Lewis acid catalysed polymerisation of cyclopentenone.

A modest structural change of a β-diketiminate-supported aluminium complex leads to dramatic differences in the reactivity towards cyclopentenone. While the bulkier complex efficiently executes Diels Alder transformations the smaller analogue performs unique polymerisation of this substrate. This observation appears to be unprecedented in the chemistry of Lewis acids and cyclic dienophiles as it represents a unique way to polymerise a functionalised olefin.

Synthesis, characterisation and reactivity studies of chiral β-diketiminate-like supported aluminium Lewis acid complexes towards difficult Diels Alder cycloadditions.

Synthesis and characterisation of several chiral, oxazoline containing β-diketiminate type ligand supported-aluminium compounds are reported. Together with 1 equiv. of Na(BAr) (Ar = 3,5-Cl-CH), these chiral Lewis acid complexes, which possess an " and " have been successfully utilised as catalysts in asymmetric Diels-Alder reactions of 1,3-cyclohexadiene and several different chalcones.

A universal mass tag based on polystyrene nanoparticles for single-cell multiplexing with mass cytometry.

Mass cytometry (MC) is an emerging bioanalytical technique for high-dimensional biomarkers interrogation simultaneously on individual cells. However, the sensitivity and multiplexed analysis ability of MC was highly restricted by the current metal chelating polymer (MCP) mass tags. Herein, a new design strategy for MC mass tags by using a commercial available and low cost classical material, polystyrene nanoparticle (PS-NP) to carry metals was reported.

Quantitative High-Field NMR- and Mass Spectrometry-Based Fatty Acid Sequencing Reveals Internal Structure in Ru-Catalyzed Deuteration of Docosahexaenoic Acid.

Ru-based catalysis results in highly unsaturated fatty acid (HUFA) ethyl esters (EE) deuterated to various extents. The products carry H (D) mainly at their -allylic positions, where they are resistant to autoxidation compared to natural HUFA and are promising as neurological and retinal drugs. We characterized the extent of deuteration at each allylic position of docosa-4,7,10,13,16,19-hexaenoic acid deuterated to completion at -allylic and allylic positions (D-DHA) by two-dimensional (2D) and high-field (600 and 950 MHz) NMR.

Carbodiphosphorane-Stabilized Parent Dioxophosphorane: A Valuable Synthetic HOP Source.

Introducing a small phosphorus-based fragment into other molecular entities via, for example, phosphorylation/phosphonylation is an important process in synthetic chemistry. One of the approaches to achieve this is by trapping and subsequently releasing extremely reactive phosphorus-based molecules such as dioxophosphoranes. In this work, electron-rich hexaphenylcarbodiphosphorane () was used to stabilize the least thermodynamically favorable isomer of HOP to yield monomeric .

Imine Reduction with MeS-BH.

Although there exists a variety of different catalysts for hydroboration of organic substrates such as aldehydes, ketones, imines, nitriles etc., recent evidence suggests that tetra-coordinate borohydride species, formed by activation, redistribution, or decomposition of boron reagents, are the true hydride donors. We then proposed that MeS-BH could also act as a hydride donor for the reduction of various imines, as similar compounds have been observed to reduce carbonyl substrates.

Approaching a "Naked" Boryl Anion: Amide Metathesis as a Route to Calcium, Strontium, and Potassium Boryl Complexes.

Amide metathesis has been used to generate the first structurally characterized boryl complexes of calcium and strontium, {(Me Si) N}M{B(NDippCH) }(thf) (M=Ca, n=2; M=Sr, n=3), through the reactions of the corresponding bis(amides), M{N(SiMe ) } (thf) , with (thf) Li- {B(NDippCH) }. Most notably, this approach can also be applied to the analogous potassium amide K{N(SiMe ) }, leading to the formation of the solvent-free borylpotassium dimer [K{B(NDippCH) }] , which is stable in the solid state at room temperature for extended periods (48 h). A dimeric structure has been determined crystallographically in which the K cations interact weakly with both the ipso-carbons of the flanking Dipp groups and the boron centres of the diazaborolyl heterocycles, with K⋅⋅⋅B distances of >3.

Deuterated Polyunsaturated Fatty Acids Reduce Oxidative Stress and Extend the Lifespan of .

Chemically reinforced essential fatty acids (FAs) promise to fight numerous age-related diseases including Alzheimer's, Friedreich's ataxia and other neurological conditions. The reinforcement is achieved by substituting the atoms of hydrogen at the bis-allylic methylene of these essential FAs with the isotope deuterium. This substitution leads to a significantly slower oxidation due to the kinetic isotope effect, inhibiting membrane damage.

