Synthesis, characterization, and reactivity of actinide complexes bearing An-E bonds (An = Th, U; E = P, As)

Organoactinide complexes bearing An-E (An = Th, U; E = P, As) bonds were synthesized and reactivity studies were performed with various unsaturated and industrially/environmentally relevant small molecules in an effort to elucidate further information regarding their functionalization, and to expand the currently limited knowledge on actinide phosphido/arsenido chemistry. Reaction of isostructural, primary pnictido complexes of the form (C5Me5)2An[P(H)Mes]2 exhibited insertion-type reactivity with tBuCN, tBuNC, CO2 and CO. The products with CO2 and tBuNC were isostructural between Th, and U, resulting in the bis(phosphinocarboxylato), and phosphaazaallene complexes, (C5Me5)2An[[kappa]2-(O,O)-O2CP(H)Mes]2, and (C5Me5)2An[(CNtBu)([eta]2-(C,N)-tBuNC=PMes)]2, respectively. Divergent reactivity was observed with tBuCN, and CO, producing the U(IV) bis(ketimido) complex (C5Me5)2U[[kappa]2-(N,N)-(N=CtBu)2(PMes)]2, formed via elimination of free H2PMes, and (C5Me5)2U[([kappa]2-(O,O)-O2C(PMes)C(H)P(H)Mes], for which mechanistic analysis (DFT) attributed the difference to lower the acidity of the U-center to that of Th. Reaction of (C5Me5)2Th[P(H)Mes]2 with MN(SiMe3)2 (M = Na, K, Rb, Cs) leads to deprotonation of the P-H proton, leading to formation of alkali-metal phosphinidiide complexes of the form {(C5Me5)2Th[[mu]2-P(Mes)][[mu]2-P(H)Mes]M(L)n}2 (L = THF, Et2O), where computational (DFT) analysis and 31P NMR spectroscopy suggests significant Th-P multiple bond character. Reaction of (C5Me5)2Th[P(H)Mes]2 with CuMes in a 2:3 molar ratio leads to the formation of the bimetallic cluster, (C5Me5)2Th[([mu]2-PH(Mes)P(Mes)]Cu}2Cu[[mu]2-PH(Mes)]. Reaction of (C5Me5)2ThMe2 with H2PMes in a 2:1 molar ratio leads to the formation of the T-shaped, bridging Th-phosphinidiide, [(C5Me5)2Th]2(P-2,6-CH2C6H2-4-CH3) as a result of C-H bond activation at the o-CH3 groups on the mesityl ring. Computational analysis (DFT) of the mechanism reveals that it progresses a different mechanism than that of the previously published and analogous reaction with H2PTipp (Tipp = 2,4,6-triisopropylphenyl), yielding [(C5Me5)2Th]2([mu]2-P[(2,6-CH2CHCH3)2-4-iPrC6H2]. A comparative study was carried out in which isostructural Th and U complexes bearing bonds to P and As was conducted, yielding primary bis(pnictido) complexes of the form (C5Me5)2An[E(H)Mes]2, dipnictido complexes of the form (C5Me5)2Th([eta]2-E2Mes2), bridging bis(pnictinidiide) complexes of the form [(C5Me5)2U]2([mu]2-AsMes)2 (with the exception of An = Th, E = P, which underwent C-H bond activation to form {(C5Me5)2Th[[mu]2-P(H)(2,4-Me2C6H2-6-CH2)]}2), and the terminal, U-phosphinidene complex, (C5Me5)2U(=PMes)OPPh3. Attempts were made to generate terminal arsinidene complexes from the bridging bis(arsinidiide) complexes by reaction with 2 molar equivalents of OPPh3, but the oxo group was abstracted in the case of the Th-arsinidiide with concomitant elimination of 0.5 Mes-As=As-Mes, resulting in the bridging oxo complex [(C5Me5)2Th]2([mu]2-AsMes)([mu]2-O). The analogous reaction between [(C5Me-5)2U]2([mu]2-AsMes)2 and OPPh3 results in reduction of the U(IV/IV) centers and concomitant coupling of the arsinidiide ligands to form the U(III/III) diarsenido/OPPh3 adduct ion pair, [(C5Me5)2U([eta]2-As2Mes2)][(C5Me5)2U(OPPh3)2]. Following this study, the An-diarsenido complexes were reacted with CO and isoelectronic analog, tBuNC, forming the adducts (C5Me5)2An([eta]2-As2Mes2)(CNtBu) and (C5Me5)2An([eta]2-As2Mes2)(CO). The latter complexes represent very are examples of characterizable carbonyl compounds of f elements

