Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004. / Vita. / Includes bibliographical references. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Semiconductor quantum dots (QDs) have tunable opto-electronic properties and can be chemically synthesized and manipulated with ease, making them a promising novel material for many diverse applications. An understanding of the physics of charge transport in QDs is not only important for realizing QD based electronic devices, but it also provides crucial insight into the chemical and optical properties of QDs. This thesis highlights how photoconductivity measurements are valuable to advancing our understanding of QD physics because they are exquisitely sensitive to the optical, chemical, and electronic properties of QDs. The work presented in this thesis emphasizes how the chemistry and physics of QD films are deeply entwined. Chapter 2 demonstrates that the photoconductivity and dark conductivity of CdSe QD films are enhanced following annealing at high temperatures. Chapter 3 illustrates that the purity of the QD capping reagent (tri-n-octylphosphine) and the methods used for film preparation can each affect the observed photocurrent by two to three orders of magnitude. In Chapter 4, the methods for CdSe film preparation developed in Chapter 3 are used to make films that exhibit photoconductivity properties consistent with having a low density of trapped charges, in contrast to previous studies. Chapter 5 also uses chemistry to bring CdSe QD films into a new regime of photoconductivity physics. Post-deposition chemical treatments that increase photocurrent by up to three to four orders of magnitude are presented. The voltage dependence of the photocurrent after treatment is consistent with having achieved unity exciton separation efficiency. Furthermore, by bringing CdSe QD films into this / (cont.) new regime of higher photoconductivity physics it is found that energetics prevent the facile injection of charges from gold electrodes into CdSe QDs, but there is no barrier to charge extraction. / by Mirna Jarosz. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004. / Vita. / Includes bibliographical references (leaves 149-162). / Major Histocompatibility Complex (MHC) proteins are heterodimeric membrane glycoproteins that bind antigens in the form of short peptides within the cell and present them to the T cell receptors on the surface T cells. In this thesis work, the structural aspects of the human class II MHC protein HLA-DR1 in complex with different peptides and also in the peptide-free form were investigated. Biochemical, crystallographic, and immunological analyses of an unusually long peptide antigen derived from HIV-gag (p24) and its interaction with HLA-DR1 and a HIV-specific CD4+ T cell clone were studied. The HIV-gag (p24) peptide binds in an unexpected conformation, with its C- terminal region making a hairpin turn that bends back over the groove. The residues at the C-terminus are critical for T-cell recognition, and disruption of the hairpin turn abrogates the immune response. The results suggest a new mode of MHC-peptide-TCR interaction. A set of viral peptide analogs designed to increase binding affinity for HLA-DR while maintaining antigenic interactions with a virus-specific T cell receptor were designed, tested and analyzed. Ultimately, a N-methyl substitution at position 7 is shown to increase binding affinity by displacement of one of three water molecules bound between the MHC and peptide. The results have implications for design of peptido-mimetic vaccines, and are discussed in the broad context of other attempts to increase protein-ligand interaction through displacement of tightly bound water molecules. The role for the P10 shelf in peptide binding site was investigated. Crystallographic studies confirm the formation of a P10 shelf that is lined with highly polymorphic residues. Biochemical studies were conducted / (cont.) on a series of peptides different at the P10 position on four HLA-DRl(P10) mutants showing that this shelf has some specificity and can be involved in the discrimination of peptides that bind to class II MHC proteins. Studies of the empty, peptide-free form of HLA-DR1 were conducted by NMR spectroscopy showing that the conformation of this empty form is not in a molten globule-like state and that in general is similar to that of the peptide-loaded form but with several differences. Preliminary characterization of the peptide-receptive and peptide-averse forms of the empty HLA-DR1 is described. / by Zarixia Zavala-Ruiz. / Ph.D.

Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Chapter 1: This chapter details mechanistic work regarding the reductive elimination of electron-rich aryl fluorides from L-Pd(Ar)F species. An unexpected dearomatization/arylation process of Pd(II) complexes bearing bulky biaryl phosphines was discovered, resulting in ligand arylation during the catalytic fluorination of aryl triflates. This process must occur prior to C-F reductive elimination. Further experimental studies of this rearrangement revealed that it likely proceeds via a concerted migratory insertion into the bottom ring of the ligand. Chapter 2: This chapter describes extensive work to understand the mechanism by which regioisomeric mixtures of products form during the Pd-catalyzed fluorination of electron-rich aryl triflates lacking ortho-substituents. Deuterium labeling experiments suggest that ortho-deprotonation of L-Pd(Ar)OTf intermediates by CsF competes with the transmetallation step of the desired catalytic process. Additional studies investigating the previously observed formation of regioisomeric products in the absence of CsF (Chapter 1) are also presented. Chapter 3: This chapter describes the key discovery that di-adamantyl ligands are superior to tBuBrettPhos for promoting the Pd-catalyzed fluorination of aryl triflates. While previously described 2-aminobiphenyl-based sulfonate precatalysts were ineffective, readily activated [(L-Pd) 2COD] (COD = cyclooctadiene) complexes proved to be general precatalysts for these reactions. Further structural and reactivity studies of this new family of precatalysts are presented. Chapter 4: The first general method for the Pd-catalyzed fluorination of aryl bromides and iodides is described using a combination of AgF and various additives, most commonly KF. Preliminary studies suggest that the additive is necessary to promote an otherwise difficult transmetallation step. In addition, the use of a "pre-modified" ligand, HGPhos, allows for the Pd-catalyzed fluorination of 6-membered nitrogen-containing heterocycles. An investigation of ligand structural effects on this reaction is also included. Chapter 5: An in-depth investigation of the Pd-catalyzed fluorination of 5-membered heteroaryl bromides is described. Preliminary crystallographic and computational evidence suggest that reductive elimination of 5-membered heteroaryl fluorides from Pd(II) is extremely difficult. Nonetheless, it was found that heteroaryl bromides bearing ortho-phenyl groups, as well as highly activated 2-bromoazoles, can be efficiently fluorinated using a catalyst based on the recently developed ligand AlPhos. / by Phillip J. Milner. / Ph. D. in Organic Chemistry

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 209-223). / In this thesis, I report on the design and construction of a new atomic and molecular beam source that exploits the unique capabilities of a buffer gas cooled ablation source. Buffer gas cooled atomic and molecular beams generate samples with > 1000 x more particles and 10x slower translational velocities than typical ablation seeded supersonic expansions. This increase in number density provides an ideal system for the observation of qualitatively new cooperative emission effects. I describe the detection of single-shot free space superradiance in a buffer gas cooled beam of barium atoms. The frequency of this emission is shifted and broadened by a factor of ~ 10⁶ x greater than the natural lifetime, indicating the presence of quantum many-body dipole-dipole effects in the cooperative emission. Additionally, the smaller lab-frame velocity reduces the Doppler broadening enough to allow for coherent manipulation of Rydberg states and a coherent coupling of an optical and millimeter-wave photon. I demonstrate this coherent coupling in an ensemble of barium atoms, and provide a theoretical description of how to provably perform complete STImulated Raman Adiabatic Passage (STIRAP). / by David Darrah Grimes. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011. / Vita. Cataloged from PDF version of thesis. / Includes bibliographical references. / Chapter 1. Geometric and Functional Versatility of Carboxylate-Bridged Nonheme- Diiron Motifs: sMMO and ToMO. Several metalloenzymes utilize a carboxylate-bridged non-heme diiron motif for dioxygen activation. Despite their conserved diiron active site structures and mechanisms of dioxygen activation, they catalyze a wide range of chemical transformations. These observations suggest that diiron-containing enzymes have distinct active sites and secondary/tertiary environments that are tuned for their dedicated biological functions. Detailed studies of two diiron-containing enzymes in the family of bacterial multicomponent monooxygenases (BMMs), soluble methane monooxygenase (sMMO) and toluene/o-xylene monooxygenase (ToMO), are described. The functions and structures of the three or four components of sMMO and ToMO are summarized. Distinctly different dioxygen activation chemistry and hydrocarbon specificity is observed for these two enzymes. A comparison of these two enzymes provides insight into the evolution of diironcontaining enzymes as well as their differing chemical mechanisms of catalysis. Chapter 2. Role of an Active Site Threonine in the Determination of Distinctive Dioxygen Reactivity in Toluene/o-Xylene Monooxygenase Hydroxylase. Dioxygen activation of toluene/o-xylene monooxygenase hydroxylase (ToMOH) exhibits the formation of a diiron(III) intermediate having unprecedented spectroscopic properties. To evaluate whether an active site threonine plays a role in the determination of the dioxygen chemistry in ToMOH, a T201S variant was prepared by site-directed mutagenesis. We reported the observation of a novel intermediate in the reaction of reduced ToMOH T201 S variant with dioxygen in the presence of its cognate regulatory protein (ToMOD). This species, T201 peroxo, is the first oxygenated intermediate of any toluene monooxygenase to display an optical band. The optical and M6ssbauer spectroscopic properties of the intermediate allowed us to assign it as a peroxodiiron(III) species, similar to Hperoxo in soluble methane monooxygenase hydroxylase (sMMOH). This result indicates that mutation of the T201 to serine altered the dioxygen chemistry of ToMOH in part to be more similar to that of sMMOH. Computational studies suggest that the T201 mutation can greatly perturb the energetics of the enzyme, which might be responsible for the distinct dioxygen reactivity of sMMOH and ToMOH. Structures of the oxygenated intermediates of ToMOH are proposed. Chapter 3. Role of an Active Site Threonine in the Kinetics of Dioxygen Activation in Toluene/o-Xylene Monooxygenase Hydroxylase. To elucidate the role of a strictly conserved T201 residue during dioxygen activation of toluene/o-xylene monooxygenase hydroxylase (ToMOH), T201S, T201G, T201C, and T201V variants of this enzyme were prepared by site-directed mutagenesis. X-ray crystal structures of all variants were obtained. Steady-state activity, regiospecificity, and single-turnover yields were also determined for the T201 mutants. Dioxygen activation by the reduced T201 variants was monitored by stopped-flow UV-vis and M6ssbauer spectroscopy. These studies demonstrated that the same dioxygen activation mechanism is preserved in the T201S, T201C, and T201G variants; however, both formation and decay kinetics of a peroxodiiron(III) intermediate, T201peroxo, were greatly altered, revealing that the T201 residue is critically involved in dioxygen activation. Rate-limiting steps in dioxygen activation of the T201S, T201C, and T201G variants were identified, revealing that T201 plays a major role in proton transfer, which is required to generate the peroxodiiron(III) intermediate. The role of the active site threonine residue in ToMOH is analogous to that of cytochrome P450 monooxygenases, suggesting it as a general threonine-dependent process in Nature to control proton transfer. / (cont.) Chapter 4. Mechanistic Studies of Reactions of Peroxodiiron(III) Intermediates in the T201 Variants of Toluene/o-Xylene Monooxygenase Hydroxylase. Site-directed mutagenesis studies of a strictly conserved T201 residue in the active site of toluene/oxylene monooxygenase hydroxylase (ToMOH) revealed that a single mutation can facilitate kinetic isolation of two distinct peroxodiiron(III) species, designated T201peroxo and ToMOHperoxo, during dioxygen activation. In Chapter 2 and 3, we characterized both oxygenated intermediates by UV-vis and M6ssbauer spectroscopy, proposed structures from DFT and QM/MM computational studies, and