Threshold protective effect of deuterated polyunsaturated fatty acids on peroxidation of lipid bilayers.

Autoxidation of polyunsaturated fatty acids (PUFAs) damages lipid membranes and generates numerous toxic by-products implicated in neurodegeneration, aging, and other pathologies. Abstraction of bis-allylic hydrogen atoms is the rate-limiting step of PUFA autoxidation, which is inhibited by replacing bis-allylic hydrogens with deuterium atoms (D-PUFAs). In cells, the presence of a relatively small fraction of D-PUFAs among natural PUFAs is sufficient to effectively inhibit lipid peroxidation (LPO).

Coordination, reactivity, and structural properties of electron-rich ethoxy- and dimethylamino-substituted 1,3-diketiminate ligands and their complexes.

In this paper we describe the synthesis, characterization, and X-ray crystal structures of two ligands, diethyl-N,N'-bis(p-tolyl)malonimidate and 1,3-bis(dimethylamino)-N,N'-bis(p-tolyl)propanediimidate. Their corresponding rhodium(i) dicarbonyl, dimethylaluminium, and bis-ligated zinc complexes have also been prepared and characterized. The donor properties of the ligands have been studied and have been compared to those of the traditional anionic N,N'-chelating ligand nacnac.

Michael Additions Catalyzed by a β-Diketiminate-Supported Aluminum Complex.

A β-diketiminate-supported aluminum bistriflate complex (LAl(OTf)·Na[BAr]; L = CH(CMe)(N-CH-Pr); Tf = OSCF; Ar = 3,5-Cl-CH) has been identified as an efficient Lewis acid catalyst for Michael additions involving numerous electron-rich (hetero)aromatic substrates and several α,β-unsaturated carbonyl compounds. In a vast majority of the attempted Michael reactions our catalytic system was significantly superior over the currently used methods for the same transformations in terms of reaction times and temperatures, catalyst loadings, isolated product yields, and/or selectivity.

E-H (E = B, Si, C) Bond Activation by Tuning Structural and Electronic Properties of Phosphenium Cations.

In this work, strategic enhancement of electrophilicity of phosphenium cations for the purpose of small-molecule activation was described. Our synthetic methodology for generation of novel two-coordinate phosphorus(III)-based compounds [{CH(MeN)C}C·PR] ([2a], R = NPr; [2b], R = Ph) was based on the exceptional electron-donating properties of the carbodicarbene ligand (CDC). The effects of P-centered substituent exchange and increase in the overall positive charge on small substrate activation were comparatively determined by incorporating the bis(amino)phosphenium ion [(PrN)P] ([1]) in this study.

Electronic Delocalization in Two and Three Dimensions: Differential Aggregation in Indium "Metalloid" Clusters.

Reduction of indium boryl precursors to give two- and three-dimensional M-M bonded networks is influenced by the choice of supporting ligand. While the unprecedented nanoscale cluster [In (boryl) ] (with an In @In @In (boryl) concentric structure), can be isolated from the potassium reduction of a bis(boryl)indium(III) chloride precursor, analogous reduction of the corresponding (benzamidinate)In Br(boryl) system gives a near-planar (and weakly aromatic) tetranuclear [In (boryl) ] system.

Highly Electron-Rich β-Diketiminato Systems: Synthesis and Coordination Chemistry of Amino-Functionalized "N-nacnac" Ligands.

The synthesis of a class of electron-rich amino-functionalized β-diketiminato (N-nacnac) ligands is reported, with two synthetic methodologies having been developed for systems bearing backbone NMe or NEt groups and a range of N-bound aryl substituents. In contrast to their (Nacnac)H counterparts, the structures of the protio-ligands feature the bis(imine) tautomer and a backbone CH group. Direct metalation with lithium, magnesium, or aluminium alkyls allows access to the respective metal complexes through deprotonation of the methylene function; in each case X-ray structures are consistent with a delocalized imino-amide ligand description.

Pursuing the active species in an aluminium-based Lewis acid system for catalytic Diels-Alder cycloadditions.

Several Al-based complexes supported by a bis(imino)aryl NCN pincer ligand have been prepared. Systematic structural and experimental evidence identified a cationic species, supported by a THF molecule, as the best Lewis acid precatalyst for a range of Diels-Alder cycloadditions. This highlighted the importance of fully isolating and characterizing the active species in any catalytic process especially when Lewis acids are used due to the presence of hidden Brønsted acids (HBAs).