Content-Based Colour Transfer

International audienceThis paper presents a novel content-based method for transferring the colour patterns between images. Unlike previous methods that rely on image colour statistics, our method puts an emphasis on high-level scene content analysis. We first automatically extract the foreground subject areas and background scene layout from the scene. The semantic correspondences of the regions between source and target images are established. In the second step, the source image is re-coloured in a novel optimization framework, which incorporates the extracted content information and the spatial distributions of the target colour styles. A new progressive transfer scheme is proposed to integrate the advantages of both global and local transfer algorithms, as well as avoid the over-segmentation artefact in the result. Experiments how that with a better understanding of the scene contents, our method well preserves the spatial layout, the colour distribution and the visual coherence in the transfer process. As an interesting extension, our method can also be used to re-colour video clips with spatially-varied colour effects

Binding, activation, and transformation of carbon dioxide mediated by anionic metal complexes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.Pages 180 and 181 blank. Cataloged from PDF version of thesis.Includes bibliographical references.The vanadium nitride complex [Na][NV(N['Bu]Ar) 3] reacts with CO to produce the vanadium tris-anilide complex V(N['Bu]Ar)3 and NaNCO. This is the first example of complete denitrogenation of a termainal nitride complex with generation of a lower coordinate metal complex. This reactivity contrasts sharply with the reactivity of the niobium analogue, where the nitride anion complex [Na][NNb(N['Bu]Ar) 3] is synthesized from the reductive decarbonylation of the niobium(IV) isocyanate complex (OCN)Nb(N['Bu]Ar) 3. Electrochemical studies of the niobium(IV) and vanadium(IV) isocyanate (OCN)V(N['Bu]Ar) 3 complexes are presented. The reactivity of the vanadium carbamate complex [(THF) 2Na][O2CNV(N['Bu]Ar) 3] with electrophilic reagents is presented. The carbamate complex reacts readily with silylation and alkylation reagents to form the carbamate ester complexes of the type ROC(O)NV(N['Bu]Ar) 3. The vanadium carbamate complex reacts with SO2 via a decarboxylation pathway to produce the sulforyl imido complex [Na][O 2SNV(N['Bu]Ar)3], the solid-state structure of which is presented. The reactivity of the vanadium carbamate complex with typical dehydrating reagents, e.g organic acid anhydrides, is shown to proceed cleanly when cobaltocene, acting as an in situ reductant, is present to form the vanadium(IV) isocyanate complex (OCN)V(N['Bu]Ar) 3. The synthesis and structure of the bimetallic complex (TPP)MnOC(O)NV(N['Bu]Ar) 3 (TPP = tetraphenylporphyrin) is presented. Although thermally stable, the complex undergoes a photochemical transformation that forms the vanadium isocyanate complex and putative OMn(TPP), which reacts with triphenylphosphine in the reaction mixture to produce triphenylphosphine oxide. The synthesis the niobium carbamate complex [Na][O 2CNNb(N['Bu]Ar) 3] from the reaction of [Na][NNb(N[Bu]Ar) 3] with CO2 is presented. Its solid-state structure in the form of the ionpair [(12-crown-4) 2Na][O2CNNb(N['Bu]Ar) 3] has been determined. Reaction of the niobium carbamate complex with organic acid anhydrides results in the production of five-coordinate carboxylate, acetate complexes (RC(O)O)(OCN)Nb(N['Bu]Ar) 3. The reduction of these complexes by two electrons results in the regeneration of the niobium nitride complex (60-80% yield) with concomitant release of CO (30-60% yield). This three-step process represents a highly controlled conversion of CO2 to CO via a ligand-based strategy. The reactivity of CO2 with anionic complexes featuring terminal multiply bonded ligands is extended to the oxo anion complex [(Et 2O)2Li][OTi(N['Bu]Ar) 3] resulting in the formation of the carbonate complex ([Li][O 2COTi(N['Bu]Ar) 3]) 6. The binding of CO2 to the oxo complex is reversible when 12-crown-4 is bound to the lithium countercation or if the complex is dissolved in THF. The thermodynamic parameters for the CO2 binding equilibrium have been measured. Exchanging the lithium countercation for sodium or potassium results in a significant weakening of the CO2 binding ability of the oxo complex.by Jared S. Silvia.Ph.D