elucidated chemical steps involved in dioxygen activation through the kinetic studies of T201peroxo formation. In Chapter 4, we investigated the kinetics of T2 0lperoxo decay to explore the reaction mechanism of the oxygenated intermediates following 02 activation. The decay rates of T201 peroxo were monitored in the absence and presence of external (phenol) or internal (tryptophan residue in I100W variant) substrates under pre-steady-state conditions. Three possible reaction models for the formation and decay of T201perX0 were evaluated, and the results demonstrate that this species is on the pathway of arene oxidation and appears to be in equilibrium with TOMOHperoxo. Chapter 5. Tracking a Defined Route of 0 2-Migration in a Dioxygen-Activating Diiron Enzyme, Toluene/o-Xylene Monooxygenase Hydroxylase. For numerous enzymes reactive toward small gaseous compounds, growing evidence indicates that these substrates diffuse into active site pockets through defined pathways in the protein matrix. Toluene/oxylene monooxygenase hydroxylase (ToMOH) is a dioxygen-activating carboxylatebridged nonheme-diiron enzyme. Structural analyses of the resting state enzyme suggest two possible pathways for dioxygen to access the c-subunit diiron center, a series of hydrophobic cavities or long solvent-exposed channel. To distinguish which pathway is utilized for dioxygen transfer, the dimensions of the cavities and channel were varied by site-directed mutagenesis and confirmed by X-ray crystallography. The rate of dioxygen access to the active site was monitored by measuring the formation rate of an oxygenated intermediate (T 2 01peroxo), a process that is dependent on 02 concentration. Altering the dimensions of the cavity but not the channel drastically changed the rate of dioxygen activation by the reduced enzyme. These results explicitly reveal that the cavities in the ToMOH a-subunit are not merely artifacts of protein packing/folding but rather programmed routes of dioxygen movement through the protein matrix. This conclusion indicates that conformational changes are required during catalysis to form a dioxygen trajectory and that the temporary opening/closing of the cavities control dioxygen transfer. Given that the cavities are present in all BMMs, the breathing motion presumably controls dioxygen consumption in all BMMs. This study represents the first approach to track kinetically a defined transient pathway by which a small gaseous molecule gains access to a diiron enzyme. / (cont.) Appendix A. Insights into the Different Dioxygen Activation Pathways of Methane and Toluene Monooxygenase Hydroxylases. The methane and toluene monooxygenase hydroxylases (MMOH and TMOH, respectively) have almost identical active sites, yet the physical and chemical properties of their oxygenated intermediates, designated P*, Hperoxo, Q and Q* in MMOH, and ToMOHperoxo in toluene/o-xylene monooxygenase hydroxylase (ToMOH), are substantially different. We review and compare the structural differences in the vicinity of the active sites of these enzymes and discuss the differences that give rise to the distinct behavior of dioxygen reactivity in sMMOH and ToMOH. In particular, analysis of multiple crystal structures reveals that T213 of MMOH and analogous T201 of TMOH, located in the immediate vicinity of the active site, have different rotamer configurations. We study the rotation energy profiles of these threonine residues with the use of molecular mechanics (MM) and quantum mechanics/molecular mechanics (QM/MM) computational methods and put forward a hypothesis according to whether T201 and T213 play an important role in the formation of different types of peroxodiiron(III) species in MMOH and ToMOH. The hypothesis is indirectly supported by QM/MM calculations of the peroxodiiron(III) models of ToMOH and the theoretically computed M6ssbauer spectra. It also helps explain the formation of two distinct peroxodiiron(III) species in the T201S mutant of ToMOH. Additionally, a role for the regulatory protein (ToMOD), which is essential for oxygenated intermediate formation and the protein functioning in the ToMO system, is advanced. Appendix B. Multiple Roles of Component Proteins in Bacterial Multicomponent Monooxygenases: Phenol Hydroxylase and Toluene/o-Xylene Monooxygenase from Pseudomonas sp. OX1. Phenol hydroxylase (PH) and toluene/o-xylene monooxygenase (ToMO) from