Gotowa bibliografia na temat „Olefin oxidation”

Carboxylic acids have been electro-oxidatively coupled to electron-rich olefins to form lactones. Kolbe decarboxylation does not appear to be a significant competing pathway. Experimental results indicate that oxidation occurs at the olefin and that the reaction proceeds through a radical cation intermediate.

Oxidation of olefins with tert-butyl hydroperoxide (TBHP), tetra-n-butylammonium periodate (TBAP) and potassium peroxomonosulfate (Oxone) in the presence of MCM-41 immobilized meso-tetra-4-carboxyphenylporphyrinatomanganese(III) acetate has been studied. The results of this study show better catalytic performance of the heterogonous catalyst using TBHP as oxidant in comparison with Oxone and TBAP in oxidation of the used olefins with the exception of cyclooctene. However, different order of reactivity of various olefins has been observed in the presence of Oxone and TBHP. In spite of the absence of good electron-withdrawing groups at the periphery of porphyrin ligand, the catalyst was recovered and reused (at least four times) without detectable catalyst leaching or a significant loss of the catalytic efficiency. All results have been obtained in the absence of using excess molar ratios of olefin to the oxidant, commonly employed as a strategy to overcome the instability of metalloporphyrins in oxidative conditions.

Several pyridine-like ligands were found to improve Pd(OAc)2-catalyzed allylic oxidation of allylbenzene to cinnamyl acetate by p-benzoquinone in acetic acid. The best ligand examined, bipyrimidine, was used to identify the catalyst precursor for this system, (bipyrimidine)Pd(OAc)2, which was fully characterized. Mechanistic studies suggest the reaction takes place through disproportionation of (bipyrimidine)Pd(OAc)2 to form a bipyrimidine-bridged dimer, which reacts with olefin to form a PdII-olefin adduct, followed by allylic C–H activation to produce (η3-allyl)PdII species. The (η3-allyl)PdII intermediate undergoes a reversible acetate attack to generate a Pd0-(allyl acetate) adduct, which subsequently reacts with p-benzoquinone to release allyl acetate and regenerate (bipyrimidine)Pd(OAc)2. No KIE is observed for the competition experiment between allylbenzene-d0 and allylbenzene-d5 (CD2=CDCD2C6H5), suggesting that allylic C–H activation is not rate-determining. Catalytic allylic acetoxylations of other terminal olefins as well as cyclohexene were also effected by (bipyrimidine)Pd(OAc)2.Key words: olefin, palladium catalysis, allylic C–H oxidation, p-benzoquinone, bipyrimidine.

Reaction of amide I with nitrous acid gave the olefins II, III and IV. On allylic oxidation of olefin IV α,β-unsaturated ketone V is formed from which olefins VIII and IX were prepared by a sequence of further reactions. Addition of hydrogen to the double bond of olefin IV and α,β-unsaturated ketone V takes place on catalytic hydrogenation from the β-side and leads to derivatives with cis-annellated rings D/E. This made the preparation of hydrocarbons VI and VII epimeric on C(18) possible, which represent reference compounds for the study of the effect of substituents on the chemical shifts of the methyl groups and the saturated carbon atoms of 18αH and 18βH-lupane derivatives. The configuration of the hydroxyl group in epimers XI and XII were derived from 1H NMR spectra. Deuteration of olefins III, IV and IX gave deuteriohydrocarbons XVI to XVIII. The 1H, 13C NMR and mass spectra of the substances prepared are discussed.

The synthesis and solution and solid-state structural characterization of a family of amine bis(phenolate) [ONNO]-vanadium complexes is reviewed. These compounds have oxidation states ranging from vanadium(II) to vanadium(V), and were evaluated as olefin polymerization catalysts. In association with EtAlCl2 cocatalyst, we studied the homopolymerization of ethylene, propene, and 1-hexene, as well as the copolymerization of ethylene with α-olefins (1-hexene, 1-octene) and cycloolefins (norbornene, cyclopentene). Some of these catalysts were shown to produce copolymers with a good activity and comonomer content.

Reactions of thiol with the C 3-vinyl group of various chlorophyll (Chl) derivatives were examined. The reactions resemble thiol-olefin co-oxidation, except that the vinyl C = C double bond was cleaved to afford a formyl group without any transition metal catalyst, and that the simple anti-Markovnikov adduct of thiol to olefin was obtained as a minor product. Peripheral substituents of Chl derivatives little affected the reaction, while the central metal atom of the chlorin macrocycle influenced the composition of the products. Oxygen and acid dissolved in the reaction mixture can facilitate the oxidation. Sufficiently mild conditions in this regioselective oxidation at the C 31-position are significant in bioorganic chemistry.

