Metal Alkyl Research Articles

Syntheses of Rare-Earth Metal Alkyl Complexes Bearing a Dianionic α-Iminopyridyl Ligand and Their Catalytic Activities toward Polymerization of 2-Vinylpyridine

Syntheses of Rare-Earth Metal Alkyl Complexes Bearing a Dianionic α-Iminopyridyl Ligand and Their Catalytic Activities toward Polymerization of 2-Vinylpyridine

The Story of 5d Metallocorroles: From Metal-Ligand Misfits to New Building Blocks for Cancer Phototherapeutics.

ConspectusPorphyrin chemistry is Shakespearean: over a century of study has not withered the field’s apparently infinite variety. Heme proteins continually astonish us with novel molecular mechanisms, while new porphyrin analogues bowl us over with unprecedented optical, electronic, and metal-binding properties. Within the latter domain, corroles occupy a special place, exhibiting a unique and rich coordination chemistry. The 5d metallocorroles are arguably the icing on that cake.New Zealand chemist Penny Brothers has used the word “misfit” to describe the interactions of boron, a small atom with a predilection for tetrahedral coordination, and porphyrins, classic square-planar ligands. Steve Jobs lionized misfits as those who see things differently and push humanity forward. Both perspectives have inspired us. The 5d metallocorroles are misfits in that they encapsulate a large 5d transition metal ion within the tight cavity of a contracted porphyrin ligand.Given the steric mismatch inherent in their structures, the syntheses of some 5d metallocorroles are understandably capricious, proceeding under highly specific conditions and affording poor yields. Three broad approaches may be distinguished.(a) In the metal–alkyl approach, a free-base corrole is exposed to an alkyllithium and the resulting lithio-corrole is treated with an early transition metal chloride; a variant of the method eschews alkyllithium and deploys a transition metal–alkyl instead, resulting in elimination of the alkyl group as an alkane and insertion of the metal into the corrole. This approach is useful for inserting transition metals from groups 4, 5, and, to some extent, 6, as well as lanthanides and actinides.(b) In our laboratory, we have often deployed a low-valent organometallic approach for the middle transition elements (groups 6, 7, 8, and 9). The reagents are low-valent metal–carbonyl or −olefin complexes, which lose one or more carbon ligands at high temperature, affording coordinatively unsaturated, sticky metal fragments that are trapped by the corrole nitrogens.(c) Finally, a metal acetate approach provides the method of choice for gold and platinum insertion (groups 10 and 11).This Account provides a first-hand perspective of the three approaches, focusing on the last two, which were largely developed in our laboratory. In general, the products were characterized with X-ray crystallography, electrochemistry, and a variety of spectroscopic methods. The physicochemical data, supplemented by relativistic DFT calculations, have provided fascinating insights into periodic trends and relativistic effects.An unexpected feature of many 5d metallocorroles, given their misfit character, is their remarkable stability under thermal, chemical, and photochemical stimulation. Many of them also exhibit long triplet lifetimes on the order of 100 μs and effectively sensitize singlet oxygen formation. Many exhibit phosphorescence in the near-infrared under ambient conditions. Furthermore, water-soluble ReO and Au corroles exhibit impressive photocytotoxicity against multiple cancer cell lines, promising potential applications as cancer phototherapeutics. We thus envision a bright future for the compounds as rugged building blocks for new generations of therapeutic and diagnostic (theranostic) agents.

Synthesis, Characterization, and Catalytic Activity of Dinuclear Rare-Earth Metal Alkyl Complexes Bearing 2,6-Diisopropylphenylamidomethyl Functionalized Pyrrolyl Ligand

Synthesis, Characterization, and Catalytic Activity of Dinuclear Rare-Earth Metal Alkyl Complexes Bearing 2,6-Diisopropylphenylamidomethyl Functionalized Pyrrolyl Ligand

Palladium‐Catalyzed Alkene Thioacylation: A C−S Bond Activation Approach for Accessing Indanone Derivatives

AbstractA palladium‐catalyzed intramolecular alkene thioacylation reaction initiated by the activation of thioester C(acyl)−S bonds is reported. This approach successfully suppressed decarbonylation and β‐hydrogen elimination with related acyl and alkyl metal thiolate intermediates, providing an efficient and atom‐economical method to access indanone scaffolds. Mechanistic studies provide support for C(acyl)−Pd bond insertion of olefins. The synthetic utility of this protocol is demonstrated by the further conversion of the newly formed methylene sulfide substituent.magnified image

