Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel-Boron Cooperativity in a PBP-Ni Complex.

The synthesis and characterization of (tBu PBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni-C bond of (tBu PBP)NiMe (1) is presented. An unexpected CO2 cleavage process involving the formation of new B-O and Ni-CO bonds leads to the generation of a butterfly-structured tetra-nickel cluster (tBu PBOP)2 Ni4 (µ-CO)2 (6). Mechanistic investigation of this reaction indicates a reductive scission of CO2 by O-atom transfer to the boron atom via a cooperative nickel-boron mechanism. The CO2 activation reaction produces a three-coordinate (tBu P2 BO)Ni-acyl intermediate (A) that leads to a (tBu P2 BO)-NiI complex (B) via a likely radical pathway. The NiI species is trapped by treatment with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to give (tBu P2 BO)NiII (η2 -TEMPO) (7). Additionally, 13 C and 1 H NMR spectroscopy analysis using 13 C-enriched CO2 provides information about the species involved in the CO2 activation process.

Ethylene Dimerization and Oligomerization Using Bis(phosphino)boryl Supported Ni Complexes.

We report the dimerization and oligomerization of ethylene using bis(phosphino)boryl supported Ni(II) complexes as catalyst precursors. By using alkylaluminum(III) compounds or other Lewis acid additives, Ni(II) complexes of the type (RPBP)NiBr (R = tBu or Ph) show activity for the production of butenes and higher olefins. Optimized turnover frequencies of 640 molethylene·molNi-1·s-1 for the formation of butenes with 41(1)% selectivity for 1-butene using (PhPBP)NiBr, and 68 molethylene·molNi-1·s-1 for butenes production with 87.2(3)% selectivity for 1-butene using (tBuPBP)NiBr, have been demonstrated. With methylaluminoxane as a co-catalyst and (tBuPBP)NiBr as the precatalyst, ethylene oligomerization to form C4 through C20 products was achieved, while the use of (PhPBP)NiBr as the pre-catalyst retained selectivity for C4 products. Our studies suggest that the ethylene dimerization is not initiated by Ni hydride or alkyl intermediates. Rather, our studies point to a mechanism that involves a cooperative B/Ni activation of ethylene to form a key 6-membered borametallacycle intermediate. Thus, a cooperative activation of ethylene by the Ni-B unit of the (RPBP)Ni catalysts is proposed as a key element of the Ni catalysis.

Activation of Si-H and B-H bonds by Lewis acidic transition metals and p-block elements: same, but different.

In this Perspective we discuss the ability of transition metal complexes to activate and cleave the Si-H and B-H bonds of hydrosilanes and hydroboranes (tri- and tetra-coordinated) in an electrophilic manner, avoiding the need for the metal centre to undergo two-electron processes (oxidative addition/reductive elimination). A formal polarization of E-H bonds (E = Si, B) upon their coordination to the metal centre to form σ-EH complexes (with coordination modes η1 or η2) favors this type of bond activation that can lead to reactivities involving the formation of transient silylium and borenium/boronium cations similar to those proposed in silylation and borylation processes catalysed by boron and aluminium Lewis acids. We compare the reactivity of transition metal complexes and boron/aluminium Lewis acids through a series of catalytic reactions in which pieces of evidence suggest mechanisms involving electrophilic reaction pathways.

The explosion of digital storytelling. Creator's perspective and creative processes on new narrative forms.

Networked digital narratives are developed in a society marked by distrust in meta-narratives, liquidity and tension between Mass Media and New Media. This research aims to delve into these narratives from the creators' perspective, analyzing new formats, authors and creative processes that are put into practice. For that purpose, the applied methodology combines in-depth interviews with creators with discourse analysis, and arts based research with the technique of the research journal. The results reveal an overflow of the classical conception of narrative, a trend towards convergence, and the dominance of visual and sequential creative thinking over alphabetical-continuous thinking. It also shows a series of clues for the creation of digital narratives: interactivity, hypermedia, transmedia, virtuality and connectivity. Finally, we highlight that creators do not have preestablished guidelines and follow the procedure of trial and error for the construction of their narratives.

Enhancing the catalytic properties of well-defined electrophilic platinum complexes.

Platinum complexes have been often considered as the least reactive of the group 10 triad metals. Slow kinetics are behind this lack of reactivity but, still, some industrially relevant catalytic process are dominated by platinum compounds and sometimes different selectivities can be found in comparison to Ni or Pd. Nevertheless, during the last years, it has been reported that the catalytic behaviour of well-defined platinum derivatives can be improved through a judicious choice of their electronic and steric properties, leading to highly electrophilic or low-electron count platinum systems. In this feature article, we highlight some catalytic processes in which well-defined electrophilic platinum complexes or coordinatively unsaturated systems play an important role in their catalytic activity.

