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Organometallic catalysis has attracted significant interest from both industry and academia due to its wide applications in organic synthetic transformations. Example of such transformations include the reaction of a zinc carbenoid with olefins to form cyclopropanes. The first project is a computational study using both density functional and correlated wavefunction methods of the reaction between ethylene and model zinc carbenoid, nitrenoid and oxenoid complexes (L-Zn-E-X, E = CH2, NH or O, L = X = I or Cl). It was shown that cyclopropanation of ethylene with IZnCH2I and aziridination of ethylene with IZnNHI proceed via a single-step mechanism with an asynchronous transition state. The reaction barrier for the aziridination with IZnNHI is lower than that of cyclopropanation. Changing the leaving group of IZnNHI from I to Cl, changes the mechanism of the aziridination reaction to a two-step pathway. The calculation results from the epoxidation with IZnOI and ClZnOCl oxenoids suggest a two-step mechanism for both oxenoids. Another important example of organometallic catalysis is the formation of alkyl arenes from arenes and olefins using transition metal catalysis (olefin hydroarylation). We studied with DFT methods the mechanism of a novel Rh catalyst (FlDAB)Rh(TFA)(η2–C2H4) [FlDAB = N,N’ -bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] that converts benzene, ethylene and air-recyclable Cu(II) oxidants to styrene. Possible mechanisms are discussed.

<p> Metal-stabilized carbenes, most commonly formed through the decomposition of  diazoacetates, are extensively employed in organic synthesis. However, several classes of carbenes,  such as vinylidenes, are challenging to utilize in transition metal catalysis due to the instability of  the required diazo precursors. To overcome this challenge, most transition metal-catalyzed  vinylidene transfer and insertion methods rely on alkynes as vinylidene precursors. Only catalysts  that form stable M=C multiple bonds and weak M(π-C≡C) interactions can promote this alkyne  isomerization, and the resultant metal(vinylidene) species is often less reactive compared to free  vinylidenes. The discovery of 1,1-dihaloalkenes as precursors to transition metal vinylidene  complexes has significantly expanded the scope of vinylidene transfer and insertion reactions.  Dinuclear catalysts were found to promote the reductive cyclization of 1,1-dichloroalkenes  containing pendant alkenes to form methylenecycloalkenes, and mechanistic studies are consistent  with the formation of a Ni2(vinylidene) species. Furthermore, these catalysts promote reductive  three-component cycloaddition reactions with 1,1-dichloroalkenes and aldehydes to generate  methylenedioxolanes, which upon treatment with aqueous acid provides access in one step to new,  unsymmetrical aliphathic α-hydroxy ketones that would be difficult to access with existing  methods. Under dilute conditions, an enone byproduct is formed and a DFT model is presented  that accounts for concentration-based reaction selectivity.</p>

Catalysis, which is primarily a molecular phenomenon, is an important field of chemistry because it requires the chemical conversion of molecules into other molecules. It also has an effect on many fields, including, but not limited to, industry, environment and life Science[1]. Surface Organometallic Chemistry is an effective methodology for Catalysis as it imports the concept and mechanism of organometallic chemistry, to surface science and heterogeneous catalysis. So, it bridges the gap between homogenous and heterogeneous catalysis[1]. The aim of the present research work is to study the effect of Nitrogen surface ligands on the activity of Alkane, Propane in particular, metathesis. Our approach is based on the preparation of selectively well-defined group (VI) transition metal complexes supported onto mesoporous materials, SBA15 and bearing amido and/or imido ligands. We choose nitrogen ligands because, according to the literature, they showed in some cases better catalytic properties in homogenous catalysis in comparison with their oxygen counterparts[2]. The first section covers the modification of a highly dehydroxylated SBA15 surface using a controlled ammonia treatment. These will result in the preparation of two kind of Nitrogen surface ligands: - One with vicinal silylamine/silanol, (≡SiNH2)(≡SiOH), noted [N,O]SBA15 and, - Another one with vicinal bis-silylamine moieties (≡SiNH2)2, noted [N,N]SBA15[3]. The second section covers the reaction of Schrock type Tungsten Carbyne [W(≡C- tBu)(CH2-tBu)3] with those N-surface ligands and their characterizations by FT-IR, multiple quantum solid state NMR (1H, 13C), elemental analysis and gas phase analysis. The third section covers the generation of the active site, tungsten hydride species. Their performance toward propane metathesis reaction using the dynamic reactor technique PID compared toward previous well-known catalysts supported on silica oxide or mesoporous materials[4]. A fairly good turn over number (TON = 43) has been obtained following hydrogen treatment of tungsten alkylidyne supported on [N,O] SBA151100, in comparison with TON of zero in the obtained with [N,N] SBA15 and classical SiO2 silica support. Therefore, the cooperation between silylamine and silanol in close vicinity are required to improve the efficiency of the catalyst in the metathesis of propane.