Synthetic and Mechanistic Studies of Small-Molecule Activation at Low-Valent Iron, Cobalt, and Iridium Centers

The preparation of transition-metal systems for catalytic multielectron transformations of small molecules remains a significant challenge for synthetic chemists. The realization of new transformations often depends critically on the design of frameworks capable of stabilizing unusual oxidation states and molecular geometries, providing a frontier molecular-orbital landscape that is well suited to interact with the molecules of interest. This thesis has sought to address two particularly noteworthy challenges in the field of small-molecule activation, dinitrogen reduction and C–H bond functionalization, through judicious ligand choice and design. Chapters 2 and 3 describe the syntheses of new tri- and tetradentate hybrid ligands incorporating a single X-type donor (amido or silyl) and multiple phosphine donors designed to stabilize low oxidation states at iron and cobalt and support dinitrogen reduction and other multielectron redox transformations. While the amidophosphine ligands do allow access to unusual monovalent iron and cobalt complexes, the isolation of dinitrogen adducts supported by these ligands remains elusive and the weakness of the silicon–nitrogen bond makes the complexes prone to decomposition. In contrast, the tris(phosphino)silyl ligands presented in Chapter 3 afford straightforward access to the first terminally bonded dinitrogen complexes of monovalent iron, and the structure of these and related complexes are described along with preliminary experiments showing that protonolysis of the iron(I)–dinitrogen complexes produces hydrazine in reasonable stoichiometric yields. Chapters 4 through 7 address the functionalization of ether and amine C–H bonds by a double C–H activation route. Chapter 4 describes the investigation of reactivity of low-valent, pincer-supported iridium species with a variety of ethers, leading to a number of selective C–H, C–C, and C–O bond cleavage events, affording in several cases iridium carbene complexes by double C–H activation and loss of dihydrogen. Chapter 5 presents an exploration of the electronic structure of the unusual square-planar iridium(I) alkoxycarbenes and their nucleophilic activation of several heterocumulene substrates, leading to multiple-bond metathesis events promoted by metal- rather than ligand-initiated reactivity. Chapter 6 describes the discovery of new atom and group transfer reactions from diazo reagents to the alkoxycarbenes and the implementation of these reactions in an unprecedented catalytic cycle for C=E bond formation by multiple C–H activations. Chapter 7 explores the related reactivity of a low-valent pincer iridium complex with methyl amines and the reactivity of the resulting iridium(III) dihydrido aminocarbenes, which is shown to diverge substantially from that observed for the iridium(I) carbene species.</p

Semantic portrait color transfer with internet images

We present a novel color transfer method for portraits by exploring their high-level semantic information. First, a database is set up which consists of a collection of portrait images download from the Internet, and each of them is manually segmented using image matting as a preprocessing step. Second, we search the database using Face++ to find the images with similar poses to a given source portrait image, and choose one satisfactory image from the results as the target. Third, we extract portrait foregrounds from both source and target images. Then, the system extracts the semantic information, such as faces, eyes, eyebrows, lips, teeth, etc., from the extracted foreground of the source using image matting algorithms. After that, we perform color transfer between corresponding parts with the same semantic information. We get the final transferred result by seamlessly compositing different parts together using alpha blending. Experimental results show that our semantics-driven approach can generate better color transfer results for portraits than previous methods and provide users a new means to retouch their portraits

