Experimental realisation of elusive multiple-bonded aluminium compounds : a new horizon in the aluminium chemistry

The synthesis and isolation of stable main group compounds featuring multiple bonds has been of great interest for several decades. A plethora of such multiply bonded complexes have been obtained by using sterically demanding substituents that provide both kinetic and thermodynamic stability. Most of these compounds have unusual structural and electronic properties that challenge the classical concept of covalent multiple bonding. In contrast, analogous aluminium compounds are scarce in spite of its high natural abundance. The parent dialumene (Al2H2) has been calculated to be extremely unstable, thus making compounds containing Al multiple bonds a challenging synthetic target. This Review provides an overview of the recent advances in the cutting edge synthetic approaches and the careful ligand design used to obtain aluminium homo‐ and heterodiatomic multiply bonded complexes. In addition, the reactivity of these novel compounds towards various small molecules and reagents will be discussed herein

CO2 fixation and catalytic reduction by a neutral aluminum double bond

CO2 fixation and reduction to value‐added products is of utmost importance in the battle against rising CO2 levels in the Earth's atmosphere. An organoaluminum complex containing a formal aluminum double bond (dialumene), and thus an alkene equivalent, was used for the fixation and reduction of CO2. The CO2 fixation complex undergoes further reactivity in either the absence or presence of additional CO2, resulting in the first dialuminum carbonyl and carbonate complexes, respectively. Dialumene (1 ) can also be used in the catalytic reduction of CO2, providing selective formation of a formic acid equivalent via the dialuminum carbonate complex rather than a conventional aluminum–hydride‐based cycle. Not only are the CO2 reduction products of interest for C1 added value products, but the organoaluminum complexes isolated represent a significant step forward in the isolation of reactive intermediates proposed in many industrially relevant catalytic processes

Reactivity of Phenylacetylene toward Unsymmetrical Disilenes: Regiodivergent [2+2] Cycloaddition vs. CH Addition

We report the regiodivergent reaction of phenylacetylene with a selection of disilenes Tip2Si=SiTipR as well as bridged tetrasiladienes Tip2Si=SiTip−LU−SiTip=SiTip2 (Tip=2,4,6-iPr3C6H2, R=aryl groups; LU=arylene linkers). The regioselectivity of the [2+2] cycloaddition as determined by NMR spectroscopy and X-ray crystallography is shown to strongly depend on the nature of the substituent R. The small size of the substituents compared to the Tip groups in both cases suggests a change in mechanism between the substrates with only hydrogen in the ortho-positions of R and LU and those with either ortho-methyl groups or condensed aromatic rings. In contrast, the presence of catalytic quantities of base completely suppresses cycloaddtion in favor of the formal CH addition of phenylacetylene. Quenching reactions with either MeI or MeOH after the stoichiometric application of deprotonated phenylacetylene as well as NMR studies at low temperature prove the intermediacy of an alkynyl-substituted disilanyl lithium and thus suggest a carbolithiation pathway for the net CH addition

Phosphorus-supported multidentate coumarin-containing fluorescence sensors for Cu<SUP>2+</SUP>

Phosphorus hydrazides PhP(O)[N(Me)NH2]2, (S)P[N(Me)NH2]3, and N3P3[N(Me)NH2]6 were condensed with 7-diethylaminocoumarin-3-aldehyde (RCHO) to afford the corresponding hydrazones PhP(O)[N(Me)NCHR]2 (1), (S)P[N(Me)=NCHR]3 (2), and N3P3[N(Me)N=CHR]6 (3). The structural characterization of 1-3 was carried out by their HRMS, 1H and 31P{1H} NMR spectra. The molecular structure of 2 was established by a single-crystal X-ray analysis. Interaction of 1 and 2 with various transition metal ions revealed substantial fluorescence enhancement upon interaction with Cu2+ enabling a selective detection mechanism for this metal ion. However, such a fluorescence enhancement was not observed in the case of 3. A 1:1 complex [2&#183;Zn][ClO4]2&#183;4CH2Cl2 was isolated in the reaction of 2 with Zn(ClO4)2&#183;6H2O. The molecular structure of this complex revealed that the ZnII is encapsulated by the ligand utilizing a 3N, 3O coordination set

Octanuclear {Ln(III)₈}(Ln = Gd, Tb, Dy, Ho) Macrocyclic Complexes in a Cyclooctadiene-like Conformation: Manifestation of Slow Relaxation of Magnetization in the Dy(III) Derivative

