Reactivity of Ce(iv) imido compounds with heteroallenes.

The reactivity of alkali metal capped Ce(iv) imido compounds [M(DME)2][Ce[double bond, length as m-dash]NArF(TriNOx)] (1-M with M = K, Rb, Cs and ArF = 3,5-bis(trifluoromethyl)phenyl) with CO2 and organic isocyanates has been evaluated. 1-Cs reacted with CO2 to yield an organocarbamate complex. Reaction of 1-K and 1-Rb with organic isocyanates yielded organoureate Ce(iv) complexes.

Thorium-nitrogen multiple bonds provide evidence for pushing-from-below for early actinides.

Although the chemistry of uranium-ligand multiple bonding is burgeoning, analogous complexes involving other actinides such as thorium remain rare and there are not yet any terminal thorium nitrides outside of cryogenic matrix isolation conditions. Here, we report evidence that reduction of a thorium-azide produces a transient Th≡N triple bond, but this activates C-H bonds to produce isolable parent imido derivatives or it can be trapped in an N-heterocycle amine. Computational studies on these thorium-nitrogen multiple bonds consistently evidences a σ > π energy ordering. This suggests pushing-from-below for thorium, where 6p-orbitals principally interact with filled f-orbitals raising the σ-bond energy. Previously this was dismissed for thorium, being the preserve of uranium-nitrides or the uranyl dication. Recognising that pushing-from-below perhaps occurs with thorium as well as uranium, and with imido ligands as well as nitrides, suggests this phenomenon may be more widespread than previously thought.

A complete series of uranium(iv) complexes with terminal hydrochalcogenido (EH) and chalcogenido (E) ligands E = O, S, Se, Te.

We here report the synthesis and characterization of a complete series of terminal hydrochalcogenido, U-EH, and chalcogenido uranium(iv) complexes, U≡E (with E = O, S, Se, Te), supported by the (Ad,MeArOH)3tacn (1,4,7-tris(3-(1-adamantyl)-5-methyl-2-hydroxybenzyl)-1,4,7-triazacyclononane) ligand system. Reaction of H2E with the trivalent precursor [((Ad,MeArO)3tacn)U] (1) yields the corresponding uranium(iv) hydrochalcogenido complexes [((Ad,MeArO)3tacn)U(EH)] (2). Subsequent deprotonation of the terminal hydrochalcogenido species with KN(SiMe3)2, in the presence of 2.2.2-cryptand, gives access to the uranium(iv) complexes with terminal chalcogenido ligands [K(2.2.2-crypt)][((Ad,MeArO)3tacn)U≡E] (3). In order to study the influence of the varying terminal chalogenido ligands on the overall molecular and electronic structure, all complexes were studied by single-crystal X-ray diffractometry, UV/vis/NIR, electronic absorption, and IR vibrational spectroscopy as well as SQUID magnetometry and computational analyses (DFT, MO, NBO).

Kinetic stabilisation of a molecular strontium hydride complex using an extremely bulky amidinate ligand.

Two extremely bulky amidinate ligands, [RC{N(Dip)}{N(Ar†)}]- (Dip = 2,6-diisopropylphenyl; Ar† = C6H2{C(H)Ph2}2Pri-2,6,4; R = 1-adamantyl (LAd), tert-butyl (LtBu)) have been developed and utilised for the kinetic stabilisation of the strontium and magnesium hydride complexes, [LAdSr(µ-H)]2 and [LRMg(µ-H)]2 (R = Ad or But). The former represents the missing link in the series of dimeric systems, [LAe(µ-H)]2 (Ae = alkaline earth metal). The structure and bonding of the complexes have been studied by crystallographic, spectroscopic and computational techniques.

Reversible Insertion of a C═C Bond into Magnesium(I) Dimers: Generation of Highly Active 1,2-Dimagnesioethane Compounds.

The insertion of 1,1-diphenylethylene into the Mg-Mg bond of two magnesium(I) dimers, [(ArNacnac)Mg-]2 (Ar = C6H2Me3-2,4,6 (Mes); C6H3Et2-2,6 (Dep)), yielding 1,2-dimagnesioethane products, [{(ArNacnac)Mg}2(µ-CH2CPh2)], is described. These reactions are readily reversible at room temperature and thus represent the first examples of room-temperature reversible redox processes for s-block metal complexes. The 1,2-dimagnesioethane products are highly activated magnesium alkyls and show unprecedented, uncatalyzed reactivity toward H2, CO, and ethylene. Computational studies have investigated the mechanisms of all presented reaction types.