EWG-activated and polar quaternary ammonium salt-tagged ruthenium metathesis catalysts have been applied in a two-step one-pot metathesis-oxidation process leading to functionalized α-hydroxyketones (acyloins). In this assisted tandem process, the metathesis catalyst is used first to promote ring-closing metathesis (RCM) and cross-metathesis (CM) steps, then upon the action of Oxone™ converts into an oxidation catalyst able to transform the newly formed olefinic product into acyloin under mild conditions.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2014.
Cataloged from PDF version of thesis. Vita.
Includes bibliographical references.
Chapter 1 describes work toward solid-supported W olefin metathesis catalysts. Attempts to tether derivatives of the known Z-selective catalyst W(NAr)(C₃H₆)(pyr)(OHIPT) (Ar = 2,6- diisopropylphenyl, pyr = pyrrolide; HIPT = 2,6-bis-(2,4,6-triisopropylphenyl)phenyl) to a modified silica surface by covalent linkages are unsuccessful due to destructive interactions between W precursors and silica. W(NAr)(C₃H₆)(pyr)(OHIPT) and W(NAr)(CHCMe₂Ph)(pyr)(OHIPT-NMe₂) (HIPT-NMe 2 = 2,6-bis-(2,4,6-triisopropylphenyl)-4- dimethylaminophenyl) are adsorbed onto calcined alumina. W(NAr)(C 3H6 )(pyr)(OHIPT) is destroyed upon binding to alumina, while W(NAr)(CHCMe 2Ph)(pyr)(OHIPT-NMe 2) appears to bind through a non-destructive interaction between the dimethylamino group and an acidic surface site. The heterogeneous catalysts perform non-stereoselective metathesis of terminal olefins, and W(NAr)(CHCMe₂Ph)(pyr)(OHIPT-NMe₂) can be washed off the surface with polar solvent and perform solution-phase Z-selective metathesis. Chapter 2 details selective metathesis homocoupling of 1,3-dienes with Mo and W monoalkoxide pyrrolide (MAP) catalysts. A catalytically relevant vinylalkylidene complex, Mo(NAr)(CHCHCH(CH₃)₂)(Me₂pyr)(OHMT) (HMT = 2,6-bis(2,4,6-trimethylphenyl)phenyl; Me₂pyr = 2,5-dimethylpyrrolide), is isolated. A series of Mo and W MAP catalysts is synthesized and tested for activity, stereoselectivity, and chemoselectivity in 1,3-diene metathesis homocoupling. Catalysts containing the OHIPT ligand display excellent selectivity in general, and W catalysts are less active but more selective than their Mo counterparts. Chapter 3 recounts the synthesis and characterization of several heteroatom-substituted alkylidene complexes with the formula Mo(NAr)(CHER)(Me₂pyr)(OTPP) (TPP = 2,3,5,6- tetraphenylphenyl; ER = OPr, N-pyrrolidinonyl, N-carbazolyl, pinacolborato, trimethylsilyl, SPh, or PPh2). Synthesis proceeds via alkylidene exchange between Mo(NAr)(CHR)(Me₂pyr)(OTPP) (R = H, CMe₂Ph) and a CH₂CHER precursor. Each complex behaves similarly to known MAP complexes in olefin metathesis processes; the electronic identity of ER has little effect on catalytic properties. Distinctive features of alkylidene isomerism and catalyst resting state are examined. Chapter 4 contains synthetic and catalytic studies of thiolate-containing Mo and W imido alkylidene complexes. The species M(NAr)(CHCMe 2Ph)(pyr)(SHMT) (M = Mo or W), Mo(NAr)(CHCMe₂Ph)(Me₂pyr)(STPP), and Mo(NAr)(CHCMe₂Ph)(STPP)₂ are synthesized by substitution of the appropriate thiol or thiolate ligands for pyrrolide or triflate ligands in metal precursors. These complexes show similar structural and spectral characteristics to alkoxidecontaining species. The thiolate complexes and their alkoxide analogues are compared for activity and selectivity in metathesis homocoupling and ring-opening metathesis polymerization processes. In general, thiolate catalysts are slower and less selective than alkoxide catalysts.
by Erik Matthew Townsend.
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: Reaction of W(CCMe3)Cl 3(dme) with one equivalent of (3,5-Me 2C6H3NCH2CH 2)3N)Li3 affords yellow, crystalline W(CCMe3)(N3N) in good yield. The reactivity of this new alkylidyne complex towards terminal alkynes was investigated. Two other new tungsten alkylidynes, W(CCMe3)(pyr) 3 (pyr = 2,5-dimethylpyrrolide) and W(CCMe3)(Ph 2N)3 were prepared by the addition of three equivalents of lithium dimethylpyrrolide or lithium diphenylamide, respectively, to W(CCMe3)Cl 3(dme). The reactivity of these new alkylidynes with various alcohols is reported. The reactivity of several tungsten alkylidyne compounds towards ligand displacement by surface silanols is reported, resulting in the synthesis of several new silicasupported tungsten alkylidynes. The alkyne metathesis activity of all new homogeneous and heterogeneous alkylidyne complexes is reported. Chapter 2: Addition of one equivalent of 2,4,6,2',4',6'-hexaisopropylterphenol to Mo(NAd)(CHCMe 2Ph)(pyr)2 results in the formation of Mo(NAd)(CHCMe 2Ph)(pyr)(HIPTO) (HIPTO = hexaisopropylterphenoxide). This new alkylidene compound was found to catalyze the metathesis of 1-hexene in 20% yield to 95% cis 5-decene, which represents the first report of highly Z-selective metathesis homocoupling of a terminal olefin. The decomposition of the catalyst in the presence of ethylene is explored. The syntheses of several new bulky achiral phenoxide ligands are presented, along with the syntheses of the corresponding MAP (monoalkoxide monopyrrolide) molybdenum imido alkylidene compounds. The reactivity of new MAP compounds containing bulky phenoxide ligands towards the Z-selective metathesis of terminal and internal olefins is presented. The cis-selectivity of this system is proposed to arise from the combination of a relatively small imido ligand in conjunction with a very bulky alkoxide forcing the substituents of the substrate to point in this same direction with each insertion. Photolysis of MAP compounds with 366 nm radiation was found to produce significant amounts of anti alkylidenes, and the kinetics of decay of unstable anti alkylidenes are investigated. Chapter 3: The reaction of 2,3-dicarbomethoxynorbomadiene (DCMNBD) with Mo(NAd)(CHCMe 2Ph)(pyr)(HIPTO) (Ad = 1-adamantyl, HIPTO = hexaisopropylterphenoxide) affords >98% cis, >98% tactic polyDCMNBD. The tacticity of this polymer is proved to be syndiotactic through polymerization of DCMenthNBD (2,3-dicarbomenthoxynorbomadiene) and IH- H COSY. A variety of related MAP alkylidene compounds are also investigated towards the ROMP of DCMNBD and found to produce polyDCMNBD in a range of tacticities and cis contents. Highly cis polyNBDF6 (poly-bis(CF 3)-norbomadiene) was also prepared using molybdenum MAP compounds, and the resulting polymer was found to be essentially insoluble in common organic solvents. Solid state CPMAS 13C NMR spectroscopy revealed insoluble polyNBDF6 to be highly tactic, and the tacticity is proposed to be syndiotactic. Cis, tactic polymer was prepared through the addition of 3,3-methylphenylcyclopropene (MPCP) to molybdenum MAP compounds. Attempts towards determination of the tacticity of cispolyMPCP are presented, including the synthesis of three 3,3-disubstituted cyclopropene monomers containing chiral tags. The cis-selective ROMP of cyclooctene and 1,5- cyclooctadiene are reported. The syndioselectivity of the catalysts is proposed to be controlled by the configuration of the 4-coordinate metal center, which alternates with each insertion of monomer. Chapter 4: Racemic 2,3-dicarbomethoxynorbornene (rac-DCMNBE) is polymerized by Mo(NAd)(CHCMe 2Ph)(pyr)(HMTO) (Ad = 1-adamantyl, pyr = pyrrolide, HMTO = hexamethylterphenoxide) to afford an all-cis polymer that is syndiotactic and composed of alternating enantiomers. The cis, syndiotactic ROMP of several other racemic chiral monomers are reported, also affording structures containing a high degree of enantiomer alteration. Attempts towards the alternating copolymerization of two different monomers are reported. The ROMP of enantiomerically pure (+)-dicarbomethoxynorbornene with Mo(NAd)(CHCMe 2Ph)(pyr)(HIPTO) leads to the production of 92% trans-isotactic polyDCMNBE. The structure of trans-isotactic polyDCMNBD is proved through hydrogenation and comparison of its 3C NMR spectrum with that of known cis-isotactic polyDCMNBE. Both cis/syndiotactic/alternating poly-rac-DCMNBE and trans/isotactic poly-(+)-DCMNBE are polymer structures that have not been previously reported. The thermal properties of all new polymers and their hydrogenated counterparts are reported and are found to correlate closely with polymer structure.
by Margaret McGuigan Flook.
Ph.D.