The synthesis of a series of macrocyclic, isostructural octanuclear lanthanide complexes [Gd₈ (LH₂)₄ (μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]·6CH₃OH·2H₂O (<b>1</b>), [Tb₈ (LH₂)₄ (μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]₄CH₃OH·4H₂O (<b>2</b>), [Dy₈(LH₂)₄ (μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]·8CH₃OH (<b>3</b>), and [Ho₈(LH₂)₄(μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]·CH₃OH·4H₂O (<b>4</b>) have been achieved, using Ln­(III) nitrate salts, pivalic acid, and a new multidentate chelating ligand (2<i>E</i>,<i>N</i>′<i>E</i>)-<i>N</i>′-(3-((bis­(2- hydroxyethyl)­amino)­methyl)-2-hydroxy-5-methylbenzylidene)-2-(hydroxyimino) propane hydrazide (LH₅), containing two unsymmetrically disposed arms; one side of the phenol unit is decorated with a diethanolamine group while the other side is a hydrazone that has been built by the condensation reaction involving 2-hydroxyiminopropanehydrazide. All the compounds, <b>1</b>–<b>4</b>, are neutral and are held by the four [LH₂]^3– triply deprotonated chelating ligands. In these complexes all the lanthanide ions are doubly or triply bridged via phenolate, alkoxy, and pivalate oxygens. The metal centers are distributed over the 8 vertices of an octagon, resembling a cyclooctadiene ring core. The details of magnetochemical analysis for complexes <b>1</b>–<b>4</b> shows that they exhibit antiferromagnetic interactions between the Ln³⁺ ions through the phenoxo, alkoxo, and pivalato bridging groups. None of the compounds exhibits slow relaxation of the magnetization at zero applied direct current (dc) magnetic field, which could be due to the existence of a fast quantum tunneling relaxation of the magnetization (QTM). In the case of <b>3</b>, the application of a small dc field is enough as to fully or partly suppress the fast and efficient zero-field QTM allowing the observation of slow relaxation above 2 K

A modular ligand design for cation sensors: phosphorus-supported pyrene-containing ligands as efficient Cu(II) and Mg(II) sensors

A modular ligand design allowed the assembly of four phosphorus-supported pyrene-containing ligands. The number of pyrene arms could be varied from 1 to 6 depending on the phosphorus support. While ligands containing one and three pyrene arms are excellent fluorescence-based sensors of Cu2+, the ligand containing two pyrene arms shows a high specificity for Mg2+

Octanuclear {Ln(III)₈}(Ln = Gd, Tb, Dy, Ho) Macrocyclic Complexes in a Cyclooctadiene-like Conformation: Manifestation of Slow Relaxation of Magnetization in the Dy(III) Derivative

The synthesis of a series of macrocyclic, isostructural octanuclear lanthanide complexes [Gd₈ (LH₂)₄ (μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]·6CH₃OH·2H₂O (<b>1</b>), [Tb₈ (LH₂)₄ (μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]₄CH₃OH·4H₂O (<b>2</b>), [Dy₈(LH₂)₄ (μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]·8CH₃OH (<b>3</b>), and [Ho₈(LH₂)₄(μ-Piv)₄ (η²-Piv)₄ (μ-OMe)₄]·CH₃OH·4H₂O (<b>4</b>) have been achieved, using Ln­(III) nitrate salts, pivalic acid, and a new multidentate chelating ligand (2<i>E</i>,<i>N</i>′<i>E</i>)-<i>N</i>′-(3-((bis­(2- hydroxyethyl)­amino)­methyl)-2-hydroxy-5-methylbenzylidene)-2-(hydroxyimino) propane hydrazide (LH₅), containing two unsymmetrically disposed arms; one side of the phenol unit is decorated with a diethanolamine group while the other side is a hydrazone that has been built by the condensation reaction involving 2-hydroxyiminopropanehydrazide. All the compounds, <b>1</b>–<b>4</b>, are neutral and are held by the four [LH₂]^3– triply deprotonated chelating ligands. In these complexes all the lanthanide ions are doubly or triply bridged via phenolate, alkoxy, and pivalate oxygens. The metal centers are distributed over the 8 vertices of an octagon, resembling a cyclooctadiene ring core. The details of magnetochemical analysis for complexes <b>1</b>–<b>4</b> shows that they exhibit antiferromagnetic interactions between the Ln³⁺ ions through the phenoxo, alkoxo, and pivalato bridging groups. None of the compounds exhibits slow relaxation of the magnetization at zero applied direct current (dc) magnetic field, which could be due to the existence of a fast quantum tunneling relaxation of the magnetization (QTM). In the case of <b>3</b>, the application of a small dc field is enough as to fully or partly suppress the fast and efficient zero-field QTM allowing the observation of slow relaxation above 2 K

Diplochory in Ulex parviflorus pourr

6 páginas, figuras, tablas.Ulex parviflorus (Fabaceae) is a fire-prone shrub of the western Mediterranean Basin that disperses their seeds both by the explosion of the legumes and the action of ants. Over 3 years we studied seed dispersal in a population from eastern Spain. We analysed the temporal and spatial patterns of primary seed dispersal and their consequences for the foraging behaviour of ants. We also studied the effect of seed manipulation by ants on germination success. Primary seed dispersal correlated positively with air temperature. The curve of seed abundance as a function of distance of the plant displayed one peak under the plant and another peak at 130 cm. Ants of the species Messor barbarus were observed collecting seeds and they were attracted by the elaiosome. However, the spatial pattern of the seeds in the soil did not shape the foraging activity of the ants. Ants brought the seeds to their nest stores, removed the elaiosome and threw away the seeds in the refuse piles. By removing the elaiosome ants increased the germination rate in relation to intact seeds. Results showed that diplochory operates on seeds of U. parviflorus allowing the species to exploit heterogeneous establishment conditions. Primary dispersal places seeds near the mother plant but at the expense of delayed germination. These seeds should be incorporated into the soil seed bank and then activated by forest-fires or canopy disturbance. Secondary seed dispersal by ants activates seed germination and allows the plant to establish immediately after seed dispersal.Peer reviewe

Synthesis, magnetism and Mössbauer studies of tetranuclear heterometallic {Fe III 2 Ln 2 }(Ln = Gd, Dy, Tb) complexes: evidence of slow relaxation of magnetization in the terbium analogue

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