imidazole derivative was axially coordinated to a multitopic receptor – a multimetalloporphyrin array around a fullerene hexakisadduct – causing a charge transfer from fullerene to porphyrin. The hexasubstituted core was not involved in the photoinduced event, due to the perturbation of both ground- and excited state energy levels of the fullerene core. In comparison to the monofunctionalized fullerene guest, hexafunctionalization resulted in a less efficient energy and electron acceptor.

A similar array should have been synthesized in this project. As in the literature compound 42 the metalloporphyrins should have been bound by click-chemistry to alkyl chains on the malonate (43, Figure 37). But instead of monomalonates, the focus here was on the application of the bisalkylated cyclo-[2]-malonate building block, described in the previous chapter. To mimic the Nierengarten molecule, the length of the alkyne chain was increased. By using a pentyl instead of a propyl group to link malonate and triazole, a similar geometry between two neighboring porphyrins should have been achieved. The main difference to 43 would then have been the malonate itself. This would move the metalloporhyrins further away from the fullerene hexakisadduct. But since no intercomponent photoinduced process could be observed with the core fullerene, the additional distance between C60 and the porphyrins did not matter.

Figure 37: Comparison of Nierengarten diporphyrin 42 and planned diporphyrin-cyclo-[2]-malonate 43 with a similar linker structure. 49

The synthetic approach was followed for the Nierengarten molecule in regards of the functional groups. Therefore the alkyne was part of the porphyrin, while the malonate should have been substituted with an azido alkyl chain. In the first step a benzaldehyde-derivative with an alkyne moiety had to be prepared following a literature known procedure (Scheme 20). In accordance with Nierengarten the chain length was kept to a minimum. For that purpose, bromobenzaldehyde 44 in TEA was treated with TMS-protected acetylene in a Sonogashira- reaction with CuI and Pd(PPH3)2Cl2 as catalysts to yield the alkyne 45 in 24 %. The analytical data was in accordance to literature data.[232] The protection group was necessary to allow the introduction of the highly reactive acetylene group. It could be removed during the “clicking” step in a one pot deprotection-triazole formation reaction, developed by Aucagne and Leigh, using the copper(I)-mediated alkyne-azide cycloaddition reaction combined with a silver(I)- catalyzed TMS-alkyne deprotection.[233]

Scheme 15: Synthesis strategy of alkyne-porphyrin 48: a) TMS-acetylene, CuI, Pd(PPh3)2Cl2, TEA, N2, rt, 16 h, 24 %; b) BF3OEt2, DDQ, CH2Cl2/EtOH, N2, rt, 4 h, 8.5 %; c) Zn(OAc)2, THF, rt, 4 h, 97 %.

50

The formation of literature known porphyrin[234] 47 was achieved according to previously described protocols (Scheme 15). Here 3,5-di(tert-butyl)benzaldehyde 46 was used instead of 3,5-(dimethoxy)benzaldehyde. The motivation for that was to increase the solubility of the porphyrin and prevent aggregation, simplifying the separation of the A3B system from both the t A4 and the two A2B2 systems. With the introduction of butyl-groups, plug to remove side products followed by column chromatography (SiO2, hexanes/CH2Cl2 8:2) once, was sufficient to obtain the porphyrin in 8.5 % yield. Again, analytical data was found in accordance with literature. Subsequent metallation following the standard protocol of stirring under reflux in the presence of Zn(OAc)2 in THF, followed by purification through column chromatography, resulted in Zn-porphyrin 48 in 97 % yield. The analytical data for both compounds was conforming to literature.[234-235]

Scheme 16: Synthesis concept towards azidopentyl-substituted cyclomalonate 53.

In parallel, the preparation of azide-chain alkylated malonate was attempted. Several different pathways were tested to determine the one that worked the best. The most promising synthesis concept is shown in Scheme 16. It follows the stepwise approach for the formation of bisalkylated cyclo-[2]-malonates, shown in the previous chapter. Starting from dibromopentane, the necessary azido compound would be obtained through substitution. In the next step, alkylation of the protected dihexylmalonate, shown in the previous chapter, would form the bisalkylated malonate species, which would then be deprotected. In the last step esterification of the free hydroxyl groups with malonyl dichloride would form the desired diazidopentyl substituted cyclo-[2]-malonate.

51

Scheme 17: Preparation of azido-bromopentane 50: a) NaN3, DMF, 50 °C, 16 h 75 %; b) NaN3, DMF, rt.

For that purpose, the azido bromopentane had to be synthesized in the first step. A successful method[236] was found by reaction of dibromopentane 49 and sodium azide in DMF at 50 °C for 18 hours, yielding the azido compound in 75 %. The analytical data was found to be in accordance with literature. In an alternative attempt tosylate 54, previously prepared according to literature[237], should be transformed to 1-azido-5-bromopentane 50 as well, following a procedure found in literature.[238] The tosylate should be replaced with an azide by stirring the precursor and sodium azide at room temperature in DMF overnight. However, this protocol did not lead to the desired product (Scheme 17).

Scheme 18: Synthesis scheme for the alkylation of 37: a) 50, K2CO3, DMF, N2, rt, 35 %.

With the azido alkyl at hand, substitution of the malonate was the next step. As before, the protected malonate was reacted with the azide functionalized bromo pentane in the presence of K2CO3 in DMF (Scheme 18). But despite the earlier success with propargyl bromide, here the bissubstituted malonate 55 was not formed. The standard reaction conditions produced only the mono alkylated species 56.

52

In the 1H-NMR spectrum (Figure 38) the protons of the methylene groups bound directly to the ester oxygen 1 resonated as multiplet between 4.15 ppm and 4.09 ppm. The CH2-protons 2 next to the ether gave a triplet signal at 3.59 ppm with a coupling constant of 3J = 6.5 Hz. The existence of an acidic proton 3 detected as triplet at 3.31 ppm with 3J = 7.5 Hz proved the assumption, that alkylation did only occur with one azido chain. The integrals of the other signals supported this. At 3.25 ppm the H-atoms on the azido-bound carbon 4 gave a triplet with 3J = 6.9 Hz. The signal of the malonate-bound methylene unit of the pentyl chain (5) was observed at 1.89 ppm as doublet of triplet with a coupling constant of 3J = 7.5, 15.3 Hz.

Between 1.65 ppm and 1.33 ppm the multiplets of the remaining 22 CH2-protons 6 were found. The signals of the protons 7, 8 of the protecting group appeared as singlets at 0.89 ppm and 0.04 ppm.

1 Figure 38: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 56. CH2Cl2 is marked with an asterisk.

After the general route to obtain alkylated malonate had not produced the expected product, several modifications to the standard procedure were tested. First of all the base was changed. DBU was used as alternative to carbonate, which did not lead to a successful substitution. Neither did NaH. Here the malonate was dissolved at 0 °C and NaH (60 % in mineral oil) was added and stirred for 30 minutes. Then bromoalkyl was added slowly to the mixture and stirred overnight. After aqueous workup only the monosubstituted malonate 56 was obtained. Next all three bases were tested in different solvents. Acetone and THF were used instead of DMF, but none of the tested conditions brought the desired compound. A last variation was made by increasing the temperature from room temperature to 75 °C, which did not succeed either. One possible explanation, why this particular reaction did not yield the expected product, even after the variation of multiple factors, was the difficulty to detect the reaction products on TLC, especially during purification by column chromatography.

53

Since the molecules did not show any UV activity, it was necessary to stain the product spots in iodine vapor. TLC directly after the workup did in fact showed the presence of newly developed spots. But due to concentration issues after chromatography, the spots were not visible anymore, making separation and subsequent characterization of the different reaction products highly impracticle.

A solution to this problem was found in the modification of the malonate (Scheme 19). Instead of the hydroxyhexyl ester, benzyl moieties were introduced into the malonate.[239] This made the compound UV active and thus detectable in TLC. After the successful alkylation, the benzyl groups should have been cleaved off through base hydrolysis to form the malonic acid derivative. Meanwhile the tBDMS-protected malonate 37 was deprotected. The bis(hydroxhexyl) malonate 41 should then form the expected cyclo-[2]-hexylmalonate 53 with the substituted malonic acid via Steglich-esterification with DCC and DMAP.[240]

Scheme 19: Attempted synthesis route towards azido-alkyl substituted malonate 61: a) BF3OEt2,

CH2Cl2/MeCN, rt, 20 min, 99 %; b) benzene, reflux, 5 h, 85 %; c) 50, NaH, THF, N2, rt.

t The cleavage of the BDMS-protection group was achieved as before by using BF3OEt3 in a

CH2Cl2/MeCN mixture. Purification was done by aqueous workup yielding the hydroxyl functionalized malonate 41 in quantitative yield. Next was the esterification of malonic acid 57 with benzyl alcohol 58 in benzene with p-toluenesulfonic acid 59 as acidic catalyst. The mixture was heated to reflux for 5 hours, while removing water via Dean-Stark apparatus. After aqueous workup and purification through column chromatography (SiO2, cyclohexane/EtOAc 2:1) the dibenzyl malonate was obtained in 85 % yield. The analytical data was identical with literature data.[239] For the alkylation of malonate 60, THF was used as solvent, and different bases (NaH, DBU, Ca2H) were tested under room temperature. Unfortunately none of them were suitable to produce the desired compound 61. In the end all attempts to synthesize azido- alkyl substituted malonate failed.

54

Scheme 20: Attempted preparation of heptyne substituted malonate 65: a) LAH, THF, N , 0 °C - rt, 2 16 h, 61 %; b) CBr4, PPh3, CH2Cl2, rt, N2, 1 h, 49 %; c) 60, NaH, THF, N2, rt, 52 % An alternative route was found (Scheme 20) in swapping azide and alkyne functionality. Now the alkyne should be bound to the malonate and the azide would be part of the porphyrin. The preparation of such azido-porphyrin was already described in previous chapters. For the purposes of mimicking the open-chain malonate from the Nierengarten group, the distance between malonate and the triazole ring, formed via click chemistry, should have been five carbon atoms. That meant the alkyne substituent needed to be prolonged in comparison to the azide derivative by two carbon atoms. 7-bromo-hept-1-yne was chosen as the new alkylating moiety.

Heptynoic acid 62 was reduced to hept-6-ynol 63 according to literature[241] in 61 % yield. In the next step the hydroxyl group was replaced by bromide, again following the literature protocol[242] to obtain the expected 7-bromoheptyne 64 in 49 % yield. Alkylation was attempted with NaH in THF according to the procedure described above. Unfortunately this did not lead to the desired bisalkylated malonate 65, but to a new compound 66, that was subsequently characterized.

In the 1H-NMR spectrum of 66 (Figure 39) signals were found, which would have been expected for the desired bissubstituted malonate 65. The aromatic protons 1 resonated as a multiplet with a chemical shift of 7.35 – 7.25 ppm. A singlet at 4.49 ppm was observed for the benzylic protons 2. The CH2-protons 3 in α–position to oxygen were observed as triplet with a chemical shift of 3.46 ppm and a coupling constant of 3J = 6.6 Hz. The signals for the alkyl chain 6 protons occurred as multiplet in the region between 1.65 ppm to 1.43 ppm. The signal for the alkyne 5 and the methylene unit bound to it (4) appeared as triplet at 1.92 ppm with 4J = 2.6 Hz and doublet of triplet at 2.20 – 2.16 ppm with coupling constants of 4J = 2.7 Hz and 3J = 4.3 Hz.

55

CDCl3

aromatic

1 Figure 39: H-NMR spectrum (400 MHz, CDCl , rt) of compounds 66. 3

The 13C-NMR spectrum of 66, presented in Figure 40, clearly disproved the assumption, that this was the desired compound 65. At first it was apparent, that the number of signals did not correspond to the number of carbon atoms in the expected molecule. The most obvious was the lack of the carbonyl signal around 165 ppm. The signals for the carbon atoms in the aryl ring 1 and 2 were found in the characteristic region between 138.6 – 127.5 ppm. Two signals for the alkyne 3 and 6 were observed at 85.3 ppm and 68.2 ppm, as well as a signal for the benzylic carbon 4 at 74.1 ppm. No signals were found for the α-carbon on the malonate, expected around 56 ppm, and the methylene group bound to it, expected at 30 ppm. Instead, one additional signal 5 appeared at 71.9 ppm. The carbon atoms in the alkyl chain 7, 8 and 9 resonated in the expected region between 29.2 ppm and 18.3 ppm. Since no signal for the carbonyl carbon was detected, it was obvious, that compound 66 was no malonate. On the other hand, the proton NMR depicted the expected shifts almost perfectly. The proposed solution was the formation of an ether. In such compound both the alkyl chain and the benzyl alcohol moiety were in place for their atoms to resonate accordingly. This would also be the explanation for the signal at 71.9 ppm in the 13C-NMR spectrum, being the signal of the oxygen- [243] bound CH2-group on the alkyl chain. Compound 66 could be found in literature. When comparing the NMR spectra of the literature molecule and 66, they were found to be identical. This further supported the assumption that the prepared compound was the proposed benzyl ether.

56

CDCl3

13 Figure 40: C-NMR spectrum (100 MHz, CDCl , rt) of compound 66. 3

In an alternative approach (Scheme 21), carbonate was used as base. Both malonate and bromo heptyne were dissolved in DMF, K2CO3 was added and the mixture stirred at 70 °C for 3 days. Workup and purification by column chromatography (SiO2, hexanes/EtOAc 8:2) gave the bissubstituted malonate 65 in 48 % yield.

Scheme 21: Synthesis plan towards bisalkylated malonate 68: a) 60, K2CO3, DMF, N2, 70 °C, 3 d, 48 %; b) KOH, EtOH/H2O 2:1, reflux, 2 d, 64 % c) 41, DMAP, DCC, CH2Cl2, N2, 0 °C - rt.

57

The 1H-NMR spectrum (Figure 41) displayed a downfield shifted multiplet for the aromatic protons 1 between 7.35 ppm and 7.24 ppm. The four protons in benzylic position 2 appeared as a sharp singlet at 5.09 ppm. The signals for the H-atom of the alkyne and the CH2-unit next to it (3, 4) were detected as doublet of triplet between 2.10 ppm and 2.07 ppm with coupling constants of 4J = 2.6 Hz and 3J = 4.3 Hz and a triplet at 1.91 ppm with a coupling constant of 4J = 5.3 Hz. The remaining protons in the alkyl chain 5, 6 and 7 appeared as four multiplets between 1.89 ppm and 1.85 ppm, 1.45 ppm and 1.37 ppm, 1.35 ppm and 1.27 ppm and 1.09 ppm and 1.02 ppm, respectively.

CH2Cl2

1 Figure 41: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 65. Solvent impurities are marked with an asterisk.

To prove the successful synthesis in contrast to the ether formation of 66, the 13C-NMR spectrum of 65 is presented in Figure 42. This time the signal for the carbonyl carbon atoms 1 was found as expected at 171 ppm. In the aromatic region four signals for carbon 2 and 3 were observed at 135.5 ppm, 128.4, 128.2 ppm and 128.2 ppm. Two signals appeared with double intensity, due to the symmetry in the benzyl moiety. The signals for the alkyne carbons 4 and 6 were found at 84.3 ppm and 68.4 ppm. At 66.7 ppm the signal for the benzylic C-atoms 5 was detected. As distinguished from the 13C-NMR spectrum of 66, a signal for the methano carbon 7 was found at 57.6 ppm. The remaining signals for the alkyl chain 8 - 12 were found as expected at 32.1 ppm, 28.7 ppm, 27.9 ppm, 23.4 ppm and 18.2 ppm.

58

CDCl3

13 Figure 42: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 65.

Following the alkylation, base hydrolysis of the ester was performed to obtain the malonic acid derivative 67 as building block for the formation of cyclo-[2]-malonate. For this purpose malonate 65 was dissolved in a 2:1 mixture of ethanol/water. An excess of KOH was added and the mixture was heated to reflux for 2 days. After cooling to room temperature, the reaction was acidified with concentrated HCl and extracted with ether. Purification by column chromatography (SiO2, hexanes/EtOAc 9:1) yielded the product in 35 % yield.

DMSO

COOH

1 Figure 43: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 67.

59

The 1H-NMR spectrum (Figure 43) clearly showed the successful hydrolysis through the lack of signals in the aromatic region and the absence of the singlet for the benzylic protons at 5.09 ppm. The single H-atom of the terminal alkyne 1 shifted downfield by 0.77 ppm and resonated at a chemical shift of 2.68 ppm with a coupling constant of 4J = 5.0 Hz. At 2.09 ppm the doublet of triplet of the methylene group 2 next to the alkyne appeared with coupling constants of 4J = 2.6 Hz and 3J = 4.3 Hz. The protons of the alkyl chain 3 - 6 appeared as expected as multiplets with a chemical shift between 1.61 ppm and 1.03 ppm.

In the last step malonic acid 67 and hydroxyl functionalized malonate 41 should have been reacted to form cyclo-[2]-hexylmalonate with two terminal alkyne functionalities 68 in a Steglich-esterification. For this purpose, the malonic acid derivative would have been dissolved in CH2Cl2. A highly diluted solution would have been necessary. Otherwise unwanted side reactions like two different malonates binding to one molecule malonic acid or vice versa could have happened. An equimolar addition of bis(hydroxyhexyl) malonate would have been necessary for the same reason. After the addition of DMAP in catalytic amounts the solution would have been cooled down to 0 °C, an equimolar amount of DCC would have been added to the mixture, slowly warmed to room temperature and stirred overnight. This last synthesis was carried out, but no product was obtained in the first run. Modifications to the reaction conditions in order to form the desired compound, could not be tested due to the closing of the laboratory as part of the move to the new building, leaving this project unfinished for the moment.

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3.1.4 Synthesis of Fullerene Monoadducts

After the successful preparation of the two alkyne functionalized building blocks 31 and 40, the next step towards cyclo-[2]-malonate bridged fullerene-porphyrin hybrids, was the synthesis of fullerene adducts using the newly developed linkers.

Scheme 22: Synthesis of fullerene monoadduct 70: a) CBr4, DBU, toluene, N2, rt, 18 h, 38 %.

The fullerene monoadduct 88 was prepared according to improved Bingel-conditions (Scheme

22). C60, malonate 32 and CBr4 were dissolved in toluene. DBU was added slowly and the mixture was stirred at room temperature for 18 hours. After workup by column chromatography (SiO2, toluene) the fullerene monoadduct 88 was obtained in 38 % yield.

1 Figure 44: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 70. H grease impurities are marked with an asterisk.

In the 1H-NMR spectrum of 70 (Figure 44) no signals for the acidic α-protons were detected at

3.34 ppm, indicating the formation of the cyclopropane ring with C60. The signal for the H- atoms of the oxygen-bound methylene units 1 and 2, 3 split into three multiplets between 4.49 – 4.44 ppm, 4.32 – 4.23 ppm and 4.15 – 4.09 ppm — same as in 32 — with the signal of the protons on the fullerene side 7 shifted downfield by 0.35 ppm. The protons of the alkyl chain 7 and 8 were split into two multiplets and shifted downfield to 1.90 – 1.83 ppm and 1.76 –

61

1.69 ppm. At 3.59 a triplet was found for the acidic proton 4 with a coupling constant of 3J = 7.72 Hz. The signal for the alkyne 5 and 6 were detected as doublet of doublet with a chemical shift of 2.78 ppm and a coupling constant of 4J = 5, 7.6 Hz and a triplet at 2.01 ppm with 4J = 2.6 Hz. The remaining methylene units 9 were unchanged and resonated as multiplet between 1.57 ppm and 1.43 ppm.

