Doctor of Philosophy

dissertationA series of 1,3-disubstituted-2-imidazolium carboxylates, an adduct of CO2 and N-heterocyclic carbenes, was synthesized and characterized using single crystal X-ray, thermogravimetric, IR, and NMR analysis. The TGA analysis of the imidazolium carboxylates shows that as steric bulk on the N-substituent increases, the ability of the NHC-CO2 to decarboxylate increases. Single crystal X-ray analysis shows that the torsional angle of the carboxylate group and the C-CO2 bond length with respect to the imidazolium ring is dependent on the steric bulk of the N-substituent. Rotamers in the unit cell of a single crystal of ItBuPrCO2 (2f) indicate that the C-CO2 bond length increases as the N-substituents rotate toward the carboxylate moiety, which suggests that rotation of the N-substituents through the plane of the C-CO2 bond may be involved in the bond breaking event to release CO2. Combination of N,N-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO2) with the Lewis acids MBPh4, where M=Li or Na, provided two separate complexes, a monomer and dimer, respectively. Combination of N,N-bis(2,4,6- trimethyllphenyl)imidazolum-2-carboxylate (IMesCO2) with LiBPh4 afforded a dimeric species that was similar in global structure to that of the IPrCO2+NaBPh4 dimer. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC·CO2. Kinetic analysis of the transcarboxylation of IPrCO2 to acetophenone with NaBPh4 to yield sodium benzoylacetate was performed. First order dependencies were observed for IPrCO2 and acetophenone while zero order dependence was observed for NaBPh4. Direct dicarboxylation of MeCN was observed after combination with ItBuCO2 in the absence of salts. An imidazolium salt, 1-2,4,6-trimethylphenyl-3-lactamidebenzylimidazolium tosylate was synthesized and characterized by 1H NMR, 13C NMR, and single crystal xray analysis. The downfield shift of the amide protons in the 1H NMR spectrum salt relative to the starting material lactamide-OTs indicate that hydrogen bonding was present in solution. The crystal structure of imidazolium tosylate showed a series of intermolecular hydrogen bonds between amide groups and tosylate anions. The amount of hydrogen bonding present in the carbene precursor is promising for attempts to observe intramolecular hydrogen bonding with a carbene and the carboxylate

Selective and catalytic carbon dioxide and heteroallene activation mediated by cerium N-heterocyclic carbene complexes

We thank the EPSRC for funding through the Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT, EP/L016419/1, R. W. F. K.), EP/J018139/1 and the UK Catalysis Hub (EP/K014714/1, P. L. A., C. W.), EP/M010554/1 (P. L. A.). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 740311, P. L. A.). K. W. thanks the China Scholarship Council (CSC) for a postgraduate fellowship. P. L. A., M. W. M., J. R. and F. E. K. thank the Technische Universität München – Institute for Advanced Study, funded by the German Excellence Initiative. A. D. S. thanks the Royal Society for a Wolfson Research Merit Award. C. J. thanks the DAAD for a scholarship, and C. J. and J. R. thank the TUM Graduate School for financial support.A series of rare earth complexes of the form Ln(LR)3 supported by bidentate ortho-aryloxide–NHC ligands are reported (LR = 2-O-3,5-tBu2-C6H2(1-C{N(CH)2N(R)})); R = iPr, tBu, Mes; Ln = Ce, Sm, Eu). The cerium complexes cleanly and quantitatively insert carbon dioxide exclusively into all three cerium carbene bonds, forming Ce(LR·CO2)3. The insertion is reversible only for the mesityl-substituted complex Ce(LMes)3. Analysis of the capacity of Ce(LR)3 to insert a range of heteroallenes that are isoelectronic with CO2 reveals the solvent and ligand size dependence of the selectivity. This is important because only the complexes capable of reversible CO2-insertion are competent catalysts for catalytic conversions of CO2. Preliminary studies show that only Ce(LMes·CO2)3 catalyses the formation of propylene carbonate from propylene oxide under 1 atm of CO2 pressure. The mono-ligand complexes can be isolated from reactions using LiCe(NiPr2)4 as a starting material; LiBr adducts [Ce(LR)(NiPr2)Br·LiBr(THF)]2 (R = Me, iPr) are reported, along with a hexanuclear N-heterocyclic dicarbene [Li2Ce3(OArCMe–H)3(NiPr2)5(THF)2]2 by-product. The analogous para-aryloxide–NHC proligand (p-LMes = 4-O-2,6-tBu2-C6H2(1-C{N(CH)2NMes}))) has been made for comparison, but the rare earth tris-ligand complexes Ln(p-LMes)3(THF)2 (Ln = Y, Ce) are too reactive for straightforward Lewis pair separated chemistry to be usefully carried out.Publisher PDFPeer reviewe

Quattrocento Female Portraiture: A Study of Literary, Cultural, and Artistic Relationships

155 pages"Quattrocento Female Portraiture: A Study of Literary, Cultural, and Artistic Relationships," is an analysis of the unique visual nature of female portraiture in fifteenth-century Italy. Although rarely commented on in modern scholarship, depictions of men and women during this period had differing rates of evolution and divergent stylistic characteristics. The distinctions between male and female portraits can be interpreted by investigating not only the early visual precedents, but also the literary ideals of women that pervaded Italian society, the examples of womanly perfection established in Catholic doctrine, and the special social roles that upper-class women fulfilled. The inter action of cultural ideals created a complex feminine image; a conflation of these ideals is revealed in the portraiture. The necessity of an image which conveyed this desirable information about a woman was determined by the transitional character of Quattrocento society

Trapping CO2 by Adduct Formation with Nitrogen Heterocyclic Carbenes (NHCs): A Theoretical Study

Carbon dioxide can form compounds with nitrogen heterocyclic carbenes (NHCs) based on azoles through noncovalent interactions or by covalent bonding. A narrow dependence on the carbene structure has been observed for the preference for one or the other type of bonding, as revealed by a series of physicochemical descriptors. In our survey, a set of NHCs based on the azole family (three classical, three abnormal, and one remote) was shown to bind CO at the accurate G4MP2 computational level. In most cases, exothermic reaction profiles towards the covalently bound form were found, which reached stabilization enthalpies of up to −77 kJ mol for the remote carbene case. Both noncovalent and covalent minima and the corresponding transition state that connects them have been identified as stationary points along the reaction coordinate.This work was carried out with financial support from the Ministerio de Econom&a y Competitividad (project no. CTQ2015- 63997-C2-2-P) and the Comunidad Autjnoma de Madrid (project FOTOCARBON, ref. S2013/MIT-2841). Computer, storage, and other resources from the CTI (CSIC) are gratefully acknowledged. M.M.M.-C. also thanks Project FOTOCARBON for her research contract.Peer Reviewe