The study and the development of innovative metal-catalysed systems for the oxygenation of organic molecules with sustainable oxidants, and especially molecular oxygen, O2, or hydrogen peroxide, H2O2, is a very attractive perspective for the Chemical Industry. In the Thesis project, different strategies have been addressed to implement benchmark oxidative transformations, including the autooxidation of benzylic derivatives, the hydroxylation of aromatic hydrocarbons and the epoxidation of olefins. In all cases, the research approach has been based on some key issues, namely the integrated use of: i) bulk oxidants with low environmental impact, such as O2 and H2O2; ii) multi-metallic catalysts with thermal, hydrolytic and oxidative resistance, tailored functionality and solubility; iii) heterogeneous catalysis techniques with membrane-based hybrid organic-inorganic functional materials and solvent-free protocols; iv) microwave irradiation and/or photoirradiation as non-conventional activation techniques, v) multiple catalysis techniques, with sequential and/or parallel processes (Concurrent Tandem Catalysis). The choice of the catalyst package has been established within the class of molecular polyanionic metals oxides clusters, known as polyoxometalates (POMs), with general formula [XxMmOy]q-, where M is the main metallic component (Mo, V, W) and X is an eventual heteroatom such as P or Si. These complexes offer a unique opportunity because of their prevalent inorganic, robust nature, and high versatility in terms of structure, chemical composition, electron density and polyanionic charge. Moreover, a rewarding approach has been recently devised for the catalyst upgrade, by decorating the POM scaffold with organic domains, yielding hybrid organic-inorganic catalysts with superior performances. Since fluorinated phases are of particular interest for performing oxidative transformations, the research activity has been focused on the synthesis, characterization and catalytic activity of novel fluorous-tagged polyoxometalates. Two diverse synthetic approaches have been adopted, based on counterion metathesis and on the covalent functionalization of the POM inorganic surface. With the first strategy, the decatungstate polyanion (W10O32)4- has been isolated in the presence of a fluorous-tagged tetraalkylammonium cation, yielding the fluorophilic salt ?[CF3(CF2)7(CH2)3]3CH3N}4W10O32 , (RfN4W10). Decatungstate is known to be an efficient initiator of autooxidation pathways under photoirradiation, in a oxygen atmosphere. Therefore, the photocatalyzed oxidation of benzylic hydrocarbons, including ethylbenzene and cumene, by RfN4W10 and O2, has been performed in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), both in homogeneous and heterogeneous conditions. The application of membrane technology for the heterogeneous catalysis, in particular, offers the combination of advanced molecular separation and selective transport properties, with the reactivity on a solid support. The photocatalyst heterogenisation has thus been obtained by incorporation of RfN4W10 in perfluorinated polymeric films of HYFLON AD 60X, thus providing novel hybrid materials to be employed and recycled in multi-turnover processes, in solvent-free conditions. Scanning electron microscopy (SEM) images of the film surface and cross-section highlight a highly dispersed, homogeneous distribution of the catalyst domains which appear as spherical particles with uniform size of approximately 2-3 ?m in diameter. Furthermore, in particular conditions, a porous membrane has been obtained, allowing the use of a continuous flow reactor. In the conditions explored, the photooxygenation by (RfN)4W10O32 yields the benzylic hydroperoxide and the corresponding alcohol and ketone. Noteworthy, tetraline and indane photooxygenation proceeds with TON>6000 and remarkable alcohol selectivity, thus providing a convenient alternative to other radical-centered oxygenation systems. Fluorous-tagged polyoxometalates have also been synthesised through a covalent functionalization approach. This alternative strategy employs vacant polyoxotungstates and the fluorinated organosilyl chloride CF3(CF2)7CH2CH2SiCl3 (RfSiCl3) to afford hybrid derivatives through the covalent attachment of the organic groups on the POM surface. The resulting complexes, with general formula Q4[(RfSi)xOySiWwOz], isolated as tetrabutylammonium (Q+) salts, have been characterised and used as catalysts for the epoxidation of different olefins in the presence of H2O2. Kinetic and mechanistic studies have provided several insights on the synergistic effect between the catalysts and the fluorinated solvent used, the hexafluoro-isopropanol (HFIP). Noteworthy, under microwave irradiation, the epoxide is produced with quantitative yield and only after 20 minutes, even for terminal olefins. A further aspect concerns the self-assembly of the POM-based fluorous-tagged amphiphiles. Aggregation phenomena in HFIP solution have been studied by DLS and monitored in the solid state by electronic microscopy. The upgrade to heterogeneous catalysis has also been achieved through the covalent functionalization approach. In this case, the vacant polyoxotungstate has been reacted with the organo silyl chloride CH2=CH(CH2)6SiCl3 (RSiCl3), bearing a terminal alkene residues. The morphology and structure of the resulting hybrid materials have been tuned upon variation of comonomers and porogenic solvents ratio. Interestingly, the hybrid polymer swells in fluorinated alcohols, where the epoxidation of cis-cyclooctene, occurs with quantitative yield after 15 min. Finally, POM-based catalysis has also been applied to the synthesis of phenol which is one of the most valuable intermediate and commodity chemical on the market. To this aim the research activity has been focussed on the implementing both the autoxidation pathway, and the direct mono-hydroxylation of benzene. (i) The application of Tandem Catalysis techniques, so to exploit the membrane-based photocatalytic production of the cumene hydroperoxide and foster its decomposition to phenol through a second step by a acid POM catalyst; (ii) the screening of several molybdovanadate catalyst to be used with H2O2 for benzene hydroxylation. In the first case, the POM mediated tandem catalysis yields 63% phenol with respect to the initial amount of cumyl-hydroperoxide.; in the second case, with the vanadium mono-substituted undecamolybdate, H4Mo11VO40, an improvement of literature results has been obtained through reaction optimization, thus giving: 17 % conversion of benzene at 50°C in CH3CN, with selectivity = 90 % and TOF = 22.5 h-1.
