"The New Chemistry" - Sustainable Catalysis with Alcohols
- Subject of the thesis are new iridium complexes stabilized by anionic P,N- or P,N,P-ligands. These complexes were used in homogeneous catalysis. Furthermore, mechanistic studies were performed to provide an insight into the catalytic cycles. Synthesis protocols for a multitude of different product classes have been developed.
The iridium complex 1, stabilized by a neutral P,N-ligand, reacts under basic conditions with 2-aminopyridines. By elimination of dipyridylamine the new catalyst species 2a was formed, which is more stable than catalyst 1.
Based on this finding eight new anionic P,N-ligands and the resulting iridium complexes were synthesized.
After optimization of the reaction conditions (solvent, base, temperature and catalyst loading) these catalysts were used in BH (borrowing hydrogen)/HA (hydrogen autotransfer) reactions. The selective monoalkylation of anilines with primary alcohols was investigated. In comparative experiments the superiority of the new class of catalysts versus the original catalyst 1 was clearly shown. Under mild reaction conditions (70 °C) the selectivity profile with respect to the monoalkylation has been preserved.
The catalytic protocol was subsequently extended to the alkylation of aromatic diamines. Therefore various diaminobenzenes were used as substrates. Also Dapsone®, an important drug in treatment of leprosy could be used as starting material. We succeeded in both symmetric and unsymmetric monoalkylations of diamines. Due to the selectivity profile of the catalyst regarding aromatic amines, also unprotected amino alcohols could be used as alkylating reagents.
By the use of tridentate P,N,P-ligands, a novel class of more stable catalysts compared to complexes 2a-9a, could be developed. Due to sealing the synthesis reactor with a semipermeable membrane, the retransfer of the “borrowed” hydrogen could be prevented and H2 is released. Dehydrogenation and condensation steps are now possible instead of BH/HA. By reacting secondary alcohols with β-amino alcohols, pyrroles were accessible.
After adapting the synthesis protocol to this new class of products the tolerance of functional groups was tested. Diversely functionalized alcohols were used. Under mild reaction conditions (90 °C) and very low catalyst loadings (down to 0.03 mol% iridium), a large number of novel pyrroles was accessible. Using this protocol 21 differently substituted α,α-pyrroles, 12 bicyclic pyrroles, symmetrically as well as non-symmetrically substituted oligopyrroles and three β-aminopyrroles were synthesized. The catalyst resting state was identified by NMR experiments and X-ray structure analysis to be an iridium trihydride. This trihydride is formed under catalytic conditions, by treatment of the pre-catalyst with alcohols or in hydrogen atmosphere.
In the final part of the work, a catalytic pyridine synthesis was developed. In this so far unknown heterocycle synthesis up to four different substituents could be introduced within a single reaction step. 2,6-, 2,5-, 2,4- and 2,3-substituted pyridines were synthesized selectively by using variously substituted primary or secondary alcohols and γ-amino alcohols. Furthermore, both the synthesis of bicyclic pyridines as well as the synthesis of pyridines that bear chiral substituents is possible.
On Efficient Solution Methods for Mixed-Integer Nonlinear and Mixed-Integer Quadratic Optimization Problems
- In this thesis we focus on solution methods for convex mixed-integer nonlinear
optimization problems (MINLP). As one main result, we propose a new algorithm
guaranteeing global optimality for convex MINLPs under standard
assumptions. The new algorithm called MIQP-supported outer approximation
(MIQPSOA) incorporates the successive solution of convex mixed-integer
quadratic programs (MIQP) in a linear outer approximation framework. An extensive
numerical competitive study based on several different MINLP solvers shows,
that a first implementation of the new method performs well in terms of both
the reliability and the efficiency. Since the new method is designed to solve simulation-based optimization problems arising in practical engineering applications, the main performance criterion is the number of function evaluations required to solve a problem.
Furthermore, the test results indicate, that the integration of mixed-integer search steps, resulting from the solution of convex MIQPs, significantly improves the reliability and the efficiency compared to well-known linear outer approximation methods.
