Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007. / Includes bibliographical references (leaves 30-33). / We present ab initio molecular calculations at different levels of density functional theory (DFT) for the spiro-biphenalenyl neurtral radical in its singlet and triplet states. We performed calculations on the dimer to study its conductivity by investigating the ground state energy, HOMO-LUMO gap, charge localization, and reorganization energies, as these are the main contributing factors to crystal conduction. We find that there is only a slight difference between the singlet state and triplet state HOMO-LUMO gaps. In addition, the negative charge spreads throughout both the interior and exterior units of the molecule in both the singlet state and the triplet state, this is in disagreement with the original argument that the conducting diamagnetic state is a result of the migration of the unpaired electrons to the interior units of the molecule. Finally, we find that the triplet state has higher reorganization energy than that of the singlet. Thus, if conduction were assumed to proceed via a hopping mechanism, the experimental observations would be explained. / by Aiyan Lu. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009. / Cataloged from PDF version of thesis. Vita. / Includes bibliographical references. / Chapter 1. Different Synthetic Approaches to Modeling the Active Sites of Carboxylate-Bridged Non-Heme Diiron Enzymes Carboxylate-bridged non-heme diiron enzymes activate dioxygen to perform a variety of biological functions. Synthetic model compounds have been prepared to gain insight into the intricacies of dioxygen activation in these enzymes. In this introductory chapter, the challenges and advances of different diiron systems with terphenyl and dendrimer-appended carboxylates, nitrogen-rich, and syn Ndonor ligands are highlighted. Chapter 2. 9-Triptycenecarboxylate-Bridged Diiron(ll) Complexes: Capture of the Paddlewheel Geometric Isomer The synthesis and characterization of diiron(ll) complexes supported by 9- triptycenecarboxylate ligands (-O2CTrp) is described. The interlocking nature of the triptycenecarboxylates facilitates formation of quadruply bridged diiron(ll) complexes of the type [Fe 2(-O 2CTrp) 4(L) 2] (L = THF, pyridine or imidazole derivative) with a paddlewheel geometry. A systematic lengthening of the Fe-Fe distance occurs with the increase in steric bulk of the neutral donor L, resulting in values of up to 3 A without disassembly of the paddlewheel structure. Reactions with an excess of water do not lead to decomposition of the diiron(ll) core, indicating that these quadruply bridged complexes are exceptionally stable. The red-colored complexes [Fe2(f-O2CTrp) 4(4-AcPy) 2] (10) and [Fe2(M-O2CTrp)4(4- CNPy)2] (11) exhibit solvent-dependent thermochromism in coordinating solvents that was studied by variable temperature UV-vis spectroscopy. / (cont.) Reaction of [Fe 2(1-O2CTrp)4(THF)2] with N,N,N',N'-tetramethylethylenediamine (TM EDA), tetra-n-butyl ammonium thiocyanate, or excess 2-methylimidazole resulted in the formation of mononuclear complexes [Fe(O 2CTrp) 2(TMEDA)] (13), (nBu 4N)2[Fe(O2CTrp) 2(SCN)2] (14), and [Fe(O 2CTrp)2(2-Melm) 2] (15) having an 04/N2 coordination sphere composition. Chapter 3. Synthesis, Characterization, and Oxygenation Studies of Carboxylate-Bridged Diiron(ll) Complexes with Aromatic Substrates Tethered to Pyridine Ligands and the Formation of a Unique Trinuclear Complex In this study, diiron(ll) complexes were synthesized as small molecule mimics of the reduced active sites in the hydroxylase components of bacterial multicomponent monooxygenases (BMMs). Tethered aromatic substrates were introduced in the form of 2-phenoxypyridines, incorporating hydroxy and methoxy functionalities into windmill-type diiron(llII) compounds [Fe 2(M-0 2CArR)2 - (O2CArR) 2(L) 2] (1-4), where -O2CArR is a sterically encumbering carboxylate, 2,6- di(4-fluorophenyl)- or 2,6-di(p-tolyl)benzoate (R = 4-FPh or Tol, respectively). The inability of 1-4 to hydroxylate the aromatic substrates was ascertained. Upon reaction with dioxygen, compounds 2 and 3 (L = 2-(m-MeOPhO)Py, 2-(p- MeOPhO)Py, respectively) decompose by a known bimolecular pathway to form mixed-valent diiron(ll,lll) species at low temperature. Use of 2-(pyridin-2- yloxy)phenol as the ligand L resulted in a doubly bridged diiron complex (4) and 5 an unprecedented phenoxide-bridged triiron(ll) complex (5) under slightly modified reaction conditions. Chapter 4. / (cont.) Modeling the Syn-Disposition of Nitrogen Donors in Non-Heme Diiron Enzymes. Synthesis, Characterization and Hydrogen Peroxide Reactivity of