Lo studio e lo sviluppo di sistemi metallo-catalizzati innovativi per l’ossidazione di molecole organiche con ossidanti sostenibili, specialmente ossigeno molecolare, O2, o acqua ossigenata, H2O2, è una prospettiva di grande attrazione per l’Industria Chimica. Nel progetto di Tesi di Dottorato, sono state sviluppate diverse strategie allo scopo di effettuare trasformazioni ossidative di riferimento quali l’autoossidazione di derivati benzilici, l’idrossilazione di idrocarburi aromatici e l’epossidazione di olefine. In tutti i casi, l’approccio alla ricerca si è basato su alcuni aspetti chiave che prevedono l’utilizzo integrato di: i) ossidanti a basso impatto ambientale quali O2 e H2O2; ii) catalizzatori multi-metallici ad elevata resistenza termica, idrolitica ed ossidativa; iii) tecniche di catalisi eterogenea per mezzo di materiali funzionali ibridi organici-inorganici costituiti da membrane catalitiche a matrice polimerica e protocolli che non prevedano l’impiego di solventi organici; iv) microonde o radiazioni fotochimiche quali tecniche di attivazione non convenzionali; v) tecniche di catalisi multipla con processi sequenziali e/o paralleli (Tandem Catalisi). I catalizzatori impiegati appartengono alla classe degli ossidi polianionici metallici, detti poliossometallati (POMs), aventi formula generale [XxMmOy]q-, dove M è il componente metallico principale (Mo, V, W) e X è un eventuale eteroatomo (P o Si). Questi complessi sono molto vantaggiosi come catalizzatori perché di natura inorganica, resistenti e sono modulabili in termini di struttura, composizione chimica, densità elettronica e carica polianionica. Particolarmente interessante è la possibilità di funzionalizzare la porzione inorganica con domìni di natura organica, potendo così ottenere catalizzatori ibridi organici-inorganici dalle prestazioni catalitiche migliori. Poiché le fasi fluorurate sono di particolare interesse per ciò che concerne le trasformazioni ossidative, l’attività di ricerca si è focalizzata sulla sintesi, caratterizzazione e attività catalitica di nuovi poliossometallati fluorurati. Sono state seguite due strategie di sintesi differenti basate sulla metatesi di controcatione e sulla funzionalizzazione covalente di superfici di POM inorganici. Con la prima strategia è stato isolato il polianione decatungstato (W10O32)4- con un controcatione tetraalchilammonio fluorurato ottenedo il sale fluorofilico ?[CF3(CF2)7(CH2)3]3CH3N}4W10O32 , (RfN4W10). Il decatungstato è noto per la sua capacità di essere iniziatore di processi radicalici se fotoirradiato in atmosfera di ossigeno. L’ossidazione fotocatalitica di etilbenzene ed altri idrocarburi benzilici tramite RfN4W10 e O2 è stata condotta in 1,1,1,3,3,3-hexafluoroisopropanolo (HFIP), sia in omogeneo che in fase eterogenea. L’applicazione della tecnologia delle membrane per la catalisi eterogenea offre, in particolare, numerosi vantaggi in termini di combinazioni di avanzati processi di separazione molecolare con proprietà di trasporto selettive, insieme alla reattività su supporti solidi. L’eterogeneizzazione del fotocatalizzatore è stata così ottenuta per incorporazione di RfN4W10 in film polimerici perfluorurati di HYFLON AD 60X, ottenendo così nuovi materiali ibridi da impiegare e reciclare in processi “multi-turnover” ed in assenza di solventi. Immagini di microscopia elettronica a scansione (SEM) della superficie e della sezione del film evidenziano una distribuzione omogenea ed altamente dispersa dei domini catalitici che appaiono come particelle sferiche a dimensioni uniformi e di diametro pari a circa 2-3 ?m. Inoltre, in condizioni controllate, è stato possibile ottenere una membrana porosa da poter utilizzare in un reattore a flusso continuo. Nelle condizioni testate, la fotoossigenazione con (RfN)4W10O32 dà benzilidroperossido ed il corrispondente alcool e chetone. E’importante evidenziare come la fotoossigenazione di tetralina ed indano proceda con TON>6000 e con una elevata selettività in alcool, fornendo così un’ importante alternativa ad altri sistemi di ossigenazione basati su meccanismi di tipo radicalico. Poliossometallati fluorurati sono stati sintetizzati anche tramite l’approccio di funzionalizzazione covalente. Questa strategia prevede l’impiego di poliossotungstati lacunari e organosilil cloruri CF3(CF2)7CH2CH2SiCl3 (RfSiCl3) a dare derivati ibridi per mezzo dell’attacco covalente dei gruppi organici sulla superficie del POM. I complessi finali risultanti, con formula generale Q4[(RfSi)xOySiWwOz], isolati come sali di tetrabutilammonio (Q+) sono stati caratterizzati ed impiegati come catalizzatori per l’epossidazione di diverse olefine in presenza di H2O2. Studi cinetici e meccanicistici hanno fornito diverse indicazioni circa l’esistenza di un effetto sinergico fra i catalizzatori e il solvente per fluorurato utilizzato (HFIP). E’importante sottolineare come questa reazione attivata da microonde produca epossido in rese quantitative dopo soli 20 minuti anche per le olefine terminali. Ulteriori aspetti trattati riguardano le caratteristiche auto-assemblanti di questi complessi fluorurati anfifilici. Fenomeni di aggregazione in soluzione di HFIP sono stati studiati tramite DLS e tramite microscopia elettronica allo stato solido. Anche l’eterogeneizzazione di questo sistema è stata ottenuta tramite l’approccio di funzionalizzazione covalente. In questo caso, il poliossotungstato lacunare è stato fatto reagire con un silano che porta una catena alchilica insatura terminale: CH2=CH(CH2)6SiCl3 (RSiCl3). La morfologia e la struttura del materiale ibrido risultante sono state modulate attraverso la variazione del rapporto dei solventi porogenici e dei comonomeri impiegati nella miscela di polimerizzazione. Il polimero ibrido finale presenta l’interessante proprietà di rigonfiare in alcool fluorurati, dove l’epossidazione di cis-cicloottene avviene con rese quantitative in 15 minuti. Infine, è stato studiato il processo POM-catalizzato per la sintesi di fenolo: uno degli intermedi e commodity a più alto valore di mercato. A questo scopo l’attività di ricerca è stata incentrata sullo studio sia del processo autoossidativo, sia della mono-idrossilazione diretta del benzene. (i) L’applicazione di tecniche di Tandem Catalisi, allo scopo di sfruttare la produzione con sistema a membrana foto catalitica del cumilidroperossido da cumene, e promuoverne la sua decomposizione a fenolo in un secondo stadio con un catalizzatore POM-acido, (ii) lo screening di diversi molibdovanadati come catalizzatori da usare con H2O2 per l’idrossilazione di benzene. Nel primo caso, la Tandem Catalisi permette di ottenere una resa in fenolo pari a 63% rispetto alle moli iniziali di cumilidroperossido, nel secondo caso, con H4Mo11VO40 si ha un miglioramento dei dati di letteratura per ottimizzazione della reazione con 17% di conversione, selettività = 90% e TOF = 22.5 h-1.