After reviewing available solution techniques for convex MINLP problems, we present the algorithmic set-up as well as the convergence proof of MIQPSOA. As pointed out in this dissertation, MIQPSOA is a first step towards a convergent MINLP solution method, that solely relies on the successive solution of convex MIQPs as proposed by Exler and Schittkowski. Finally, we present an extensive numerical test case study considering different solution methods for convex MINLPs.
The second part of this thesis deals with efficient solution techniques for
convex mixed-integer quadratic programs, that arise as subproblems during the
solution of MINLPs by MIQP-based algorithms, such as MIQPSOA. First, we
briefly review latest developments in state-of-the-art mixed-integer linear
(MILP) solvers, since we want to develop a MIQP solver that incorporates the most successful components of MILP solvers. As we focus on branch-and-bound methods, one main component is an efficient and robust sub-solver for continuous quadratic programs, which is able to perform warmstarts. On the other hand, cutting planes have led to a tremendous speed-up of mixed-integer linear solvers during the last 20 years. As a consequence, we extend an efficient construction method for disjunctive cutting planes, such that it can be applied for MIQPs.
Extensive numerical tests show, that the performance of a branch-and-bound solver can be significantly increased by exploiting warmstarts. Furthermore, it turns out, that in a majority of the test cases, where disjunctive cutting planes exist, the calculation times are reduced up to a factor of more than 5. Nevertheless there are also instances, where the presents of disjunctive cutting planes significantly slows down the performance. Due to the efficient cut generation method developed within this thesis, the generation of cutting planes has almost no influence on the calculation time, if no disjunctive cuts exist, which is the case in about 45 \% of all test instances. As a consequence, the application of cutting planes for MIQPs needs further attention and especially a dynamic cut management might be very profitable. Finally, we compare the performance of our branch-and-cut solver MIQL with the solver SCIP, which is one of the state-of-the-art MILP solvers, that can also solve MIQPs. These tests indicate, that MIQL outperforms SCIP on hard MIQP instances, while SCIP is faster for simpler test cases.
RNA interference with allatoregulating neuropeptide genes affecting circadian rhythm, development, mating and reproduction of Spodoptera frugiperda (Lepidoptera: Noctuidae)
Intisar Taha Elhag Hassanien
- Juvenile hormones (JHs) have juvenoid functions but also act as a true gonadotropin in the Lepidoptera. JHs are released by the corpora allata (CA) into the hemolymph, which are under allatotropic and allatostatic neuropeptide control as well as under somatic and environmental stimulus.
Two types of allatostatins (Spofr-AS type Manse-AS and Spofr-AS type A or FGLamides) and two allatotropins (Spofr-AT 1 or Manse-AT and Spofr-AT 2) were identified and cloned from Spodoptera frugiperda. Their functions were already investigated in our laboratory. Most of these peptides are pleiotropic in function but their specific roles in the various developmental stages of S. frugiperda are still unclear.
My work mainly emphasizes on the AT 1 gene function on JH and ecdysteroid titers in the hemolymph of larvae and adults as well as on females’ and males’ reproductive tissues and on the daily egg rate of the females. Studies were carried out by knockdown of the AT 1 gene using RNA interference. My results show a significant role of this neuropeptide on the circadian rhythm of prepupal commitment and metamorphosis, but also on the profile of egg laying and the number of deposited eggs. In general, Spofr-AT 1 acts as a true allatotropin in larvae and adults, but its functions may be substituted, at least in part, by Spofr-AT 2.
Silencing of Spofr-AT 1 and AS type A genes in males supported either allatotropic or allatostatic actions on the accessory glands (AGs) of the males, but had no effect on the JH transferred to the female bursa copulatrix (BC) during mating, nor on the fertility of the females.