Functional –ESiMe3 Containing Reagents: From Organo-polychalcogenolates to NHC Ligated M-E-SiMe3

The reaction of M[ESiMe3] (M = Li/Na; E = S, Se) with polyorganobromides, has afforded polychalcogenotrimethylsilane complexes Ar(CH2ESiMe3)n: 1,4-(Me3SiECH2)2(C6Me4) (E = S, 1; E = Se, 2), 1,3,5-(Me3SiECH2)3(C6Me3) (E = S, 3; E = Se, 4) and 1,2,4,5-(Me3SiECH2)4(C6H2)(E = S, 5; E = Se, 6). The powerful potential of these complexes as precursor to combine with other organic reagents such as acyl halides (here ferrocenoyl chloride) lead to polyferrocenylchalcogenoesters: [1,4-{FcC(O)ECH2}2(C6Me4)] (E = S, 7; E = Se, 8), [1,3,5-{FcC(O)ECH2}3(C6Me3)] (E = S, 9; E = Se, 10) and [1,2,4,5-{FcC(O)ECH2}4(C6H2)] (E = S, 11; E = Se, 12). Two new dichalcogenotrimethylsilane reagents 1,2-(Me3SiSCH2)2(C6H4), 13 and 1,2-(Me3SiSeCH2)2(C6H4), 14 were prepared to further expand the series above. These two new reagents were prepared from 1,2-(BrCH2)2(C6H4) and Li[ESiMe3]. Their reactivity towards metal salts and M-E bond formation was demonstrated when 13 and 14 were reacted with [PdCl2(dppp)] to give two analogous dinuclear organochalcogenolate-bridged complexes [(dppp)2Pd2-μ-κ2S-{1,2-(SCH2)2C6H4}]X2, [15]X2 and [(dppp)2Pd2-μ-κ2Se-{1,2-(SeCH2)2C6H4}]X2, [16]X2 (X = Cl, Br) respectively. To expand this methodology, the tetranuclear palladium complex [(dppp)4Pd4-μ-κ4S-{1,2,4,5-(SCH2)4C6H2}]X4, [17]X4 (X = Cl, Br) was isolated when complex 5 was reacted with a suspension of [PdCl2(dppp)] in the presence of LiBr, as a source of counter ion. The reactivity of the polychalcogenotrimethylsilanes was developed with a different coordination chemistry system, namely the addition of [(IPr)CuOAc] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to solutions of 1, 2, 3, 4 and 6 and the previously reported 1,1´-fc(CH2ESiMe3)2 to yield the poly(NHC)-copper-chalcogenolate complexes, 1,4-[{(IPr)CuECH2}2(C6Me4)] (E = S 18, E = Se 19), 1,1’-[fc{CH2ECu(IPr)}2] (E = S 20, E = Se 21), 1,3,5-[{(IPr)CuECH2}3(C6Me3)] (E = S 22, E = Se 23) and 1,2,4,5-[{(IPr)CuSeCH2}4(C6H2)] (24). The copper-chalcogenolate [(IPr)Cu-ESiMe3] (E = S 25, Se 26, Te 27) have been prepared from [(IPr)CuOAc] and E(SiMe3)2. Single crystal X-ray analysis illustrates that the structures of complexes 25-27 exhibit a pendant –SiMe3 group bonded to a chalcogen atom with a near linear coordination geometry about the copper centre. Reaction of Hg(OAc)2 with freshly prepared 25 [(IPr)Cu-SSiMe3] yielded the ternary cluster [{(IPr)CuS}2Hg], 28 via activation of the S-Si bonds. This straightforward approach has also been extended by i) substituting copper(I) with silver(I) and ii) by using the smaller NHC iPr2-bimy (1,3-diisopropylbenzimidazolin-2-ylidene) instead of IPr. The reaction of [(IPr)AgOAc] with one equivalent of E(SiMe3)2 (E = S, Se) yielded [(IPr)Ag-ESiMe3] (E = S 29, Se 30). The addition of two equivalents of [(IPr)Ag-SSiMe3] to a solution of one equivalent of Hg(OAc)2 in THF led to the first example of a Ag-Hg-sulfide cluster [{(IPr)CuS}2Hg], 31, which is isostructural with 28. Similar reactions between [(iPr2-bimy)CuOAc] and E(SiMe3)2 (E = S, Se) led to the formation of two new metal-chalcogen complexes, [(iPr2-bimy)Cu-ESiMe3] (E = S 32, Se 33). Unlike the IPr containing complexes 25-27, 29 and 30, [(iPr2-bimy)Cu-ESiMe3] exist as dimers in the solid state; this can be attributed to the smaller size of the coordinated iPr2-bimy compared to IPr. One consequence of the varying ligand size is demonstrated with the reaction between [(iPr2-bimy)Cu-SSiMe3] and Hg(OAc)2 which leads to the formation of a ternary cluster with a Cu10S8Hg3 core surrounded by six iPr2-bimy ligands, [(iPr2-bimy)6Cu10S8Hg3], 34