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Chapter 1 details the synthesis of tungsten imidoalkylidene compounds bearing strongly electron-withdrawing imido ligands. An alternative synthesis involving the treatment of WCl6 with 4 equivalents of N-trimethylsilyl-substituted anilines and subsequent workup with 1,2-dimethoxyethane (DME) has been employed to form complexes of the type W(NAr)2C12(dme); syntheses employing WO2C 2(dme) as the tungsten precursor were unsuccessful. Alkylation with neopentylmagnesium chloride (ClMgNp) and subsequent treatment with trifluoromethanesulfonic acid (HOTf) affords imidoalkylidene species W(NAr)(CHCMe 3)(OTf)2(dme) (OTf = trifluoromethanesulfonate); analogous neophylidene ([W]CHCMe 2Ph) species could not be made under these conditions. Treatment of these compounds with two equivalents of LiO(2,6-(CHCPh 2)C6H3)-Et2O affords the bisaryloxide complexes of the type W(NAr)(CHCMe3)(OR)2. Ring-Opening Metathesis Polymerization (ROMP) studies using a series of these bisaryloxides show that rates of ROMP increase as the electron-withdrawing power of the substituents on the imido ligand increase if steric bulk about the metal center is held constant. A similar trend between two bisaryloxides is observed for anti-to-syn alkylidene rotation rates at 50*C in toluene-d8 . Difficulties synthesizing bis-pyrrolide complexes of the type W(NAr)(CHCMe3)(pyr)2 precluded their use as catalyst precursors; some MAP species containing the more sterically encumbering 2,5-dimethylpyrrolide ligand are presented and the metathesis activity of MAP species bearing the 2,5-dimethylpyrrolide ligand is discussed. Chapter 2 introduces Mo and W complexes bearing the current extreme in sterically bulky imido ligands, the NHIPT (HIPT = 2,6-(2,4,6-iPr 3CH2)CH3) ligand, in an effort to generate all anti alkylidene species. A non-traditional synthetic route is employed in order to install this ligand first as an anilide, and after subsequent proton transfer, as an imido ligand to form a mixed imido species of the type M(NHIPT)(N'Bu)(NH'Bu)Cl. Addition of one equivalent of 2,6-lutidinium chloride, followed by alkylation affords dialkyl species M(NHIPT)(N'Bu)Np 2, and treatment with three equivalents of pyridinium chloride yields all anti imidoalkylidene dichloride species as mono-pyridine adducts, M(NHIPT)(CHCMe 3)C 2(py) (M = Mo, W). General reactivity, including strategies for removal of the pyridine adduct as well as substitution and metathesis chemistry, are discussed. ROMP of MPCP (MPCP = 3-methyl-3-phenylcyclopropene) by a Mo-based MAP species bearing the NHIPT ligand yields predominantly cis,syndiotactic poly(MPCP) and in the homo-metathesis of 1 -octene yields ~81% cis-7-tetradecene. The possible source of trans olefinic product is addressed. Chapter 3 presents the synthesis of the first (1-adamantyl)imido species of tungsten. The functional equivalent of common bisimido precursors for other Mo/W alkylidene species, [W(NAd) 2C 2(AdNH2)1 2, is shown to be a dimer stabilized by hydrogen-bonding interactions between adamantylamine protons and adjacent chlorides bound to the second metal of the dimer. Subsequent alkylation with ClMgNp affords the expected dialkyl species, and treatment with three equivalents of 3,5-lutidinium chloride affords imidoalkylidene complex W(NAd)(CHCMe 3)(C) 2(lut)2 (lut = 3,5-dimethylpyridine). The most desirable synthetic route toward monoalkoxide pyrrolide (MAP) species proceeds through a monoaryloxide monochloride intermediate W(NAd)(CHCMe 3)(Cl)(OAr)(lut) (Ar = 2,6-(2,4,6-Me 3)C6H3, 2,6-(2,4,6-'Pr 3)C6H3). Removal of lutidine with B(C6 F5 )3 and subsequent treatment with lithium pyrrolide affords W(NAd)(CHCMe3)(pyr)(OAr) (pyr = pyrrolide); 2,5-dimethylpyrrolide analogues (W(NAd)(CHCMe3)(Me2pyr)(OAr) can be accessed via protonolysis by HOAr from W(NAd)(CHCMe3)(Me2pyr)2(lut).
by Jonathan Clayton Axtell.
Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.
Vita.
Includes bibliographical references.
Enantiomerically pure molybdenum imido alkylidene complexes of the type Mo(NAr)(CHCMe₂Ph)[Ar'](THF), which contained 3,3'-diaryl (Ar' = Mes (21), Ph (22)) substituted binaphtholate ligands, were prepared and structurally characterized. Complex 21 was a trigonal bipyramidal anti alkylidene complex; both 21 and 22 were anti-THF adducts. Temperature and concentration dependent enantioselective desymmetrization of prochiral trienes by catalyst 21 afforded five- and six-membered heterocycles in >90% conversion and >90% ee. Consumption of the six-membered substrate followed pseudo first-order kinetics. The new catalyst was compatible with a variety of common functional groups. The longevity of the catalysts depended on the concentration of ethylene in solution. The resting state of the catalytic cycle, unsubstituted molybdacyclobutane 70, slowly decomposed to yield propylene. This observation suggests that β-hydride elimination can compete with bimolecular coupling of methylene complexes under some conditions. Chapter 2: Racemic and enantiomerically pure tungsten imido alkylidene complexes, W(NAr)-(CHCMe₂Ph)(Biphen) (23a, Ar = 2,6-i-Pr₂C₆H₃) and W(NAr')(CHCMe₂Ph)(Biphen) (23b, Ar' = 2,6-Me₂C₆H₃) were prepared and shown to be viable catalysts for representative asymmetric ring- closing metathesis reactions. Both catalysts were compatible with a variety of common functional groups. Intermediate tungstacyclobutane complexes were observed when a stoichiometric amount of desymmetrization substrate 62 was added to 23a. The final stable complex 78, formed between the ring-closed product and a tungsten methylene complex, was structurally characterized. Isotopic labeling experiments with ¹³C₂H₄ allowed the observation of
(cont.) unsubstituted tungstacyclobutane complexes (82), ethylene complexes (84), tungstacyclopentane complexes (86), and a heterochiral methylene dimer (85a). The tungstacyclopentane complexes catalyzed slow dimerization of ethylene to 1-butene. The observation of the methylene dimer provides the first direct evidence of a bimolecular decomposition pathway for methylene complexes. Chapter 3 Racemic and enantiomerically pure molybdenum alkylimido alkylidene complexes, Mo(NAd)(CHCMe₂Ph)(Biphen) (19d, Ad = 1-adamantyl) and Mo(NAd)(CHCMe₂Ph)[Trip]-(THF) (20d) were prepared and structurally characterized. Complex 19d was observed almost exclusively as a syn alkylidene isomer, in contrast with 20d which was observed almost exclusively as an anti-THF adduct. Complexes 19d and 20d are the only reported chiral alkylimido alkylidene complexes for enantioselective olefin metathesis reactions. Complex 19d is the first crystallographically characterized four-coordinate adamantylimido alkylidene complex in its base-free form. It offers unique reactivity and selectivity profiles in tandem AROM/RCM and AROM/CM reactions. Complex 19d is compatible with a variety of common functional groups, including boron-containing reagents. Van't Hoff analyses suggest that the bias toward syn-19d isomer is entropy-driven. Chapter 4: Solvent- and base-free molybdenum methylene complexes, Mo(NAr)(Biphen)(CH₂) (114a, Ar = 2,6-i-Pr₂C₆H₃) and Mo(NAd)(Biphen)(CH₂) (114d, Ad = 1-adamantyl) ...
by W.C. Peter Tsang.
Ph.D.