CDCl3

2 C60-sp 3 C60-sp

13 Figure 45: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 70.

A more fitting characterization method for fullerenes is obviously 13C-NMR spectroscopy. In [26] pure C60, only one signal can be found at 143.2 ppm, for all carbon atoms are equal. In the case of fullerene adducts, the sp2–hybridized carbon atoms resonate between 140 and 150 ppm with a signal pattern that is dependent on the number of addends. The reason is that due to exohedral modifications of the core, the carbon atoms are no longer chemically and magnetically equal and the symmetry of the fullerene decreases. Additional signals for the sp3- hybridized carbon — where the cyclopropane ring is formed — resonate at around 70 ppm. Here as well, the symmetry of the fullerene adduct has an influence on the number of signals. In the case of hexakisadducts with one symmetric substituent, for example, the 48 sp2 carbon atoms resonate as just two signals, and only one single signal can be found for the 12 sp3- hybridized carbon atoms. Therefore it is possible to learn the number of addends and the addition pattern by determining the number and intensity of the signals and the line pattern. In Figure 45 the 13C-NMR spectrum of 70 is shown. The carbonyl C-atoms 1, 2 resonated as expected at 167.9 ppm and 163.6 ppm. Although the compound belonged to the CS point group – having only one mirror plane – just 15 signals for the 58 sp2-hybridized carbon atoms were found between 145.3 ppm and 139.1 ppm, instead of the expected 30. This effect could be explained by a local C2V symmetry of the fullerene core. The influence of the single propargyl substituent on the symmetry of the carbon sphere was negligible, resulting in the change of the point group and the reduction of the number of signal displayed for the sp2 carbons. Here only 15 of the theoretical 16 resonances were found, probably due to superposition. The alkyne carbon atoms 3, 4 showed two signals at 80.0 ppm and 71.5 ppm. The sp3-hybridized C-atom 62

displayed a signal at 70.4 ppm. At 67.3 ppm and 65.7 ppm the signals for the oxygen-bound carbon atoms 5, 6, respectively were found. The methano carbon atom 7 was found at 52.0 ppm and the α-carbon 8 on the opposite side of the molecule gave a signal at 51.2 ppm. The C-atoms in the alkyl chain 9–12 appeared at 28.6 ppm, 28.5 ppm, 25.7 ppm and 25.7 ppm. For the carbon atom 13 in α-position to the alkyne, a signal at 18.3 ppm was found.

Figure 46: UV/Vis spectrum of fullerene monoadduct 70 recorded in CH2Cl2.

Another efficient characterization method for fullerenes is UV/Vis absorption spectroscopy. In the case of pristine C60 intense absorption bands in the region between 210 and 400 nm can be found. A very weak absorption in the visible region at 625 nm causes the purple color of C60 in solution.[244] Different UV/Vis spectra are measured for exohedral functionalized fullerenes, depending on the number of addends and their addition pattern.[86, 97d, 245] Higher functionalization causes a decrease in symmetry and a rupture of the conjugated π–electron system. Therefore the color of fullerene adducts brightens from brown to red, orange and [245] yellow with each additional addend. The UV/Vis spectrum of compound 70 in CH2Cl2 is depicted in Figure 46. It showed the typical absorption bands of a fullerene monoadduct with maxima at 267, 271, 326 nm and notably the small characteristic absorption at 429 nm. MALDI-TOF analysis of the compound exhibited the expected molecular ion peak at + m/z = 1128, but no fragmentation for C60 was detected at m/z = 720. HiRes-MALDI-TOF showed the correct molecular composition of [M+Na]+ at m/z = 1151.1693 with a marginal deviation from the calculated value of m/z = 1151.1676.

63

Scheme 23: Preparation of [60]fullerene monoadduct 71: a) CBr4, DBU, toluene, N2, rt, 18 h, 38 %.

For the second building block 40 the same protocol as before was applied (Scheme 23). C60, functionalized malonate and CBr4 were dissolved in toluene and DBU was added slowly. The mixture was stirred at room temperature overnight. Purification by column chromatography

(SiO2, toluene) gave the desired product in 38 % yield.

toluene

1 Figure 47: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 71. H grease impurities are marked with an asterisk. Water from CDCl3 is marked with a circle.

In Figure 47 the 1H-NMR spectrum of 71 is presented. Like in the NMR spectrum of compound

70, the signal for the acidic protons vanished, due to the functionalization with C60. The signals for the methylene units next to oxygen were split, the protons close to fullerene 1 appeared as triplet shifted downwards to 4.46 ppm with a coupling constant of 3J = 6.8 Hz. On the other side of the cyclo-[2]-malonate the protons 2 resonated as triplet with a chemical shift of 4.20 ppm and a coupling constant of 3J = 6.7 Hz. In contrast to 70, no further splitting was visible, due to the different environments caused by the presence of either one or two propargyl chains. The signal for the alkyne protons 3 and 4 were observed as doublet at 2.99 ppm and 4J = 2.7 Hz and a triplet at 2.04 ppm with a coupling constant of 4J = 2.4 Hz. Like above, the signals for the protons 5 and 6 of the methylene units in β-position to the oxygen atoms were split into two multiplets and shifted downfield to 1.88 – 1.82 ppm and 1.75 – 1.69 ppm. A slight downfield shift was found for the multiplet of the remaining alkyl chain protons 7 in the region of 1.54 ppm to 1.40 ppm.

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The 13C-NMR spectrum (Figure 48) displayed similar signals as compound 70 which were also in accordance with precursor 40. The carbonyl carbon atoms 1, 2 gave a signal at 168.7 ppm and 163.6 ppm. Like above for monoadduct 70, the sp2-hybridized C-atoms split in 15 signals between 145.2 ppm and 137.9 ppm – due to the double intensity of one signal and potential superposition – proving the existence of a fullerene monoadduct with CS symmetry. The signal for the sp3-hybridized carbon atom of the cyclopropane ring resonated at 71.5 ppm. At 51.9 ppm the signal for the methano C-atom 8 was observed. The propargyl moiety 3, 4 and 13 showed signals at 78.3 ppm, 71.8 ppm and 23.1 ppm. The signals for the methylene carbon atoms 5, 6 next to oxygen atoms were found at 67.3 ppm and 66.0 ppm. The tertiary carbon atom 7 gave a signal at 56.4 ppm. In the aliphatic region the signals for the C-atoms 9–12 of the methylene units showed signals at 28.6 ppm, 28.5 ppm, 25.7 ppm and 25.6 ppm.

CDCl3

3 2 C60-sp C60-sp

toluene 3

13 Figure 48: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 71.

The UV/Vis spectrum of 71 in CH2Cl2 is depicted in Figure 49. It showed maxima at 233, 271 and 326 nm, as well as the small characteristic absorption at 426 nm. Again, these absorption bands were typical for [60]fullerene monoadducts. The correct molecular ion peak at m/z = 1166 was observed in MALDI-TOF mass spectrometry. Here as well, the typical signal at + m/z = 720 for C60 was missing. In MALDI-TOF-HiRes, the expected signal was found at m/z = 1166.1985, with a calculated value of m/z = 1166.1935.

65

Figure 49: UV/vis spectrum of fullerene monoadduct 71 with two alkyne functionalities recorded in

CH2Cl2. In this project the synthesis of hexakisadducts containing the described malonates were not performed, due to the limited amount of building blocks available. After the synthesis of monoadducts 70 and 71, the quantity of malonate was too low to perform the hexakis formation in a sensible scale. Furthermore the hexakisadduct formed with malonate 32 would not be of use in this project, as explained above (see page 41).

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3.1.5 Formation of Cyclo-[2]-Malonate-Linked Porphyrin-Fullerene Dyads

After the successful synthesis of [60]fullerene monoadducts with the two novel alkyne bearing cyclo-[2]-malonates, it was required in the last step to join both fullerene and azido-porphyrin 29. Click-chemistry was applied to achieve this goal. Literature shows several porphyrin- fullerene hybrids using malonates and cyclopropanation for fullerene modification.[144a, 216a] But contrary to the molecules of this thesis all these literature examples share the common motive of porphyrin “clicked” to the alkyl chain in monomalonates.

As described earlier, a 1,2,3-triazole ring is formed between an azide and an alkyne in the presence of base and a Cu(I) catalyst. For that purpose, porphyrin and C60-derivative 70 in almost equimolar amounts were dissolved in a small volume of CH2Cl2 (Scheme 24). Care had to be taken that an inert atmosphere was present and all light was excluded, to improve the yield of the reaction. Next, Cu(II)-sulfate pentahydrate was dissolved in an equally small amount of water. It was treated with sodium ascorbate as reducing agent to form the active Cu(I) species in situ. The bluish solution turned orange and was added to the organic mixture. The mixture was stirred vigorously. Subsequently, DIPEA was added and the reaction stirred for 7 days.

After workup and column chromatography (SiO2, CH2Cl2), the purified porphyrin-fullerene dyad 72 was obtained in 49 %.

Scheme 24: Preparation of novel porphyrin-fullerene dyad 72: a) CuSO4*5H2O, Na-ascorbate, DIPEA,

CH2Cl2/H2O, N2, rt, 7 d, 49 %.

67

Figure 50: UV/Vis spectrum of porphyrin-fullerene dyad 72 recorded in CH2Cl2.

The first successful verification of the target molecule was MALDI-TOF-MS, where the product + molecular ion peak at m/z = 2039 was well observed. The fragmentation to C60 at m/z = 720 could not be observed. With high-resolution mass spectrometry the molecular composition was clearly confirmed. With a calculated mass of m/z = 2039.4188, the signal for the desired dyad was detected at m/z = 2039.5649. The UV/Vis spectrum of clicked porphyrin-fullerene dyad 72 is depicted in Figure 50. The spectrum was recorded in CH2Cl2 and revealed the expected characteristic bands of the fullerene monoadduct already described for 70 at 232, 265 and 326 nm. The small characteristic absorption at 429 nm was overlaid by the Soret band of the porphyrin, which was found at the expected 422 nm. The two Q-bands of the zinc- porphyrin absorption feature appeared at 548 and. 590 nm, respectively. Unfortunately no NMR spectra could be obtained for this compound, due a very low amount of product and solubility problems.

Sadly the respective synthesis could not be attempted with the [60]fullerene monoadduct 71. Not enough material of porphyrin 29 was produced in the timeframe of this project, permitting the attempt to form the double clicked porphyrin-fullerene conjugate. The procedure for this porphyrin-fullerene triad 73 would have been similar to that of compound 72, except two equivalents of porphyrin being used instead of one (Scheme 25).

68

Scheme 25: Proposed synthesis of novel porphyrin-fullerene triad 73: a) CuSO4*5H2O, Na-ascorbate,

DIPEA, CH2Cl2/H2O, N2, rt,

Despite the fact, that six-fold Bingel-reaction on C60 could not be attempted due to a lack of malonate, such a hexakisadduct is easily conceivable. As described above, the formation of fullerene hexakisadducts can be achieved in relatively good yield by adding DMA as template to a standard Bingel-Hirsch reaction. Such compound could then in turn be reacted with an excess of porphyrin under “click chemistry“ conditions to produce a fullerene hybrid 74 carrying 12 porphyrins in its outer periphery (Figure 51). Similar hexakisadducts have been prepared,[216a, 246] although with different malonates. Purification of the target compound might be more challenging, for a series of not completely reacted fullerene hybrids are possible besides the desired twelve-fold porphyrin-fullerene hybrid. However an even number of successful click reactions is to be expected. The group of Jux showed that in the case of multiple possible reaction sides the triazole formation is favored on alkynes in close proximity to an already reacted alkyne, therefore leading to pairs of triazole species. A [60]fullerene hexakisadduct of such kind is definitely worthy of further investigation. Its Th-octahedral symmetry renders a unique architecture. The use of click chemistry opens the way for easy attachment of all kinds of addends other than porphyrins with distinct properties, to modify the fullerene core and use it in different sorts of application. As already mentioned earlier, an electron transfer from porphyrins to an additional C60-imidazole derivative sandwiched between two porphyrins is also imaginable.[205b]

69

It remains to be seen if such a behavior could be observed in this molecule as well. Regardless whether this might be the case, such porphyrin-fullerene hexakis hybrid would be one of a kind and its aesthetically pleasing form alone would justify its synthesis.

Figure 51: Proposed fullerene hexakisadduct 74 with twelve porphyrins attached to its periphery by the means of click chemistry.

70

3.2 Novel Cyclo-[n]-Bridged Fullerene-Trimer

3.2.1 Synthesis of Fullerene Trimer from Diethyl Pentakisadduct

The synthesis of cyclo-[2]-malonate was one of the central aspects in previous chapters. The main project of this thesis was based on the application of a cyclic bismalonate as bridging unit between the [60]fullerene core and other addends, in this case porphyrins. As described in the introduction, these malonates could also be used to link different exohedrally functionalized fullerenes with each other. Previous work from our group showed the synthesis of fullerene dimers, dumbbell shaped molecules consisting of two fullerenes fused by cyclo-[2]-malonate, and heptamers,[119, 247] a fullerene hexakisadduct with six additional fullerenes in an octahedral addition pattern around the core. Other systems of connected fullerenes are conceivable. Here a new fullerene trimer is presented, consisting of three [60]fullerene cores bound to each other via cyclo-[3]-malonate.

The idea was based on the already mentioned dumbbell shaped fullerene dimer. With an effective synthesis already developed, larger oligomers should have been, in theory, accessible by using cyclo-[n]-malonate with an n-value higher than 2. The first compound following this scheme would have been a fullerene trimer, using cyclo-[3]-malonate as bridging-unit. As described earlier, cyclo-[3]-malonate is the main byproduct of the synthesis of cyclo-[2]- malonate, and is obtained in moderate amounts, despite its low yield, due to the very good scalability of the procedure. Therefore the preparation of a C60 trimer with this tris-malonate linker was an obvious choice. As described in the introduction, cyclo-[3]-octylmalonate has been used before for the selective formation of C60 trisadducts, in a new approach to the tether-directed functionalization of fullerene.[104]The reaction of the regioselective tris- malonate only led to compounds with rotational symmetry, namely e,e,e, trans-4,trans-4,trans-4 and trans-3,trans-3,trans-3 isomer, with e,e,e as main product. A fourth imaginable isomer, cis- 1,cis-1,cis-1, is sterically impossible with malonate addends. Cyclo-[3]-octylmalonate was also used as “template” for the formation of mixed [3+3] hexakisadducts with controlled addition pattern.

To achieve the formation of the novel fullerene trimer, the chain length of the malonate was increased from hexyl-chains used shown in previous chapters (see page 35) to octyl-chains. The reason for this was to increase the distance between the malonates and thus between the bound fullerenes. If three C60 with bulky functionalities were to be used, a short chain might have been problematic in regards of steric hindrance. Besides, as mentioned, dimers consisting of fullerenes and cyclo-[2]-octylmalonate already existed. For comparability, the use of the identical chain length was advisable.

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Scheme 26: Planned synthesis of fullerene trimer 76 from pristine C60: a) malonyl dichloride, pyridine, CH 2Cl2, rt, 4 d, 8 %; b) CBr4, DBU, toluene, N2, rt.

The synthesis of cyclo-[3]-octylmalonate 75 followed the general protocol already described (Scheme 26). 1,8-octanediol 74 was reacted with malonyl dichloride in the presence of pyridine in CH2Cl2 in 8 % yield. Purification was achieved through column chromatography (SiO2,

CH2Cl2/EtOAc 97:3), with the desired product being the second distinct spot visible on TLC. Cyclo-[1]-malonate in general, with a lesser polarity than other malonate oligomers, was only formed in traces and was seldom observed during TLC control. Analytical data was found to be in accordance with literature.[104] Contrary to cyclo-[2]-octylmalonate, which is a white solid, the cyclo-[3]-variety, with an uneven number of moieties, was obtained as yellow oil. In the next step the fullerene trimer 76 should have been prepared under Bingel-Hirsch conditions. For that purpose a 5-fold excess of C60 was dissolved in toluene. Compound 75 and CBr4 were added, followed by the addition of DBU. The solution turned from the purple color of dissolved

C60 to dark brown, indicating the successful formation of fullerene monoadducts and possibly the desired product. Unfortunately the formation of trisfullerene 76 could not be proven. The obtained product was highly insoluble, thus purification and characterization was not possible.

Scheme 27: Scheme for the preparation of [5:1]-hexakisfullerene 78 and photo cleavage to obtain

pentakisadduct 79: a) diethyl malonate, DMA, CBr4, DBU, oDCB, N2, rt, 41 %; b) maleic anhydride, hν, toluene, rt, 24 h, 75 %. 72

In order to overcome the complication regarding solubility, the same approach was tried using diethyl malonate functionalized fullerene pentaadduct instead of C60. The synthesis of such compound afforded a protection-deprotection protocol (Scheme 27), which has been developed by our group.[119] For that purpose isoxazolinofullerene 77 was synthesized following the literature known procedure.[248] In the next step, fivefold cyclopropanation with diethyl malonate, DMA, CBr4 and DBU in oDCB gave the mixed [5:1]-fullereno isoxazoline adduct 78, with analytical data identical to literature.[119] Irradiation with a halogen flood light at room temperature in toluene, in the presence of a 30-fold excess of maleic anhydride to trap the nitrile oxide forming during the retro-cycloaddition, led to deprotection of 97. With the unprotected pentakisadduct 79[119] at hand, the synthesis of a fullerene trimer was repeated (Scheme 28). Therefore three equivalents of the fullerene were reacted with cyclo-[3]- malonate in toluene. Again CBr4 was used as halogen source. After DBU addition, the mixture was stirred for 5 days. Subsequent purification by column chromatography (SiO2, toluene/EtOAc 8:2) yielded the expected trisfullerene 80 in 19 %.

Scheme 28: Synthesis of trisfullerene 80 from [60]fullerene pentakisadduct: a) CBr4, DBU, toluene,

N 2, rt, 5 d, 19 %.

The successful formation of 80 was proven by mass spectrometry. MALDI-TOF showed the correct molecular ion peak at m/z = 5171 together with the signals for [M+Na]+ at m/z = 5193 + + and [M+K] at m/z = 5211 as well as the fullerene cation C60 at m/z = 720. High-resolution mass spectrometry clearly confirmed the molecular composition. At m/z = 5193.1824 the correct signal was observed. In Figure 52 the UV/Vis of fullerene trimer 80 is shown. The observed absorption maxima at 249, 270, 280, 316, 335 and 380 nm were congruent with those of other fullerene hexakisadducts.

73

Figure 52: UV/Vis spectrum of fullerene trimer 80 recorded inCH2Cl2.

In Figure 53 the 1H-NMR spectrum of compound 80 is presented. The alkoxy protons 1 of the diethyl malonate addends gave five quartets that overlapped, resulting in a signal at 4.31 ppm with a coupling constant of 3J = 7.0 Hz next to a triplet with a chemical shift of 4.23 ppm and a coupling constant of 3J = 6.4 Hz, belonging to the protons of the oxygen-bound methylene units 2 in cyclo-[3]-octylmalonate. The protons of the terminal methyl group 3 resonated as triplet at 3 1.30 ppm with a coupling constant of J = 7.1 Hz. The remaining signals for the CH2-groups 4 gave a broad signal between 1.28 ppm and 1.23 ppm. Minor impurities were caused by incomplete purification process.

toluene

1 Figure 53: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 80.

74

In the 13C-NMR spectrum of 80 (Figure 54) the signals for the five distinguishable carbonyl C- atoms in 1 overlapped to one signal. It was found together with the signal for carbonyl carbon 2 at 163.8 ppm and 163.8 ppm with the expected ratio of 1:5. The signals for the sp2-hybridized carbon atoms mostly overlapped, resulting in only two signals observable in this region for. Both signals were split only slightly, the first into three distinct peaks at 145.8 ppm, 145.8 ppm and 145.7 ppm, the second into two at 141.1 ppm respectively. The splitting is caused by the two different malonate addends bound to the C60 core. No Th-symmetry was achieved in the fullerene, but the difference between the addends was too small to result in further signal splitting. At 69.1 ppm the signals for the sp3-hybridized carbon atoms were observed. The oxygen-bound carbon atoms 3 of the alkyl chain resonated at 66.8 ppm. The signal for the CH2- unit 4 in α-position to oxygen in the ethyl moiety was detected at 62.8 ppm. The methano carbon atoms 5 gave a split signal at 45.4 ppm and 45.3 ppm for the same reason described above. In the aliphatic region the signals for the remaining alkyl carbon atoms 6 were found at 28.4 ppm, 25.8 ppm and 22.7 ppm. At 14.0 ppm the signal for the terminal methyl unit 7 was observed.

