Substituent effects in eta5-cyclopentadienyl (Cp) transition metal complexes have been intensely studied since the discovery of the first such complex, ferrocene. Modifications of the Cp ligand framework effect changes in the physical properties and chemical reactivity of the coordinated transition metal. This concept is useful when applied to catalysis mediated by Cp complexes, because the performance of the catalyst can be markedly improved using well-chosen ligand substituents. Studies of electronic substituent effects ideally employ a wide range of electron-donating and electron-withdrawing groups. Unfortunately, most of the available electron-withdrawing groups suffer from problems with Cp ligand synthesis, Cp anion stability, and electron-withdrawing group stability under catalytic conditions. This dissertation shows that the pentafluorophenyl (C6F5) substituent is highly electron-withdrawing but avoids all of these problems. Several new C6F5-substituted cyclopentadienes are prepared by the reaction of sodium cyclopentadienide and hexafluorobenzene (C6F6) under varying conditions. Corresponding C6F5-substituted cyclopentadienyl ligands (sodium salts) are obtained upon deprotonating the dienes with NaH. Complexes of Mn(I), Re(I), Fe(II), Co(II), Zr(IV) are synthesized by reacting these ligands with transition metal halides. The acidities of several C6F5- and C5F4N-substituted cyclopentadienes and indenes are measured using 19F NMR spectroscopy. The electron-withdrawing fluorinated aryl groups have a substantial acidifying effect. The identity and number of substituents (C6F5, C5F4N, CH3, and t-Bu), the position of the substituents on the cyclopentadiene, and the intramolecular (vicinal) steric effects also influence acidity. The electron-withdrawing ability of the C6F5 group is also characterized by infrared spectroscopic analysis of substituted CpM(CO)3 (M = Mn(I) and Re(I)) and electrochemical analysis of substituted ferrocenes. X-ray crystal structures of several C6F5-substituted Cp complexes reveal interesting structural motifs, including pi-stacking of the C6F5 substituents, Cp-M bond elongation, and CO-C6F5 interactions. In addition, dynamic Cp-C6F5 and Cp-M rotational barriers are measured by variable temperature NMR spectroscopy. Finally, ethylene polymerizations and ethylene/1-hexene copolymerizations are conducted using C6F5- and C6H5-substituted zirconocene dichlorides as catalysts. Contrary to findings published elsewhere, this study shows that substituent electronic effects induce substantial changes in comonomer incorporation. / Ph. D.

This dissertation explores fundamental aspects of the reaction of group 4 metallocenes with methylaluminoxane (MAO) that lead to active Ziegler-Natta olefin polymerization catalysts. A novel experimental approach is described, in which a unique spectroscopic probe (a fluorinated substituent) is attached to the metallocene ancillary ligands and the metallocene/MAO mixtures are analyzed using 19F NMR spectroscopy. Group 4 metallocene dimethides bearing pentafluorophenyl (C6F5) substituents were synthesized and treated with MAO in benzene-d6. 19F NMR spectroscopic analysis demonstrated reversible methide transfer to form "cation-like" methylmetallocenium methylaluminates. A series of quantitative titration studies showed that fewer than 10% of the aluminum centers in MAO actually participate in the methide transfer process. A systematic study of metallocene substituent effects suggested that MAO contains active centers of extremely high but varying Lewis acidity. Activation of group 4 metallocene dichlorides using MAO was also analyzed using 19F NMR. Initial Cl/CH3 exchange was followed by Cl transfer to aluminum, whereas "normal" subsequent transfer of CH3 from Al to the methylmetallocenium cation was apparently inhibited by the abstracted chloride. Additional studies showed that the 19F NMR probe is sensitive to the interactions of Zr-Cl bonds with simple alkylaluminum species such as Me3Al, Me2AlCl, MeAlCl2, and Et3Al. However, the method was arguably less useful than 1H NMR spectroscopy in following the metathesis of Zr-Cl and Al-R (R = Me, Et) bonds. New methods of preparing methylhalometallocenes were investigated. The reactions of eleven metallocene dimethyls with triphenylmethyl chloride were highly selective (> 95%) with the five most electron-deficient metallocenes studied. Two other examples showed good selectivity on an NMR scale but could not be isolated from the 1,1,1-triphenylethane byproduct. Reactions of dimethylmetallocenes with benzyl bromide were also selective for formation of the corresponding methylbromo-metallocenes, however the reactions were too slow to be of practical value. The observation of long initation periods and the analysis of organic byproduct distributions suggested that these halogenation reactions may proceed by a radical chain mechanism rather than simple sigma bond metathesis. To demonstrate "proof of concept" in the use of 19F NMR to analyze the reactions of paramagnetic metallocenes, the coordination of CO and CN- to C6F5-substituted chromocenes were analyzed. Whereas CO coordinates readily to chromocene, cyanide coordinates effectively to 1,1'-bis(pentafluorophenyl)chromocene. This observation is interpreted in terms of the electron-withdrawing effect of the C6F5 substituent, which should strengthen bonding to sigma-donor ligands (CN-) and weaken bonding to pi-acceptors (CO). / Ph. D.