Use of renewable resources to replace petroleum base stocks in lubricants is attractive. Research on additives enhanced by current advances in genetic and chemical modifications has resulted in improved oxidative stability of vegetable oils. Like most oxidation processes, the oxidative degradation of vegetable oils is complex. The auto-oxidation free radical mechanisms and hydroperoxide theories of oxidation have been well studied. Factors that influence the degradation of oils include temperature, surface reactivity, rates of formation of radicals, chemical composition factors such as olefin and aromatic content and additive effectiveness. This uses pressurized differential scanning calorimetry to evaluate the oxidative stability of four biodegradable fluids with and without additives. The oleic acid content of the four fluids ranged from 83 to 23 percent. Reaction kinetics are used to explain observed differences in phase transformation and polymerization reactions. Additive selection to obtain maximum effectiveness in the base stocks is reported.

The antioxidation properties of methylene bis(di-n-butyldithiocarbamate) (V 7723) - and tolutriazole derivative (V 887) - containing poly-a-olefin (PAO)-derived lubricants were evaluated by differential scanning calorimetry (DSC) and modified penn state micro-oxidation test (PMOT). DSC test measures incipient oxidation temperature (OT) and oxidation induction time (IT) of the lubricant at high temperatures and the oxidation stability of oil weight loss is measured by PMOT test. DSC test shows that OT and IT of V 7723-containing PAO were improved significantly by V 887 addition. PMOT test indicates that when combining with V 7723 antioxidants, V 887 can also effectively reduce the increase in weight loss of PAO. In addition, FTIR results from PMOT test confirm that addition of V 887 can significantly enhance the oxidation induction time of oils. These results suggest that the V 7723 shows a good oxidative synergism with V 887 antioxidant.