Ambiphilic boryl groups in a neutral Ni(ii) complex: a new activation mode of H2.

The concept of metal-ligand cooperation opens new avenues for the design of catalytic systems that may offer alternative reactivity patterns to the existing ones. Investigations of this concept with ligands bearing a boron center in their skeleton established mechanistic pathways for the activation of small molecules in which the boron atom usually performs as an electrophile. Here, we show how this electrophilic behavior can be modified by the ligand trans to the boron center, evincing its ambiphilic nature. Treatment of diphosphinoboryl (PBP) nickel-methyl complex 1 with bis(catecholato)diboron (B2Cat2) allows for the synthesis of nickel(ii) bis-boryl complex 3 that promotes the clean and reversible heterolytic cleavage of dihydrogen leading to the formation of dihydroborate nickel complex 4. Density functional theory analysis of this reaction revealed that the heterolytic activation of H2 is facilitated by the cooperation of both boryl moieties and the metal atom in a concerted mechanism that involves a Ni(ii)/Ni(0)/Ni(ii) process. Contrary to 1, the boron atom from the PBP ligand in 3 behaves as a nucleophile, accepting a formally protic hydrogen, whereas the catecholboryl moiety acts as an electrophile, receiving the attack from the hydride-like fragment. This manifests the dramatic change in the electronic properties of a ligand by tuning the substituent trans to it and constitutes an unprecedented cooperative mechanism that involves two boryl ligands in the same molecule operating differently, one as a Lewis acid and the other one as a Lewis base, in cooperation with the metal. In addition, reactivity towards different nucleophiles such as amines or ammonia confirmed the electrophilic nature of the Bcat moiety, allowing the formation of aminoboranes.

Bottom-Up Approaches to Synthetic Cooperation in Microbial Communities.

Microbial cooperation pervades ecological scales, from single-species populations to host-associated microbiomes. Understanding the mechanisms promoting the stability of cooperation against potential threats by cheaters is a major question that only recently has been approached experimentally. Synthetic biology has helped to uncover some of these basic mechanisms, which were to some extent anticipated by theoretical predictions. Moreover, synthetic cooperation is a promising lead towards the engineering of novel functions and enhanced productivity of microbial communities. Here, we review recent progress on engineered cooperation in microbial ecosystems. We focus on bottom-up approaches that help to better understand cooperation at the population level, progressively addressing the challenges of tackling higher degrees of complexity: spatial structure, multispecies communities, and host-associated microbiomes. We envisage cooperation as a key ingredient in engineering complex microbial ecosystems.

Tendencias de las publicaciones especializadas en el campo de la educomunicación y alfabetización mediática en Latinoamérica / Research trends in specialist publications from the field of educommunication and media literacy in Latin America / Tendências das publicações especializadas no campo da educomunicação e alfabetização midiática na América Latina

Se analizan tendencias recientes de investigación en comunicación publicadas en revistas de comunicación latinoamericanas más visibles en bases de datos de referencia y citación. La revisión se centra en los artículos de investigación publicados entre 2013 y 2017 en las nueve revistas latinoamericanas de comunicación incluidas en Scopus. La metodología se basa en la consulta de bases de datos, su sistematización a través de gestores bibliográficos y el análisis de contenido cualitativo de los textos recopilados, apoyado con el software de QDA NVIVO11. Se recopilan 167 artículos que abordan temáticas de educomunicación, alfabetización mediática y narrativas transmedia. Predomina la autoría individual y la afiliación a un solo país e institución, entre los cuales destacan Brasil y España. En relación con el contenido, predomina un enfoque temático sobre los medios y los entornos digitales y un abordaje cualitativo de las investigaciones.

This study analyzed recent research trends in communication research published in nine leading communication journals in Latin America. A literature review of scientific articles published between 2013 and 2017 was conducted using the Scopus database. A database query was run, together with the systematization of data using bibliographic management software and qualitative content analysis of selective texts using the QDA software NVivo 11. A total of 167 articles addressing the themes educommunication, media literacy, and transmedia narrative were analyzed. The majority of articles were written by individual authors belonging to a single institution and country, with emphasis on Brazil and Spain. With respect to content, the predominant themes were media and digital environments and the majority of studies used a qualitative approach.