Diiron(lll) Complexes with the Syn N-Donor Ligand H2BPG2DEV In order to model the syn disposition of histidine residues in carboxylate-bridged non-heme diiron enzymes, we prepared a new dinucleating ligand, H2BPG 2DEV, that provides this geometric feature. The ligand incorporates biologically relevant carboxylate functionalities, which have not been explored as extensively as nitrogen-only analogs. Three novel oxo-bridged diiron(lll) complexes [Fe 2( - O)(H20) 2(BPG2DEV)](CI0 4)2 (6), [Fe 2(p-O)(-O02CAriPro)(BPG 2DEV)](CIO 4) (7), and [Fe 2(,1-O)(-CO 3)(BPG 2DEV)] (8) were prepared. Single crystal X-ray structural characterization confirms that two pyridines are bound syn with respect to the Fe-Fe vector in these compounds. The carbonato-bridged complex 8 forms quantitatively from 6 in a rapid reaction with gaseous CO02 in organic solvents. A common maroon-colored intermediate (max = 490 nm; e= 1500 M- 1 cm - 1) forms in reactions of 6, 7, or 8 with H20 2 and NEt 3 in CH 3CN/H 20 solutions. Mass spectrometric analyses of this species, formed using 180-labeled H20 2, indicate the presence of a peroxide ligand bound to the oxo-bridged diiron(lll) center. The Mossbauer spectrum at 90 K of the EPR-silent intermediate exhibits a quadrupole doublet with 6 = 0.58 mm/s and AEQ = 0.58 mm/s. The isomer shift is typical for a peroxodiiron(lll) species, but the quadrupole splitting parameter is unusually small compared to related complexes. / (cont.) These Mossbauer parameters are comparable to those observed for a peroxo intermediate formed in the reaction of reduced toluene/o-xylene monooxygenase hydroxylase (ToMOH) with dioxygen. Resonance Raman studies reveal an unusually low-energy 0-0 stretching mode in the peroxo intermediate that is consistent with a short diiron distance. Although peroxodiiron(lll) intermediates generated from 6, 7, and 8 are poor O-atom transfer catalysts, they display highly efficient catalase activity, with turnover numbers up to 10,000. In contrast to hydrogen peroxide reactions of diiron(Ill) complexes that lack a dinucleating ligand, the intermediates generated here could be reformed in significant quantities after a second addition of H20 2, as observed spectroscopically and by mass spectrometry. Appendix 1. Supporting Tables and Figures for Chapter 2 Appendix 2. Supporting Information for Chapter 4 Appendix 3. Synthesis of Triptycene Carboxylate-Bridged Dimetallic Complexes with First Row Transition Metals The synthesis and structural characterization of dimetallic complexes of the type [M2(1t-02CTrp) 4(THF)2] (M = Mn, Co, Ni, Cu, Zn) supported by triptycenecarboxylate ligands (-O2CTrp) is described. Appendix 4. Synthesis and Structure of a Molecular Ferrous Wheel, [Fe(0 2CH)(O 2CArPro)(1,4-dioxane)]6 The structural characterization of a novel, hexanuclear iron(ll) compound with the carboxylate ArPrOCO2- is described. / by Simone Friedle. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Chemistry, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 59-61). / The chemistry of metaphosphate acids has historically been studied in aqueous media, where acid-catalyzed hydrolysis and solvent leveling effects of these strong acids have prevented their observations and rigorous characterization. Solubilization of tri-, tetra-, and hexametaphosphates in aprotic media using the IPPN + cation ([PPNI+ bis(triphenylphosphine)imninium) has revealed the rich acid chemistry of metaphosphates that has previously been elusive in aqueous media. Protonation of imetaphosphates in organic media has resulted in six metaphosphate acids. X-ray diffraction studies display that the structural configurations of metaphosphate acids are dictated by strong hydrogen bonding interactions. As a consequence of anti-cooperative effect, intramolecular hydrogen bonds are preferred at low degrees of protonation, and intermolecular hydrogen bonds are preferred at high degrees of protonation, resulting in oligomeric and polymeric structures. Because of the symmetry of the hydrogen bonds in metaphosphate acids, Low-Barrier Hydrogen Bonds (LBHB) are formed if the conformation of the metaphosphate ring allows. Metaphosphate anhydrides result from the dehydration of metaphosphate acids. They can undergo hydrolysis to regenerate metaphosphate acids, or alternatively alcoholysis to generate metaphosphate esters. Alcoholysis of metaphosphiate anhydrides presents a novel method to quantitatively phosphorylate organic substrates, of particular interest are substrates of biological significance such as nucleosides. The phosphorylating ability of metaphosphate anhydrides makes them promising candidates for biological phosphorylation. / by Khetpakorn Chakarawet. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1995. / Includes bibliographical references. / by Christopher H. McCoy. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009. / Vita. / Includes bibliographical references. / In this thesis is summarized the progress toward completing our understanding of the Rydberg system of CaF and developing Pure Electronic Spectroscopy. The Rydberg system of CaF possesses a paradigmatic character due to its strongly polar ion-core. The first characterization of the Stark effect in a Rydberg system of this nature is presented here, and a diagnostic application of the Stark effect for making assignments of N+ and f quantum numbers has been demonstrated. In addition, a general method, which relies on polarization diagnostics and is applicable not only to studies of Rydberg states, for making unambiguous rotational assignments in the absence of rotational combination differences, has been described for the case of unresolved doublet states. New information, obtained using the Stark effect and polarization diagnostics, has furthered our knowledge of the partially core-penetrating character of nominally core-nonpenetrating states. In order to systematically obtain the same information that is contained in a Stark effect spectrum, but with less difficulty, we are developing experimental methods to record same-n* Rydberg-Rydberg transitions directly, using Time Domain THz and Chirped-Pulse Microwave Spectroscopies. In both of these methods, the spectrum is recorded in the time domain, which results in reliable relative transition intensities. We show that the relative transition intensities in a Rydberg-Rydberg spectrum provide information that permits separation of different interaction mechanisms between the Rydberg electron and the ion-core. / by Vladimir Petrović. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010. / In title on title-page, [alpha] appears as a Greek symbol. Vita. Cataloged from PDF version of thesis. / Includes bibliographical references. / Chapter 1 begins with a review of the current literature on cross-coupling methods to generate a-arylcarbonyl compounds, with a special emphasis on asymmetric arylations. The second section of chapter 1 describes the development of an asymmetric Negishi arylation of a-bromoketones using a nickel/pybox catalyst. The third section details the development of a Suzuki arylation of a-bromo- and a-chloroamides using aryl-(9-BBN) reagents. Both of these cross-coupling procedures are stereoconvergent, as they convert the racemic starting electrophile to an enantioenriched product. Chapter 2 describes new studies into the chemistry of boratabenzene-containing transition-metal complexes. In particular, a new method for preparing complexes bearing a diphenylphosphidoboratabenzene ligand is disclosed, starting from a transition metal-diphenylphosphide and a boracycle, which is an intermediate in the synthetic route previously used in the preparation of these complexes. In addition, the preparation and characterization of a new, tri-ortho-substituted variant of potassium diphenylphosphidoboratabenzene is described. This new species is used as a ligand in an iron complex, which is characterized. In addition, preliminary studies towards the synthesis of palladium complex bearing this new ligand are disclosed. / by Pamela M. Lundin. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007. / Vita. / Includes bibliographical references. / The development of an improved synthesis of nucleophilic planar-chiral catalysts is described in Chapter 1. This route is amenable to scale-up and preparative chiral HPLC is unnecessary to resolve the racemic catalysts. Using planar-chiral catalysts, two synthetic methodology projects have been developed: Chapter 2 describes the first asymmetric synthesis of trans P-lactams, and Chapter 3 describes the asymmetric synthesis of tertiary a-chloroesters. In the chapter describing the asymmetric synthesis of trans [beta]-lactams, we present mechanistic data supporting a novel mechanism, in which the N-triflylimine, rather than the ketene, reacts with the catalyst first. In the chapter describing the asymmetric synthesis of tertiary a-chloroesters, we introduced an under-utilized commercially available chlorinating reagent (2,2,6,6-tetrachlorocyclohexanone). Finally, in chapter 4, the Cu-catalyzed asymmetric synthesis of [alpha]-aminoesters via an N-H insertion is described. We have demonstrated that carbamates such as BocNH2 and CbzNH2 are efficient coupling partners in reactions with a-diazoesters to generate highly useful Boc- or Cbz-protected a-aminoesters. / by Elaine C. Lee. / Ph.D.

Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The studies in the present dissertation were aimed at developing and applying synthetic methods mediated by palladium catalysis. In Chapters 1 and 2, the palladium-catalyzed amidation and amination of five-membered heterocyclic bromides containing multiple heteroatoms are described. These methods provide efficient access to N-arylated imidazoles and pyrazoles in moderate to excellent yields. In Chapter 3, a series of novel triptycene-based compounds were synthesized using a palladium-catalyzed C-N, C-C, C-N cross-coupling sequence. Experimental results suggest that this series of compounds could potentially be used as delayed singlet emitters for organic light emitting devices. Chapter 1. Palladium-Catalyzed Amidation of Five-Membered Heterocyclic Bromides Palladium-catalyzed C-N cross-coupling between primary amides and five-membered heterocyclic bromides that contain multiple heteroatoms was achieved for the first time using the Pd/AdBrettPhos catalyst system. This system allows for efficient access to Narylated imidazoles, pyrazoles, thiazoles, pyrroles, and thiophenes in moderate to excellent yield. Experimental results and DFT calculations point to the need for electronrich and especially sterically demanding biaryl dialkylphosphine ligands to promote these difficult cross-coupling reactions. The same protocol was also extended to forming tertiary amides from secondary amides and five-membered heterocyclic bromides. Preliminary studies showed promising results using a Pd/AdRockPhos catalyst system. Chapter 2. Palladium-Catalyzed Amination of Unprotected Five-Membered Heterocyclic Bromides An efficient method for the palladium-catalyzed amination of unprotected bromoimidazoles and bromopyrazoles is presented. The transformation is facilitated by the use of our newly developed Pd-precatalyst based on the bulky biarylphosphine ligand, tBuBrettPhos. The mild reaction conditions employed allow for the preparation of a broad scope of aminoimidazoles and aminopyrazoles in moderate to excellent yields. Chapter 3. Synthesis of Delayed Singlet Emitters for OLED Development The development of novel thermally activated delayed fluorescence (TADF) materials for use in organic light emitting devices (OLEDs) is reported. A series of triptycenebased delayed singlet emitters have been synthesized using a palladium-catalyzed C-N, C-C, C-N cross-coupling sequence. Preliminary investigations have demonstrated that these compounds could serve as delayed singlet emitters at a range of wavelengths from orange to blue, which is highly desirable for organic electronics applications. / by Mingjuan Su. / Ph. D. in Organic Chemistry

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2017. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. Page 308 blank. / Includes bibliographical references. / Molybdate, a molecular metal oxide, readily binds CO₂ at room temperature to produce a robust monocarbonate complex, [MoO₃(k²-CO₃)]²-. In the presence of excess CO₂, a pseudo-octahedral dioxo dicarbonate complex, [MoO₃(k²-CO₃)₂]²-, is formed. The monocarbonate [MoO₃(k²-CO₃)]²- reacts with triethylsilane to produce formate together with silylated molybdate. A different system investigated in the context of CO₂ reduction to formate was sodium borohydride. The uptake of three equivalents of CO₂ by NaBH₄ is described, along with full spectroscopic and crystallographic characterization of the resulting triformatoborohydride, Na[HB(OCHO)₃]. In order to develop catalytic transformations for CO₂ utilization, we undertook an extensive investigation into the synthesis of novel phosphine ligand architectures that could support transition metal catalysts. A new, chelating, cationic P,N-ligand, [pyP₂dmb₂][SbF₆], was synthesized by treatment of the robust bicyclic diphosphane, 3,4,8,9-tetramethyl-1,6-diphosphabicyclo(4.4.0)deca-3,8-diene or P₂dmb₂, with 2-iodopyridine, followed by an anion exchange. This phosphino-phosphonium salt was investigated as a ligand for group 6 and group 10 transition metals. Other cationic and zwitterionic ligand frameworks were also briefly investigated. A family of cis-macrocyclic diphosphines was prepared in just three steps from white phosphorus and commercial materials using a modular synthetic approach. Alkylation of bicyclic diphosphane P₂dmb₂ produced phosphino-phosphonium salts [RP₂dmb₂]X, where R is methyl, benzyl, isobutyl, or neopentyl. Treatment of these salts with organometallic reagents yielded macrocyclic diphosphines of the form cis-1-R-6-R2-3,4,8,9-tetramethyl-2,5,7,10-tetrahydro-1,6-DiPhospheCine, or R,R2-DPC, in which R2 is methyl, cyclohexyl, phenyl, mesityl or neopentyl. Alternatively, symmetric diphosphine Cy₂-DPC was synthesized from the dichlorodiphosphine Cl₂P₂dmb₂. Multidentate ligands with additional S, P and N donor atoms have also been prepared. The coordination chemistry of these cis-macrocyclic diphosphines was explored, with a focus on nickel and cobalt complexes. An unusual iodide-bridged cobalt(I) dimer, [(Cy₂-DPC)CoI]₂, was prepared and structurally characterized. These nickel and cobalt complexes supported by cismacrocyclic diphosphines were investigated as potential catalysts for the coupling of carbon dioxide and ethylene to produce acrylate, a valuable polymer precursor. The nickel complexes studied showed similar or better turnover numbers for acrylate production compared to complexes of commercial diphosphine ligands. Although not yet catalytic, the first examples of cobalt complexes capable of mediating acrylate formation from CO₂ and ethylene are reported. / by Ioana Knopf. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1994. / Includes bibliographical references. / by Jody J. Klaassen. / Ph.D.