In this paper, we studied the high temperature oxidation stability of hydrogenated lubricant base oils used in automobile engine oil formations. Different oil from Daqing, Lanzhou and Kelamayi were investigated, and a hydro-isomerised poly alpha olefin oil PAO-6 produced by Mobile company was used as model oil. The influence of aromatic hydrocarbon, sulfur and nitrogen content of the base oils to their oxidation stability was investigated. The result indicated that, the high temperature oxidation stability of all these base oil was not good, but their thermo-stability was very good.

Catalytic partial oxidation (CPOX) of liquid fuels is an attractive option for producing a hydrogen-rich gas stream for fuel cell applications. However, the high sulfur content along with aromatic compounds present in liquid fuels may deactivate reforming catalysts. Deactivation of these catalysts by carbon deposition and sulfur poisoning is a key technical challenge. The relationship between catalyst supports and deactivation have been studied here for three catalysts (Rh/Ce0.5Zr0.5O2, Pt/Ce0.5Zr0.5O2, and Pt/Al2O3) in a fixed bed catalytic reactor using a mixture of n-tetradecane, 1-methylnaphthalene, and dibenzothiophene to simulate logistic fuels. Carbon production during CPOX reforming was directly related to olefin formation. Olefins, which are known coke precursors, were observed on the Pt catalysts during CPOX of n-tetradecane with no sulfur (particularly from Pt/Al2O3), but not on Rh/Ce0.5Zr0.5O2. For the Rh/Ce0.5Zr0.5O2, yields of H2 and CO dropped to a stationary level after the introduction of sulfur-containing feed (1000 ppm sulfur) or aromatic-containing feed (5 wt%), however, the catalyst activity was restored after removing the sulfur or aromatics from the feed. For the Pt catalysts, H2 and CO yields dropped continuously over time in the presence of sulfur or aromatics in feed. The superior performance of Rh/Ce0.5Zr0.5O2 can be attributed to the higher oxygen-ion conductivity of the Ce0.5Zr0.5O2 support as well as the activity of the Rh sites.