Analisam-se as tendências recentes de pesquisa em comunicação publicadas nas nove revistas de comunicação mais significativas da América Latina. A pesquisa se centra na revisão dos artigos científicos publicados entre 2013 e 2017 em Scopus. A metodologia se baseia na consulta de bases de dados, sua sistematização por meio de gestores bibliográficos e a analise do conteúdo qualitativo dos textos selecionados, com o uso do software QDA NVIVO11. Estudam-se 167 artigos que abrangem temáticas de educomunicação, alfabetização midiática e narrativas transmídia. Pode-se identificar o predomínio da autoria individual, assim como a filiação a uma só instituição e a um só país, com destaque para Brasil e Espanha. A respeito do conteúdo, predomina o foco temático sobre mídia e os entornos digitais, assim como uma abordagem qualitativa das pesquisas.

Population dynamics of synthetic terraformation motifs.

Ecosystems are complex systems, currently experiencing several threats associated with global warming, intensive exploitation and human-driven habitat degradation. Because of a general presence of multiple stable states, including states involving population extinction, and due to the intrinsic nonlinearities associated with feedback loops, collapse in ecosystems could occur in a catastrophic manner. It has been recently suggested that a potential path to prevent or modify the outcome of these transitions would involve designing synthetic organisms and synthetic ecological interactions that could push these endangered systems out of the critical boundaries. In this paper, we investigate the dynamics of the simplest mathematical models associated with four classes of ecological engineering designs, named Terraformation motifs (TMs). These TMs put in a nutshell different ecological strategies. In this context, some fundamental types of bifurcations pervade the systems' dynamics. Mutualistic interactions can enhance persistence of the systems by means of saddle-node bifurcations. The models without cooperative interactions show that ecosystems achieve restoration through transcritical bifurcations. Thus, our analysis of the models allows us to define the stability conditions and parameter domains where these TMs must work.

Modelo procedimental de la evaluación de las políticas públicas a través de la ludificación / Modelo procedimental na avaliação das políticas públicas por meio da gamificação / Procedural model in the evaluation of public policy through gamification

Resumen Este artículo tiene por objeto proponer un modelo procedimental diseñado para optimizar la experiencia de la ciudadanía en la toma de decisiones de las políticas públicas a través de la ludificación. Se parte de la consideración que la ludificación promueve la motivación hacia una actividad prolongando su participación dentro de un ámbito específico. En este caso, se encamina su aplicación para motivar la integración de los ciudadanos en la toma de decisiones. Para ello se contrastan tres modelos de evaluación de políticas públicas que incorporan la participación civil en tres roles diferentes: auditor, pasivo y activo. Al aplicar la metodología Delphi, los resultados de fiabilidad y consistencia interna demuestran que el modelo de participación activa tiene mayor valoración por parte de los expertos respecto a la ludificación, Como conclusión, el modelo generado abre una nueva área de conocimiento dentro de la evaluación de políticas públicas imbuida en la interactividad del contexto mediático.

Resumo Este artigo tem como objetivo propor um modelo procedimental concebido para otimizar a experiência dos cidadãos na tomada de decisões de políticas públicas por meio da gamificação. Parte-se do pressuposto de que a gamificação promove a motivação para uma atividade, aumentando a participação dentro de um âmbito específico. Nesse caso, a gamificação é utilizada para incentivar o envolvimento dos cidadãos na tomada de decisões. Com esse objetivo, comparam-se três modelos de avaliação de políticas públicas que incorporam a participação civil em três papéis diferentes: auditor, passiva e ativa. Ao aplicar a metodologia Delphi, os resultados de fidelidade e consistência interna revelam que o modelo de participação ativa é alvo de uma valoração superior por parte dos especialistas, no que se refere à gamificação. Em conclusão, o modelo gerado abre uma nova área de conhecimento no âmbito da avaliação de políticas públicas, integrada na interatividade do contexto midiático

Abstract This article proposes a procedural model designed to optimize the experience of citizens in decision making of public policies through gamification. The study assumes that gamification increases motivation and contributes to increase involvement within a specific area. In this case, gamification is used to encourage citizens' engagement in decision-making, based on three models of evaluation of public policies that incorporate civil participation in three different roles: auditor, passive and active. After applying the Delphi methodology, the results of reliability and internal consistency show that experts attribute a higher value to the model of active participation using gamification. In conclusion, the model designed opens a new area of knowledge within the evaluation of public policies, embedded in the interactivity of the media context.

An Unsaturated Four-Coordinate Dimethyl Dimolybdenum Complex with a Molybdenum-Molybdenum Quadruple Bond.