The thesis entitled ‘Studies on the Chemistry of Carbonates and Carbamates’ comprises of seven chapters. Chapter 1 The reactivity of propargyloxycarbonyl (Poc) derivatives of amines and alcohols with various sulphur nucleophiles is addressed in this chapter. The chapter is divided into three different parts. Part 1: The difference in reactivity of propargyloxycarbonyl (Poc) derivatives of amines and alcohols with benzyltriethylammonium tetrathiomolybdate [(PhCH2NEt3)2MoS4, 1] is studied in detail and the results are discussed. It has been shown that amino alcohols can be protected as their diPoc derivatives using 2 equiv of propargyloxycarbonyl chloride (2). The selective deprotection of the O-Poc group using 1 equiv of 1 without affecting the N-Poc group is achieved (Scheme 1). Scheme 1 Part 2: The reactivity of propargyloxycarbonyl derivatives of various alcohols, phenols and primary and secondary amines with benzyltriethylammonium tetrathiomolybdate (1) is compared with the reactivity of these Poc derivatives with other sulphur nucleophiles such as sodium thiophenoxide, lithium sulphide, hydrogen sulphide and ammonium sulphide. The study reveals that tetrathiomolybdate (1) is the best sulphur nucleophile for the deprotection of Poc group. Poc derivatives of primary amines cyclized to the corresponding 4-methylene-2-oxazolidinones when treated with other sulphur nucleophiles (Scheme 2). Scheme 2 Part 3: The reaction between different propargyloxycarbonyl derivatives of alcohols and benzyltriethylammonium tetrathiomolybdate (1) is studied. It is found that propargyloxycarbonyl derivatives can be made more reactive towards tetrathiomolybdate by substituting the propargyl system with electron withdrawing substituents. Chapter 2 The application of propargyloxycarbonyl group for the protection of the side chain hydroxyl groups of serine, threonine and tyrosine is discussed. The O-Poc derivatives are shown to be stable to a variety of acidic and basic conditions and the applications of these derivatives in solution phase peptide synthesis is addressed. The easy and effective deprotection of the O-Poc group provides a new strategy for the synthesis of peptides bearing the hydroxy amino acid residues: serine, threonine and tyrosine. Scheme 3 Chapter 3 Development of a novel C2-symmetric protecting group for amines and amino acids is described in this chapter. But-2-ynyl-1,4-bisoxycarbonyl chloride (BbcCl, 3) is synthesized from 1,4-dihydroxybut-2-yne and used as a reagent for protecting amines as biscarbamates (Scheme 4). These biscarbamates (Bbc derivatives) are deblocked using benzyltriethylammonium tetrathiomolybdate (1) to get the amines back. Scheme 4 The orthogonal stability of the Bbc group with Boc, Cbz and Fmoc groups is established. It is also shown that Bbc group can be deblocked to the corresponding amines using resin-bound tetrathiomolybdate. The application of Bbc protected amino acids in solution phase peptide synthesis is demonstrated (Scheme 5). Scheme 5 Chapter 4 The simultaneous protection and activation of amino acids using various pentafluorophenyl carbonates is described in two parts. Part 1: A very efficient and high yielding method for the simultaneous protection of the amino group and activation of carboxylic acid group using propargyl pentafluorophenyl carbonate (PocOPfp, 4) is discussed. Treating amino acids with 2 equiv of 4 protects the amino group as a propargyl carbamate and activates the carboxylic acid group as a pentafluorophenyl ester (Scheme 6). Scheme 6 Part 2: The generality of the methodology developed for the simultaneous protection and activation of amino acids using PocOPfp (4) is studied with five different pentafluorophenyl carbonates viz. AlocOPfp, CbzOPfp, BocOPfp, EocOPfp and TrocOPfp. The studies reveal that the effectiveness of the methodology depends on the nature of the pentafluorophenyl carbonates and on the nature of the amino acids. Sterically bulky pentafluorophenyl carbonates such as BocOPfp reacted slowly with amino acids while electron deficient pentafluorophenyl carbonates such as TrocOPfp reacted faster and gave the N-protected active esters in very good yields. Amino acids bearing longer aliphatic side chains reacted better than the other amino acids. Chapter 5 The chapter describes results of the detailed studies on the base catalyzed cyclization of N-alkyl and N-aryl-O-propargyl carbamates to the corresponding 4-alkylidene-2-oxazolidinones. The effect of various bases and solvents on these cyclization reactions is studied systematically to design the most suitable conditions. The best results