Comprendre les réactions biologiques requiert l'utilisation de composés capables de transférer des électrons de manière sélective et de stabiliser des intermédiaires réactionnels. Ce travail s'est intéressé à la conception et à la réactivité de complexes de lanthanide divalents qui ont ce type de propriétés.Dans un premier temps, la réduction de deux molécules organiques, la phénanthroline et la benzophenone, a été étudiée. Les données thermodynamiques obtenues avec la phénanthroline ont permis de construire un ensemble de données de références de différentes fonctionnelles de la densité. Des méthodes de type TDDFT et CASSCF ont été ensuite mises en oeuvre afin de reproduire les spectres UV-visibles.Par la suite, les radicaux benzophenone et phénanthroline ont été utilisés afin de réaliser des réactions radicalaires. L'utilisation du radical tempo a permis de réaliser des réactions de réduction induite par les effets stériques des complexes. La compétition entre la benzophenone et la phénanthroline a également été étudiée et a permis de réaliser des couplages de type Minisci, qui sont inédits pour des complexes de lanthanides.Enfin, la réduction de composés organométalliques via un ligand N-hétérocyclique a été réalisée. Deux de ces composés ont été comparés vis à vis de la stabilisation de complexes de palladium au degré d'oxydation +IV. L'importance du ligand a été de plus étudiée grâce à des calculs CASSCF et DFT qui ont montré que certains types de ligands permettaient un transfert électronique plus direct jusqu'au palladium. / Understanding biological reactions require the use of molecules that can transfer electrons selectively and stabilise key intermediates. This work is interested into the design and the reactivity of divalent lanthanides that possess this kind of property.Firstly, organic molecules, i.e. phenanthroline and benzophenone, were reduced by samarium complexes. The thermodynamic data obtained for phenanthroline reduction was used to perform a benchmark study on different density functionals. TDDFT and CASSCF methods were then used to understand the electronic structure of the complexes and compared to the UV-visible spectrum of the molecules.Then, benzophenone ketyl and phenanthroline radicals have been used to perform radical reactions. Reactions with tempo led to already observed sterically induced reduction which mechanism was investigated. The competition between phenanthroline and benzophenone led to Minisci couplings that were never described with lanthanide complexes.Finally, the electron was transferred to organometallic species containing palladium via a bridge N-heterocycle ligand. Two of such species were compared towards the stabilisation of palladium at the IVth oxidation state. The importance of the ligand was further assessed by a combination of DFT and CASSCF calculations showing that certain ligands enabled a more direct transfer towards the palladium centre.