CDCl3

2 C60-sp 3 C60-sp

toluene 3

13 Figure 54: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 80.

75

After the successful preparation of this novel fullerene trimer, the same method should have been applied for the formation of a fullerene tetramer (Scheme 34). For this purpose cyclo-[4]- octylmalonate[104] was used as the bridging unit between four [60]fullerene cores. As with the synthesis of cyclo-[3]-octylmalonate, the larger tetrakis-malonate is another byproduct in the general synthesis of cyclo-[n]-malonates described above. It was obtained in very low yield (4 %) as the third fraction in the purification via column chromatography, with an even higher polarity than cyclo-[3]. Due to its even number of parts, the product was again obtained as white solid, in contrast to the oil obtained with cyclo-[3]-malonate. In the next step (Scheme 29) malonate 81 was reacted with pentakisadduct 79 in the Bingel-Hirsch reaction in toluene with

CBr4 and DBU. Sadly, a first attempt did not lead to the desired compound 82. Even after several days of stirring and a repeated addition of CBr4 and base, no evidence for the formation of the expected compound was found in TLC investigations of the crude mixture. This result is surprising, since you would expect at least a partial reaction between the cyclo-[4]-malonate and the fullerene pentakisadducts. Based on the successful formation of the fullerene trimer under the same conditions, the formation of a fullerene tetramer should be possible as well. There is in fact no explanation, in regards of reaction conditions or steric hindrance that would permit the formation of the desired compound 82. Unfortunately, the experiment could not be repeated due to time constrains, so the novel fullerene tetramer could not be obtained in this work.

Scheme 29: Proposed preparation of tetrakisfullerene 82: a) CBr4, DBU, toluene, N2, rt.

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3.2.2 Attempted Synthesis of Fullerene Trimer with Terminal Alkynes

With the protocol for the synthesis at hand, derivatives of this kind of trisfullerene should have been prepared, making the compound class more versatile. The idea was to modify the properties of the trimer by exchanging diethyl malonate for a malonate that could bind different functional groups. Following the proposition of the previous project, click chemistry should have been used. The use of the newly developed alkyne cyclo-[2]-malonate would be conceivable. What was problematic was that only a limited amount of linker was available and the synthesis to make more was quite tedious. Therefore it was decided to use an open chain malonate. Bis(5-(trimethylsilyl)pent-4-yn-1-yl) malonate was chosen. This literature known malonate was easier in preparation, due to commercially available precursor and a simple one- step synthesis. Furthermore this compound had already been used in similar click-chemistry approaches in fullerene chemistry.[216a] The formation of the fullerene pentakisadduct was attempted using the same isoxazoline protection-deprotection scheme as before. The reaction with cyclo-[3]-octylmalonate would have resulted in a new fullerene trimer. After removal of the TMS protecting group, 30 alkyne moieties would have been applicable for click-chemistry, to introduce different functionalities onto the trisfullerene.

Scheme 30: Synthesis scheme for alkyne-functionalized pentakisadduct 86: a) malonyl dichloride, pyridine, CH2Cl2, N2, rt, 24 h, 62 %; b) DMA, CBr4, DBU, oDCB, N2, rt, 7 d, 50 %; c) maleic acid, toluene, hν, N2, rt.

77

The synthesis of said malonate was done according to literature (Scheme 30). Two equivalents of 5-(trimethylsilyl)pent-4-yn-1-ol 83 were reacted with malonyl dichloride in the presence of pyridine in CH2Cl2 and afforded the desired compound 84 in 62 % yield. Analytical data was found to be according to literature.[120b] In the next step the isoxazoline protected pentakisadduct 85 was formed. Fullerene 77 was dissolved in oDCB. DMA was added and the mixture stirred for 5 hours. Next the malonate and CBr4 were added and stirred for 30 minutes. Subsequently DBU was added slowly and stirring continued at room temperature for 7 days, yielding the product as orange solid in 50 %.

CDCl3

1 Figure 55: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 85. H grease impurities are marked with an asterisk. Solvent impurities are marked with a circle.

The 1H-NMR spectrum of 85 (Figure 55) showed the signals for the aromatic protons 1, 2 as two doublets at 7.82 ppm with a coupling constant of 8.7 Hz and 6.66 ppm with 3J = 8.4 Hz. The

α-CH2-groups 3 appeared as multiplet between 4.41 ppm and 4.29 ppm. At 2.97 ppm the singlet for the two amine-bound methyl group 4 was observed. The second methylene-unit 5 was detected as multiplet between 2.35 ppm and 2.26 ppm. Another multiplet for the last CH2- group 6 resonated between 1.95 ppm and 1.87 ppm. The three methyl groups 7 in TMS were found as multiplet between 0.14 ppm and 0.11 ppm.

78

CDCl3

3 C60-sp

2 C60-sp

Figure 565: 13C-NMR spectrum (100 MHz, CDCl , rt) of compound 85. Minor impurities from solvent 3 remains.

The 13C-NMR spectrum of 85 is shown in Figure 56. For the carbonyl carbon atoms 1 signals were found at 163.7, 163.7, 163.6, 163.4 and 163.3 ppm. The signals for the sp2-hybridized carbon atoms of the fullerene core were detected between 146.8 ppm and 139.2 ppm. In the aromatic region, the signals for the acrylic carbon atoms resonated between 130.4 ppm and 111.6 ppm. The alkyne group 2, 3 was observed as two signals at 105.1 ppm and 85.7 ppm. For 3 the C60-sp carbon atoms three signals were found at 104.9 ppm, 76.7 ppm and 69.8 ppm. A signal for the carbon atom 4 in α-position to oxygen appeared at 65.8 ppm, while the other two alkyl chain carbon atoms 7, 8 were observed at 27.5 ppm and 16.5 ppm respectively. The methano C-atom 5 resonated at 45.3 ppm. The methyl carbon atoms 6 bound to nitrogen gave a signal at 40.1 ppm. At 0.09 ppm the signal for the TMS-methyl groups 9 was detected.

In the next step, the isoxazoline protection group should have been removed, to bind the free [60]fullerene addition side with cyclo-[3]-octylmalonate, resulting in a novel trisfullerene that could have been further functionalized through its terminal alkyne moieties. Unfortunately even after several days with large excesses of maleic acid, the fullerene could not be deprotected completely. It always resulted in a mixture of unprotected product and protected precursor. Separation of the two could not be achieved by the means of column chromatography. The Bingel-reaction of the following step was tried several times without 79

further purification, in an attempt to form the fullerene trimer 86 with the deprotected pentakisadduct available in the mixture. In this way, the yields would have been reduced; on the other hand separation of the desired trisfullerene and the isoxazoline precursor would have been facilitated. The synthesis procedure was identical to that of compound 80, with cyclo-[3]-octylmalonate in toluene and CBr4 and DBU as reagents. Sadly, no product could be obtained through this approach. In the last step the trimethyl silyl protection group would have been removed by the reaction with TBAF in CH2Cl2 to give the terminal alkyne moieties 87 (Figure 57).

Figure 57: Planned fullerene trimer 87 with thirty terminal alkynes in its periphery to allow potential functionalization by the means of click chemistry.

80

3.3 Synthesis of Alkyne-Functionalized Fullerene Monoadducts as Dyes for the formation of Hierarchical Structures on Nanoparticles

Fullerene compounds, which were synthesized for a collaboration with Judith Wittmann from the group of Prof. Halik, are the subject of the following chapter. The aim of this project was the construction of hierarchical structures based on metal oxide nanoparticles and the study of their optical properties(Scheme 31). For that, Al2O3 nanoparticles were functionalized with phosphonic acids derivatives, according to literature procedure[249], carrying either an chain or a chain with a terminal azide group (Figure 59). The azide allowed post- functionalization by click-reaction, with dyes that contained a terminal alkyne such as pyrenes, porphyrins and fullerenes. The two phosphonic acid compounds were applied in different molar ratios. Assuming a statistical distribution of phosphonic acid derivatives on the nanoparticle surface, a defined ratio of azide to alkane functionalization was achieved. Thus, in the subsequent click-step, the amount of dye per particle could be controlled, which in turn had an influence on the coloration. Through comparison of the different dye-functionalization degrees, the influence of the dye on the optical properties of the nanoparticle could be examined.

Scheme 31: Functionalization of Al2O3-Nanoparticle with different ratios of alkyl/azide-phosphonic acid derivatives for post-functionalization with dyes.

The reason for the use of copper(I)-catalyzed alkyne-azide cycloaddition in this project was the small number of possible side-products and the theoretically high yields. In practice the ideal case of a large proportion of successful reactions can only be assumed. The verification by TGA is hardly possible, due to the difference of starting material and product being too small to measure. In addition, the click-reaction offered the possibility to attach a variety of alkyne- functionalized dyes to the nanoparticle, with the synthesis of both azide-phosphonic acid and alkyne-dye being fairly simple. Another advantage was the potential to practically control the degree of post-functionalization via the click reaction quantitatively through the molar ratios of the phosphonic acids. Those were chosen for the very high stability of the bond with

81

nanoparticles. In comparison to other anchoring groups, like carboxylic acids or catechol anchoring groups, phosphonic acid is very hard to remove. This guaranteed a constant functionalization ratio, even after the several washing steps necessary to remove unbound phosphonic acid derivatives. Besides, due to their structure, the phosphonic acid chains could arrange itself differently in space. This can have an influence, through distance and spatial alignment of the dyes to each other, on the interactions between the dyes, affecting the optical properties as well. Furthermore, the use of CuAAC could enable the formation of dye combinations. By adding a third phosphonic acid, already functionalized with another dye, to the alkane/azide mixture, a nanoparticle functionalization with two different dyes could be accessible. This would allow the study of interactions between the dyes and their influence on the optical properties of nanoparticles.

Figure 59: Azido- and alkyl-phosphonic acid derivative.

The focus of this work was on the synthesis of the required fullerene dyes. For that purpose monofunctionalized malonates should be prepared to only allow one click reaction for each C60 core. Different monoadducts should be measured, varying in the length of the alkyne chain on the malonate, to examine the influence of chain length on the binding between [60]fullerene and nanoparticle and its effect on optical properties.

The first compound prepared in this project was a malonate with a very short alkyne chain. Propargyl was chosen as functional group, even if the shorter ethynyl group would have been imaginable in principle, its synthesis would have been highly unpractical and it might have caused some problems in this project. Therefore an additional carbon atom was preferred in this context. The synthesis was done according to literature procedure.[250]

82

Scheme 32: Synthesis of alkyne-fullerene monoadduct 93: a) pyridine, CH2Cl2, N2, rt, 24 h, 90 %; b) C60, I2, DBU, toluene, N2, rt, 7 h, 57 %.

Methyl propynylmalonate was prepared following the standard malonate synthesis protocol

(Scheme 32). Propargyl alcohol was reacted with methyl malonylchloride in CH2Cl2 in the presence of pyridine. The desired product 92 was obtained after column chromatography

(SiO2, hexanes/EtOAc 6:1) in 90 % yield. The fullerene monoadduct was achieved, in contrast to previous fullerene adducts, with iodine as halogen source for the Bingel-reaction.[108, 251] The reaction of malonate and C60 with iodine and DBU in toluene gave the monoadduct 93 in 7 hours. Purification by column chromatography (SiO2, toluene/hexanes 2:1) yielded the dark brown solid in 57 %. The analytical data of both compounds were in accordance with the literature.[250]

Scheme 33: Preparation plan for alkyne-fullerene monoadduct 96: a) pyridine, CH2Cl2, N2, rt, 24 h, 81 %; b) C60, I2, DBU, toluene, N2, rt, 7 h, 55 %.

83

For the next malonate, the chain length between the terminal alkyne and the malonate should be increased. A longer chain was more flexible and should form the triazole ring in the click reaction step better than the short propargyl chain. Therefore an extension by two carbon atoms to pentynyl instead of propargyl was chosen. In contrast to the preceding malonate, here the use of an alkyne-protecting group was advised. In general, it is possible for an alkyne to react with the C60 core in a [2+2] cycloaddition-reaction. In the case of propargyl, this causes no problem, because of the very short chain. The malonate sterically hinders the cycloaddition, favoring the Bingel cyclopropanation. By increasing the chain length the problem might occur, due to the increased flexibility of the alkyne linker. For that reason a precursor was chosen, which had the TMS-protecting group bound to the terminal alkyne. Again both compounds were prepared according to literature (Scheme 33).[252]

The desired malonate 95 was obtained by reacting 5-(trimethylsilyl)pent-4-yn-1-ol with methyl malonylchloride and pyridine in CH2Cl2. Purification by column chromatography (SiO2, hexanes/EtOAc 6:1) gave the product in 81 % yield. The monoadduct was prepared by reacting

C60 and malonate in the presence of iodine. DBU was added and the mixture stirred for 7 hours.

Column chromatography (SiO2, toluene/hexanes 2:1) yielded the fullerene 96 in 55 %.

Scheme 34: Synthesis of alkyne-fullerene monoadduct 96: a) n-BuLi, TMS-chloride, THF N2, -78 °C, 16 h, 50 %; b) 91, pyridine, CH2Cl2, N2, rt, 24 h, 62 %; c) C60, I2, DBU, toluene, N2, rt, 12 h, 26 %.

For the third malonate, the alkyne chain was elongated once more to heptynyl. The longer chain was even more flexible and could further facilitate the click reaction later on. Furthermore, the high flexibility of the linker should have a larger influence on the spatial arrangement of the fullerene dye on the nanoparticle. For this compound the terminal alkyne was protected with trimethylsilyl as well, to prevent side reactions between alkyne and C60. Since the alcohol precursor for the malonate synthesis was not commercially available, it had to be prepared beforehand, following a literature protocol. The consequent malonate and the fullerene monoadduct were synthesized using the standard methods, resulting in two novel compounds (Scheme 34).

84

For the preparation of 7-(trimethylsilyl)hept-6-yn-1-ol 97, heptynol 64 was deprotonated with n-BuLi in THF at -78 °C, before TMS-chloride was added to the mixture. After aqueous work up, the desired product was obtained in 50 % yield. Analytical data was identical to literature.[253] Next, the malonate was prepared as before. Methyl malonyl chloride and the alcohol were reacted in CH2Cl2 in the presence of pyridine overnight. Aqueous work up and purification by column chromatography (SiO2, hexanes/EtOAc 6:1) gave the product as yellow oil in 62 % yield. In the last step the fullerene monoadduct was synthesized following the same procedure as the previous two. C60 was dissolved in toluene and malonate and iodine were added. DBU was added to the mixture and stirred for 12 hours. After column chromatography (SiO2, toluene) the dark brown monoadduct 99 was obtained in 26 % yield. The drop in yield, compared to the two previous examples, might be caused by the longer alkyl chain. The higher flexibility might allow the alkyl chain to react in unwanted side reactions, causing a reduction in yield. The silyl protecting group should prevent this from happening, however the possibility cannot be rulled out.

1 Figure 60: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 98.

The 1H-NMR spectrum of 98 (Figure 60) exhibited the signal of the alkoxy protons 1 as triplet at 4.14 ppm with a coupling constant of 3J = 6.7 Hz. The signal of the protons in the methyl ester 2 was found as singlet at 3.72 ppm. At 3.37 ppm the two acidic H-atoms 3 were observed as singlet. The signal for the CH2-group 4 next to alkyne resonated as triplet at 2.22 ppm with 3J = 6.9 Hz. The alkyl chain 5 appeared as multiplet between 1.68 ppm and 1.38 ppm. A singlet at 0.11 ppm was detected for the methyl units 6 in the TMS-moiety.

85

1 In Figure 61 the H-NMR spectrum of 99 is presented. The oxygen-bound CH2-group 1 resonated as triplet at 4.49 ppm with a coupling constant of 3J = 6.6 Hz. At 4.08 ppm the singlet of the methyl ester 2 was observed. The protons next to the alkyne moiety 3 were found as triplet with a chemical shift 2.24 ppm and 3J = 6.7 Hz. The remaining alkyl chain protons 4 showed three multiplets between 1.89 – 1.84 ppm and 1.59 – 1.55 ppm. The three methyl groups in TMS 5 gave a singlet at 0.14 ppm.

4

1 Figure 61: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 99. Grease impurities are marked with an asterisk; water impurities from CDCl3 are marked with a circle.

Figure 62 shows the 13C-NMR spectrum for compound 99. Two signals for the carbonyl carbon atoms 1, 2 were observed at 164.1 ppm and 163.6 ppm. The sp2-hybridized carbon atoms resonated between 145.3 ppm and 138.9 ppm. The alkyne 3 and 4 gave signals at 106.9 ppm and 84.8 ppm. The signal for the sp3-carbon atom was observed at 71.5 ppm. At 67.3 ppm the

CH2-group next to hydrogen 5 was displayed. The methyl ester 6 gave a signal at 54.0 ppm while the α-carbon between the carbonyls 7 resonated at 52.0 ppm. The signals for the remaining methylene units 8 appeared between 28.1 ppm and 19.8 ppm. TMS 9 gave a signal at 0.17 ppm.

86

CDCl3

12

2 C60-sp

3 C60-sp 8-11

*

Figure 62: 13C-NMR spectrum (100 MHz, CDCl , rt) of compound 99. Solvent impurity is marked with 3 an asterisk.

The UV/Vis spectrum of 99 (Figure 63) reflected the typical mono-functionalization of [60]fullerene with maxima at 230, 257 and 327 nm, as well as the small characteristic absorption at 426 nm. The correct molecular ion peak at m/z = 1002 was observed in MALDI- + TOF mass spectrometry, together with the signal for the typical C60 fragmentation at m/z = 720.

Figure 63: UV/Vis spectrum of alkyne-fullerene monoadduct 99 recorded in CH2Cl2.

87

The compounds were then given to the Haliks group to be used in the functionalization of nanoparticles. A darkening in the colour of the particle was observed with increasing amount of clicked fullerene. The absorption of the fullerene compounds, however, was quite weak, demonstrated through the colour of the particle as well as UV/Vis. In comparison, the pyrene derivative showed a much stronger absorption. Further investigations are currently ongoing.

88

Results and Discussion

3.4 Fullerene Diamino Monoadduct as Bidentate Ligand for the Coordination to a Metalloporphyrin-Dimer

The fullerenes of the last chapter as well, were prepared as part of a collaboration together with Dr. Dominik Lungerich from the group of Prof. Jux and Maximilian Wolf from the group of Prof. Guldi. Central for this project was porphyrin-dimer 100 (Figure 64). Similar compounds have been studied for decades. Different kinds of spacer – including alkenes, alkynes and phenyls[254] – have been used. Due to the spacer, a broad distribution of conformations is possible. Here, the two halves of this porphyrin-HBC-conjugate are bridged with a butadiyn- linker.

Figure 64: Porphyrin-HBC conjugate 100.

For the coplanar conformation of the porphyrins, an extended conjugated π-system with a maximum of mutual electronic communication between the two porphyrins is obtained,[255] which causes a redshift in the absorption spectra. Planar conformers are enthalpically more favorable than perpendicular conformers and can be achieved by reducing the temperature. Alternatively bidentate ligands, which are short and rigid enough, can force the system in the planar conformation.[254d] For Zn-porphyrins, amino-ligands are typically used, like diaminoalkanes or the rigid ligand 101 (Figure 65).[256]

Figure 65: Bidentate ligand 101.

89

Results and Discussion

Besides the expected shifts in the spectra of the porphyrin-ligand-complex, very high binding constants in the order of 108 M-1 were observed as well. High binding constants are required for an effective interaction in an electron-donor-acceptor-system. Due to these high binding constants, it was planned to investigate these systems further for their use in donor-acceptor systems. A [60]fullerene with a similar diamino motif should now be tested as ligand and potential electron acceptor in this system. By using a monoadduct with two terminal amino groups on the malonate, the diaminoalkane should be mimicked. To prove that the observed electronic communication between the porphyrins was caused by planarization of the dimer, a monoamino fullerene should be tested as reference. Similar monoamino fullerenes can be found in literature, however, no examples using methyl moieties or of diamino fullerenes.