were obtained using catalytic amount of LiOH in DMF. The cyclization reactions of N-aryl-O-propargyl carbamates were faster than the cyclization of N-alkyl-O-propargyl carbamates. The effect of substitutions on the propargyl group in these reactions is studied by preparing various substituted propargyl carbamate derivatives from the corresponding amines and propargyl chloroformates (Scheme 7). Scheme 7 Chapter 6 An efficient procedure for the synthesis of dehydroalanine and dehydroamino butyric acid derivatives from the preformed carbonate derivatives of serine and threonine respectively, by treating with K2CO3 in DMF is discussed in this chapter. The reaction proceeds stereoselectively through a trans E2-elimination pathway to give only the Z-isomer of dehydroamino butyric acid derivatives from the carbonate derivatives of threonine. The methodology offers an easy access to dehydropeptides and proceeds without racemization of other stereogenic centers present in the peptide (Scheme 8). Scheme 8 Chapter 7 This chapter describes the use of propargyloxycarbonyl derivatives of lysine as an efficient tool for the synthesis of peptide conjugates using a click chemistry approach. The Cu(I) catalyzed cycloaddition reaction between azides and alkynes is employed in the synthesis of conjugates of lysine. Peptides bearing an Nε-Poc Lysine residue can be synthesized using traditional strategies and these peptides can be easily conjugated with azide derivatives of sugars and amino acids (Scheme 9). Scheme 9 The efficiency of the method is demonstrated by carrying out more than one click reaction in one pot using di and tri-propargyl derivatives of lysine. A dendritic core (6) is prepared from a tri-propargyl derivative (5) of lysine and an azide derived from leucine (Scheme 10). Scheme 10 The abbreviations used in the thesis are consistent with those reported in J. Org. Chem. 2007, 71, 23A. Less common abbreviations are defined, the first time they are mentioned in the thesis.

No description available.

As reações de metatese assim como o desenvolvimento de complexos metal-carbeno (W, Mo, Ru) se tornaram amplamente conhecidos na química graças aos avanços que trouxeram. Na química orgânica, possibilitou a síntese de macrocíclos por meio da RCM e na química de polímeros a ROMP permitiu um alto grau de controle da polimerização além da alta reatividade dos catalisadores. Isso fez desta reação uma poderosa ferramenta no desenvolvimento de novos materias. A tentativa de combinar a processabilidade dos polímeros com as propriedades luminescentes de determinandos compostos tem sido tema de muitas pesquisas.O objetivo deste trabalho é derivatizar compostos luminescentes , como o complexo metálico [Ru(bpy)3] (PF6)2e a porfirina tetrakis-(pentafluorfenil)porfirina (TPPF20), com o monômero norborneno (NBE) para obtenção de monômeros lumiscentes passíveis de serem polimerizados via ROMP. Aqui será apresentado e discutido a síntese e a caracterização desses compostos partindo-se dos reagentes: ácido-5-norborneno-2carboxílico; etilenodiamina e o ácido-2,2\'-bipiridina-4,4\'-dicarboxílico, cis-[RuCl2(bpy)2] e a porfirina TPPF20. Os compostos foram sintetizados com rendimentos superiores a 60%, com exceção da obtenção da porfirina, e caracterizados por RMN - 1H e 13C; FTIR; UV-vis. Os estudos de copolimerização entre NEN (norborneno-etilenodiamina-norborneno), NBE-TPPF e [Ru(bpy)2(NBbpy)](PF6)2 foram feitos usando o catalisador de Grubbs segunda gereação. Os polímeros gerados foram caracterizados usando TG-FTIR e RMN-1H, as massas moleculares não puderam ser calculadas por GPC porém os estudos indicam obtenção de baixo peso molelcular. O material obtido foi testado como sensibilizador em vidro condutor ITO, porém não houve adsorção do composto necessitam algumas modificações no metalomonômero. / The metathesis reactions as well as the development of metal-carbene complexes (W, Mo, Ru) became widely known in chemistry thanks to advancements brought. In organic chemistry, it enabled the synthesis of macrocycle by RCM. Useful for the synthesis of natural products. In polymer chemistry, ROMP, allow a high degree of polymerization control. This made the ROMP reaction a powerful tool in the development of new materials. In attempt to combine the processability of polymers with luminescent properties of such compounds has been the subject of several researchs. The aim of this work is to synthesize luminescent compounds based on [Ru(bpy)3] (PF6)2 metal complex and on the porphyrin tetrakis-(pentafluorphenyl)porphyrin (TPPF20), funcionalized with pendant norbornene monomer (NBE) to