Metathesis of a UV imido complex: a route to a terminal UV sulfide.

Herein, we report the synthesis and characterisation of the first terminal uranium(v) sulfide and a related UV trithiocarbonate complex supported by sterically demanding tris(tert-butoxy)siloxide ligands. The reaction of the potassium-bound UV imido complex, [U(NAd){OSi(OtBu)3}4K] (4), with CS2 led to the isolation of perthiodicarbonate [K(18c6)]2[C2S6] (6), with concomitant formation of the UIV complex, [U{OSi(OtBu)3}4], and S[double bond, length as m-dash]C[double bond, length as m-dash]NAd. In contrast, the reaction of the UV imido complex, [K(2.2.2-cryptand)][U(NAd){OSi(OtBu)3}4] (5), with one or two equivalents of CS2 afforded the trithiocarbonate complex, [K(2.2.2-cryptand)][U(CS3){OSi(OtBu)3}4] (7), which was isolated in 57% yield, with concomitant elimination of the admantyl thiocyanate product, S[double bond, length as m-dash]C[double bond, length as m-dash]NAd. Complex 7 is likely formed by fast nucleophilic addition of a UV terminal sulfide intermediate, resulting from the slow metathesis reaction of the imido complex with CS2, to a second CS2 molecule. The addition of a solution of H2S in thf (1.3 eq.) to 4 afforded the first isolable UV terminal sulfide complex, [K(2.2.2-cryptand)][US{OSi(OtBu)3}4] (8), in 41% yield. Based on DFT calculations, triple-bond character with a strong covalent interaction is suggested for the U-S bond in complex 7.

Synthesis and Reactivity of a Scandium Terminal Hydride: H2 Activation by a Scandium Terminal Imido Complex.

Dihydrogen is easily activated by a scandium terminal imido complex containing the weakly coordinated THF. The reaction proceeds through a 1,2-addition mechanism, which is distinct from the σ-bond metathesis mechanism reported to date for rare-earth metal-mediated H2 activation. This reaction yields a scandium terminal hydride, which is structurally well-characterized, being the first one to date. The reactivity of this hydride is reported with unsaturated substrates, further shedding light on the existence of the terminal hydride complex. Interestingly, the H2 activation can be reversible. DFT investigations further eludciate the mechanistic aspects of the reactivity of the scandium anilido-terminal hydride complex with PhNCS but also on the reversible H2 activation process.

Accessing Stable Magnesium Acyl Compounds: Reductive Cleavage of Esters by Magnesium(I) Dimers.

The first examples of magnesium acyls, [(Nacnac)Mg{µ-C(Ph)O}(µ-OR)Mg(Nacnac)] (R=Me, tBu or Ph; Nacnac=[HC(MeCNAr)2 ]- ; Ar=C6 H2 Me3 -2,4,6 (Mes Nacnac), C6 H3 Et2 -2,6 (Dep Nacnac), C6 H3 iPr2 -2,6 (Dip Nacnac)), have been prepared by reductive cleavage of a series of esters using dimeric magnesium(I) reducing agents, [{(Nacnac)Mg}2 ]. Crystallographic studies reveal the complexes to be dimeric, being bridged by both phenyl-acyl and alkoxide/aryloxide fragments. The crystal structures, combined with results of spectroscopic and computational studies suggest that the nature of the acyl ligands within these complexes should be viewed as lying somewhere between anionic umpolung acyl and oxo-carbene. However, reactions of the acyl complexes with a variety of organic electrophiles did not provide evidence of umpolung acyl reactivity. A number of attempts to prepare alkoxide free magnesium acyls were carried out, and while these were unsuccessful, they did lead to unusual products, the crystallographic and spectroscopic details of which are discussed.

Highly Reactive Scandium Phosphinoalkylidene Complex: C-H and H-H Bonds Activation.

The first scandium phosphinoalkylidene complex was synthesized and structurally characterized. The complex has the shortest Sc-C bond lengths reported to date (2.089(3) Å). DFT calculations reveal the presence of a three center π interaction in the complex. This scandium phosphinoalkylidene complex undergoes intermolecular C-H bond activation of pyridine, 4-dimethylamino pyridine and 1,3-dimethylpyrazole at room temperature. Furthermore, the complex rapidly activates H2 under mild conditions. DFT calculations also demonstrate that the C-H activation of 1,3-dimethylpyrazole is selective for thermodynamic reasons and the relatively slow reaction is due to the need of fully breaking the chelating effect of the phosphino group to undergo the reaction whereas this is not the case for H2.