The main aspect of this work was the synthesis of the required diamino fullerene monoadduct and the monoamino reference. For this purpose two novel fullerene monoadducts were synthesized. The malonates used were functionalized with primary amines, which should coordinate to the metal center in the porphyrin. It was decided to use pentyl chains to bridge malonate and amine. This would give the linker enough flexibility and prevent steric hindrance through the C60 core. Since it is not uncommon for primary amines to react with [60]fullerene, it was necessary to take precautions to prevent unwanted side reactions in the Bingel reaction step forming the monoadduct. Thus Boc-protecting group, the standard method to protect amines,[257] was introduced to the amine. The so formed Boc-amine was unreactive towards the addition to C60 allowing the formation of the desired product without byproducts. Afterwards the Boc-group could easily be removed with strong acids,[258] resulting in a fullerene monoadduct with primary amines as functionalities.

For the synthesis of both malonate derivatives, first the Boc-protected amino pentanol 104 had to be prepared (Scheme 35), according to literature, from amino pentanol 102 and di-tert-butyl dicarbonate 103 in 55 % yield.[259]

Scheme 35: Synthesis scheme of Boc-protected amino pentanol 104: a) CH2Cl2, N2, rt, 2 h, 55 %.

90

Results and Discussion

Scheme 36: Synthesis of amino-fullerene monoadduct 107: a) Pyridine, CH2Cl2, N2, rt, 12 h, 71 %; b) I2, DBU, toluene, N2, rt, 1 h,46 %; c) TFA, rt, 1 h, 96 %.

Next the variant 107 with one amino chain should be prepared by the reaction of the protected amino pentanol and methyl malonyl chloride in the presence of pyridine in CH2Cl2 (Scheme 36).

Purification by column chromatography (SiO2, CH2Cl2/EtOAc 9:1) gave the malonate 105 in

71 % yield. Subsequent cyclopropanation of C60 in toluene yielded the monoadduct 106 in 46 %. Iodine was used as halogen source and DBU as base. In the last step the Boc-group was cleaved off by stirring fullerene in TFA for one hour. The solvent was removed in vacuo and co- evaporated multiple times with MeOH.[260] This led to the formation of the trifluoroacetic salt, which was necessary for solubility. Earlier attempts to deprotect the amine without counter ion, had resulted in a fullerene, that was hardly soluble in most solvents.

1 Figure 66: H-NMR spectrum (400 MHz, CDCl3, rt) of compound 105.

91

Results and Discussion

The formation of malonate 105 could be demonstrated by 1H-NMR spectrum (Figure 66), which was almost identical to that of the Boc-protected amino pentanol. The alkoxy protons 1 resonated as triplet with a chemical shift of 4.09 ppm with a coupling constant of 3J = 6.5 Hz. At 3.70 ppm the methyl ester group 2 gave a new singlet signal, confirming the existence of the malonate unit as well as the singlet for the malonate protons 3 between the carbonyl atoms at

3.33 ppm. The CH2-group 4 in α–position to nitrogen was detected as multiplet between 3.09 ppm and 3.04 ppm. The remaining methylene units 5 were found as multiplets between 1.65 – 1.60 ppm and 1.49 – 1.38 ppm. A singlet was observed for the Boc-group 6 at 1.37 ppm.

CDCl3

2 C60-sp

3 C60-sp 11 12 *

13 Figure 67: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 106. Solvent impurities are marked with an asterisk.

After Bingel reaction, the 1H-NMR spectrum of 106 was consistent with the precursor malonate, except for the expected omission of the α-proton signal at 3.33 ppm and a general downshift of the proton signals. In the 13C-NMR spectrum, depicted in Figure 67, the existence of the fullerene monoadduct was apparent. Two signals for the two distinct malonate carbonyl atoms 1, 2 were found at 164.1 ppm and 163.5 ppm. At 155.9 ppm the carbonyl 3 in the Boc- group resonated. Between 145.2 ppm and 138.9 ppm appeared the 30 signals for the 2 [60]fullerene sp -carbon atoms, proving the expected Cs-symmetry. The tert-butyl carbon 4 next to oxygen displayed at 79.2 ppm. At 71.4 ppm the signal for the sp3 carbon atoms was found. The oxygen-bound methylene unit 5 was observed at 67.2 ppm, while the methyl ester 6 gave a signal at 54.0 ppm. The methano bridge 7 in the cyclopropane ring was detected at

51.9 ppm. At 40.4 ppm the signal for the CH2-group 8 next to nitrogen was found. The other methylene carbon atoms 9 appeared at 29.7 ppm, 28.2 ppm and 21.0 ppm. The methyl groups 10 of tert-butyl were detected at 28.4 ppm.

92

Results and Discussion

The absence of the signals for the Boc-group in the 1H-NMR spectrum of 107 indicated the successful deprotection of the amine. Likewise the 13C-NMR spectrum (Figure 68) looked similar to that of the precursor, except that it showed no sign of the tert-butyl group and only the carbonyl signal of the malonate. Two very small signals around 118 ppm and a weak quartet at 163 ppm could be attributed to the trifluoroacetate anions.

2 C60-sp

3 C60-sp

13 Figure 68: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 107.

In Figure 69, the UV/Vis spectrum of 107 in CH2Cl2 is shown. Like before, the three maxima at 225, 258 and 326 nm, as well as the small characteristic absorption at 426 nm could be seen, + proving the successful formation of a [60]fullerene monoadducts. Besides the typical C60 fragmentation signal at m/z = 720, the expected molecular ion peak was found at m/z = 921 in MALDI-TOF mass spectrometry. In MALDI-TOF-HiRes, the correct signal was found at m/z = 922.1700, with a calculated value of m/z = 922.1074.

Figure 69: UV/Vis spectrum of amino-fullerene monoadduct 107 recorded in CH2Cl2.

93

Results and Discussion

Scheme 37: Preparation of diamino fullerene monoadduct 127: a) malonyl dichloride, pyridine, CH Cl , N , rt, 12 h, 45 %; b) I , DBU, toluene, N , rt, 1 h,37 %; c) TFA, rt, 4 h, 94 %. 2 2 2 2 2

In a parallel approach (Scheme 37), the corresponding malonate with two amino pentyl chains was prepared under the same conditions. Reaction of Boc-protected amino-pentanol with malonyl dichloride and pyridine gave the expected malonate 125 in 45 % yield. The fullerene monoadduct 126 was obtained in 37 % by Bingel reaction of malonate and C60 in toluene. As above, deprotection was achieved by stirring the Boc-amino fullerene in TFA. Solubility was an even greater problem for the di-amino malonate. Without trifluoroacetic counter ion, the free amino compound 127 was completely insoluble and therefore could neither be characterized nor used in experiments.

7

6 NH

1 Figure 70: H-NMR spectrum (400 MHz, CDCl3, rt) of compounds 108. The 1H-NMR spectrum of 108 (Figure 70) was similar to that of its precursor. The protons of the oxygen-bound methylene unit 1 appeared as triplet at 4.09 ppm with 3J = 6.6 Hz. The successful synthesis was proven by the singlet signal of the α-protons 2 with a chemical shift of

3.32 ppm. At 3.06 ppm the signal of the CH2-group 3 next to nitrogen was observed as 94

Results and Discussion multiplet. The H-atoms 4 in β-position to the ester showed a multiplet at 1.65 ppm and 1.58 ppm. The protons in methylene units 5 and 6 gave a multiplet between 1.49 ppm and 1.29 ppm. At 1.39 ppm the tert-butyl protons 7 were found as singlet.

CDCl3

2 C60-sp

3 C60-sp

13 Figure 71: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 109.

For compound 109 the 1H-NMR was almost identical to that of its precursor. No signal was found at 3.32 ppm, indicating the formation of the cyclopropane ring on C60. All protons experienced a slight shift downfield in comparison to 108. In Figure 71 the 13C-NMR spectrum is shown. The two carbonyl carbon atoms 1, 2 were found at 163.6 ppm and 155.9 ppm. In the 2 region of the sp -hybridized carbon 14 signals were detected for C60 between 145.2 ppm and 138.9 ppm, superposition probably causing the lack of two signals. Two signals for the tert- butyl carbon atoms 3 and 8 appeared at 79.1 ppm and 28.2 ppm. At 71.5 the signal for the sp3- hybridized carbon atom was found. The methylene unit 4 in α-position to oxygen resonated at

67.2 ppm and the signal for the nitrogen-bound CH2-group 6 appeared at 40.4 ppm. At 52.2 ppm the α-carbon 5 between the carbonyls was detected. In the aliphatic region the signals for the alkyl chain 7 were found at 29.7 ppm, 28.4 ppm and 23.2 ppm.

No signals for the protecting group were found in the 1H-NMR spectrum of 110. The deprotection seemed to be successful. Figure 72 shows the 13C-NMR spectrum. Here as well no signal of the tert-butyl group and only the malonate’s carbonyl signal were observed. Otherwise the spectrum was essentially identical to that of the protected variety. Two very small signals around 118 ppm and a weak quartet at 163 ppm could be attributed to the trifluoroacetate anion that was necessary to get the compound in solution. The carbonyl carbon atoms 1 resonated at 164.7 ppm. Between 146.9 ppm and 142.4 ppm the fullerenes sp2-carbon signals were observed. Of the 16 expected signals, only 13 were found, probably due to superposition and the double intensity of one of the signals. The signal for the sp3-C-atoms was detected at

95

Results and Discussion

73.1 ppm, next to the signal for the carbons bound to the ester 2 at 68.3 ppm. The methano bridge 3 gave a signal at 54.8 ppm. At 40.6 ppm, the C-atoms 4 next to the amine were observed. The remaining signals for the alkyl chain resonated at 29.3 (5), 28.2 (6), and 24.1 (7), respectively.

CD3OD

2 C60-sp

3 C60-sp

13 Figure 72: C-NMR spectrum (100 MHz, CDCl3, rt) of compound 110.

MALDI-TOF further proved the deprotection, with a molecular ion peak at m/z = 992. The + typical fragmentation signal for C60 at m/z = 720 was not found. Figure 73 depicts the UV/Vis spectrum of 110 in CH2Cl2. The existence of the desired monoadduct was demonstrated by the existence of the typical maxima at 225, 255 and 320 nm. The extinction coefficients were in the area between 24000 to 5000 M-1cm-1. The small characteristic absorption at 426 nm could not be observed in the UV/Vis measurements of this compound.

Figure 73: UV/Vis spectrum of di-amino fullerene monoadduct 110 recorded in CH2Cl2.

96

Results and Discussion

The compounds were then given to the group of professor Guldi from the department to be measured in the presence of porphyrin dimer 100. As with the diaminoalkane, a high binding constant was obtained for the diamino fullerene monoadduct to the dimer of around 107 M-1. The absorption spectrum fit nicely to that of the dimer- diaminoalkane-complex. With this new electron-donor-acceptor-system, a charge separated state could be generated, that ranged from UV (~350 nm) to the NIR (~800 nm) and lived up to 1 ns. The publication of these results is in preparation.

97

Summary

4 Summary

The aim of this thesis was the synthesis and characterization of different, novel fullerene derivatives as extension to the concept of fullerene functionalization with cyclic malonates. One aspect was the development of novel porphyrin-fullerene conjugates bridged by cyclomalonate, in contrast to the open-chain malonates that were used in comparable literature examples. This method promised the advantage that by using the rigid cyclomalonate as linker, the position of the porphyrins were defined, in contrast to the high flexibility of the open-chain malonates, commonly used in literature examples. Different malonate linker and fullerenes with varying number of addends should be prepared to obtain fullerne-conjugates with different numbers of porphyrins in their periphery. Furthermore, larger malonic cycles, which were obtained as byproducts of the synthesis of cyclo-[2]-malonate, were investigated as novel linker, forming fullerene multimers, as well.

The first part dealt with the preparation of porphyrin-fullerene conjugates. In addition to already existing literature, both units should be bridged with cyclo-[2]-malonate. In that respect, different concepts of binding porphyrins to a cyclic malonate were investigated. A successful method was found in the use of copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC). Furthermore, this strategy allowed for the binding of two porphyrins to a malonate, which was important in the case of higher fullerene-adducts to prevent the formation of several different diastereoisomers. The approach required the introduction of a terminal alkyne chain at the malonate’s α-carbon. Using nucleophilic substitution, the synthesis of malonat-spacer 41, linked with a propargyl moiety, was achieved. Moreover, a new method was developed that allowed the stepwise build-up of cyclic malonate by way of using protecting groups. By this means, both of the malonate’s reactive sites can be substituted individually. Cyclic malonate 50 with two propargyl groups at one side was thus achieved (figure 74).

Figure 74: Two novel cyclo-[2]-hexylmalonate linker, substituted with propargyl chains, for the post-

functionalization of fullerene adducts via click-chemistry.

Subsequent cyclopropanation lead to the two corresponding fullerene monoadducts 88 and 89 (Figure 75). The synthesis of the first novel porphyrin-fullerene dyad 90, bound via a cyclic malonate linker succeeded with the concluding CuAAC (Figure 76). The hybrid of two porphyrins and 89, as well as higher fullerene adducts with the twice substituted malonate 50 and its subsequent products with porphyrin 40 could not be accomplished. 98

Summary

Figure 75: Two novel fullerene monoadducts carrying alkyne-linker, as building block for functionalization via click-chemistry..

Figure 76: Novel porphyrin-fullerene dyade, fused via click-chemistry to a cyclo-[2]-hexylmalonate- linker.

In a second approach, the chain length of the alkyne spacer should have been increased, to examine supramolecular properties of the new cyclomalonate bridged porphyrin-fullerene conjugate. Heptynyl was employed as an alternative to propargyl. However, this required further adjustments to the synthesis strategy, because the substituted malonate was difficult to detect. The problem was circumvented by esterification of malonic acid with aromatic groups. After the successful substitution, the malonic acid derivative 85 could be regained through base hydrolysis. In the following step, ring closure should have been carried out with open chain hydroxyl malonate; unfortunately, this could not be achieved in the scope of this thesis. An exchange of alkyne chain for azido pentyl was not productive. Despite testing different reaction conditions and precursor molecules, the desired substitution did not take place.

The second part is dedicated to fullerene trimers, joined through the use of cyclo-[3]-malonate 94. In this way, the concept of cyclomalonate linked fullerene multimers, developed in our group, should have been expanded. The relevant malonate was easily accessible, being a side product of the synthesis of cyclo-[2]-malonate. In preliminary experiments with pristine C60, the desired trisfullerene could not be observed – most likely due to the products insolubility in all tested organic solvents. To increase the solubility of the trimer, in the following attempt a fullerene pentakisadduct 98 was used, which was functionalized five times with diethyl 99

Summary malonate. Thus, after the successful Bingel reaction the fullerene trimer 99 was obtained (Figure 77). First attempts to transfer the synthesis concept onto cyclo-[4]-malonate 101, to form a fullerene tetramer, were not successful. This is surprising, because there are no reasons permitting the successful formation of the fullerene tetramer. Due to time constraints, the experiment could not be repeated. The same reaction should have been conducted with an additional fullerene pentakisadduct 105. In this case, the malonates were bound with terminal alkyne chains, to enable post-functionalization. The usage of an isoxazoline protecting group should have enabled the selective synthesis of the desired pentakisadduct. The following complete removal of the protective group and the separation of the deprotected product, however, did not succeed. An attempt, to do the reaction with the unpurified precursor, did not yield the desired product.

Figure 77: Novel fullerene trimer from cyclo-[3]-octylmalonate and diethylmalonate pentakisadduct.

The following chapters dealt with two side projects, pursued in collaboration with other groups of the SFB. In this context, first fullerene monoadducts, functionalized with alkyne chains of varying length, were synthesized (Figure 78). Methyl malonyl chloride was reacted with alkyne alcohols of different chain sized, starting from propargyl alcohol with a stepwise increase of two carbon atoms. Both the two short malonates 110 and 112 and the resulting fullerene derivatives 111 and 113, respectively, were literature known. For heptynyl malonate 115, a multistep synthesis, starting from heptynoic acid, was developed, followed by the formation of

100

Summary the monoadduct 116. The fullerenes were then used in a CuAAC to post-functionalize nanoparticles, which carried alkane and azido-alkane chains in different, defined ratios on its surface. By increasing the amount of fullerene dye on the nanoparticle, an increasing absorption was observed. Further studies are currently performed.

Figure 78: Alkyne-functionalized fullerene monoadducts as dyes in hierarchically nanoparticle- structures.

Additionally, novel fullerene monoadducts have been synthesized, whose malonates were functionalized on one (124) or both sides (127) with an amino pentyl chain (Figure 79). The application of a Boc-protecting group was necessary, due to unwanted side reactions between the amine and the [60]fullerene. The problem of solubility, occurring after the deprotection of the amine functionality, was circumvented by the addition of trifluoro acetate as counter ion. The diamino fullerene monoadduct was tested as potential ligand for a porphyrin dimer. High binding constants could be observed for the resulting complex. Due to the rigid diamino ligand coordinating to the metal centers, the HBC-porphyrin conjugate was planarized, causing a red shift in the absorption spectrum. The resulting novel electron-donor-acceptor system, with an absorption ranging from the UV to the NIR, generated a charge separated state with high efficiency.

101

Summary

Figure 79: Novel fullerene monoadducts with amino-functionalized malonat as conjugates for a porphyrin-dimer.

102

Zusammenfassung

5 Zusammenfassung

Das Ziel dieser Arbeit war die Synthese und Charakterisierung verschiedener, neuartiger Fulleren-Derivate als Erweiterung zum Konzept der Funktionalisierung von Fullerenen mit cyclischen Malonaten. Ein Aspekt war die Entwicklung neuartiger Porphyrin-Fulleren Konjugate, die über einen Cyclomalonat-Linker verknüpft waren. Im Gegensatz dazu sind vergleichbare Literaturbeispiele meist über offenkettige Malonate verbunden. Diese Methode versprach den Vorteil, dass durch die Verwendung des starren Cyclomalonat-Linkers die Position des Porphyrins in der Peripherie des Fulleren-Kerns klar definiert war, im Unterschied zur hohen Flexibilität der offenkettigen Malonate, die üblicherweise in Literaturbeispielen verwendet werden. Verschiedene Malonat-Linker und Fullerene mit unterschiedlicher Zahl an Addenden sollte hergestellt warden, um Fullerene-Konjugate zu erhalten, die unterschiedliche viele Porphyrine in ihrer Peripherie tragen. Außerdem wurden größere Malonat-Zyklen, ebenfalls als neuartige Linker untersucht. Diese fallen als Nebenprodukt bei der Synthese von Cyclo-[2]-Malonat an. Mit ihnen sollten Fulleren Multimere geschaffen werden.

Der erste Teil der Arbeit beschäftigt sich mit der Herstellung von Porphyrin-Fulleren- Konjugaten. Dabei sollten die beiden Einheiten, als Ergänzung zur bereits vorhandenen Literatur, über Cyclo-[2]-Malonate miteinander verbunden werden. Diesbezüglich wurden verschiedene Konzepte untersucht, um Porphyrine an ein cyclisches Malonat zu binden. Ein erfolgreicher Ansatz wurde in der Verwendung der Kupfer-katalysierter Alkin-Azid 1,3- dipolarer Cycloaddition (CuAAC) gefunden. Gleichzeitig ermöglichte diese Vorgehensweise die Verknüpfung des Malonats mit zwei Porphyrinen, was im Fall höherer Fulleren-Addukte bedeutend war, um die Entstehung vieler verschiedener Diastereoisomere zu verhindern. Dieser Ansatz machte das Einbringen einer terminalen Alkin-Kette am α–ständigen Kohlenstoffe des Malonats notwendig. Mittels nukleophiler Substitution gelang die Synthese eines Malonat-Spacers 41, der mit einer Propargyl-Einheit verknüpft war. Daneben wurde eine neue Methode entwickelt, die durch den Einsatz von Schutzgruppen-Chemie, den schrittweisen Aufbau cyclischer Malonate ermöglichte. Die beiden reaktiven Stellen des Malonats können auf diese Art unterschiedlich substituiert werden. Ein cyclisches Malonat 50 mit zwei Propargyl-Resten auf einer Seite wurde auf diesem Weg erhalten Figure 74).