Documentation of the EVENT-HMMS Experiment 2012 – Microclimatological effects of rain-out shelters within EVENT II
- no abstract
The making of meaning in Africa : Word, Image and Sound
Gilbert Ndi Shang
Diderot Djialla Mellie
- The Making of Meaning in Africa; Word, Image and Sound
Duncan Omanga and Gilbert Ndi Shang
The present collection addresses the intricate ways in which events, processes and phenomena are apprehended and reproduced in Africa by graduate students at BIGSAS. Inasmuch as the contributions fall under the gamut of media, literary, linguistic and translation studies, they are all underlined by an investigative quest for the understanding of meaning making processes in Africa. The papers in this volume therefore attempt to offer a glimpse into some of these processes of meaning making in the continent.
Synthesis of Group (lV) Transition Metal Complexes and their Applications as Catalysts for Ethylene Polymerization
- The aim of the project included the synthesis and characterization of new group (IV) metal complexes and their applications as catalysts in homogeneous ethylene polymerization reactions. For this purpose, different types of organic compounds and their group (IV) metal complexes were synthesized and tested for ethylene polymerization after activation with MAO. The first part of this work describes the synthesis of symmetric and asymmetric metallocene dichloride complexes bearing bulky alkoxy substituents on indenyl moieties and the investigation of their potential as ethylene polymerization catalysts. Indenyl compounds bearing bulky alkoxy substituents can be prepared by refluxing phenol or naphthol derivatives with w-bromo-1-indenylalkanes and potassium carbonate in the presence of catalytic amounts of 18-crown-6 in acetone. They can be prepared in better yields by the reaction of w-bromo-1-phenoxyalkanes with indenyl lithium. Symmetric metallocene dichloride complexes were synthesized by deprotonating the alkoxy substituted indenyl compounds with n-butyllithium followed by the reaction with metal tetrachlorides. Asymmetric metallocene dichloride complexes were synthesized by deprotonating alkoxy substituted indenyl compounds with n-butyllithium followed by the reaction with indenyl zirconium trichloride. The second part of this work deals with the synthesis of bis (indenyl) zirconium dichloride complexes bearing bulky 9-methyl fluorenyl substituents. 9-Methyl fluorenyl substituted indenyl compounds can be synthesized by the reaction of w-bromo-1-indenylalkanes with the lithium salt of 9-methyl fluorene. The reaction of zirconium tetrachloride with the lithium salts of the substituted indenyl compounds afford the bis (indenyl) zirconium dichloride complexes in good yields. Asymmetric chelating diamide complexes of titanium and zirconium were also synthesized and tested for ethylene polymerization as a part of the project. Reaction of the desired aniline with an appropriate dibromoalkane compound affords the N-substituted bromoalkyl aniline derivative which can react with tertiary butyl amine to yield the desired asymmetric diamine compound. Deprotonation of the diamine compounds with n-butyllithium followed by the reaction with titanium tetrachloride or zirconium tetrachloride yields the desired chelating diamide complexes. Titanium and zirconium complexes with a Schiff base derivative of 2-(2-aminophenyl)benzothiazole were also synthesized. The reaction of 2-(2-aminophenyl)benzothiazole with benzaldehyde yields its Schiff base derivative which can react with titanium tetrachloride or zirconium tetrachloride to afford the desired complexes. The above mentioned complexes were used for homogeneous ethylene polymerization after activation with MAO (M:Al = 1:2000). The alkoxy substituted metallocene catalysts showed good to moderate activities which depend on the length of the bridging alkylidene chain between alkoxy group and indenyl ligand of the zirconocene dichloride complex as well as the steric bulk of the alkoxy substituent. The activity maximum (27467 kg PE/mol cat. h) was found for a chain length of four carbon atoms. Further increase or decrease in the chain length resulted in a decrease of activity. The decrease of steric bulk at the phenoxy group also resulted in a decrease of activity. The 9-methyl fluorenyl substituted metallocene catalysts showed good activities towards ethylene polymerization. The catalyst with butylidene bridge between 9-methyl fluorenyl group and indenyl ligand showed the maximum activity (15786 kg PE/mol cat. h). The activated asymmetric chelating diamide complexes of titanium and zirconium (M:Al = 1:1000) showed low activities. The complex bearing bulky isopropyl groups at the aniline moiety showed the highest activity (263 kg PE/mol cat. h). The activity decreased by decreasing the steric bulk at the aniline