obtain lumiscentes monomers which can undergo ROMP polymerization. Here will be discussed the synthesis and characterization of these compounds using as starting materials: 5-norbornene-2-carboxylic acid; ethylenediamine; 2,2\'-bipyridine-4,4\'dicarboxylic acid, cis-[RuCl2(bpy)2] and the porphyrin TPPF20. The compounds were synthesized with yields higher than 60%, with the exception of the porphyrin, and characterized by 1H and 13C-NMR; FTIR; UV-vis. Copolymerization reaction between NEN (Norbornene-Ethylenediamine-Norbornene), NBE-TPPFe [Ru(bpy)2(NBbpy)] (PF6)2 were performed using Grubbs second generation catalyst. Resultinf polymers were characterized by TG-FTIR and 1H-NMR, molecular weight could not be measured by GPC, since polymers were insoluble, but studies indicate low molelcular weight. The material obtained was tested as sensitizer in conductive glass ITO. The polymer didn\'t adsorb in to the ITO surface. Some changes in the compound molecular structure are required to improve adsorption.

As reações de metatese assim como o desenvolvimento de complexos metal-carbeno (W, Mo, Ru) se tornaram amplamente conhecidos na química graças aos avanços que trouxeram. Na química orgânica, possibilitou a síntese de macrocíclos por meio da RCM e na química de polímeros a ROMP permitiu um alto grau de controle da polimerização além da alta reatividade dos catalisadores. Isso fez desta reação uma poderosa ferramenta no desenvolvimento de novos materias. A tentativa de combinar a processabilidade dos polímeros com as propriedades luminescentes de determinandos compostos tem sido tema de muitas pesquisas.O objetivo deste trabalho é derivatizar compostos luminescentes , como o complexo metálico [Ru(bpy)3] (PF6)2e a porfirina tetrakis-(pentafluorfenil)porfirina (TPPF20), com o monômero norborneno (NBE) para obtenção de monômeros lumiscentes passíveis de serem polimerizados via ROMP. Aqui será apresentado e discutido a síntese e a caracterização desses compostos partindo-se dos reagentes: ácido-5-norborneno-2carboxílico; etilenodiamina e o ácido-2,2\'-bipiridina-4,4\'-dicarboxílico, cis-[RuCl2(bpy)2] e a porfirina TPPF20. Os compostos foram sintetizados com rendimentos superiores a 60%, com exceção da obtenção da porfirina, e caracterizados por RMN - 1H e 13C; FTIR; UV-vis. Os estudos de copolimerização entre NEN (norborneno-etilenodiamina-norborneno), NBE-TPPF e [Ru(bpy)2(NBbpy)](PF6)2 foram feitos usando o catalisador de Grubbs segunda gereação. Os polímeros gerados foram caracterizados usando TG-FTIR e RMN-1H, as massas moleculares não puderam ser calculadas por GPC porém os estudos indicam obtenção de baixo peso molelcular. O material obtido foi testado como sensibilizador em vidro condutor ITO, porém não houve adsorção do composto necessitam algumas modificações no metalomonômero. / The metathesis reactions as well as the development of metal-carbene complexes (W, Mo, Ru) became widely known in chemistry thanks to advancements brought. In organic chemistry, it enabled the synthesis of macrocycle by RCM. Useful for the synthesis of natural products. In polymer chemistry, ROMP, allow a high degree of polymerization control. This made the ROMP reaction a powerful tool in the development of new materials. In attempt to combine the processability of polymers with luminescent properties of such compounds has been the subject of several researchs. The aim of this work is to synthesize luminescent compounds based on [Ru(bpy)3] (PF6)2 metal complex and on the porphyrin tetrakis-(pentafluorphenyl)porphyrin (TPPF20), funcionalized with pendant norbornene monomer (NBE) to obtain lumiscentes monomers which can undergo ROMP polymerization. Here will be discussed the synthesis and characterization of these compounds using as starting materials: 5-norbornene-2-carboxylic acid; ethylenediamine; 2,2\'-bipyridine-4,4\'dicarboxylic acid, cis-[RuCl2(bpy)2] and the porphyrin TPPF20. The compounds were synthesized with yields higher than 60%, with the exception of the porphyrin, and characterized by 1H and 13C-NMR; FTIR; UV-vis. Copolymerization reaction between NEN (Norbornene-Ethylenediamine-Norbornene), NBE-TPPFe [Ru(bpy)2(NBbpy)] (PF6)2 were performed using Grubbs second generation catalyst. Resultinf polymers were characterized by TG-FTIR and 1H-NMR, molecular weight could not be measured by GPC, since polymers were insoluble, but studies indicate low molelcular weight. The material obtained was tested as sensitizer in conductive glass ITO. The polymer didn\'t adsorb in to the ITO surface. Some changes in the compound molecular structure are required to improve adsorption.