A journey into metal–carbon bond homolysis

This article surveys the current knowledge in metal alkyl complexes with homolytically weak metal–carbon bonds, therefore prone to thermally produce alkyl radicals. It outlines the role of a metal complex as a moderator to control the radical reactivity (“persistent radical effect”). It describes the methods that have been used so far (as well as others that are potentially available) to investigate the metal–carbon bond cleavage thermodynamic and kinetic parameters, including their caveats and limitations. A number of systems scrutinized in the author’s own laboratory and in those of collaborators are presented and discussed. These investigations have combined metal complexes and alkyl radicals, with guidance and understanding provided by DFT calculations, to achieve higher performance in the controlled radical polymerization of challenging monomers (vinyl acetate, vinylidene fluoride) and in olefin radical cross-coupling, and have brought to light mechanistic questions of more general relevance.

Olefin oligomerization by main group Ga3+ and Zn2+ single site catalysts on SiO2

In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+ and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+ and Ga3+ ion sites catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+ is similar to Ni2+, while Ga3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250 °C where oligomerization is catalytically relevant. This work illuminates new chemistry for main group metal catalysts with potential for development of new oligomerization processes.

Heavy Chalcogenide-Based Ionic Liquids in Syntheses of Metal Chalcogenide Materials near Room Temperature.

This minireview describes two strategically different and unexplored approaches to use ionic liquids (IL) containing weakly solvated and highly reactive chalcogenide anions [E‐SiMe3]− and [E−H]− of the heavy chalcogens (E=S, Se, Te) in materials synthesis near room temperature. The first strategy involves the synthesis of unprecedented trimethylsilyl chalcogenido metalates Cat+[M(E‐SiMe3)n]− (Cat=organic IL cation) of main group and transition metals (M=Ga, In, Sn, Zn, Cu, Ag, Au). These fully characterized homoleptic metalates serve as thermally metastable precursors in low‐temperature syntheses of binary, ternary and even quaternary chalcogenide materials such as CIGS and CZTS relevant for semiconductor and photovoltaics (PV) applications. Furthermore, thermally and protolytically metastable coinage metalates Cat+[M(ESiMe3)2]− (M=Cu, Ag, Au; E=S, Se) are accessible. Finally, the use of precursors BMPyr[E‐SiMe3] (E=Se,Te; BMPyr=1‐butyl‐1‐methylpyrrolidinium) as sources of activated selenium and tellurium in the synthesis of high‐grade thermoelectric nanoparticles Bi2Se3 and Bi2Te3 is shortly highlighted. The second synthesis strategy involves the metalation of ionic liquids Cat[S−H] and Cat[Se−H] by protolytically highly active metal alkyls or amides RnM. This rather general approach towards unknown chalcogenido metalates Catm[Rn‐1M(E)]m (E=S, Se) will be demonstrated in a research paper following this short review head‐to‐tail.

Unique reactivity of an α-ketiminopyridine ligand with metal–alkyls: Synthesis and ROP of ε-caprolactone

The reaction of an α-ketimininopyridine ligand 2-((Me)CN(C6H3-2,6-iPr2))-6-(OMe)C5H3N (L1) with metal–alkyls, such as MeLi, Et2Zn, Me3Al and Me2AlCl, was studied.

Correlating axial and equatorial ligand field effects to the single-molecule magnet performances of a family of dysprosium bis-methanediide complexes.

Treatment of the new methanediide–methanide complex [Dy(SCS)(SCSH)(THF)] (1Dy, SCS = {C(PPh2S)2}2−) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS)2][Dy(SCS)2(K(DME)2)2] (2Dy), [Dy(SCS)2][Na(DME)3] (3Dy) and [Dy(SCS)2][K(2,2,2-cryptand)] (4Dy). For further comparisons, the bis-methanediide complex [Dy(NCN)2][K(DB18C6)(THF)(toluene)] (5Dy, NCN = {C(PPh2NSiMe3)2}2−, DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for 2Dy–5Dy, with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s−1). Fitting the alternating current magnetic susceptibility data for 2Dy–5Dy gives energy barriers to magnetic relaxation (Ueff) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus 2Dy–4Dy join a privileged group of SMMs with Ueff values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For 2Dy–4Dy, the Dy-components can be grouped into 2Dy–cation/4Dy and 2Dy–anion/3Dy, where the former have almost linear C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> DyC units with short average DyC distances, and the latter have more bent CDyC units with longer average DyC bonds. Both Ueff and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M–L distances produces enhanced SMM properties. Comparison with 5Dy demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between Ueff barrier and axial linearity in structurally comparable systems.