Surface Organometallic Chemistry (SOMC) is an excellent approach to erase the gap between homogeneous and heterogeneous catalysis by grafting the molecular organometallic complex on various oxide surfaces, forming well-defined and single-site catalysts. This strategy allows for better characterization as well as the improvement and development of existing and new catalysts. These surface species could promote a wide range of catalytic applications (i.e., metathesis of hydrocarbons, hydrogenolysis of alkanes, and olefin polymerization reactions) depending on the metal center and its coordination sphere. In particular, the grafting of alkylated organometallic complexes of groups 4, 5, and 6 metals on the surface oxide is a thermodynamically favored reaction generally leading to strongly bonded well-defined surface species, which are highly reactive catalysts. This thesis has focused on the preparation, characterization, and catalytic investigation of different supported complexes that contain methyl, alkyl, and alkylidyne ligands. The first part compares the catalytic activity of [(≡Si−O−)W(-CH3)5] and [(≡Si-O-)Mo(≡CtBu)(-CH2tBu)2] surface species experimentally and by DFT calculations in the metathesis reactions of linear classical and functionalized olefins. Both pre-catalysts perform almost equally in the α-olefin metathesis reaction. However, in the functionalized olefin metathesis reaction, W pre-catalyst provides selective metathesis products and performs much better than Mo that gives a range of isomerization products. The second part deals with the synthesis and characterization of [(THF)2Zr(-CH3)4] and its grafting on silica support for the first time. The generated surface species [(≡Si−O−)Zr(CH3)3(THF)2] and [(≡Si−O−)2Zr(CH3)2(THF)2] are used for the conversion of CO2 and propylene oxide to cyclic propylene carbonates achieving a TON of 4227. The third part describes the first synthesis and characterization of the highly unstable homoleptic [Ti(-CH3)4] without any coordinating solvent. This complex was stabilized by grafting on SiO2-700, yielding two fully characterized surface species [(≡Si-O-)TiMe3] and [(≡Si-O-Si≡)(≡Si-O-)TiMe3], which were used in the hydrogenolysis reaction of propane and n-butane, with TONs of 419 and 578, respectively. Finally, the fourth part reports the immobilization and characterization of [TiMe2Cl2], an intermediate in the synthesis of [Ti(-CH3)4], on SiO2-700 resulting in [(≡Si-O-)TiMeCl2] and [(≡Si-O-)TiMe2Cl] surface species. These complexes reacted with a demethylating Lewis acid agent (BARF), forming the corresponding cationic Ti species [(≡Si-O-)TiMeCl]+ and [(≡Si-O-)TiCl2]+. Both neutral and cationic complexes were tested in the ethylene polymerization reaction affording linear HDPE with high molecular weights of 500,367 and 486,612 g/mol.

<p>The present body of work has focused on the development of the chemistry of iron complexes of macrocyclic ligands, specifically HMC and HMTI. This has proceeded along two distinct, though related, lines. First, metal-alkynyl complexes have been synthesized, and the effects of the macrocyclic ligand on the metal center – and therefore on the metal-alkynyl bond – have been extensively explored. This is first described for a mono- and bis-alkynyl pair in Chapter 2, in which the general structural and electrochemical features of the Fe(HMTI) motif are delineated. In Chapter 3, the detailed characterization of an iron HMC/HMTI family of complexes is described, which is accompanied by spectroelectrochemical (SEC) analyses and extensive DFT and TD-DFT. Finally, as described in Chapter 4, the understanding gained in the aforementioned works is leveraged to control the properties of mixed-valent complexes based on Fe(HMC/HMTI) bis-alkynyl motif, with a motivation to explore fundamental questions for the development of molecular wires.</p> <p><br></p> <p>The second realm of exploration has been concerned with understanding ferrous complexes of HMTI at a deeper level – which species have been previously reported but largely uninvestigated. Collaborative efforts have shown that these FeII(HMTI) species can have unusually long excited state lifetimes under the appropriate conditions, as discussed in Chapter 5. Further (unpublished) characterization of this family of complexes is the focus of Chapter 6, which highlights the relationship between the energy of the charge-transfer absorption band and the nature of the axial ligand.</p> <p><br></p> <p>The novel work outlined above is preceded by introductory material (Chapter 1). This chapter serves to briefly contextualize the body which follows within the landscape of the earlier established (though limited) literature on Fe(HMTI) species. Chapter 1 thus represents an attempt to illustrate the ties throughout what might otherwise (and perhaps still does) appear a disjointed conglomerate of text.</p>