Figure 74: Zwei neue Cyclo-[2]-Hexylmalonat-Linker, mit Propargyl-Ketten substituiert, zur Post-

Funktionalisierung von Fulleren-Addukten mittels Click-Chemie.

103

Zusammenfassung

Durch anschließende Bingel-Reaktion konnten die beiden entsprechenden Fulleren- Monoaddukte 88 und 89 erhalten werden (Figure 75). In der abschließenden CuAAC gelang die Synthese der ersten, neuartigen Porphyrin-Fulleren-Dyade 90, die über einen cyclischen Malonat-Linker verknüpft war (Figure 76). Der Hybrid aus zwei Porphyrinen und 89, höhere Fulleren-Addukte mit dem zweifach substituierten Malonat 50, sowie deren Reaktion mit Porphyrin 40 konnte aus nicht mehr erfolgen.

Figure 75: Zwei neuartige Fulleren-Monoaddukte, die Alkin-Linker tragen – Bausteine zur Funktionalisierung mittels Click-Chemie.

Figure 76: Neuartige Porphyrin-Fulleren-Dyade, verknüpft mittels Click-Chemie an einem Cyclo-[2]- Hexylmalonat-Linker.

In einem zweiten Ansatz sollte die Kettenlänge des Alkin-Spacers verlängert werden, um supramolekulare Eigenschaften der neuen Cyclomalonat-verbrückten Porphyrin-Fulleren Konjugate zu untersuchen. Als Alternative zu Propargyl wurde Heptynyl eingesetzt. Dies machte allerdings eine weitere Anpassung der Synthesestrategie erforderlich, da das substituierte Malonat nur schwer zu detektieren war. Dieses Problem konnte dadurch umgangen werden, dass das Malonat mit aromatischen Resten verestert wurde. Nach der erfolgreichen Substitution konnte durch Verseifung das Malonsäure-Derivat 85 erhalten werden. Der Ringschluss sollte im nachfolgenden Schritt über eine Steglich Veresterung mit dem offenkettigen Hydroxy-Malonat erfolgen, wurde aber im Rahmen dieser Arbeit leider ebenfalls nicht erreicht. Der Austausch der Alkin-Kette durch Azido-Pentyl war nicht zielführend. Es wurden verschiedene Reaktionsbedingungen und Vorstufen getestet, trotzdem konnte die gewünschte Substitution nicht erzielt werden.

104

Zusammenfassung

Der zweite Teil widmet sich Fulleren-Trimeren, welche mit Hilfe von Cyclo-[3]-Malonat 94 verknüpft wurden. Dadurch sollte das in unserer Gruppe entwickelte Konzept der Cyclomalonat-verknüpften Fulleren-Multimere weiter ausgebaut werden. Das entsprechende Malonat war als Nebenprodukt der Synthese von Cyclo-[2]-Malonat leicht zugänglich. Bei ersten Versuchen mit reinem C60 konnte das gewünschte Trisfulleren nicht nachgewiesen werden. Der Grund hierfür lag höchstwahrscheinlich in der Unlöslichkeit des Rohprodukts in allen getesteten organischen Lösungsmittelen. Um die Löslichkeit des Trimers zu erhöhen wurde im nachfolgenden Ansatz Fulleren-Pentakis-Addukt 98 verwendet, das mit Diethylmalonat fünffach funktionalisiert wurde. Nach erfolgreicher Bingel-Reaktion konnte so das Fulleren-Trimer 99 erhalten werden (Figure 77). Erste Versuche, das Synthesekonzept auf Cyclo-[4]-Malonat 101 zu übertragen, um ein Fulleren-Tetramer zu erhalten, waren nicht erfolgreich. Dies ist überraschend, da keine Gründe vorliegen, die einer erfolgreichen Synthese des Fulleren-Tetramers widersprechen. Auf Grund zeitlicher Beschränkung konnte das Experiment leider nicht wiederholt werden. Dieselbe Reaktion sollte mit einem weiteren Fulleren-Pentakis-Addukt durchgeführt werden. Hierbei waren die Malonate zur nachträglichen Funktionalisierung mit terminalen Alkin-Ketten verknüpft. Der Einsatz einer Isoxazolin-Schutzgruppe sollte die selektive Synthese des gewünschten Pentakis-Addukts 105 ermöglichen. Es gelang jedoch nicht, die Schutzgruppe anschließend restlos zu entfernen und das entschützte Produkt abzutrennen. Der Versuch, die Reaktion mit ungereinigter Fulleren- Vorstufe durchzuführen, lieferte leider nicht das gewünschte Ergebnis.

Figure 77: Neuartiges Fulleren-Trimer aus der Reaktion von Cyclo-[3]-Octylmalonat und

Diethylmalonat-Pentakisadduct. 105

Zusammenfassung

Die folgenden Kapitel befassten sich mit zwei Nebenprojekten, die in Zusammenarbeit mit anderen Arbeitsgruppen aus dem SFB verfolgt wurden. In diesem Zusammenhang wurden Fulleren-Monoaddukte synthetisiert, die mit Alkin-Ketten unterschiedlicher Länge funktionalisiert waren (Figure 78). Dafür wurde Methyl-Malonylchlorid mit Alkin-Alkoholen unterschiedlicher Kettenlänge, ausgehend von Propargyl-Alkohol mit schrittweiser Erhöhung der Kohlenstoff-Anzahl um 2, umgesetz. Die beiden kürzeren Malonate 110 und112 und die daraus gebildeten Fulleren-Derivate 111 und 113 waren literaturbekannt. Für das Heptynyl- Malonat 115 wurde eine mehrstufige Synthese, ausgehend von Heptinsäure, entwickelt und anschließend das Monoaddukt 116 gebildet. Die Fullerene wurden in einer CuAAC eingesetzt, um Nanopartikel nachträglich zu funktionalisieren. Diese trugen auf ihrer Oberfläche Alkan- und Azidoalkan-Ketten in verschiedenen, definierten Verhältnissen. Mit steigendem Anteil Fulleren-Farbstoffs auf dem Nanopartikel, war eine Zunahme in der Absorption feststellbar. Weitere Untersuchungen werden zur Zeit durchgeführt.

Figure 78: Alkine-funktionalisierte Fullerene Monoadducts als Farbstoffe in hierarchischen Nanopartikel-Strukturen.

Des Weiteren wurden neuartige Fulleren-Monoaddukte 124 und 127 synthetisiert, deren Malonate auf einer bzw. beiden Seiten mit einer Amino-Pentyl Kette funktionalisiert waren

(Figure 79). Die Möglichkeit einer unerwünschten Nebenreaktion zwischen Amin und C60 machte den Einsatz der Boc-Schutzgruppe erforderlich. Probleme der Löslichkeit, die nach dem Entschützen der Amin-Funktionalität auftraten, konnten durch den Einsatz von Trifluoracetat als Gegenion umgangen werden. Das Diamino-Fulleren Monoaddukt wurde als möglicher Ligand für ein Porphyrin-Dimer getestet. Eine hohe Bindungskonstante wurde für den entstehenden Komplex beobachtet.

106

Zusammenfassung

Da sein Metallzentrum mit dem starren Diamino-Liganden koordiniert war, wurde das HBC- Porphyrin Konjugat in eine planare Konformation gezwungen, was eine Rotverschiebung im Absorptionsspektrum zur Folge hatte. Dieses neuartige Elektronen-Donor-Akzeptor-System, mit einer Absorption die vom UV bis zum NIR reicht, erzeugte einen ladungsgetrennten Zustand mit hoher Effizienz.

Figure 79: Neue Fullerene Monoaddukte mit Amino-funktionalisiertem Malonat als Konjugate für ein Porphyrin-Dimer.

107

Experimental Section

6 Experimental Section

6.1 General Information

Solvents and chemicals: All reagents were purchased from Sigma-Aldrich©, Acros Organics©, Fluka©, Fisher Scientific© or Alfa Aesar© and used without further purification. HPLC grade solvents were purchased from VWR. Solvents, except for oDCB, were distilled prior to usage. Ethyl acetate and dichloromethane were distilled over potassium carbonate. C60 was purchased from Iolitec © (99.0% purity).

Reactions: Reactions carried out under inert conditions, were degassed by three cycles of sonication

(1 min), while performing a repetitive exchange of the atmosphere (vacuum/N2-gas), using standard Schlenk-techniques and Schlenk-glassware. Reaction vessels from 100 to 500 mL were heated, using heat-on mantles from Heidolph©, smaller vessels were heated in a oil bath.

Silica gel for column chromatography: Column chromatography was performed on Kieselgel 60 M, deactivated (0.04 – 0.063 mm /230 – 400 mesh ASTM) Macherey-Nagel©, Düren, Germany.

Thin Layer Chromatography (TLC): TLC was performed on silica gel 60 F254 TLC-aluminium foils, MERCK, Darmstadt, Germany. Visualization was performed by using a UV lamp (254 or 366 nm) or by developing (1% potassium permanganate in aqueous solution acidified with , elemental bromine or iodine).

IR spectroscopy: IR spectra were recorded on a Bruker© FTIR Tensor 27 (Pike Miracle ATR). The ATR unit was equipped with a diamond crystal plate and high-pressure clamp. Spectra were recorded as solid samples directly from the diamond crystal. All absorptions were given in wave numbers [cm-1].

UV/Vis spectroscopy: UV/Vis spectra were recorded qualitatively on a Varian© Cary 5000 UV-vis-NIR spectrophotometer at rt. Spectra were recorded in CH2CL2. The absorption maxima λmax were given in [nm],.

108

Experimental Section

Mass spectrometry (MS): LDI/MALDI-TOF mass spectra were recorded with a Shimadzu© Biotech Axima Confidence (nitrogen UV-laser, 50 Hz, 337 nm) with 2,5-dihydroxybenzoic acid (DHB), trans-2-(3-(4-tert- butylphenyl)-2-methyl-2-propenylidene)-malononitrile (DCTB) or sinapic acid (sin) used as matrices. ESI and APPI mass spectra were recorded with Bruker© micrOTOF II focus.

NMR spectroscopy: NMR spectra were recorded on a Jeol© EX 400, Bruker© Avance 300 or Bruker© Avance 400, operating at 400 MHz (1H NMR) and 100 MHz (13C NMR) and JEOL Alpha 500 operating at 500 MHz (1H NMR) and 125 MHz (13C NMR). Deuterated solvents were purchased from Deutero© and Euriso-Top© and used as received. The chemical shifts were reported in parts per million (ppm) and referenced to the residual solvent. The resonance multiplicities are indicated as “s” (singlet), “d” (doublet), “t” (triplet), “q” (quartet) and “m” (multiplet) or as combinations thereof. Signals referred to as br (broad) are not clearly resolved or significantly broadened. The raw data was processed using MestReNova 5.2.5 Lite.

If a chemical shift was stated twice, the two corresponding signals could be clearly distinguished in the spectrum, but the peak positions were rounded to the same value. The protons responsible for the stated signal were in italics. The assignment of the signals to the corresponding atoms in the molecule was done in analogy to the literature and the experience of similar compounds.

109

Experimental Section

6.2 General Remarks

The organic compounds were named in accordance with the IUPAC nomenclature. The fullerene compounds were not named according to recent IUPAC recommendation for the nomenclature of fullerenes, but by a reasonable, trivial nomenclature system.

6.2.1 Synthesis According to Literature

The following compounds were prepared according to literature procedures. The synthetic procedure and spectroscopic data can be found in the original publication.

 4-(Bromomethyl)benzaldehyde 24[220]  5-(4-((trimethylsilyl)ethynyl)phenyl)-10,15,20-tris(3,5-di(tert-butyl)phenyl)porphyrin 47[234]  1-Azido-5-bromopentane 50[236]  Dibenzyl malonate 60[239]  Hept-6-yn-1-ol 63[241]  7-Bromohept-1-yne 64[242]  Cyclo-[3]-octylmalonate 75[104]  Isoxazolinofullerene 77[248]  Diethylmalonyl-dimethylaminophenylisoxazolino–[5,1]–hexakis– 1,2,18,22,23,27,45,31,32,36,55,60–dodecahydro[60]–fullerene 78[119]  Diethylmalonyl-[5,0]–pentakis–1,2,18,22,23,27,45,31,32,36,–decahydro[60]–fullerene 79[119]  Cyclo-[4]-octylmalonate 81[104]  Bis(5-(trimethylsilyl)pent-4-yn-1-yl) malonate 84[120b]  Methyl prop-2-yn-1-yl malonate 92[250a]  Methyl prop-2-yn-1-yl malonyl –[1,0]–mono–1,2,–dihydro[60]–fullerene 93[250b]  Methyl (5-(trimethylsilyl)pent-4-yn-1-yl) malonate 95[252]  Methyl (5-(trimethylsilyl)pent-4-yn-1-yl) malonyl –[1,0]–mono–1,2,–dihydro[60]– fullerene 96[252]  7-(Trimethylsilyl)hept-6-yn-1-ol 97[253]  tert-Butyl (5-hydroxypentyl)carbamate 104[259]

110

Experimental Section

6.2.2 Synthesis of Literature Known Compounds

Compounds, whose syntheses are known, in which however the synthesis protocol was modified or the substance obtained through a different pathway, are listed below with their synthesis procedure.

1,5,12,16-Tetraoxacyclodocosane-2,4,13,15-tetraone 31[222]

A 1 L Schlenk-RBF equipped with a magnetic stir bar and 25 mL dropping funnel was charged with deprotected malonate 41 (200 mg; 0.660 mmol), pyridine (0.160 mL; 1.97 mmol) and dissolved in dry

CH2Cl2 (400 mL) under N2. Via dropping funnel malonyl dichloride (64.0 µL; 0.660 mmol) dissolved in

CH2Cl2 (5.00 mL) was dropped to the mixture over a period of 30 min and the mixture was stirred at room temperature for 4 d. The solvent was removed and the crude product plug filtrated (SiO2; CH2Cl2/EtOAc 7:3), followed by a column chromatography purification (SiO2; CH2Cl2/EtOAc 9:1), yielding the product as white solid in 60 % (147 mg; 0.396 mmol) yield.

Rf (SiO2): 0.74 (CH2Cl2/EtOAc 9:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.32 – 1.42 (m, 8H, CH2COOCH2CH2CH2), 1.58 – 1.68 3 (m, 8H, CH2COOCH2CH2), 3.34 (s, 4H, OOCCH2COO), 4.12 (t, J = 6.6 Hz, 4H CH2COOCH2)

13 C NMR (100 MHz; CDCL3; rt): δ [ppm] = 25.5, 28.4, 42.2, 65.3, 66.4

MS (MALDI, dctb): m/z = 373 [M+H]+, 395 [M+H+Na]+,

IR (ATR; rt): [cm-1] = 613, 673, 730, 763, 788, 825, 852, 890, 954, 983, 998, 1023, 1054, 1067, 1109, 1137, 1154, 1213, 1231, 1257, 1328, 1387, 1413, 1456, 1478, 1738, 2858, 2871, 2897, 2919, 2960, 2989

111

Experimental Section

6-((tert-Butyldimethylsilyl)oxy)hexan-1-ol 36[229]

A 500 mL RBF equipped with a magnetic stir bar and 100 mL dropping funnel was charged with 1,6-hexanediol (14.2 g; 120 mmol), imidazole (1.36 g; 20.0 mmol) and dissolved in THF (100 mL). Via dropping funnel tBDMS-Cl (3.02 g; 20.0 mmol) dissolved in THF (100 mL) was dropped to the mixture over a period of 1 h and the mixture was stirred at room temperature for 6 h. Water (50.0 mL) was added and the organic solvent evaporated. The residue was extracted with EtOAc (3*50 mL), dried over MgSO4 and concentrated. Purification by column chromatography (SiO2; /EtOAc 4:1) yielded the product as yellow oil in 68 % (2.94 g; 13.6 mmol) yield.

Rf (SiO2): 0.56 (hexane/EtOAc 4:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.01 (s, 6H, SiCCH3), 0.86 (s, 9H, SiCH3), 1.32 – 1.34 (m,

4H, OCH2CH2CH2CH2), 1.46 – 1.57 (m, 4H, OCH2CH2, SiOCH2CH2), 3.55 – 3.65 (m, 4H, OCH2,

SiOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = -5.3, 18.3, 25.5, 25.6, 26.0, 32.5, 32.8, 62.9, 63.2

MS (ESI): m/z = 233[M+H]+, 255[M+H+Na]+

IR (ATR; rt): [cm-1] = 661, 773, 832, 939, 1005, 1034, 1254, 1361, 1388, 1463, 2857, 2929

112

Experimental Section

Bis(6-hydroxyhexyl) malonate 41[230]

A 500 mL RBF equipped with a magnetic stir bar was charged with protected malonate 37 (500 mg; 0.940 mmol) and dissolved in a mixture of

CH2Cl2/MeCN (2:1; 45 mL). trifluoride diethyl etherate (1.52 mL; 12.0 mmol) was added and the mixture was stirred at room temperature for 20 min. A sat. solution of NaHCO3

(300 mL) was added, the layers separated and the aq. layer was extracted with CH2Cl2

(3*150 mL). The combined organics were washed with water, dried over Na2SO4 and concentrated, yielding the product as yellow oil in 99 % (353 mg; 0.930 mmol) yield.

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.28 – 1.42 (m, 8H, CH2COOCH2CH2CH2CH2), 1.48 –

1.68 (m, 8H, CH2COOCH2CH2, OCH2CH2), 2.52 (s, 2H, OH), 3.34 (s, 2H, OOCCH2COO), 3.61 (t, 3 3 J = 6.1 Hz, 4H, HOCH2), 4.11 (t, J = 6.6 Hz, 4H, CH2COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 25.3, 25.5, 28.3, 32.5, 41.7, 62.6, 65.5, 166.7

MS (ESI): m/z = 304 [M]+, 305 [M+H]+, 327 [M+H+Na]+

113

Experimental Section

4-((trimethylsilyl)ethynyl)benzaldehyde 45[232]

A 250 mL Schlenk-RBF equipped with a magnetic stir bar and condenser was charged with bromobenzaldehyde (5.55 g; 30.0 mmol), CuI (57.0 mg;

0.300 mmol), Pd(PPh3)2Cl2 (421 mg; 0.600 mmol) and dissolved in TEA (120 mL). The mixture was degased for 30 min, TMS-acetylene (3.40 mL; 36 mmol) was added and the mixture stirred at 100 °C overnight. After removing the solvent, the resulted black crude product was purified by

column chromatography (SiO2; hexane/CH2Cl21:1). The product was obtained as white solid in 24 % (1.75 g; 8.70 mmol) yield.

Rf (SiO2): 0.55 (hexane/CH2Cl21:1)

1 3 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.24 (s, 9H, SiCH3), 7.57 (d, J = 8.4 Hz, 2H, Ar-H), 7.79 (d, 3J = 8.2 Hz, 2H, Ar-H), 9.97 (s, 1H, CHO)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = -0.2, 99.0, 103.8, 128.7, 129.4, 132.4, 135.5, 191.5

MS (APPI): m/z = 203 [M+H]+

IR (ATR; rt): [cm-1] = 639, 661, 696, 758, 837, 857, 955, 1016, 1101, 1162, 1205, 1248, 1281, 1312, 1423, 1561, 1602, 1682, 2156, 2956

UV/Vis (CH2Cl2; rt): λ [nm] = 281

114

Experimental Section

5-(4-((trimethylsilyl)ethynyl)phenyl)-10,15,20-tris(3,5-di(tert-butyl)phenyl) porphyrinato- ZnII 48[235]

A 50.0 mL RBF equipped with a magnetic stir bar and condenser was charged with porphyrin 47 (397 mL; 0.380 mmol),

Zn(OAc)2 (250 mg; 1.14 mmol) and dissolved in THF (20 mL). The mixture was stirred at 90 °C for 4 h. After evaporation and purification by column

chromatography (SiO2; CH2Cl2) the product was obtained as red solid in 97 % (411 mg; 0.370 mmol) yield.