We describe the synthesis and the molecular and electronic structures of the complex [Mo2 Me2 {µ-HC(NDipp)2 }2 ] (2; Dipp=2,6-iPr2 C6 H3 ), which contains a dimetallic core with an Mo-Mo quadruple bond and features uncommon four-coordinate geometry and has a fourteen-electron count for each molybdenum atom. The coordination polyhedron approaches a square pyramid, with one of the molybdenum atoms nearly co-planar with the basal square plane, in which the trans coordination position with respect to the Mo-Me bond is vacant. The other three sites are occupied by two trans nitrogen atoms of different amidinate ligands and the methyl group. The second Mo atom occupies the apex of the pyramid and forms an Mo-Mo bond of length 2.080(1) Å, consistent with a quadruple bond. Compound 2 reacts with tetrahydrofuran (THF) and trimethylphosphine to yield the mono-adducts [Mo2 Me(µ-Me){µ-HC(NDipp)2 }2 (L)] (3⋅THF and 3⋅PMe3 , respectively) with one terminal and one bridging methyl group. In contrast, 4-dimethylaminopyridine (dmap) forms the bis-adduct [Mo2 Me2 {µ-HC(NDipp)2 }2 (dmap)2 ] (4), with terminally coordinated methyl groups. Hydrogenolysis of complex 2 leads to the bis(hydride) [Mo2 H2 {µ-HC(NDipp)2 }2 (thf)2 ] (5⋅THF) with elimination of CH4 . Computational, kinetic, and mechanistic studies, which included the use of D2 and of complex 2 labelled with 13 C (99 %) at the Mo-CH3 sites, supported the intermediacy of a methyl-hydride reactive species. A computational DFT analysis of the terminal and bridging coordination of the methyl groups to the Mo≣Mo core is also reported.

Cationic Platinum(II) σ-SiH Complexes in Carbon Dioxide Hydrosilation.

The low-electron-count cationic platinum complex [Pt(ItBu')(ItBu)][BArF ], 1, interacts with primary and secondary silanes to form the corresponding σ-SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η1 -SiH. The reaction of 1 with Et2 SiH2 leads to the X-ray structurally characterized 14-electron PtII species [Pt(SiEt2 H)(ItBu)2 ][BArF ], 2, which is stabilized by an agostic interaction. Complexes 1, 2, and the hydride [Pt(H)(ItBu)2 ][BArF ], 3, catalyze the hydrosilation of CO2 , leading to the exclusive formation of the corresponding silyl formates at room temperature.

Selective reduction of carbon dioxide to bis(silyl)acetal catalyzed by a PBP-supported nickel complex.

The selective reduction of CO2 to the formaldehyde level remains an important challenge and to date only a few catalysts have been developed for this reaction. Herein, we report an efficient catalyst that consists of a bis(phosphino)boryl nickel hydride complex in combination with B(C6F5)3, for the highly selective hydrosilation of CO2 to bis(silyl)acetal derivatives.

Lithium Di- and trimethyl dimolybdenum(II) complexes with Mo-Mo quadruple bonds and bridging methyl groups.

New dimolybdenum complexes of composition [Mo2{µ-Me}2Li(S)}(µ-X)(µ-N^N)2] (3a-3c), where S = THF or Et2O and N^N represents a bidentate aminopyridinate or amidinate ligand that bridges the quadruply bonded molybdenum atoms, were prepared from the reaction of the appropriate [Mo2{µ-O2CMe}2(µ-N^N)2] precursors and LiMe. For complex 3a, X = MeCO2, while in 3b and 3c, X = Me. Solution NMR studies in C6D6 solvent support formulation of the complexes as contact ion pairs with weak agostic Mo-CH3···Li interactions, which were also evidenced by X-ray crystallography in the solid-state structures of the molecules of 3a and 3b. Samples of 3c enriched in (13)C (99%) at the metal-bonded methyl sites were also prepared and investigated by NMR spectroscopy employing C6D6 and THF-d8 solvents. Crystallization of 3c from toluene:tetrahydrofuran mixtures provided single crystals of the solvent separated ion pair complex [Li(THF)4] [Mo2(Me)2(µ-Me){µ-HC(NDipp)2}2] (4c), where Dipp stands for 2,6-iPr2C6H3. A computational analysis of the Mo2(µ-Me)2Li core of complexes 3a and 3b has been developed, which is consistent with a small but non-negligible electron-density sharing between the C and Li atoms of the mainly ionic CH3···Li interactions.

Experimental and computational studies of the molybdenum-flanking arene interaction in quadruply bonded dimolybdenum complexes with terphenyl ligands.