An insight into real and average structure from diffuse X-ray scattering - a case study.

Two-dimensional diffuse X-ray scattering from an organic salt [N-(3-(2,6-dimethylanilino)-1-methylbut-2-enylidene)-2,6-dimethylanilinium chloride, C21H27N2(+)Cl(-)] was interpreted with the help of an analytical model of diffuse scattering. An analysis of the relationship between symmetry and diffuse scattering for the studied system has been undertaken. The symmetry of the system explains the extinction pattern, taking the form of curves, on the diffuse scattering planes.

Bis(carbodicarbene)phosphenium trication: the case against hypervalency.

The first example of a phosphenium trication has been prepared by using the exceptional nucleophilic properties of a carbodicarbene ligand. According to theoretical investigations the trication contains quite polarized P-C bonds suggesting a substantial contribution from the dative bond model. As one of the resonance forms for the title compound depicted a hypervalent phosphoranide we also showed that phosphoranides, in general, do not contain a hypervalent P centre.

Oxidation of a P-C Bond under Mild Conditions.

The reactivity of phosphenium dication [(Ph3P)2C-P-NiPr2](2+), 1(2+), towards pyridine N-oxide (O-py) has been investigated. The resulting oxophosphonium dication [(Ph3P)2C(NiPr2)P(O)(O-py)](2+), 2(2+), was surprisingly stabilized by a less nucleophilic O-py ligand instead of pyridine (py). This compound was then identified as an analogue of the elusive Criegee intermediate as it underwent oxygen insertion into the P-C bond through a mechanism usually observed for Baeyer-Villiger oxidations.

A Well-Defined Aluminum-Based Lewis Acid as an Effective Catalyst for Diels-Alder Transformations.

A catalytically active aluminum-based system for Diels-Alder transformations is reported. The system was generated by mixing a β-diketiminate-stabilized aluminum bistriflate compound with Na[BAr(Cl) 4 (Ar(Cl) =3,5-Cl2 C6 H3). Solid-state analysis of the catalytic system reveals a unique structure incorporating a two-dimensional coordination polymer.

Extending the chemistry of carbones: P-N bond cleavage via an S(N)2'-like mechanism.

The reactivity of nucleophilic carbodiphosphorane (C(PPh3)2, 1) and carbodicarbene (C(C(NMe)2C6H4)2, 2) towards various dichlorophosphines has been explored. In most cases the expected carbone-for-chloride ligand exchange was observed. However, the use of MeN(PCl2)2 resulted in a unique P-N bond cleavage that, according to computational studies, occurred via an SN2'-like mechanism.

C-F bond activation by transient phosphenium dications.

C-F bond cleavage by transient phosphorus(III)-based dications [RP(C(PPh3)2)](2+) (4a(2+), R = Ph; 4b(2+), R = 4-F-Ph) is reported. These dications were generated by reaction of the corresponding monocationic precursors with excess Na[BAr4(Cl)]. Evidence for the existence of transient dicationic species was obtained by trapping the dication 4a(2+) with PMe3.

A dicationic iminophosphane.

A novel dicationic system containing a PN fragment has been synthesized and structurally characterized. According to the solid-state analysis and theoretical investigation, the dicationic iminophosphane resonance form is the most appropriate description for the dication. However, the contribution from the phosphorus mononitride resonance form is not negligible.

Dihaloborenium cations stabilized by a four-membered N-heterocyclic carbene: electron deficiency compensation by asymmetric structural changes.

The synthesis, characterization and X-ray analysis of dichloro- and dibromo-borenium cations stabilized by a 4-membered carbene are reported. The ligand's structural changes, atypical for similar systems, were caused by coordination to electron deficient fragments and its CN2P ring strain.

Isolation of a bis(oxazol-2-ylidene)-phenylborylene adduct and its reactivity as a boron-centered nucleophile.

An isolable phenylborylene species supported by two oxazol-2-ylidene ligands was synthesized and structurally characterized. Computational studies revealed the presence of lone-pair electrons on the boron atom in this molecule; therefore, there are eight electrons around the three-coordinate boron center. The nucleophilic property was confirmed by the reactions with trifluoromethanesulfonic acid and [(thf)Cr(CO)5], which gave the corresponding conjugate acid and a chromium-borylene complex, respectively.