Individualized Models of Colour Differentiation through Situation-Specific Modelling

In digital environments, colour is used for many purposes: for example, to encode information in charts, signify missing field information on websites, and identify active windows and menus. However, many people have inherited, acquired, or situationally-induced Colour Vision Deficiency (CVD), and therefore have difficulties differentiating many colours. Recolouring tools have been developed that modify interface colours to make them more differentiable for people with CVD, but these tools rely on models of colour differentiation that do not represent the majority of people with CVD. As a result, existing recolouring tools do not help most people with CVD. To solve this problem, I developed Situation-Specific Modelling (SSM), and applied it to colour differentiation to develop the Individualized model of Colour Differentiation (ICD). SSM utilizes an in-situ calibration procedure to measure a particular user’s abilities within a particular situation, and a modelling component to extend the calibration measurements into a full representation of the user’s abilities. ICD applies in-situ calibration to measuring a user’s unique colour differentiation abilities, and contains a modelling component that is capable of representing the colour differentiation abilities of almost any individual with CVD. This dissertation presents four versions of the ICD and one application of the ICD to recolouring. First, I describe the development and evaluation of a feasibility implementation of the ICD that tests the viability of the SSM approach. Second, I present revised calibration and modelling components of the ICD that reduce the calibration time from 32 minutes to two minutes. Next, I describe the third and fourth ICD versions that improve the applicability of the ICD to recolouring tools by reducing the colour differentiation prediction time and increasing the power of each prediction. Finally, I present a new recolouring tool (ICDRecolour) that uses the ICD model to steer the recolouring process. In a comparative evaluation, ICDRecolour achieved 90% colour matching accuracy for participants – 20% better than existing recolouring tools – for a wide range of CVDs. By modelling the colour differentiation abilities of a particular user in a particular environment, the ICD enables the extension of recolouring tools to helping most people with CVD, thereby reducing the difficulties that people with CVD experience when using colour in digital environments

Transfert de couleurs et colorisation guidés par la texture

National audienceCet article se concentre sur deux problèmes de manipulation de couleurs liés : le transfert de couleurs qui modifie les couleurs d'une image, et la colorisation qui ajoute des couleurs à une image en niveaux de gris. Les méthodes automatiques pour ces deux applications modifient l'image d'entrée à l'aide d'une image de référence contenant les couleurs désirées. Les approches précédentes visent rarement les deux problèmes simultanement et souffrent de deux principales limitations : les correspondances créées entre les images d'entrée et de référence sont incorrectes ou approximatives, et une mauvaise cohérence spatiale autour des structures de l'image. Dans cet article, nous proposons un pipeline unifiant les deux problèmes, basé sur le contenu texturel des images pour guider le transfert ou la colorisation. Notre méthode introduit un descripteur de textures préservant les contours de l'image, basé sur des matrices de covariance, permettant d'appliquer des transformations de couleurs locales. Nous montrons que notre approche est capable de produire des résultats comparables ou meilleurs que d'autres méthodes de l'état de l'art dans les deux applications