moiety. Titanium and zirconium complexes of the Schiff base derivative of 2-(2-aminophenyl) benzothiazole also showed low activities (432 and 276 kg PE/mol cat. h) after activation with MAO (M:Al = 1:2000). A possible reason for the low activity could be the coordination of the sulphur atom to the active species. The symmetric alkoxy substituted metallocene catalysts produced polyethylenes of lower melting points, melting enthalpies, crystallinities and viscosity average molecular weights (112.9 J/mol, 126 °C, 0.39 and 270000 g/mol than their asymmetric analogues (155.3 J/mol, 137.2 °C, 0.54 and 420000 g/mol). The polyethylenes produced by 9-methyl fluorenyl substituted metallocene catalysts are of medium melting points, melting enthalpies and crystallinities (142 J/mol, 129.3 °C and 0.49). The polyethylenes produced by the asymmetric chelating diamide catalysts have medium melting points but low melting enthalpies and crystallinities (137.8 J/mol, 116.5 °C and 0.44).
Mononuclear and Dinuclear Complexes of Allylated alpha-Diimines as Catalysts for the Polymerization of Ethylene
- It was the goal of this project to synthesize dinuclear catalysts that provide two different active sites for the oligomerization and polymerization of alpha-olefins, especially ethylene. The plan of synthesis involves precursors consisting of a diimine moiety coordinated to a late or early transition metal and a metallocene or half sandwich moiety. In order to achieve these goals, some alpha-diimine compounds were functionalized with allyl or alkyl halide groups and then coupled with a metallocene or a half sandwich complex. Three different alpha-diimine compounds were synthesized and characterized by GC-MS, 1H NMR, and 13C NMR spectroscopy. These compounds are bearing allyl functions at their backbones and different ortho substituents at the arene moieties of their frameworks. 21 different complexes were prepared using these compounds and they were characterized by mass spectroscopy and elemental analysis. These complexes were activated with methylalumoxane (MAO) and tested for the catalytic polymerization of ethylene. The ethylene polymerization results revealed that the bulkier the substituents at the aryl rings of the catalyst structure, the lower the polymerization activity. These results are compatible with the chain running mechanism which suggests that bulky substituents can hinder the monomers from reaching the active catalytic centers due to their interaction with the axial coordination sites of the metal centers. The palladium catalysts showed no polymerization activity as distinguished behavior. That may attribute to the allyl functions attached to the backbone of the catalyst structures which can interact with the active sites of the palladium catalysts resulting in blocking the active sites and deactivating the catalyst. Five alpha-diimine complexes bearing allyl groups were coupled with a bridged zirconocene complex possessing a hydride silane moiety via hydrosilylation reaction in the presence of Karstedts catalyst to afford five new dinuclear precursors. These dinuclear precursors were activated with methylalumoxane (MAO) and tested for the polymerization of ethylene. The bridged silyl zirconocene moiety is the same for all these dinuclear complexes. Therefore, the ethylene polymerization activities of their catalysts showed a dependence on the variant metal centers of the á-diimine moiety. The trend of polymerization activities was: Ni > Pd > V > Zr > Ti. The produced polyethylenes were analyzed via gel permeation chromatography (GPC). The GPC results showed broad molecular weight distributions due to the dual sites of these catalysts. The GPC spectrum of polyethylene produced with the dinuclear catalyst 13 was discussed as an example and compared with the GPC spectrum of polyethylene produced with its mononuclear catalyst 6f. Six novel dinuclear precursors consisting of alpha-diimine moieties connected to half sandwich metallocene complexes were prepared and characterized via mass spectroscopy and elemental analysis. These dinuclear precursors were activated with methylalumoxane (MAO) and tested for the polymerization of ethylene. The ethylene polymerization activities of these dinuclear catalysts demonstrated a dependence on the size of the ortho substituents at the aryl rings of the catalysts structures. The results of ethylene polymerization agreed with the chain running mechanism: the bulkier the substituents the lower the polymerization activities. The results of gel permeation chromatography (GPC) of polyethylene produced by these catalysts exhibited bimodal molecular weight distributions. These results can be assigned to the different active sites of the dinuclear catalysts. The GPC spectra of polyethylenes produced with the dinuclear catalysts 18a,b were discussed as examples.