Rf (SiO2): 0.57 (CH2Cl2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.42 (s, 9H, SiCH3), 1.56 (s, 54H, CCH3), 7.83 – 7.84 (m, 3H, p-Ar-H), 7.91 (d, 3J = 8.1, 2H, Ar-H), 8.13 - 8.14 (m, 6H, o-Ar-H), 8.23 (d, 3J = 8.1, 2H, Ar-H), 8.95 (d, 3J = 4.7 Hz, 2H, β-pyr.), 9.04 (d, 3J = 4.0 Hz, 6H, β-pyr.)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 0.59, 32.3. 35.5. 95.7, 105.8, 120.2, 121.3, 122.7, 123.1, 123.3, 130.12, 130.1, 131.9, 132.7, 132.8, 132.9, 134.7, 142.3, 143.9, 148.1, 149.1, 150.2, 150.9, 150.9, 151.0

MS (MALDI, om):m/z = 1110 [M]+

115

Experimental Section

(Hept-6-yn-1-yloxy)methyl)benzene 66[243]

A 5 mL Schlenk-RBF equipped with a magnetic stir bar and condenser was charged with a suspension of

NaH (60 % in mineral oil) in THF (2.00 mL) under N2 and cooled to 0 °C. Malonate 60 (1.60 g; 5.75 mmol),

alkine 64 (2.00 g; 11.5 mmol) and K2CO3 (1.60 g; 11.5 mmol) were added separately. The mixture was stirred at 75 °C for 2 d. After cooling to 0 °C, the reaction was quenched by adding 1M HCl and brine to the mixture. The raw product was extracted with EtOAc (3*10.0 mL). The combined organic layers were washed with a solution of NaHCO3 (20.0 mL) and brine (20.0 mL), dried over MgSO4 and concentrated.

Purification by column chromatography (SiO2; hexane/CH2Cl2 8:2) yielded the product as light yellow oil in 52 % (605 mg; 2.99 mmol) yield.

Rf (SiO2): 0.15 (hexane/CH2Cl2 8:2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.42 – 1.68 (m, 6H, OCH2CH2CH2CH2), 1.93 (t, 4 4 J = 2.7 Hz, 1H, CH2CCH), 2.10 – 2.22 (m,2H, OCH2), 3.36 (t, J = 6.6 Hz, 2H,CH2CCH), 4.49 (s,

2H, Ar-CH2), 7.25 – 7.35 (m, 5H, Ar-H)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 18.3, 25.4, 28.3, 29.2, 68.2, 70.2, 72.9, 84.5, 127.5, 127.6, 128.3, 138.6

IR (ATR; rt): [cm-1] = 629, 697, 714, 734, 849, 909, 1028, 1098, 1205, 1275, 1362, 1454, 1495, 1720, 2859, 2939, 3030, 3296

UV/Vis (CH2Cl2; rt): λ [nm] = 231

116

Experimental Section

6.3 Synthetic Procedure and Spectroscopic Data

6.3.1 Synthesis of Precursors for Covalently Bound Porphyrins

5-(4-(Bromomethyl)phenyl)-10,15,20-tris(3,5-dimethoxyphenyl)porphyrin 27

A 1.00 L Schlenk-RBF equipped with a magnetic stir bar was charged with pyrrole (671 mL; 10.0 mmol), 3,5-dimethoxy benzaldehyde (1.25 g; 7.50 mmol), 24 (500 mg; 2.50 mmol) and dissolved in a

mixture of CH2Cl2 (400 mL) and EtOH

(3.60 mL) under N2 and exclusion of light. Boron trifluoride diethyl etherate (0.310 mL, 2.50 mmol) was added slowly and the mixture was stirred at room temperature for 70 min. DDQ (858 mg; 3.78 mmol) was added and the mixture stirred for another 3 h. After plug

filtration (SiO2; CH2Cl2/MeOH 98:2), the crude product was concentrated and purified by column chromatography (SiO2; CH2Cl2/MeOH

98:2; toluene/CH2Cl2 7:3) to give the product as purple solid in 11 % (244 mg; 0.275 mmol) yield.

Rf (SiO2): 0.1 (toluene/CH2Cl2 7:3)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = -2.83 (s, 2H, NH2), 3.96 (s, 18H, OCH3), 4.86 (s, 2H, Ar- 4 4 3 CH2-Br), 6.90 (dd, J = 2.3 Hz, 3H, p-Ar-H), 7.40 (dd, J = 2.2 Hz, 6H, o-Ar-H), 7.80 (d, J = 8.1, 2H, Ar-H), 8.20 (d, 3J = 8.1, 2H, Ar-H), 8.81 (d, 3J = 4.8 Hz, 2H, β-pyr.-H), 8.93 – 8.95 (m, 6H, β-pyr.-H)

MS (LDI): m/z = 887 [M]+

79 + HRMS (APPI): m/z calc. for C51H43 BrN4O6 886.2360 [M] , found: 886.2367

IR (ATR; rt): [cm-1] = 605, 627, 664, 797, 1021, 1096, 1261, 1376, 1458, 1558, 1585, 2027, 2330, 2346, 2846, 2925, 2958

UV/Vis (CH2Cl2; rt): λ [nm] = 420, 515, 549, 590, 644

117

Experimental Section

5-(4-(Bromomethyl)phenyl)-10,15,20-tris(3,5-dimethoxyphenyl)porphyrinato-ZnII 28

A 50.0 mL RBF equipped with a magnetic stir bar and condenser was charged with porphyrin 27 (50.0 mg; 0.0560 mmol),

Zn(OAc)2 (37.0 mg; 0.170 mmol) and dissolved in THF (20 mL). The mixture was stirred at 90 °C for 4 h. After evaporation and purification by column chromatography

(SiO2; CH2Cl2) the product was obtained as red solid in 94 % (50 mg; 0.0526 mmol) yield.

Rf (SiO2): 0.21 (CH2Cl2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 3.92 (s, 18H, OCH3), 4.86 (s, 2H, Ar-CH2-Br)6.92 (d, 4J = 2.3 Hz, 3H, Ar-H), 7.24 (d, 4J = 2.2 Hz, 6H, Ar-H), 7.87 (d, 3J = 8.0, 2H, Ar-H), 8.07 (d, 3J = 8.0, 2H, Ar-H), 8.92 (d, 3J = 4.7 Hz, 2H, β-pyr.-H), 9.02 – 9.05 (m, 6H, β-pyr.-H)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 55.6, 68.4, 100.1, 107. 1, 113.8, 127.3, 131.8, 132.0, 134.7, 144.6, 150.0, 158.7

MALDI, om): m/z = 951 [M]+

79 + HRMS (APPI; CH2Cl2): m/z calc. for C51H41 BrN4O6: 948.1495 [M] , found: 948.1485

IR (ATR; rt): [cm-1] = 692, 792, 1013, 1057, 1258, 1312, 1418, 1449, 1587, 1772, 2352, 2855, 2923, 2962

UV/Vis (CH2Cl2; rt):λ [nm] = 399, 421, 548, 590

118

Experimental Section

6.3.2 Synthesis of Propargyl Substituted Cyclo-[2]-Malonate and its Precursors

5-(4-(Azidomethyl)phenyl)-10,15,20-tris(3,5-dimethoxyphenyl)porphyrinato-ZnII 29

A 250 mL Schlenk-RBF equipped with a magnetic stir bar and condenser was charged with porphyrin 28 (100 mg; 0.100 mmol), sodium azide (33.0 mg; 0.500 mmol) and dissolved in DMF (150 mL). The mixture was stirred at 50 °C for 24 h. The mixture was poured over an

ice/NH4Cl-mixture and stirred until the ice was molten. The red precipitate was filtered off and

dissolved in CH2Cl2. The organic phase was

washed with water, dried over MgSO4, filtered and concentrated. After purification by column

chromatography (SiO2; CH2Cl2), the product was obtained as red solid in 82 % (74.9 mg; 0.0820 mmol) yield.

Rf (SiO2): 0.13 (CH2Cl2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 3.96 (s, 18H, OCH3), 4.83 (s, 2H, Ar-CH2-Br) 6.90 (dd, 4J = 2.3 Hz, 3H, p-Ar-H), 7.40 (dd, 4J = 2.3 Hz, 6H, o-Ar-H), 7.87 (d, 3J = 8.0, 2H, Ar-H), 8.07 (d, 3J = 8.0, 2H, Ar-H), 8.82 (d, 3J = 4.8 Hz, 4H, β-pyr.-H), 8.97 – 8.99 (m, 4H, β-pyr.-H)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 33.5, 55.6, 100.2, 113.9, 119.2, 119.9, 125.3, 127.4, 128.2, 129.0, 134.9, 142.3, 144.0

(MALDI, dhb): m/z = 913 [M]+

+ HRMS (ESI): m/z calc. for C51H41N7O6Zn: 911.240426[M] , found: 911.2384

IR (ATR; rt): [cm-1] = 695, 719, 935, 1001, 1019, 1059, 1149, 1191, 1202, 1259, 1341, 1417, 1448, 1585, 2359, 2849, 2918, 2962

UV/Vis (CH2Cl2; rt): λ [nm] = 399, 420, 548, 590

119

Experimental Section

3-(Prop-2-yn-1-yl)-1,5,12,16-tetraoxacyclodocosane-2,4,13,15-tetraone 32

A 500 mL Schlenk-RBF equipped with a magnetic stir bar and 25 mL dropping funnel was charged

with malonate 31 (500 mg; 1.34 mmol), K2CO3 (279 mg; 2.01 mmol) and dissolved in DMF

(250 mL) under N2. 80 wt % propargyl bromide (100 µL; 0.890 mmol) in DMF (5 mL) was added dropwise and the mixture was stirred at room temperature for 2 d. The solvent was evaporated and water (50 mL) was added, followed by extraction with EtOAc (3*50 mL). The combined organic layers were dried over Na2SO4 and concentrated. Purification by column chromatography (SiO2; CH2Cl2) yielded the product as white solid in 21 % (76.0 mg; 0.187 mmol) yield.

Rf (SiO2): 0.55 (CH2Cl2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.30 – 1.40 (m, 8H, COOCH2CH2CH2CH2), 1.56 – 4 4 1.66 (m, 8H, COOCH2CH2), 1.99 (t, J = 2.6 Hz, 1H, COOCHCH2CC H), 2.75 (dd, J = 2.6, 5.0 Hz, 3 2H, OOCCHCH2CCH), 3.34 (s, 2H, OOCCH2), 3.53 (t, J = 7.7 Hz, 1H, COOCHCH2), 4.02 –

4.25 (m, 8H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 18.2, 25.5, 28.5, 42.2, 51.1, 65.4, 65.7, 70.3, 80.0, 166.4, 167.8

MS (MALDI, dctb): m/z = 411 [M+H]+, 433 [M+H+Na]+

IR (ATR; rt): [cm-1] = 644, 687, 727, 854, 895, 966, 998, 1054, 1146, 1164, 1194, 1239, 1266, 1279, 1317, 1331, 1478, 1728, 2338, 2359, 2865, 2936, 3289

120

Experimental Section

3-Chloro-1,5,12,16-tetraoxacyclodocosane-2,4,13,15-tetraone 33

A 5 mL Schlenk-RBF equipped with a magnetic stir bar and condenser was charged with malonate 31 (1.00 g; 2.69 mmol), sulfuryl chloride

(217 µL; 2.69 mmol) and dissolved in CHCL3 (1.50 mL)

under N2. The mixture was stirred at 70 °C for 24 h,

diluted in CH2Cl2 (200 mL) and slowly purified by column chromatography (SiO2; CH2Cl2). The product was obtained as lightly green solid in 54 % (514 g; 1.27 mmol) yield.

Rf (SiO2): 0.58 (CH2Cl2/EtOAc 19:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.36 (m, 8H, COOCH2CH2CH2), 1.64 (m, 8H,

COOCH2CH2), 3.34 (s, 2H, OOCCH2COO), 4.14 (m, 6H, CH2COOCH2/ CHClCOOCH2), 4.26 (m,

2H, CHClCOOCH2), 4.84 (s, 1H, CHCl)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 25.4, 25.5, 28.3, 28.4, 42.2, 55.8, 65.3, 67.0, 164.3, 166.4

MS (MALDI, dctb): m/z = 407 [M]+, 429 [M+Na]+

IR (ATR; rt): [cm-1] = 631, 664, 684, 729, 808, 895, 920, 981, 998, 1022, 1055, 1110, 1140, 1166, 1199, 1261, 1304, 1357, 1380, 1468, 1478, 1735, 2864, 2939

121

Experimental Section

3-Chloro-3-(prop-2-yn-1-yl)-1,5,12,16-tetraoxacyclodocosane-2,4,13,15-tetraone 35

A 500 mL Schlenk-RBF equipped with a magnetic stir bar and 25 mL dropping funnel was charged

with malonate 33 (500 mg; 1.27 mmol), K2CO3 (264 mg; 1.91 mmol) and dissolved in

DMF (250 mL) under N2. Propargyl bromide (80 wt % in toluene, 95.1 µL; 0.847 mmol) in DMF (5 mL) was added dropwise and the mixture was stirred at room temperature for 2 d. The solvent was evaporated and water (50 mL) was added followed by extraction with EtOAc

(3*50 mL). The combined organic layers were dried over Na2SO4 and concentrated. Purification by column chromatography (SiO2; CH2Cl2) yielded the product as white solid in 49 % (277 mg; 0.622 mmol) yield.

Rf (SiO2): 0.10 (CH2Cl2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.35 (m, 8H, COOCH2CH2CH2), 1.63 (m, 8H, 4 4 COOCH2CH2), 2.10 (t, J = 2.6 Hz, 1H, CH2CCH), 3.14 (d, J = 2.6 Hz, 2H, CH2CCH), 3.33 (s, 2H,

OOCCH2COO), 4.11 (m, 4H, COOCH2), 4.21 (m, 4H CClCOOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 25.4, 25.5, 28.2, 28.4, 29.2, 42.1, 65.3, 67.3, 68.2, 72.5, 165.5, 166.3

MS (MALDI, dctb): m/z = 445 [M]+, 467 [M+Na]+, 483[M+K]+

IR (ATR; rt): [cm-1] = 668, 800, 897, 1003 , 1039, 1097, 1154, 1187, 1236, 1272, 1386, 1416, 1467, 1729, 1742, 2860, 2939, 3287

122

Experimental Section

Bis(6-((tert-butyldimethylsilyl)oxy)hexyl)malonate 37

A 100 mL Schlenk-RBF equipped with a magnetic stir bar and 25 mL dropping funnel was charged with the protected alcohol 46 (4.00 g; 17.2 mmol), pyridine (1.70 mL; 21.5 mmol) and dissolved in

CH2Cl2 (50.0 mL) under N2. Via dropping funnel malonyl dichloride (0.83 mL; 8.60 mmol) dissolved in CH2Cl2 (20.0 mL) was dropped to the mixture over a period of 30 min. The mixture was stirred at room temperature overnight. The crude product was washed with brine

(3*50.0 mL), dried over Na2SO4 and concentrated. Purification by column chromatography

(SiO2; CH2Cl2/EtOAc 97:3) gave the product as yellow oil in 64 % (2.94 g; 5.50 mmol) yield.

Rf (SiO2): 0.5 (CH2Cl2/EtOAc 97:3)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.02 (s, 12H, SiCH3), 0.86 (s, 18H, SiCCH3), 1.28 – 1.68 3 (m, 12H, COOCH2CH2CH2CH2), 3.34 (s, 2H, COOCH2COO), 3.57 (t, J = 6.5 Hz, 4H, SiOCH2), 3 4.11 (t, J = 6.7 Hz, 4H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = -5.3, 25.4, 25.6, 25.9, 28.5, 32.7, 63.0, 65.6, 166.7

MS (MALDI, om): m/z = 533 [M+H]+, 555 [M+H+Na]+, 571 [M+H+K]+,

IR (ATR; rt): [cm-1] = 661, 773, 833, 939, 1005, 1094, 1147, 1254, 1388, 1472, 1736, 2368, 2856, 2929

123

Experimental Section

Bis(6-((tert-butyldimethylsilyl)oxy)hexyl) 2,2-di(prop-2-yn-1-yl)malonate 38

A 5 mL Schlenk-RBF equipped with a magnetic stir bar was charged with the protected malonate 47 (413 mg; 0.770 mmol),

K2CO3 (532 mg; 3.85 mmol), and dissolved in DMF

(2.00 mL) under N2. Propargyl bromide (80 wt % in toluene 292 µL; 2.69 mmol) was added and the mixture was stirred at room temperature for 2 d. EtOAc (5.00 mL) was added and the mixture was washed with water (3*5 mL) and brine (5 mL), dried over MgSO4 and concentrated.

Purification by column chromatography (SiO2; CH2Cl2/hexane 6:4) yielded the product as light yellow oil in 63 % (295 mg; 0.485 mmol) yield.

Rf (SiO2): 0.67 (CH2Cl2/hexane 6:4)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.02 (s, 12H, SiCH3), 0.86 (s, 18H, SiCCH3), 1.30 – 1.32

(m, 8H, COOCH2CH2CH2CH2), 1.44 – 1.51 (m, 4H, COOCH2CH2), 1.57 – 1.64 (m, 4H, 4 4 COOCH2CH2), 2.00 (t, J = 2.6 Hz, 2H, CCH2CCH), 2.96 (d, J = 2.7 Hz, 4H, CCH2CCH), 3.56 (t, 3 3 J = 6.5 Hz, 4H, SiOCH2), 4.13 (t, J = 6.6 Hz, 4H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = -5.3, 18.3, 22.5, 25.4, 25.6, 25.9, 28.4, 32.7, 63.0, 65.6, 71.7, 78. 4, 168.6

MS (MALDI, dhb): m/z = 631 [M+Na]+, 647 [M+K]+,

IR (ATR; rt): [cm-1] = 647, 773, 833, 1093, 1186, 1251, 1289, 1323, 1361, 1388, 1429, 1463, 1739, 2359, 2857, 2930, 3313

124

Experimental Section

Bis(6-hydroxyhexyl) 2,2-di(prop-2-yn-1-yl)malonate 39

A 500 mL RBF equipped with a magnetic stir bar was charged with substituted malonate 48 (650 mg; 1.07 mmol) and dissolved

in a mixture of CH2Cl2/MeCN (2:1; 45 mL). Boron trifluoride diethyl etherate (1.70 mL; 13.7 mmol) was added and the mixture was stirred at room temperature for 20 min. Sat. solution of NaHCO3 (300 mL) was added and the layers separated.

The aq. layer was extracted with CH2Cl2 (3*150 mL). The combined organics were washed with water, dried over Na2SO4 and concentrated, yielding the product as yellow oil in 99% (403 mg; 1.06 mmol) yield.