Correction: Inner-sphere vs. outer-sphere reduction of uranyl supported by a redox-active, donor-expanded dipyrrin.

[This corrects the article DOI: 10.1039/C6SC02912D.].

Activation of SO2 by [Zn(Cp*)2] and [(Cp*)ZnI-ZnI(Cp*)].

Interesting reactivity was observed in reactions of SO2 with [Zn(Cp*)2] and [(Cp*)ZnI-ZnI(Cp*)]. These reactions proceeded with insertion of SO2 into the Zn-C bonds. Spectacularly, the lability of the C-S bond in the O2SCp* ligands led to the thermal decomposition of [Zn(O2SCp*)2(tmeda)] to afford [Zn2(µ-SO3)(µ-S2O4)(tmeda)2].

Uranium(iv) terminal hydrosulfido and sulfido complexes: insights into the nature of the uranium-sulfur bond.

Herein, we report the synthesis and characterization of a series of terminal uranium(iv) hydrosulfido and sulfido complexes, supported by the hexadentate, tacn-based ligand framework (Ad,MeArO)3tacn3- (= trianion of 1,4,7-tris(3-(1-adamantyl)-5-methyl-2-hydroxybenzyl)-1,4,7-triazacyclononane). The hydrosulfido complex [((Ad,MeArO)3tacn)U-SH] (2) is obtained from the reaction of H2S with the uranium(iii) starting material [((Ad,MeArO)3tacn)U] (1) in THF. Subsequent deprotonation with potassium bis(trimethylsilyl)amide yields the mononuclear uranium(iv) sulfido species in good yields. With the aid of dibenzo-18-crown-6 and 2.2.2-cryptand, it was possible to isolate a terminal sulfido species, capped by the potassium counter ion, and a "free" terminal sulfido species with a well separated cation/anion pair. Spectroscopic and computational analyses provided insights into the nature of the uranium-sulfur bond in these complexes.

Context management platform for tourism applications.

The notion of context has been widely studied and there are several authors that have proposed different definitions of context. However, context has not been widely studied in the framework of human mobility and the notion of context has been imported directly from other computing fields without specifically addressing the tourism domain requirements. In order to store and manage context information a context data model and a context management platform are needed. Ontologies have been widely used in context modelling, but many of them are designed to be applied in general ubiquitous computing environments, do not contain specific concepts related to the tourism domain or some approaches do not contain enough concepts to represent context information related to the visitor on the move. That is why we propose a new approach to provide a better solution to model context data in tourism environments, adding more value to our solution reusing data about tourist resources from an Open Data repository and publishing it as Linked Data. We also propose the architecture for a context information management platform based on this context data model.

A methodology and a web platform for the collaborative development of context-aware systems.

Information and services personalization is essential for an optimal user experience. Systems have to be able to acquire data about the user's context, process them in order to identify the user's situation and finally, adapt the functionality of the system to that situation, but the development of context-aware systems is complex. Data coming from distributed and heterogeneous sources have to be acquired, processed and managed. Several programming frameworks have been proposed in order to simplify the development of context-aware systems. These frameworks offer high-level application programming interfaces for programmers that complicate the involvement of domain experts in the development life-cycle. The participation of users that do not have programming skills but are experts in the application domain can speed up and improve the development process of these kinds of systems. Apart from that, there is a lack of methodologies to guide the development process. This article presents as main contributions, the implementation and evaluation of a web platform and a methodology to collaboratively develop context-aware systems by programmers and domain experts.

Context-based tourism information filtering with a semantic rule engine.

This paper presents the CONCERT framework, a push/filter information consumption paradigm, based on a rule-based semantic contextual information system for tourism. CONCERT suggests a specific insight of the notion of context from a human mobility perspective. It focuses on the particular characteristics and requirements of travellers and addresses the drawbacks found in other approaches. Additionally, CONCERT suggests the use of digital broadcasting as push communication technology, whereby tourism information is disseminated to mobile devices. This information is then automatically filtered by a network of ontologies and offered to tourists on the screen. The results obtained in the experiments carried out show evidence that the information disseminated through digital broadcasting can be manipulated by the network of ontologies, providing contextualized information that produces user satisfaction.