Synthesis of Mononuclear Transition Metal Complexes and their Applications as Catalysts for Ethylene Polymerization
- The synthesis of titanium, zirconium and vanadium complexes with bis(benzimidazole)s, bis(benzothiazole)s and bis(benzoxazole)s is a main objective of this study. Their catalytic performance towards ethylene polymerization reactions was also studied. The ligand systems mentioned above were synthesized via condensation reactions using polyphosphoric acid which acts as solvent, oxidizing and dehydration agent. The condensation reactions proceeded readily to produce high yield products. Bis(benzimidazole)s can also be prepared by refluxing the reactant in 4 N hydrochloric acid for ten hours or longer. The organic compounds mentioned above, when reacted with the tetrahydrofuran adducts of titanium and zirconium tetrachloride, are capable to produce 1:1 complexes via ligand displacement in very good yields. The vanadium complexes were prepared using the vanadium trichloride salt in diethylether. Secondly, titanium, zirconium and vanadium complexes derived from 2-(benzimidazolyl)pyridine, 2-(benzothiazolyl)pyridine and 2-(benzoxazolyl)pyridine were prepared and used as olefin polymerization catalysts upon activation with MAO. The potential ligand precursors were obtained in high yields and very good purity. The titanium, zirconium and vanadium complexes were synthesized as described earlier. The synthesis of titanium, zirconium and vanadium complexes with N-allyl substituted benzimidazoles was one of the study goals. These complexes were tested for ethylene polymerization reactions. Their ability of self immobilization was also investigated. The ligands were synthesized by the reaction of allylbromide with benzimidazole in the presence of potassium carbonate and DMF as a solvent. The titanium, zirconium and vanadium complexes were synthesized as described earlier. The titanium, zirconium and vanadium complexes after activation with methylaluminoxane (MAO) were used for the homogeneous polymerization of ethylene. They showed good to moderate catalytic activities towards ethylene polymerization reactions. The vanadium complexes showed the highest activities, followed by titanium complexes, while zirconium complexes showed the lowest activities. The catalytic activities seem to depend on several factors but the substitution patterns and types played significant roles in addition to the ligand structures and the natures of the metal ions. It was observed that both electron withdrawing and electron releasing groups meta to the imino nitrogen atom reduced the activities compared to the unsubstituted complexes. However, complexes with electron releasing groups showed higher activities compared to those with electron withdrawing groups. The nature of the hetero atoms (N, O and S) also influenced the catalytic activities of the complexes. The introduction of one allyl substituent in 2-(benzimidazolyl)pyridine complexes increased the activities of the complexes compared to unsubstituted ones. However, the activity of the vanadium complex was increased by a factor of 20. The introduction of two allyl substituents in 1,2-bis(benzimidazole) complexes lowered the activities compared to the unsubstituted complexes and to those with only one allyl group. The polyethylenes produced by the above mentioned complexes as catalysts were in most cases of higher molecular weights (> 1000000g/mol) associated with broad and/or bimodal molecular weight distributions. The bimodality was thought to arise from the presence of more than one isomer (diastereomer) for each complex in addition to the different active centres resulting from different kinds of interactions with the cocatalyst MAO.