The antioxidation properties of molybdenum dialkyldithiocarbamate (M 807)- and p, p-dioctyldiphenylalmine (V 81)- or mixed octylated and butylated diphenylalmines (V 961)-containing poly-α-olefin (PAO)-derived lubricants were evaluated by differential scanning calorimetry (DSC) and modified penn state micro-oxidation test (PMOT). DSC test measures incipient oxidation temperature (OT) and oxidation induction time (IT) of the lubricant at high temperatures and the oxidation stability of oil weight loss is measured by PMOT test. DSC test shows that OT and IT of V 81-or V 961-containing PAO were improved significantly by M 807 addition. PMOT test indicates that when combining with V 81 antioxidants, M 807 can also effectively reduce the increase in weight loss of PAO and deposits formed in oils. These results suggest that the M 807 shows a good antioxidative synergism with alkylated diphenylamine antioxidants. In addition, FTIR results from PMOT test confirm that addition of M 807 can significantly enhance the oxidation induction time of oils containing V 81 and inhibit formation of oxidation products including carbonyl bonds or hydroxyl group.

High oleic palm oil (HOPO) is the result of an agricultural innovation. A non-GMO palm, more resistant to diseases such as bud rot, with a higher oil yield per area than E.guineensis palm, was obtained. Its oil is mostly unsaturated; its oleic acid content is 10-15% higher compared to African palm oil. It has a higher content of beta-carotene (pro-vitamin A) and natural antioxidants such as tocotrienols and tocopherols (Vitamin E).HOPO can be refined by a special process that allows the oil to retain most of the nutritional components that are present in the crude oil. A refined red colored oil is obtained, with high beta-carotene and vitamins content, which can be fractionated to produce red oleins and stearins, for various applications where its color and nutritional value can be exploited.The objective of this conference is to share our experience in the use and commercialization of HOPO, highlighting its advantages in the formulation of edible oils and in industrial applications.High oleic red palm olein can be used as a cooking oil in households, imparting a pleasant reddish-gold color to food. Both red olein and stearin can be used in the production of baked goods, allowing these foods to retain part of the vitamins given by the oil, and as a source of natural beta-carotene.Traditionally refined high oleic palm olein, being more unsaturated than E. guineensis palm olein, is more resistant to crystallization in cold climates, which allows it to replace imported seed oils in edible oil formulas. Industries that produce snacks and fried foods also use this oil due to its high resistance to oxidation and its lower content of saturated fatty acids than traditional palm olein, facilitating the production of shortenings reduced in saturated fat, which is increasingly required by different industries in Latin America.

The aim of this study was to analyze the properties of cold pressed pumpkin and walnut oil. Pumpkin and walnut are plant crops that have a long tradition of cultivation in Serbia, but are insufficiently used for oil production. Cold pressed oils have a high nutritional and market value. The production of cold-pressed oils is more environmentally friendly, simpler, and the oils retain important nutrients, compared to producing oils by extraction and refining. Pumpkin seed oil is characterized by a high content of polyunsaturated fatty acids in relation to the content of monounsaturated and saturated fatty acids. The dominant fatty acid is oleic or linoleic. Oils with a higher proportion of oleic acid are more oxidatively stable. Specifically, pumpkin oil is dominated by the presence of ∆7 sterols, unlike other vegetable oils. Walnut oil is dominated by polyunsaturated fatty acids, with a significant amount of C18:3, which makes it sensitive to oxidation. The oxidative stability of walnut oil is correlated with a decrease in the content of C18:3 fatty acids. The chemical composition of the oil varies significantly depending on the variety and growing conditions in both pumpkin and walnuts. then there is a potential in the determination of suitable genotypes with oil of greater oxidative stability.