New complex silicon-containing molecules were made by B(C6F5)3-catalyzed hydrosilation, dehydrocoupling, and dealkylative coupling reactions starting from Si-H reagents. The scope of reactions starting from disilane was expanded to include the formation of silicon-sulfur1, silicon-oxygen and silicon-alkyl side-chains. Reaction inhibition was found with some heteroatom substrates, such as phenols and imines, that strongly bound to B(C6F5)3, and was consistent with the proposed mechanism (Chapter 2). B(C6F5)3 was found to be selective for Si-H activation in reactions of disilane and no competing Si-Si bond cleavage side-reactions were observed. This result will guide future studies and application of B(C6F5)3-catalyzed reactions with polysilanes. A different type of selectivity, the competing B(C6F5)3-catalyzed over-reduction, is evaluated and discussed in Chapter 3. This over-reduction reaction was classified into two distinct cases: alkyl groups for which over-reduction reaction was dependent on the steric bulk of the alkyl group and benzylic groups for which over-reduction was dependent on having an alpha-aryl group. These reactions are consistent with the proposed Piers-Oestreich mechanism (see Chapter 3) and suggest the rate-determining step for over-reduction is the nucleophilic attack of the alkoxysilane (R -O-SiR3) to the R3Si•••H•••B(C6F5)3 complex. Benzylic side-chains were over-reduced regardless of the steric bulk of the aryl groups. Literature precedents suggest that benzyl over-reductions must undergo an alternative mechanism to the Piers-Oestreich mechanism. A number of mechanisms have been proposed in the literature and in Chapter 3, suggesting conventional heteroatom substrate borane or silane-borane complexation. Furthermore, over-reduction of benzylic sulfur containing side-chains was found and this reaction was exploited in the B(C6F5)3-catalyzed synthesis of unique silicon-sulfur silicon-containing products. These over-reduction reactions highlighted the role of the silane for over-reduction and the challenges associated with the post-polymerization modification of poly(phenylsilane). The advances in B(C6F5)3-catalyzed synthesis of small silane molecules suggested reaction conditions and gave spectroscopic benchmarks that were applied to the post polymerization modification of poly(phenylsilane) (Chapter 4). New X-modified poly(phenylsilane) derivatives with thiolato (sulfur), alkoxy/aryloxy (oxygen), amido (nitrogen) and alkyl(carbon) side-chains were prepared with 10-40% incorporation of the ‘X’ group into poly(phenylsilane). These new polysilanes were characterized by the following methods: 1H/13C/29Si NMR, IR, MALS-GPC, EA, and UV-vis absorption spectroscopy. Together, these characterization methods showed that the polysilane had not undergone Si-Si cleavage and thus demonstrated the utility of B(C6F5)3 for the selective activation of Si-H bonds. Thermal decomposition of X-modified poly(phenylsilane) derivatives and parent poly(phenylsilane) showed interesting redistribution pathways (Chapter 5). The thermal decomposition products of poly(phenylsilane) were identified: volatile monosilanes, a structurally complex not-yet-identified phenylsilicon-containing material generated at 500 °C, and a mixture of silicon carbide (SiC) and elemental carbon generated at 800 °C. The B(C6F5)3-catalyzed post-polymerization method (Chapter 4) was evaluated based on the substitution percentage for X-functionalized poly(phenylsilane) derivatives. Reactions of highly electron-donating substrates gave a low amount of X incorporation (10%, e.g. aryloxy side-chains derived from phenol). Aryloxy groups were alternatively introduced via demethanative coupling, which gave a polymer with a greater substitution percentage (25%). The overall impact of the H-to-X substitution reactions was gauged by UV-vis absorption spectra and desirable UV absorption properties would require the modified poly(phenylsilane) to have a high degree of substitution. / Graduate / 2017-09-02