Pseudomonas sp. OXI require three or four protein components to activate dioxygen for the oxidation of aromatic substrates at a carboxylate-bridged diiron center. In this study, we investigated the influence of the hydroxylases, regulatory proteins, and electron-transfer components of these systems on substrate consumption and product generation. Single-turnover experiments revealed that only complete systems containing all three or four protein components are capable of oxidizing phenol, a major substrate for both enzymes. Under ideal conditions, the hydroxylated product yield was -50% of the diiron centers for both systems, suggesting that these enzymes operate by half-sites reactivity mechanisms. Single-turnover studies indicated that the PH and ToMO electron-transfer components exert regulatory effects on substrate oxidation processes taking place at the hydroxylase active sites, most likely through allostery. Steady state NADH consumption assays showed that the regulatory proteins facilitate the electron-transfer step in the hydrocarbon oxidation cycle in the absence of phenol. Under these conditions, electron consumption is coupled to H20 2 formation in a hydroxylase-dependent manner. Mechanistic implications of these results are discussed. / by Woon Ju Song. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1999. / Includes bibliographical references. / by Benjamin E. Turk. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008. / Vita. / Includes bibliographical references. / New tools and probes are constantly being developed for chemical and biological sensing. As novel materials emerge, growing demand for sensing in specific applications can be addressed. One such class of materials is fluorescent inorganic semiconductor nanocrystals (NCs), popularly known as quantum dots. The unique, size-dependent properties of NCs are promising for biological microscopy applications in cancer research; however, obstacles such as biocompatibility and sensitivity must be overcome (Chapter I). This Thesis work addresses the challenge of converting the chemically inert NCs into a dynamic equilibrium-based sensor. A strategy of implementing fluorescence resonance energy transfer (FRET) as the signal transduction mechanism of a CdSe/ZnS NC-molecule donor-acceptor pair with a rhodamine-based acceptor dye is investigated. Energy transfer in NC-dye pairs is found to be efficient, with kFRET rates approaching 108 s-1 (Chapter II). A reversible and ratiometric NC pH sensor is synthesized by tethering NCs to a squaraine-based pH dye. The presence of an isosbestic point between the two emission maxima from the NC and the dye allows the sensor to be self-calibrating (Chapter III). The ratiometric nature of the NC-based sensor signifies potential for emission-based sensing in biological environments. Various NC surface modifications and coupling strategies using a physiologically relevant pH dye are compared to determine the characteristics needed to introduce NC based sensors into a biological environment (Chapter IV). NCs functionalized with poly(ethylene glycol) ligands (PEG) were deemed best suited to impart biocompatibility, and first generation PEGylated bio-applicable NC pH sensors were photophysically characterized under single and two-photon excitation and its stability evaluated (Chapter V). The PEGylated NC pH sensors were introduced into an in vivo tumor environment, and using multiphoton laser scanning microscopy (MPLSM), the sensors are able to ratiometrically report a change in pH induced by an external stimulus. Challenges such as calibration in in vivo experiments are currently being addressed (Chapter VI). / (cont.) New conjugation techniques with NCs are further explored with Click Chemistry (Chapter VII). The NC-molecule sensing developed during this Thesis work is general and may be applied towards sensing of other analytes in other applications, using a variety of NC materials (Chapter VIII). / by Rebecca C. Somers. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007. / Vita. / Includes bibliographical references. / Chapter 1. Suzuki-Miyaura coupling reactions of aryl and heteroaryl halides with aryl-, heteroaryl and vinyl boronic acids proceed in very good to excellent yield with the use of 2-(2',6'-dimethoxybiphenyl)-dicyclohexylphosphine, SPhos. Additionally, a comparison of the reactions with SPhos and with 2- (2',4',6'-triisoprc'pylbiphenyl)-diphenylphosphine is presented that is informative in determining the relative importance of ligand bulk and electron-donating ability in the high activity of catalysts derived from ligands of this type. Further, when the aryl bromide becomes too hindered, an interesting C-H bond functionalization-cross-coupling sequence intervenes to provide product in high yield. Chapter 2. The direct transformation of aryl bromides into the corresponding Weinreb amides via Pd-catalyzed aminocarbonylation at atmospheric pressure is described. Electron-deficient, -neutral and -rich aryl bromides were all efficiently transformed to product. Furthermore, the process tolerates a wide variety of functional groups, is mild, and is operationally simple. Chapter 3. A general, functional group tolerant, and mild system for the Pd-catalyzed Heck carbonylation of aryl chlorides into the corresponding benzamides has been developed. / (cont.) This catalyst operates at one atmosphere of carbon monoxide using an inexpensive, air-stable and commercially available ligand. A variety of aryl chlorides were all successfully transformed to the corresponding amides using primary, a-branched primary, cyclic secondary, acyclic secondary, or aryl amines. Additionally, the mechanism of this reaction was studied using in situ IR spectroscopy and revealed the unique effect of sodium phenoxide in this reaction. Chapter 4. Pressurized microreactor systems greatly expand the range of reaction conditions and accelerate gas-liquid mass transfer. Heck aminocarbonylation reactions exemplify the potential for quickly and safely scanning of reagents and reaction conditions (1 to 15 bar and 100 - 160'C). The results reveal a general trend of increased yield of amide with temperature and selectivity for a-ketoamide production at lower temperature: and higher pressure. / by Joseph R. Martinelli. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012. / Vita. Cataloged from PDF version of thesis. / Includes bibliographical references. / Chapter 1. A general introduction is given. Chapter 2. The biscarboxylate species, Mo(NR)(CHCMe 2Ph)(O 2CPh3)2 (R = 2,6-i-Pr2C6H3, 2,6- Me2C6H3, 2-t-BuC 6H4, or 1 -adamantyl) are compared to newly synthesized bis(terphenylcarboxylate) species, Mo(NR)(CHCMe 2Ph)(O 2CTer)2 (Ter = 2,6-diphenyl-4- methylphenyl or 2,6-diphenyl-4-methoxyphenyl). Preparation of bis(terphenylcarboxylate) species was accomplished through protonolysis of Mo(NR)(CHCMe2R')(Me2Pyr)2 with two equivalents of TerCO2H and one of them was characterized through X-ray crystallography. Photolysis experiments of many of the biscarboxylate complexes led to rate constants for the converstion of anti to syn species, which are much slower than bisalkoxide species. Trimethylphosphine adducts of selected triphenylacetate complexes have been isolated and studied in solution. Protonolysis of Mo(NAr)(CHCMe 2R')(Me 2Pyr)2 (Ar = 2,6-i-Pr 2C6H3) with one equivalent of TerCO2H led to the isolation of a handful of monocarboxylate species, Mo(NAr)(CHCMe 2Ph)(O 2CAr')(Me2Pyr). An X-ray structure of one of them was also characterized. Several of the bis(triphenylacetate) complexes and all of the monocarboxylates are active initiators for the regioselective polymerization of diethyl dipropargylmalonate (DEPDM). In the case of the latter compounds, activity towards olefins is also observed and briefly mentioned. / (cont.) Chapter 3. Monaryloxide pyrrolide (MAP) molybdenum imido alkylidene complexes of the type Mo(NArx)(CHCMe 2R)(Me2Pyr)(OR') (Me2Pyr = 2,5-dimethylpyrrolide) have been prepared in which NArx is an ortho-substituted phenylimido group (X = Cl (NArci), CF3 (NAr ), i-Pr (NAr"), t-Bu (NArtBu), mesityl (NArM), or TRIP (TRIP = triisopropylphenyl; NArT)) and OR' = O-2,3,5,6-(C 6H5)4C6H (OTPP), O-2,6-(2,4,6-Me 3C6H2)2C6H3 (OHMT), or O-2,6-(2,4,6-i- Pr 3C6H2 )2 C6 H3 (OHIPT). The object was to explore to what extent relatively "large" NArM or NArT ligands would alter the performance of MAP catalysts in reactions that have been proposed to depend upon the relative size of the imido and OR' groups. Preliminary studies employing the ring-opening metathesis polymerization of 5,6-dicarbomethoxynorbornadiene as a measure of selectivity suggest that a single ortho-substituent in the phenylimido group, even in an NArm or NArT group, does not produce any unique behavior and that the outcome of the ROMP reaction correlates with