Rf (SiO2): 0.18 (CH2Cl2/hexane 6:4)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.35 – 1.39 (m, 8H, OCH2CH2CH2CH2), 1.63 – 1.66 (m, 4 4 8H, OCH2CH2; COOCH2CH2), 2.03 (t, J = 2.6 Hz, 2H, OOCCCH2CCH), 2.99 (d, J = 2.6 Hz, 4H, 3 3 OOCCCH2), 3.62 (t, J = 6.5 Hz, 4H, OCH2), 4.16 (t, J = 6.5 Hz, 4H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 22.9, 25.7, 28.8, 32.9, 56.9, 63.1, 66.5, 72.2, 78.9, 169.3

MS (MALDI, om): m/z = 403 [M+H+Na]+

IR (ATR; rt): [cm-1] = 646, 968, 1056, 1076, 1166, 1290, 1429, 1465, 1719, 2355, 2860, 2936, 3287

125

Experimental Section

3,3-Di(prop-2-yn-1-yl)-1,5,12,16-tetraoxacyclodocosane-2,4,13,15-tetraone 40

A 1 L Schlenk-RBF equipped with a magnetic stir bar and 25 mL dropping funnel was charged with deprotected malonate 49 (300 mg; 0.790 mmol),

TEA (1.90 mL; 1.00 mmol) and dissolved in dry CH2Cl2

(240 mL) under N2 and cooled to 0 °C. Via dropping funnel malonyl dichloride (80.0 µL; 0.790 mmol) dissolved in CH2Cl2 (5.00 mL) was dropped to the mixture over a period of 30 min. The mixture was stirred at room temperature for 4 d. The solvent was removed and the crude product plug filtrated (SiO2; CH2Cl2/EtOAc 7:3), followed by column chromatography purification (SiO2;

CH2Cl2), yielding the product as white solid in 58 % (205 mg; 0.457 mmol) yield.

Rf (SiO2): 0.38 (CH2Cl2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.31 – 1.40 (m, 8H, COOCH2CH2CH2), 1.59 – 1.66 (m, 3 3 8H, COOCH2CH2), 2.01 (t, J = 2.7 Hz, 2H, OOCCCH2CCH), 2.96 (d, J = 2.7 Hz, 4H, 3 OOCCCH2CCH), 3.34 (s, 2H, OOCCH2COO), 4.13 (m, J = 6.84, 7.64 Hz, 8H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 22.6, 25.5, 25.5, 28.4, 28.5, 42.2, 56.3, 65.3, 66.0, 71.7, 78.4, 166.4, 168 6

MS (MALDI, dctb): m/z = 471 [M+Na]+, 487 [M+K]+

+ HRMS (APPI; CH2Cl2): m/z calc. for C24H33O8: 449.2170 [M+H] , found:449.2168

IR (ATR; rt): [cm-1] = 654, 896, 979, 1054, 1075, 1186, 1208, 1286, 1387, 1428, 1467, 1728, 2860, 2937, 3283

126

Experimental Section

6.3.3 Synthesis of Fullerene Monoadducts with Propargyl Substituted Cyclo-[2]-Malonate

3-(Prop-2-yn-1-yl)-1,5,12,16-tetraoxacyclodocosane-2,4,13,15-tetraone–[1,0]–mono–1,2,– dihydro[60]–fullerene 70

A 100 mL Schlenk-RBF equipped with a magnetic stir bar was charged with

C60 (58.0 mg; 0.08 mmol), cyclo-[2]-malonate 32 (50.0 mg; 0.12 mmol) and

CBr4 (40.0 mg; 0.12 mmol) . Toluene (58.0 mL) was added and the mixture degassed for 30 min. DBU (29.0 µL; 0.20 mmol) was added slowly and the mixture was stirred at room temperature for 18 h under nitrogen atmosphere. The crude product was plug filtrated

(tolueneEtOAc) and concentrated. After column chromatography (SiO2; toluene) the product was obtained as dark brown solid in 38 % (32.0 mg; 0.03 mmol) yield.

Rf (SiO2): 0.10 (toluene)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.43 – 1.74 (m, 8H, COOCH2CH2CH2CH2), 1.69 – 4 1.76 (m, 4H, COOCH2CH2), 1.83 – 1.90 (m, 4H, COOCH2CH2), 2.01 (t, J = 2.6 Hz, 1H, 4 3 OOCCHCH2CCH), 2.78 (dd, J = 2.6, 5.0 Hz, 2H, OOCCHCH2CCH), 3.59 (t, J = 7.7 Hz, 1H,

OOCCHCH2), 4.10 – 4.50 (m, 8H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 1.0, 18.3, 25.7, 26.0, 28.5, 29.7, 51.2, 52.0, 65.7, 67.3, 70.4, 71.5, 80.0, 139.6, 141.4, 142.4, 142.7, 143.5, 143.5, 143.6, 145.1, 145.1, 145.2, 145.4, 145.7, 145.8, 163.6, 167.9

MS (MALDI, dctb): m/z = 1128 [M]+

+ HRMS (MALDI-TOF): m/z calc. for C81H28NaO8: 1151.1676 [M] , found: 1151.1693

IR (ATR; rt): [cm-1] = 660, 703, 793, 1011, 1175, 1229, 1257, 1427, 1463, 1731, 2097, 2346, 2850, 2918, 2961, 3285

UV/Vis (CH2Cl2; rt): λ [nm] = 267, 271, 326, 429

127

Experimental Section

3,3-di(prop-2-yn-1-yl)-1,5,12,16-tetraoxacyclodocosane-2,4,13,15-tetraone–[1,0]–mono– 1,2,–dihydro[60]–fullerene 71

A 250 mL Schlenk-RBF equipped with a magnetic stir bar was charged with

C60 (137 mg; 0.190 mmol), cyclo-[2]-malonate 40 (100 mg; 0.220 mmol) an

d CBr4 (73.0 mg; 0.220 m mol). Toluene (137.0 mL) was added and the mixture degassed for 30 min. DBU (55.0 µL; 0.370 mmol) was added slowly and the mixture was stirred at room temperature for 18 h under nitrogen atmosphere. The crude product was plug filtrated (tolueneEtOAc) and concentrated. After column chromatography (SiO2; toluene) the product was obtained as dark brown solid in 34 % (75.0 mg; 0.0643 mmol) yield.

Rf (SiO2): 0.14 (toluene)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.39 – 1.56 (m, 8H, COOCH2CH2CH2CH2), 1.69 – 1.75 4 (m, 4H, COOCH2CH2), 1.82 – 1.89 (m, 4H, COOCH2CH2), 2.03 (t, J = 2.4 Hz, 2H, 4 3 OOCCCH2CCH), 2.99 (d, J = 2.7 Hz, 4H, OOCCCH2CCH), 4.20 (t, J = 6.7 Hz, 4H, CCOOCH2), 3 4.46 (t, J = 6.8Hz, 4H, CCOOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 22.6, 25.6, 25.7, 28.5, 28.5, 29.7, 52.0, 56.4, 66.0, 67.3, 71.5, 71.8, 78.3, 125.3, 128.2, 129.0, 137.9, 139.7, 141.5, 142.5, 142.8, 143.5, 143.6, 143.6, 144.4, 145.2, 145.2, 145.2, 145.5, 145.7 (2x), 145.8, 163.6, 168.7

MS (MALDI, dctb): m/z = 1166 [M]+

+ HRMS (MALDI): m/z calc. for C84H30O8: 1166.1935 [M] , found: 1166.1985

IR (ATR; rt): [cm-1] = 660, 702, 793, 863, 1012, 1184, 1259, 1425, 1458, 1733, 2359, 2854, 2918, 2961,

UV/Vis (CH2Cl2; rt): λ [nm] = 233, 271, 326, 426

128

Experimental Section

6.3.4 Synthesis of Novel Clicked Porphyrin-Fullerene Dyad.

Porphyrin-Fullerene-Dyad 72

A 5 mL Schlenk-RBF equipped with a magnetic stir bar was charged with fullerene 71 (10.0 mg; 8.90 µmol), porphyrin 29

(9.00 mg; 10.0 µmol) and dissolved in CH2Cl2

(1.00 mL) under N2. Sodium ascorbate

(1.4 mg; 7.00 µmol) and CuSO4*5H2O (0.70 mg; 2.70 µmol) dissolved in water (1.00 mL) were added and the mixture was stirred vigorously under the exclusion of light. DIPEA (10.0 µL; 57.0 µmol) was added dropwise and the mixture stirred for 7 d. The layers were separated and the aq. layer was extracted with

CH2Cl2 (3*5.00 mL). The combined organic layers

were dried over Na2SO4 and concentrated.

Purification by column chromatography (SiO2;

CH2Cl2) yielded the product as purple solid in 49 % (8.91 mg; 4.36 µmol) yield.

Rf (SiO2): 0.57 (CH2Cl2)

MS (MALDI, dctb): m/z = 2039[M]+

+ HRMS (APPI; CH2Cl2): m/z calc. for C132H69N7O14Zn: 2039.4188[M] , found:2039.5649

IR (ATR; rt): [cm-1] = 626, 707, 794, 964, 1058, 1152, 1457, 1590, 1705, 1734, 2360, 2851, 2922, 3305

-1 -1 UV/Vis (CH2Cl2; rt): λ [nm] (ε [M cm ]) = 232 (4000), 265 (3500), 326 (750), 422 (16000), 548 (1000), 590 (300)

129

Experimental Section

6.3.5 Synthesis of Cyclo-[2]-Malonate, Substituted with Heptynyl Chains

Bis(6-((tert-butyldimethylsilyl)oxy)hexyl) 2-(5-azidopentyl)malonate 56

A 5 mL Schlenk-RBF equipped with a magnetic stir bar and condenser was charged with malonate 37 (400 mg; 0.750 mmol), azide 50 (500 mg; 2.62 mmol) and

K2CO3 (517 mg; 3.74 mmol), and dissolved in in

DMF (2.00 mL) under N2. The mixture was stirred under reflux for 2 d. EtOAc (5.00 mL) was added and the mixture was washed with water (3*5 mL) and brine (5 mL), dried over MgSO4 and concentrated. Purification by column chromatography (SiO2; CH2Cl2) yielded the product as yellow oil in 35 % (169 mg; 0.263 mmol) yield.

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.04 (s, 12H, SiCH3), 0.89 (s, 18H, SiCCH3), 1.33 - 1.65

(m, 22H, COOCH2CH2CH2CH2CH2, OOCCHCH2CH2CH2CH2), 1.87 – 1.91 (m, 15.3 Hz, 2H, 3 3 OOCCHCH2), 3.25 (t, J = 6.9 Hz, 2H, N3CH2), 3.31 (t, J = 7.5 Hz, 1H, OOCCH), 3.59 (t, 3 J = 6.5 Hz, 4H, SiOCH2), 4.09 – 4.15 (m, 4H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 5.0, 18.7, 25.8, 26.0, 26.3, 26.7, 27.2, 28.9, 28.9, 33.1, 51.7, 52.3, 53.8, 63.4, 65.8, 169.9

MS (MALDI, dctb): m/z = 666 [M+Na]+, 682 [M+K]+

130

Experimental Section

Dibenzyl 2,2-di(hept-6-yn-1-yl)malonate 65

A 5 mL Schlenk-RBF equipped with a magnetic stir bar and condenser was charged with malonate 60 (1.60 g; 5.75 mmol), alkyne 64

(2.00 g; 11.5 mmol), K2CO3 (1.60 g; 11.5 mmol),

and dissolved in DMF (2.00 mL) under N2. The mixture was stirred at 70 °C for 3 d. Water (5.00 mL) was added. The aq. layer was extracted with EtOAc (3*5.00 mL). The combined organic layers were dried over

Na2SO4 and concentrated. Purification by

column chromatography (SiO2; hexane/EtOAc 8:2) yielded the product as light yellow oil in 48 % (1.31 g; 2.77 mmol) yield.

Rf (SiO2): 0.10 (hexane/EtOAc 8:2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.01 – 1.10 (m, 4H, OOCCCH2CH2CH2CH2), 1.27-1.35

(m, 4H, OOCCCH2CH2CH2), 1.37 – 1.45 (m, 4H, OOCCCH2CH2), 1.84 – 1.90 (m, 4H, 4 4 OOCCCH2), 1.91 (t, J = 2.6 Hz, 2H, CH2CCH), 2.08 (dt, J = 2.6, 6.7 Hz, 4H, CH2CCH), 5.09 (s,

4H, CCOOCH2), 7.24 – 7.35 (m, 10H, Ar-H)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 18.2, 23.4, 28.0, 28.8, 32.2, 57.6, 66.7, 68.2, 84.3, 128.2, 128.2, 128.4, 135.5, 171.4

MS (MALDI, dhb): m/z = 495 [M+H+Na]+, 511 [M+H+K]+

IR (ATR; rt): [cm-1] = 695, 737, 793, 907, 1028, 1081, 1148, 1212, 1258, 1377, 1455, 1497, 1732, 2352, 2853, 2923

UV/Vis (CH2Cl2; rt): λ [nm] = 234, 265

131

Experimental Section

2,2-Di(hept-6-yn-1-yl)malonic acid 67

A 25 mL RBF equipped with a magnetic stir bar was charged with substituted malonate 65 (400 mg; 0.850 mmol), KOH (167 mg; 2.98 mmol) and dissolved in a mixture of water/EtOH (1:2; 7.50 mL). The mixture was stirred under reflux overnight. The solvent was removed and the crude product was dissolved in water. While cooling, conc. HCl was added to lower the

pH to 1. The product was extracted with Et2O (5*5 mL) and the combined organics were washed with brine (10 mL), dried and concentrated. The product was obtained as yellow oil in 64 % (159 g; 0.544 mmol) yield.

Rf (SiO2): 0.11 (hexane/EtOAc 9:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.00 – 1.10 (m, 4H, OOCCCH2CH2CH2CH2), 1.20-1.30

(m, 4H, OOCCCH2CH2CH2), 1.31 – 1.41 (m, 4H, OOCCCH2CH2), 1.55 – 1.65 (m, 4H, 4 4 OOCCCH2), 2.08 (dt, J = 2.6, 6.9 Hz, 4H, CH2CCH), 2.68 (t, J = 2.6 Hz, 2H, CH2CCH),

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 17.5, 24.4, 27.8, 28.4, 54.9, 71.0, 84.4

MS (APPI): m/z = 293 [M+H]+

IR (ATR; rt): [cm-1] = 629, 697, 734, 908, 1003, 1024, 1102, 1154, 1212, 1259, 1456, 1708, 1729, 2343, 2859, 2936, 3293

132

Experimental Section

6.3.6 Synthesis of Novel Fullerene Trimer Bridged by Cyclo-[3]-Malonate

((Diethyl malonyl)-(cyclo-[3]-octylmalonyl)-[5,1]–hexakis–1,2,18,22,23,27,45,31,32,36– dodecahydro[60]–fullerene 80

A 25 mL Schlenk-RBF equipped with a magnetic stir bar was charged with pentakis fullerene 79 (100 mg; 66.0 µmol). Toluene (10 mL) was added and the mixture degassed for 20 min under the

exclusion of light. CBr4 (22.0 g; 66.0 µmol) and cyclo-[3]- malonate 75 (11.0 mg; 19.0 µmol) were added and the mixture stirred for another 30 min. DBU (22.0 µL; 143 µmol) was added and the mixture was stirred at room temperature for 5 d. The crude product was concentrated. After column chromatography

(SiO2; toluene/EtOAc 8:2) the product was obtained as yellow glassy solid in 19 % (64.0 mg; 0.0124 mmol) yield.

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.80 – 0.90 (m, 36H, CCOOCH2CH2CH2CH2) 1.29 – 3 3 1.32 (t, J = 7.0 Hz, 90H, COOCH2CH3), 4.22 – 4.25 (t, J = 6.4 Hz, 12H, CCOOCH2CH2), 4.28 – 3 4.34 (q, J = 7.0 Hz, 60H, COOCH2CH3)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 14.0, 22.7, 25.8, 28.4, 45.3, 45.4, 62.8, 66.8, 69.1, 69.1, 141.1, 141.1, 145.7, 145.8, 145.8, 163.8, 163.8

+ + + + MS (MALDI, dctb): m/z = 720 [C60] , 5171[M] , 5194[M+Na] , 5211[M+K]

+ HRMS (ESI): m/z calc. for C318H198NaO72: 5193.2046 [M] , found: 5193.1824

IR (ATR; rt): [cm-1] = 713, 807, 855, 1014, 1077, 1206, 1261, 1367, 1463, 1740, 2363, 2850, 2919

UV/Vis (CH2Cl2; rt): λ [nm] = 244, 270, 280, 316, 335, 380

133

Experimental Section

Bis(5-(trimethylsilyl)pent-4-yn-1-yl)malonyl-dimethylaminophenylisoxazolino–[5,1]– hexakis–1,2,18,22,23,27,45,31,32,36,55,60–dodecahydro[60]–fullerene 85

A 500 mL Schlenk-RBF equipped with a magnetic stir bar was charged with isoxazolinofullerene 77 (250 mg; 0.283 mmol), DMA (584 mg; 2.83 mmol), dissolved in oDCB (283 mL) under nitrogen atmosphere, degassed and stirred for 5 h under the exclusion of light. Malonate 84

(1.08 g; 2.83 mmol) and CBr4 (9.39 g; 28.3 mmol) were added and the mixture stirred for additional 30 min. DBU (845 µL; 5.66 mmol) was added slowly. The reaction mixture was stirred at room temperature for 7 d. After filtration through

a silica gel plug (SiO2; toluene/EtOAc 7:3), the product was concentrated and purified

by column chromatography (SiO2; toluene  toluene/EtOAc 95:5), yielding the product as yellow solid in 50 % (396 mg; 0.142 mmol) yield.

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.10 – 0.14 (m, 90H, SiCH3), 1.80 – 2.00 (m, 20H,

COOCH2CH2CH2), 2.25 – 2.35 (m. 20H, COOCH2CH2), 2.97 (s, 6H, NCH3), 4.27 – 4.41 (m 20H, 3 3 COOCH2), 6.66 (d, J = 8.4 Hz, 2H, Ar-H), 7.82 (d, J = 8.7 Hz, 2H, Ar-H)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 0.1, 16.5, 27.5, 40.1, 45.3, 65.8, 69.8, 85.7, 105.1, 111.6, 120.7, 129.5, 139.2, 139.4,.139.4, 139.6, 140.3, 141.1, 141.1, 141.6, 141.7, 142.1, 143.3, 143.7, 144.1, 145.3, 145.4, 145.5, 145.5, 145.7, 146.1, 146.3 146.6, 146.8, 162.1, 163.3, 163.7

MS (MALDI, om): m/z = 2773[M]+

IR (ATR; rt): [cm-1] = 638, 698, 758, 837, 1030, 1145, 1274, 1402, 1745, 2177, 2960

134

Experimental Section

6.3.7 Synthesis of Alkyne-Functionalized Fullerene Monoadduct

Methyl (7-(trimethylsilyl)hept-6-yn-1-yl) malonate 98

A 100 mL Schlenk-RBF equipped with a magnetic stir bar and 25 mL dropping funnel was charged with 7-(trimethylsilyl)hept-6-yn-1-ol 97 (0.500 mg; 2.71 mmol), pyridine

(0.219 mL; 2.71 mmol), dissolved in CH2Cl2 (30.0 mL) and cooled to 0 C under nitrogen atmosphere. Via dropping funnel methyl malonic acid (0.219 mL; 2.71 mmol) dissolved in

CH2Cl2 (5.00 mL) was added dropwise and the mixture was stirred for 2 h. After raising the temperature to room temperature, the mixture was stirred overnight. The crude product was filtered and washed with brine (3*75 mL). The organics were concentrated and dried over

Na2SO4. Purification by column chromatography (SiO2; hexane/EtOAc 6:1) yielded the product as clear oil in 62 % (482 mg; 1.69 mmol) yield.

Rf (SiO2): 0.5 (hexane/EtOAc 6:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.11 (s, 9H, SiCH3), 1.38 – 1.56 (m, 4H, 3 COOCH2CH2CH2CH2), 1.61 – 1.68 (m, 2H, COOCH2CH2), 2.15 – 2.22 (t, J = 6.9 Hz 3H, 3 CH2CCSiCH3), 3.37 (s, 2H, OOCCH2COO), 3.72 (s, 3H, OCH3 ), 4.10 – 4.14 (t, J = 6.7 Hz, 2H,

COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 0.56, 20.2, 25.4, 28.4, 28.6, 41.8, 52.9, 65.9, 85.1, 107.5, 167.0, 167.5

MS (MALDI, om): m/z = 308 [M+Na]+

+ HRMS (ESI): m/z calc. for C14H24NaO4Si: 307.133606[M] , found: 307.1334

IR (ATR; rt): [cm-1] = 638, 699, 736, 759, 838, 1023, 1147, 1249, 1334, 1437, 1734, 2174, 2955

135

Experimental Section

Methyl (7-(trimethylsilyl)hept-6-yn-1-yl) malonyl –[1,0]–mono–1,2,–dihydro[60]– fullerene 99

A 2 L Schlenk-RBF equipped with a

magnetic stir bar was charged with C60 (648 mg; 0.900 mmol), iodine (254 mg; 1.00 mmol) and methyl (7- (trimethylsilyl)hept-6-yn-1-yl) malonate 98 (250 mg; 0.880 mmol). Toluene (820 mL) was added and the mixture degassed under the exclusion of light. DBU (310 µL; 2.10 mmol) was added slowly and the mixture was stirred at room temperature for 7 h under nitrogen atmosphere. The crude product was plug filtrated (SiO2; CH2Cl2/EtOAc 1:1) and concentrated. After column chromatography

(SiO2; toluene) the product was obtained as dark brown solid in 26 % (234 mg; 0.230 mmol) yield.