Synthesis of Bridged and Unbridged Group (lV) Metallocene Complexes as Catalyst Precursors for Ethylene Polymerization
Mohamed Elnaiem Mohamed Abdelbagi
- The aim of this project was the synthesis and characterization of novel bridged and unbridged bis(indenyl) complexes of group IV metals including a study of their catalytic performance in the homogeneous polymerization of ethylene. To accomplish this goal, various ligand precursors were prepared which include 1- and 2-substituted silylindenyl compounds, 1,2-bis(inden-1-yldimethylsilyl)benzene, 2,2’-bis(inden-1-ylmethyl)-1,1’-biphenyl and 9-substituted silylfluorenes. The corresponding dichloride complexes of group IV metals were synthesized and used as catalyst precursors in ethylene polymerization reactions. The first part of this work deals with the synthesis of symmetrical unbridged complexes of zirconium and hafnium derived from 1- and 2-substituted silylindenes and the investigation of their potential in ethylene polymerization reactions. The 1-substituted silyindenyl compounds were obtained by the reactions of chlorosilanes and indenyllithium. The 2-substituted silylindenyl ligand precursors were obtained by a Grignard coupling reaction of aryldimethylchlorosilanes and 2-bromoindene. The corresponding dichloride complexes were synthesized by deprotonation of the substituted indenyl compounds with n-butyllithium and subsequent reactions with zirconium or hafnium tetrachloride in diethyl ether. Applying MAO as a co-catalyst, the synthesized complexes were used in the polymerization of ethylene and the dependence of the activity on the substitution pattern was studied. Among the 1-substituted metallocene catalysts 13-18, catalyst 17 bearing a fluoro atom at the para position of the silyl phenyl group showed the highest activity (4470 kg PE/mol cat. h) while catalyst 16 bearing a methoxy group at the same position was the least active (50 kg PE/mol cat. h). A similar trend was observed for the 2-substituted catalysts (19-24). In general, the 1-substituted catalysts were much more active than the 2-substituted counterparts. The obtained polymers were analyzed by differential scanning calorimetry (DSC) and viscosimetry. The second part describes the synthesis and characterization of a new class of ansa bis(indenyl) complexes of zirconium and hafnium in which the two indenyl moieties are linked at the 1-,1’-positions via a 1,2-bis(dimethylsilyl)-benzene unit. The ligand precursor was prepared via three reaction steps including Grignard coupling of chlorodimethylsilane and 1,2-dibromobenzene, PdCl2-catalyzed chlorination, and the reaction with indenyllithium. The corresponding zirconium and hafnium complexes were obtained by deprotonation of the corresponding bis-(indenyl) compound with n-BuLi followed by metalation reactions of MCl4 (M = Zr, Hf) in THF. The solid state molecular structures of both complexes were established by single crystal X-ray diffraction analyses. In ethylene polymerization reactions, both complexes exhibited high activities. The zirconocene catalyst 34 showed a higher activity (7610 kg PE/mol cat. h) compared to the hafnium catalyst 35 (3590 kg PE/mol cat. h). A second type of ansa-metallocene complexes was synthesized and tested in the homogeneous polymerization of ethylene. The ligand system comprises two indenyl moieties tethered at 3,3’-positions via a 2,2’-dimethyl biphenyl bridge. The ligand precursor was obtained by the reduction of diphenic acid using lithium aluminum hydride (LiAlH4), the reaction with phosphorus tribromide, and, finally, the reaction with indenyllithium. The corresponding group (IV) metal complexes were synthesized by deprotonation of the ligand precursors using n-BuLi followed by reactions of the corresponding metal tetrachloride. The series of the unsubstituted ansa-complexes (R = H) showed higher activities compared to the methyl substituted counterparts. The zirconium complex 42 showed the highest activity (12460 kg PE/mol cat. h) followed by the hafnium complex 43 (3820 kg PE/mol cat. h) while the titanium complex 40 was inactive which could be attributed to thermal instability and a tendency to decomposition. The introduction of methyl groups at the 1-position of the indenyl moieties leads to a remarkable decrease in the activity probably due to steric hindrance resulting from the two methyl groups. The obtained polyethylenes were analyzed by differential scanning calorimetry (DSC) and viscosimetry. A series of symmetric unbridged 9-substituted dimethyl(tolyl)silyl-fluorenyl complexes of zirconium and hafnium was synthesized, characterized and tested in catalytic ethylene polymerization reactions. These complexes were inactive in the MAO assisted polymerization of ethylene. This could be referred to their instability towards ring-slippage reactions changing the hapticity (η5→ η3→ η1) of the fluorenyl rings.