Nitrogen Cycle Chemistry with Metal-Pincer Complexes Relevant to Electrochemical Nitrogen Fixation

The large-scale industrial fixation of N2 to NH3 through the Haber-Bosch process has cemented itself as the primary means to provide N for fertilizer and commodity chemicals globally. However, our dependence on this process is unsustainable in the long term due to its reliance on fossil fuels to generate H2 and to provide the substantial energy input for the reaction, paired with high infrastructure requirements that necessitate centralized synthesis plants and sophisticated transportation networks. As an alternative, electrochemical fixation of N2, coupling water oxidation to provide proton (H+) and electron (e–) equivalents with the N2 reduction reaction (NRR) to achieve the 6H+/6e– reduction of N2 to 2 NH3, could operate on a smaller, localized scale while utilizing renewable sources to generate electrical energy to drive the reaction. A key challenge in achieving electrochemical N2 fixation is the development of catalysts for electrochemical NRR. Existing heterogeneous catalysts for NRR suffer from poor activity, selectivity, and robustness. Insights that aid the development of better NRR catalysts may be found by studying molecular systems that can reduce N2. This thesis probes potential N2 functionalization pathways that could be involved in electrochemical NRR by studying molecular model systems in which N2 binds to, or is cleaved by, reduced metal-pincer complexes. Chapter 1 describes electrochemical N2 fixation as an alternative to the Haber-Bosch process. A molecular approach towards understanding electrochemical NRR is proposed, especially through bimetallic N2 cleavage to form metal nitrides. Strategies for the subsequent functionalization of the metal nitride are discussed, primarily via proton-coupled electron transfer (PCET) reduction of the nitride into NH3. Challenges involved in PCET nitride reduction, as well as opportunities inspired by molecular N2 reduction catalysts and recent discoveries of potent PCET reagents, are identified and applied to a hypothetical system for electrochemical NRR. Chapter 2 describes the protonation and electrochemical reduction of Ir- and Rh-pincer complexes that can strongly bind N2. The potential utility of these complexes in an electrochemical NRR system are assessed by complimentary electrochemical and spectroscopic studies exploring their stepwise protonation and electrochemical reduction. Protonation was found to be a prerequisite for electrochemical reduction of the N2 complexes, with protonation occurring at the metal center to form metal hydrides. Protonation triggers release of the N2 ligand, preventing reductive N2 functionalization with these complexes. Chapter 3 investigates the possibility of oxidative functionalization of an N2-derived Re nitride in order to form NOx species. Although no N–O bond formation was achieved at the nitride, a series of Re nitrides was synthesized and characterized in which the metal center is oxidized by 1e– and/or the supporting pincer ligand is oxidized to a nitroxide. The Re-nitride interaction was monitored over the series using NMR and IR spectroscopies, X-ray crystallography, and computational methods. Cooperative oxidation of both the metal center and the supporting ligand results in the weakest Re-nitride interaction, more localization of the LUMO at the nitride ligand, and an umpolung in nitride reactivity. Chapter 4 applies PCET methods to N2-derived Re nitrides in an attempt to reduce the nitride to NH3, thus closing the cycle of N2 to NH3. Stepwise PCET mechanisms were prohibited by high-energy intermediates in both systems; however, the combination of SmI2 and H2O to generate a strong concerted PCET reagent resulted in formation of 74% yield of NH4+ in one system, but exclusive production of H2 in the other. Other PCET methods, such as pairing organic H-atom transfer reagents with SmI2, are also assessed for PCET nitride reduction. Chapter 5 studies the conversion of NH3 to a nitride in a Re system that can also cleave N2. Re-ammine and Re-amide intermediates were isolated, and the mechanisms of H atom removal from these to form the nitride were identified. Experimental determination of the N–H bond enthalpies in the Re-amide were used to benchmark computational studies elucidating the thermodynamics of N–H bond cleavage (and formation, the microscopic reverse). The putative Re-imide intermediate in the PCET reduction pathway was found to feature a particularly weak N–H bond, representing a thermodynamic bottleneck to PCET nitride reduction in this system