the overall relative size of the imido and OR' group. Single crystal X-ray structures of six species that contain the new NArM or NArT groups are reported. Chapter 4. Several bipyridine adducts of molybdenum imido alkylidene bispyrrolide complexes of the type Mo(NR)(CHCMe 2Ph)(Pyr)2(bipy) (9-15; R = 2,6-i-Pr2C6H3 (Ar), adamantyl (Ad), 2,6- Me2 C6H3 (Ar'), 2-ClC 6H4 (ArcI), 2-i-PrC6-14 (AriPr), 2-t-BuC 6H4 (ArtBu), 2-MesitylC 6H4 (Arm), respectively; have been prepared using three different methods. Up to three isomers of the adducts are observed that are proposed to be the trans and two possible cis pyrrolide isomers of syn alkylidenes. Sonication of a mixture containing 9-15, HMTOH (2,6-(2',4',6'- Me3C6H2 )2 C6H30H), and ZnCl2(dioxane) led to the formation of MAP species of the type Mo(NR)(CHCMe 2Ph)(Pyr)(OHMT) (16-22), which were isolated by filtration and purified by recrystallization. DCMNBD (2,3-dicarbomethoxynorbornadiene) is polymerized employing 16- 22 as initiators to yield >98% cis,syndiotactic poly(DCMNBD). Attempts to prepare bipy adducts of bisdimethylpyrrolide complexes led to the formation of imido alkylidyne complexes of the type Mo(NR)(CHCMe 2R')(Me2Pyr)(bipy) (Me2Pyr = 2,5-dimethylpyrrolide); 23-28) through a ligand-induced migration of an alkylidene a proton to a dimethylpyrrolide ligand. Xray structures of Mo(NAr)(CHCMe 2Ph)(Pyr) 2(bipy) (9), Mo(NAriP)(CHCMe 2Ph)(Pyr)(OHMT) (20), Mo(NAr)(CCMe 2Ph)(Me2Pyr)(bipy) (23), Mo(NAr')(CCMe 2Ph)(Me2Pyr)(bipy) (24), Mo(NArT)(CCMe 3)(Me 2Pyr)(bipy) (ArT = 2-(2',4',6'-i-Pr 3C6H2)C6H4, 28) showed structures with the expected characteristic bond lengths and angles. / (cont.) Chapter 5. The formation of Mo(NAr)(CHCMe2Ph)(OC(CF 3)2(CH 3))(O2CTerme) (Ar = 2,6-i-Pr2C6H3, O2CTerMe= 4,4'-dimethylterphenylcarboxylate, 1) from Mo(NR)(CHCMe2Ph)(OC(CF3)2(CH 3))2 via protonolys with TerMeCO2H, as well as formation of complexes of the general formula Mo(NR)(CHCMe2Ph)(OC(CF3)2(CH 3))(X) (R = 2,6-iPr2C6H3 (Ar), 2; 2,6-Me2C6H3 (Ar'), 3; 2- iPrC6H4 (Ar' ), 4; 1-adamantyl (Ad), 5; X = 2,2',4,4',6,6'-hexamethylterphenoxide (HMTO)) (2,6-Me2C6H3 (Ar'), 6, 2-iPrC6H4 (Ar'P'), 7; X = 2,2',4,4',6,6'-hexamethylterphenylamine (HMT(H)N)) (R = 1-adamantyl, X = 2,2',4,4',6,6'-hexamethylterphenyl (HMT), 8) via saltmetathesis of Mo(NR)(CHCMe 2Ph)(OC(CF 3)2(CH 3))2 with one equivalent of LiX is presented as an efficient synthetic route for the preparation of monoalkoxide monoanionic (MAX) complexes. The X-ray studies of 5, 7, and 8 show that complexes 5 and 8 have similar structures; whereas 7 differs considerably due to the overall spacial arrangement of the N(H)HMT in the complex, which is orthogonal to the arrangement of OHMT in 5 or HMT in 8. The distance of the terphenyl backbone is shown to be one Angstrom shorter for 8, in comparison to 5 and 7, which results in failed attempts to prepare Mo(NR)(CHCMe 2Ph)(OC(CF 3)2(CH 3))(HMT) complexes with bigger R groups. The catalytic reactivity complexes 1-8 is probed with diallyl ether (DAE), 1 -hexene, 1 -octene, and dicarbomethoxynorbornadiene (DCMNBD). For comparison, the same olefin-metathesis reactions are carried-out with the analogous monoanionic monopyrrolide (MXP) complexes of general formula Mo(NR)(CHCMe 2Ph)(Pyr)(X) (Pyr = C4H4N, 2,5- Me2C4H2N). Overall, the reactivity of MAX and MXP complexes differs least when cis or trans bond formation is involved, and differs most when tacticity is considered, showing that during catalysis the transition states may differ significantly between the two kinds of complexes. Appendix The preparation of pure (R)-Mo(NAr)(CHCMe 2Ph)(Me2Pyr)(OR*) (Ar = 2,6-iPr2C6H3, R*O (1S,2S,4R)-2-(4-ClC 6H4)-1,7,7-Me 3-bicyclo[2.2.1]heptan-2-oxide), Me2Pyr = 2,5-Me2C4H2N, 1) and Mo(NAd)(CHCMe 2Ph)(OR*)2 (Ad = 1-adamantyl, R*O = 3,3'-Br2-2'-(OSi(Me2)2(t-Bu))- 5,5',6,6',7,7',8,8'-H-[1,1'-binaphthalen]-2-oxide, 21) are discussed. X-ray studies of both complexes are also presented. The polymerization of diethyl dipropargylmalonate (DEPDM) is probed with a variety of monoalkoxidemonopyrrolide (MAP) complexes, including 1, that either contain PMe3 bound to the metal center or not. In addition, a variety of bisalkoxide/bisphenoxide complexes, among them 21, are also used to polymerize DEPDM. / by Alejandro G. Lichtscheidl / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1997. / Includes bibliographical references. / by David Gosalvez-Blanco. / Ph.D.