Highly Efficient Catalysts for the Dimerization of α-Olefins
- The aim of my work was the catalytic dimerization of a-olefins, especially the dimerization of propylene. The focus was laid on the optimization of product selectivity, catalyst lifetime, and product separation. Previous studies in our group have shown the enormous potential of bis(imino)pyridin vanadium(III) complexes as catalysts for the oligomerization and dimerization of ethylene after activation with MAO. A series of new and literature known complexes was synthesized and tested for the homogeneous catalytic dimerization of propylene after activation with MAO. High selectivities towards dimeric products and within the hexene isomers were observed. The evaluation of the dimerization reactions showed a remarkable influence of the substitution pattern at the ligand framework on the product distribution. Steric demanding substituents at the ortho positions of the iminophenyl ring had positive effects on the dimer yield. The influence of triphenylphosphine as an additive was investigated and strong dependencies could be observed. Addition of triphenylphosphine had no effect on the dimer / oligomers ratio but resulted in the formation of mainly 4-methyl-1-pentene instead of 2-methyl-1-pentene (without additive). Because of the moderate activities of 95–215 10e3 g(dimer)/mol h of the vanadium catalysts, the optimization of the catalytic activity was studied with a phosphine chelated nickel system in the presence of EtAlCl2. Very high activities of up to 52•10e6 g(dimer)/mol•h were observed with an activation ratio of 1:1000 (Ni:Al). These results are comparable to the most active literature known systems. Applying this activation ratio, catalyst life time experiments were performed. Even after seven repetitions of the dimerization experiments, the catalysts showed high activities of up to 87 % of the starting activity. Higher activation ratios resulted in higher selectivities of dimeric products (94 %) but lower activities. After the heterogenization of the catalysts, the amounts of dimeric products were constantly 100%. Under homogeneous and heterogeneous reaction conditions, the same product distributions within the dimer fractions were observed. The use of a fixed bed reactor changed the contact times of the reactants and the catalyst and consequently prevented the formation of higher oligomers and determined the product selectivities. The facile product separation of a heterogeneous system is a great advantage in contrast to the homogeneous system. The simplification of the product separation was the idea for the design of a series of catalysts for the dimerization of propylene. Nickel complexes with phenoxyimine or bisimine ligands were substituted with functional groups for a subsequent covalent linkage with a core shell support material. This silica functionalized magnetic iron core can be separated from the reaction solution by a strong magnetic field. The nickel complexes showed comparable high selectivities and activities for the dimerization of propylene after activation with MAO both under “free” and supported conditions in a closed system. Under both settings, the same products were formed. The described complexes can be used in open or closed systems and offer a high potential for a number of applications. The last chapter of this thesis deals with a very selective system for the dimerization of α-olefins C3-C6 and cis-butene. The special shape of the ligand allows various coordination states for the central metal. The early and late transition metals titanium, cobalt and nickel were combined in different ratios with the potential ligand and tested in dimerization reactions after activation with MAO. While nickel complexes provided the highest activities for the short chain olefins propylene and 1-butene, titanium complexes were more active for the higher olefins 1-pentene and 1-hexene. A change of the activation ratio from 1:500 to 1:1000 raised the activities in all cases. Nickel containing complexes showed high selectivities of even 100% for dimeric products. Titanium and cobalt complexes were selective as well, but did not reach the values of the nickel system.