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.14 (s, 9H, SiCH3), 1.21 – 1.31 (m, 2H,

COOCH2CH2CH2CH2), 1.55 – 1.60 (m, 2H, COOCH2CH2CH2), 1.84 – 1.89 (m, 2H, 3 3 COOCH2CH2), 2.24 (t, J = 6.7 HZ, 2H, CH2CCSiCH3), 4.08 (s, 3H, OCH3 ), 4.49 (t, J = 6.6 Hz, 2H,

COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 0.2, 19.8, 25.2, 28.0, 28.1, 52.0, 54.0, 67.2, 71.5, 84.8, 106.9, 139.5, 139.6, 141.5, 142.4, 142.4, 142.8, 143.5, 143.6, 143.6, 144.4, 145.2, 145.2 145.5, 145.7, 145.7, 145.8, 145.8, 163.6, 164.1

+ + MS (MALDI, dctb): m/z = 720 [C60] , 1002 [M]

IR (ATR; rt): [cm-1] = 755, 836, 1055, 1097, 1179, 1231, 1507, 1700, 1734, 2346, 3751

-1 -1 UV/Vis (CH2Cl2; rt): λ [nm] (ε [M cm ]) = 231, 258, 328, 426

136

Experimental Section

6.3.8 Synthesis of Fullerene Amino-Monoadducts

5-((tert-Butoxycarbonyl)amino)pentyl methyl malonate 105

A 100 mL Schlenk-RBF equipped with a magnetic stir bar and 25 mL dropping funnel was charged with tert- butyl (5-hydroxypentyl)carbamate 104 (2.00 g; 9.85 mmol), pyridine

(1.00 mL; 12.3 mmol) and dissolved in CH2Cl2 (50.0 mL) under N2. Via dropping funnel methyl malonyl chloride (1.06 mL, 9.85 mmol) dissolved in CH2Cl2 (5.00 mL) was added over a period of 15 min and the mixture was stirred at room temperature overnight. The mixture was washed with brine (3*50 mL) dried over NaSO4, filtered and concentrated. Purification by column chromatography (SiO2; CH2Cl2/EtOAc 7:3) yielded the product as yellow oil in 71 % (2.12 g; 6.99 mmol) yield.

Rf (SiO2): 0.49 (CH2Cl2/EtOAc 9:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.28 - 1.49 (m, 13 H, COOCH2CH2CH2, NCH2CH2, 3 CCH3), 1.58 –1.65 (m, 2H, COOCH2CH2), 3.06 (dt, J = 12.6, 6.5 Hz, 2H, NCH2), 3.34 (s, 2H, 3 OOCCH2COO), 3.70 (s, 3H, OCH3), 4.09 (t, J = 6.5 Hz, 2H, COOCH2), 4.58 (br, 1H, NH)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 23.0, 28.0, 28.3, 29.5, 40.2, 41.3, 52.4, 65.3, 79.0, 156.0, 166.5, 167.0

MS (MALDI, dctb): m/z = 304 [M+H]+, 326 [M+H+Na]+, 342 [M+H+Ka]+

IR (ATR; rt): [cm-1] = 525, 658, 690, 787, 864, 1011, 1260, 1503, 2963

137

Experimental Section

5-((tert-Butoxycarbonyl)amino)pentyl methyl malonyl –[1,0]–mono–1,2,–dihydro[60]– fullerene 106

A 2 L Schlenk-RBF equipped with a magnetic stir

bar was charged with C60 (1.09 g; 1.51 mmol), 5- ((tert-butoxycarbonyl)amino)pentyl methyl malonate 105 (500 mg; 1.51 mmol) and iodine (288 mg; 2.27 mmol). Toluene (1.00 L) was added and the mixture degassed under the exclusion of light. DBU (560 µL; 3.78 mmol) was added slowly and the mixture was stirred at room temperature for 1 h under nitrogen atmosphere. The crude product was plug filtrated (CH2Cl2/EtOAc 1:1) and concentrated. After column chromatography (SiO2; CH2Cl2/EtOAc 8:2) the product was obtained as dark brown solid in 46 % (716 mg; 0.700 mmol) yield.

Rf (SiO2): 0.68 (CH2Cl2/EtOAc 9:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.23 (m, 2H, COOCH2CH2CH2), 1.41 –1.54 (m, 13 H, 3 COOCH2CH2, NCH2CH2,, CCH3), 3.12 (m, 2H, NCH2), 4.07 (s, 3H, OCH3), 4.47 (t, J = 6.5 Hz, 2H,

COOCH2), 4.55 (br, 1H, NH)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 23.2, 28.2, 28.4, 29.7, 40.4, 52.0, 54.0, 67.2, 71.4, 79.2, 139.4, 139.6, 141.5, 142.4, 142.4, 142.7, 143.5, 143.5, 143.6, 144.4, 145.2, 145.2, 145.4, 145.6, 145.7, 145 7, 145.7, 145.8, 145.8, 155.9, 163.5, 164.1

+ + MS (MALDI): m/z = 720 [C60] ,1044 [M+Na]

+ HRMS (MALDI-TOF): m/z calc. for C74H23NO6: 1021.1520 [M] , C74H23NNaO6: 1044.1418 [M+Na]+, found: 1021.1503, 1044.1417

IR (ATR; rt): [cm-1] = 527, 583, 702, 737, 1167, 1234, 1366, 1392, 1427, 1457, 1510, 168, 1698, 1747, 2858, 2925

-1 -1 UV/Vis (CH2Cl2; rt): λ [nm] (ε [M cm ]) = 226, 258, 325, 426

138

Experimental Section

5-Aminopentyl methyl malonyl –[1,0]–mono–1,2,–dihydro[60]–fullerene 107

A 10 mL RBF was charged with 5-((tert- butoxycarbonyl)amino)pentyl methyl malonate fullerene monoadduct 106 (664 mg; 0.650 mmol) and dissolved in TFA (5 mL) under the exclusion of light. After stirring overnight, excess TFA was removed in vacuo and co- evaporated with methanol several times to give 107 as dark brown solid in 96 % (599 mg; 0.650 mmol) yield.

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 0.97 – 1.03 (m, 2H, COOCH2CH2CH2), 1.10 –1.16 (m,

2 H, COOCH2CH2), 1.10 –1.16 (m, 2 H, NCH2CH2,) 2.33 (m, 2H, NCH2), 3.25 (br, 1H, NH2), 3.60 3 (s, 3H, OCH3), 4.03 (t, J = 6.5 Hz, 2H, COOCH2)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 23.1, 27.3, 28.3, 40.4, 53.1, 55.3, 67.9, 72.2, 139.2, 139.4, 141.4 (2x), 142.2, 142.3, 142.6, 142.6, 143.4 (2x), 143.4, 143.4, 143.5, 144.2 (2x), 145.0, 145.0, 145.1, 145.1 (2x), 145.2, 145.5, 145.5, 145.5, 145.6, 145.6 (2x), 145.9, 146.1, 163.5, 164.1

+ + MS (MALDI, dctb): m/z = 720 [C60] , 922 [M+H]

+ HRMS (MALDI, dctb): m/z calc. for C69H16NO4: 922.1074 [M+H] , found: 922.1700

IR (ATR; rt): [cm-1] = 527, 581, 699, 736, 1060, 1095, 1115, 1187, 1233, 1258, 1430, 1579, 1747, 2358, 2848, 2921

UV/Vis (CH2Cl2; rt): λ [nm] = 226, 256, 325, 426

139

Experimental Section

Bis(5-((tert-butoxycarbonyl)amino)pentyl) malonate 108

A 250 mL Schlenk-RBF equipped with a magnetic stir bar and 50 mL dropping funnel was charged with tert- butyl (5-hydroxypentyl)carbamate 104 (8.00 g; 39.4 mmol), malonic acid (2.05 g; 19.7 mmol) and dissolved in dry MeCN (50.0 mL) under N2. Via dropping funnel DCC (8.13 g; 39.4 mmol) dissolved in dry MeCN (50.0 mL) was dropped to the mixture over a period of 20 min and the mixture was stirred at room temperature overnight. The resulting white precipitate was filtered and washed with CH2Cl2 (3*50 mL). The organics were concentrated. Purification by column chromatography (SiO2; CH2Cl2/EtOAc 8:2) yielded the product as yellow oil in 78 % (7.30 g; 15.4 mmol) yield.

Rf (SiO2): 0.73 (CH2Cl2/EtOAc 9:1)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.28 - 1.49 (m, 26 H, COOCH2CH2CH2, NCH2CH2,

CCH3), 1.58 –1.65 (m, 4H, COOCH2CH2), 3.06 (m, 4H, NCH2), 3.32 (s, 2H, OOCCH2COO), 4.09 3 (t, J = 6.5 Hz, 4H, COOCH2), 4.62 (br, 2H, NH)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 23.0, 28.0, 28.3, 29.6, 40.3, 41.5, 65.3, 79.0, 155.9, 166.6

MS (MALDI): m/z = 497 [M+H+Na]+

+ HRMS (ESI-TOF): m/z calc. for C23H42N2NaO8: 497.283337[M] , found:497.283559

IR (ATR; rt): [cm-1] (ε [M-1cm-1]) = 520, 660, 684, 790, 866, 1013, 1089, 1146, 1164, 1256, 1365, 1457, 1520, 1692, 2850, 2923, 2960

140

Experimental Section

Bis(5-((tert-butoxycarbonyl)amino)pentyl) malonyl –[1,0]–mono–1,2,–dihydro[60]–fullerene 109

A 2 L Schlenk-RBF equipped with a magnetic stir bar was

charged with C60 (756 mg; 1.05 mmol), Bis(5-((tert- butoxycarbonyl)amino)pent yl) malonate 108 (500 mg; 1.05 mmol) and iodine (199 mg; 1.57 mmol). Toluene (700 mL) was added and the mixture degassed under the exclusion of light. DBU (400 µL; 2.63 mmol) was added slowly and the mixture was stirred at room temperature for 1 h under nitrogen atmosphere.

The crude product was plug filtrated (SiO2; CH2Cl2/EtOAc 1:1) and concentrated. After column chromatography (SiO2; CH2Cl2/EtOAc 8:2) the product was obtained as dark brown solid in 37 % (461 mg; 0.390 mmol) yield.

Rf (SiO2): 0.27 (hexane/EtOAc 8:2)

1 H NMR (400 MHz; CDCl3; rt): δ [ppm] = 1.41 –1.57 (m, 26 H, COOCH2CH2, NCH2CH2,, CCH3), 3 1.81 –1.87 (m, 4H, COOCH2CH2), 3.11 (m, 4H, NCH2), 4.47 (t, J = 6.5 Hz, 4H, COOCH2), 4.63 (br, 2H, NH)

13 C NMR (100 MHz; CDCl3; rt): δ [ppm] = 23.0, 28.2, 28.4, 29.7, 40.4, 52.2, 67.2, 71.4, 79.1, 139.5, 141.5, 142.4, 142.8, 143.5, 143.5, 143.6, 143.8, 144.4, 145.2, 145.2, 145.4, 145.7, 145.7, 145.8, 156.0, 163.6

+ + MS (MALDI, dctb): m/z = 720 [C60] , 1192 [M]

+ HRMS (APPI; CH2Cl2): m/z calc. for C83H40N2NaO8 1215.2677 [M] , found: 1215.2674

IR (ATR; rt): [cm-1] = 527, 735, 866, 1164, 1234, 1267, 1361, 1392, 1425, 1455, 1510, 1694, 1744, 2853, 2928

UV/Vis (CH2Cl2; rt): λ [nm] = 226, 257, 325, 426

141

Experimental Section

Bis(5-aminopentyl) malonyl –[1,0]–mono–1,2,–dihydro[60]–fullerene 110

A 10 mL RBF was charged with Bis(5- ((tert-butoxycarbonyl)amino)pentyl) malonate fullerene monoadduct 109 (305 mg;0.260 mmol) and dissolved in TFA (5 mL) under the exclusion of light. After stirring overnight, excess TFA was removed in vacuo and co- evaporated with methanol several times to give 110 as dark brown solid in 94 % (258 mg; 0.260 mmol) yield.

1 H NMR (400 MHz; CD3OD; rt): δ [ppm] = 0.85 – 0.89 (m, 4 H, COOCH2 CH2CH2, NCH2CH2,),

1.55 –1.78 (m, 8H, COOCH2CH2, NCH2CH2,), 1.90 (bs, 4H, NH2), 2.95 – 2.98 (m, 4H, NCH2), 4.51

(bs, 4H, COOCH2)

13 C NMR (100 MHz; CD3OD; rt): δ [ppm] = 24.1, 28.2, 29.3, 40.6, 54.8, 68.3, 73.1, 117.1, 119.3, 142.4, 143.4, 143.8, 144.6, 144.6, 145.4, 146.1, 146.3, 146.5, 146.6, 146.8, 146.9, 162.7, 162.8, 163.0, 163.0, 164.7

MS (MALDI, dctb): m/z = 992 [M]+

IR (ATR; rt): [cm-1] = 527, 656, 744, 798, 1023, 1092, 1260, 1374, 1455, 1681, 1730, 2329, 2387, 2851, 2921, 2959

UV/Vis (CH2Cl2; rt): λ [nm] = 226, 254, 318

142

References

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Appendix

8 Appendix

Publications

Maximilian Wolf, Benedikt Platzer, Stefan Bauroth, Dominik Lungerich, Maximilian Popp, Timothy Clark, Norbert Jux, Andreas Hirsch, and Dirk M. Guldi, “Chemically and Excitonically Coupled Hexabenzocoronene– (Metallo)porphyrin–Fullerene Assemblies” – in preparation

Oral Presentations

M. Popp, “A New Approach To Porphyrin-Fullerene-Conjugates“, Tetrapyrroles in , ICCP Symposium 2016, Erlangen

M. Popp, “ A New Building Block For Fullerene Chemistry“ Winterschool der Graduate School Molecular Science, 2016, Kirchberg (Austria)

Poster Contributions

M. Popp, A. Hirsch, “Novel Fullerene Trimers from Pentakisadducts”, Ulm-Erlangen Mini- Symposium on Functional Organic Materials, 2017, Ulm

M. Popp, A. Hirsch, “Triazole linked porphyrin-cyclo-[2]-malonate conjugates - a new building block for fullerene chemistry”, International Conference on Porphyrins and Phthalocyanines 9, 2016, Nanjing (China)

M. Popp, A. Hirsch, “Preparation of [60]fullerene hexakisadduct linked to porphyrins via Click-chemistry to cyclo-[2]-malonate”,3rd Erlangen Symposium on Synthetic Carbon Allotropes, 2015, Erlangen

153

Danksagungen

An dieser Stelle möchte ich mich bei allen ganz herzlich bedanken, ohne deren Hilfe und Unterstützung diese Arbeit nicht zustande gekommen wäre.

Zunächst möchte ich mich bei meinem Doktorvater, Prof. Dr. Andreas Hirsch, für die Aufnahme in seinem Arbeitskreis und die Vergabe des interessanten Themas, sein stetes Interesse am Fortgang der Arbeit und den benötigten kreativen Freiraum für die Forschung bedanken. Des Weiteren bei Prof. Dr. Norbert Jux für seine zahlreichen Ratschläge und meine freundliche Aufnahme als externer „Anhang“ seines Arbeitskreises.

Mein Dank gilt auch den akademischen Räten Dr. Michael Brettreich (vielen Dank für das Korrekturlesen), Dr. Marcus Speck, Dr. Thomas Röder und Dr. Frank Hauke, die mir immer mit Rat und Tat zur Seite standen und zu der tollen Atmosphäre im Lehrstuhl beitrugen. Ein großer Dank gilt auch Heike Fischer, für ihre Hilfe und die vielen tollen Gespräche. Ohne sie wäre diese Arbeit vielleicht nie begonnen worden.

Danken möchte ich auch den Angestellten und Mitarbeitern des Instituts für Organische Chemie, ohne die diese Arbeit nicht möglich gewesen wäre: Prof. Dr. Walter Bauer, Dr. Harald Maid und Christian Placht, für deren fachliche Unterstützung bei NMR Messungen, Margarete Dzialach und Wolfgang Donaubauer für das Messen der Massenspektren, sowie den weiteren Kräften des Instituts: Detlef Schagen, Robert Panzer, Hannelore Oschmann, Stefan Fronius, Bahram Saberi, Holger Wohlfahrt und Horst Mayer.

Allen Freunden und Kollegen, den aktuellen und ehemaligen, in den Arbeitskreisen Hirsch, Jux (danke, dass ihr mich als externen Mitglied in euren Kreis aufgenommen habt), Mokhir, von Delius und Amsharov ein ganz großes Dankeschön für die freundliche Atmosphäre und Unterstützung in den letzten Jahren. Ich hatte wirklich viel Spaß und bin froh Teil dieser Gemeinschaft zu sein. Unsere Gespräche in der Mittagspause, die vielen Kuchenpausen und Feiern haben so manchen Tag deutlich bereichert. Mit euch war es nie langweilig. Natürlich ist neben dem Spaß der wissenschaftlich Aspekt unserer Arbeit in der OC auch nicht zu kurz gekommen, deswegen Danke auch für die vielen Anregungen, Vorschläge und produktiven Debatten zu meinem Thema und der Chemie im Allgemeinen. Besonders hervorheben möchte ich dabei meine Laborkollegen Andreas, Cornelius, Carolin, Anshu (Danke besonders auch fürs Korrekturlesen) und Isabel. Vielen Dank für die angenehme Atmosphäre, die Unterstützung und Ratschläge und die tollen Gespräche. Im 3.09 war es dank euch nie langweilig. Bessere Kollegen kann man sich nicht wünschen. Besonderer Dank geht außerdem an Kathrin fürs Korrektur lesen, sowie Maria Eugenia und Katerina für ihre große Hilfe bei der Verbesserung meines Promotionsvortrages.

Bei den Mitgliedern des JCF möchte ich mich für die gute Zeit in den letzten Jahren bedanken. Auch wenn ich meinen Einstand damals immer noch nicht ganz überwunden habe, möchte ich die Erlebnisse und Erfahrungen, die ich mit euch gesammelt habe nicht missen.

Ein großer Dank gilt natürlich auch meinen Kooperationspartner Judith und Maximilian, dass ihr mir die Möglichkeit gegeben habt, mit meinen Verbindungen zur Forschung in anderen Themengebieten beizutragen.

Dem GSMS-Team bestehend aus Dominik, Rene und David danke ich für die Zusammenarbeit bei der GSMS Winter School. Unser Projekt war top…die Welt war nur noch nicht bereit dafür.

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Danken möchte ich auch meinen beiden Bachelor-Studenten, Susanne und Lukas, dass sie die Herausforderung meiner Themen angenommen und diese mehr oder weniger erfolgreich abgeschlossen haben. Außerdem den zahlreichen Nano-Praktikanten, die meine Verbindungen für mich nachgezogen haben.

Der größte Dank gebührt jedoch meinen Eltern und meinen Schwestern. Vielen Dank für Eure Hilfe, Eure Geduld und dafür, dass ihr immer an mich geglaubt habt

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