This thesis documents efforts to synthesize Metal-Organic Frameworks (MOFs) and study their charge transport, electrocatalytic, and photoredox catalytic properties. Chapter 1 introduces concepts of pre-synthetic and post-synthetic metalation of MOFs. A series of four chemically identical but structurally different hydrolytically robust ZrIV-MOFs constructed from tetrakis(4-carboxyphenyl) porphyrinato iron (III) are examined to understand the influence of topological construction on redox hopping conductivity. The structural variation fixes center-to-center distances in the four MOFs and defines the hopping rate. The spin-state variation of the central metal in the porphyrin unit helps in further tuning the TCPP(FeIII/II) reorganization energy of the self-exchange process. The hopping rate significantly increased upon axial coordination of 1-methyl imidazole to the iron center, which converts a weakly halide bound five-coordinated high-spin (HS) TCPP(FeIII/II) to the six-coordinated low-spin (LS) complex. The population of LS vs HS species is shown to be a function of topology in the presence of an excess ligand. Chapter 2 investigates this idea further by using MOFs for electrocatalytic oxygen reduction reaction (ORR). Two cobalt-centered porphyrin-based MOFs are synthesized and deposited on various substrates to afford working electrodes that can be used in an electrochemical cell to catalyze the ORR. Chapter 3 investigates the linker-dependent photoredox catalytic activity of MOFs that possess the same topology. This is the first MOF-based study wherein a heavy metal like ruthenium is not employed to carry out the visible light-dependent photoredox catalysis.

This dissertation focuses on the computational investigation of gold(I) acyclic diaminocarbene (ADC) complexes and their application in homogeneous gold(I) catalysis. Chapter 2 is an in-depth computational investigation of the σ- and π-bonding interactions that make up the gold-carbene bond. Due to the inherent conformation flexibility of ADC ligands, distortions of the carbene plane can arise that disrupt orbital overlap between the lone pairs on the adjacent nitrogen atoms and the empty p-orbital of the carbene. This study investigated the affect these distortions have on the strength of the σ- and π-bonding interactions. This investigation demonstrated that while these distortions can affect the σ- and π-bonding interactions, the ADC ligand have to become highly distorted before any significant change in energy of either the σ- or π-bonding interactions occurs. Chapter 3 is a collaborative investigation between experimental and computational methods, DFT calculations were employed to support the experimental catalytic results and determine the role that steric effects have in controlling the regioselectivity of a long-standing electronically controlled gold(I)-catalyzed tandem 1,6-enyne cyclization/hydroarylation reaction with indole. This study demonstrated that by sterically hindering nucleophilic attack of indole at the favored position, nucleophilic attack would occur at a secondary position leading to the selective formation of the electronically unfavored product. Chapter 4 is a collaborative investigation between experimental and computational methods. DFT calculations were employed to investigate and rationalize the importance of secondary non-covalent interactions and their influence on the enantioselectivity of a gold(I)-catalyzed intramolecular hydroamination of allene reaction. Through computational investigation of the enantiodetermining step, and the non-covalent interactions present between 2′-aryl substituent and the rest of the catalyst, it was determined that the presence of CF3 group on the 3,5-position of the 2′-aryl ring is crucial to maintaining a more rigid chiral pocket leading to higher enantiomeric excesses in this dynamic system. This increased rigidity is believed to be attributable to the several weak non-covalent interactions that arise between the allene substrate or diisopropyl N-substituent and the fluorine atoms of the CF3 groups.

<p dir="ltr">This work describes the electronic and geometric structure of molecular metal complexes involving different ligand environments. These include the Cu-redox active ligand reduction series, Tp*₂U imido and anilido transformations, Lewis base activation by Tp*₂U, silyluranium synthesis and reactivity, and electrochemistry of plutonyl.</p>