To clarify the nature of the Mo-Carene interaction in terphenyl complexes with quadruple Mo-Mo bonds, ether adducts of composition [Mo2 (Ar')(I)(O2 CR)2 (OEt2)] have been prepared and characterized (Ar'=Ar(Xyl) 2 , R=Me; Ar'=ArMes2, R=Me; Ar'=Ar(Xyl2), R=CF3) (Mes=mesityl; Xyl=2,6-Me2 C6 H3, from now on xylyl) and their reactivity toward different neutral Lewis bases investigated. PMe3 , P(OMe)3 and PiPr3 were chosen as P-donors and the reactivity studies complemented with the use of the C-donors CNXyl and CN2 C2 Me4 (1,3,4,5-tetramethylimidazol-2-ylidene). New compounds of general formula [Mo2 (Ar')(I)(O2 CR)2 (L)] were obtained, except for the imidazol-2-ylidene ligand that yielded a salt-like compound of composition [Mo2 (Ar(Xyl2))(O2 CMe)2 (CN2 C2 Me4)2]I. The Mo-Carene interaction in these complexes has been analyzed with the aid of X-ray data and computational studies. This interaction compensates the coordinative and electronic unsaturation of one of the Mo atoms in the above complexes, but it seems to be weak in terms of sharing of electron density between the Mo and Carene atoms and appears to have no appreciable effect in the length of the Mo-Mo, Mo-X, and Mo-L bonds present in these molecules.

Boryl-assisted hydrogenolysis of a nickel-methyl bond.

A stable nickel(II) methyl complex containing a diphosphino-boryl (PBP) pincer ligand is described. Mechanistic studies on the hydrogenolysis of the Ni-Me bond suggest a metal ligand cooperation mechanism that involves the intermediacy of a σ-B-H Ni(0) species that further undergoes B-H oxidative addition to form a Ni(II) hydride complex.

Terphenyl complexes of molybdenum and tungsten with quadruple metal-metal bonds and bridging carboxylate ligands.

Mono- and bis-terphenyl complexes of molybdenum and tungsten with general composition M2(Ar')(O2CR)3 and M2(Ar')2(O2CR)2, respectively (Ar' = terphenyl ligand), that contain carboxylate groups bridging the quadruply bonded metal atoms, have been prepared and structurally characterized. The new compounds stem from the reactions of the dimetal tetracarboxylates, M2(O2CR)4 (M = Mo, R = H, Me, CF3; M = W, R = CF3) with the lithium salts of the appropriate terphenyl groups (Ar' = Ar(Xyl2), Ar(Mes2), Ar(Dipp2), and Ar(Trip2)). Substitution of one bidentate carboxylate by a monodentate terphenyl forms a M-C σ bond and creates a coordination unsaturation at the other metal atom. Hence in M2(Ar')2(O2CR)2 complexes the two metal atoms have formally a low coordination number and an also low electron count. However, the unsaturation seems to be compensated by a weak M-C(arene) bonding interaction that implicates one of the aryl substituents of the terphenyl central aryl ring, as revealed by X-ray studies performed with some of these complexes and by theoretical calculations.

Experimental and theoretical studies on arene-bridged metal-metal-bonded dimolybdenum complexes.

The bis(hydride) dimolybdenum complex, [Mo2(H)2{HC(N-2,6-iPr2C6H3)2}2(thf)2], 2, which possesses a quadruply bonded Mo2(II) core, undergoes light-induced (365 nm) reductive elimination of H2 and arene coordination in benzene and toluene solutions, with formation of the Mo(I)2 complexes [Mo2{HC(N-2,6-iPr2C6H3)2}2(arene)], 3⋅C6H6 and 3⋅C6H5Me, respectively. The analogous C6H5OMe, p-C6H4Me2, C6H5F, and p-C6H4F2 derivatives have also been prepared by thermal or photochemical methods, which nevertheless employ different Mo2 complex precursors. X-ray crystallography and solution NMR studies demonstrate that the molecule of the arene bridges the molybdenum atoms of the Mo(I)2 core, coordinating to each in an η(2) fashion. In solution, the arene rotates fast on the NMR timescale around the Mo2-arene axis. For the substituted aromatic hydrocarbons, the NMR data are consistent with the existence of a major rotamer in which the metal atoms are coordinated to the more electron-rich C-C bonds.

Quadruply bonded dimolybdenum complexes with highly unusual geometries and vacant coordination sites.

New quadruply bonded dimolybdenum complexes of the terphenyl ligand Ar(Xyl(2)) (Ar(Xyl(2)) = C(6)H(3)-2,6-(C(6)H(3)-2,6-Me(2))(2)) have been prepared and structurally characterized. The steric hindrance exerted by the Ar(Xyl(2)) groups causes the Mo atoms to feature unsaturated four-coordinate structures and a formal fourteen-electron count.