Arylation of gem-difluoroalkenes using a Pd/Cu Co-catalytic system that avoids β-fluoride elimination.

PdII/CuI co-catalyze an arylation reaction of gem-difluoroalkenes using arylsulfonyl chlorides to deliver α,α-difluorobenzyl products. The reaction proceeds through a β,β-difluoroalkyl–Pd intermediate that typically undergoes unimolecular β-F elimination to deliver monofluorinated alkene products in a net C–F functionalization reaction. However to avoid β-F elimination, we offer the β,β-difluoroalkyl–Pd intermediate an alternate low-energy route involving β-H elimination to ultimately deliver difluorinated products in a net arylation/isomerization sequence. Overall, this reaction enables exploration of new reactivities of unstable fluorinated alkyl–metal species, while also providing new opportunities for transforming readily available fluorinated alkenes into more elaborate substructures.

Electrode and Interface Design for High-Performance Lithium/Sodium-Selenium Batteries

Lithium/sodium-selenium (Li/Na-Se) batteries are promising energy storage systems due to their relatively low cost and high volumetric energy density of Se cathode. Rechargeable lithium-ion batteries (LIBs) play a critical role in portable devices, electric vehicles and large-scale stationary energy storage, due to their relatively high energy density and low cost among available technologies [1]. Sodium-selenium (Na-Se) batteries have also drawn much attention, because of the large abundance and low cost of sodium and decent energy density of Se [2]. As a cathode material, Se provides a moderate gravimetric capacity of 678 mAh g−1, a high volumetric capacity of 3270 mAh cm−3, and possesses a high electronic conductivity of 1 ×10 −3 S m−1 [3, 4]. These advantages of Se have stimulated growing research in developing Li-Se and Na-Se batteries over the past years. However, the practical application of these batteries has been hindered by the polyselenides dissolution (or shuttle effect phenomena), which could cause low Coulombic efficiency and poor cycling lifetime. Microporous carbon (MPC) has been fabricated through a facile carbonization method from polyvinylidene fluoride (PVDF) and used without any further activation as selenium host to produce MPC/Se composite employed as cathode in rechargeable lithium/sodium-selenium (Li/Na-Se) batteries and the electrochemical properties of the prepared cell have been investigated in Li-Se batteries. (figures 1 and 4).Basically, in linear carbonate-containing electrolytes, the metal readily decomposes at the anode side, causing capacity drop over cycling. To address this problem, electrolyte design should accompany manifested cathode structure. Hence, fluoroethylene carbonate (FEC) has been used as an additive in the electrolyte solution for stabilizing the capacity in Na-Se batteries. Our investigation showed that exceptional cell stability could be reached by using the FEC in carbonate-based electrolyte. In lithium/sodium-selenium batteries, diethyl carbonate (DEC) electrolyte decomposes in contact with metal, producing some radicals and metal alkyl carbonates. These radicals start a chain reaction, causing the destruction of over cycles. By adding the FEC to the electrolyte solution, this side reaction will be prohibited. [5] FEC readily decomposes on the surface of the metal prior to any reduction of linear carbonates, making the protective and stable surface film on the metal. This layer makes the capacity much more stable for the cell contains FEC in the electrolyte. For the cell without FEC in the electrolyte, the capacity starts to fade from initial cycles and continue fading during the cycling. In sodium/selenium batteries, at the current rate of 0.1 C, the cell contains no FEC in the electrolyte, showed a capacity of 317 and 245 mAh g-1 after 100 and 200 cycles, respectively. However, the cell with an electrolyte solution containing 3% FEC, showing excellent cyclability by way of delivering 382 and 350 mAh g-1 capacity at those above-mentioned cycles, respectively (figures 2 and 5). Another important finding was that the use of FEC additive could prevent the corrosion of metal anode from soluble polyselenides, and preserve the structural integrity of metal anode, contributing to the enhanced cycling stability and specific capacity of Na-Se batteries.The utilization of nanoscale Al2O3 surface coating by atomic layer deposition (ALD) to protect a MPC/Se cathode and reduce polyselenide dissolution was also investigated in another stage. It was found that Al2O3 surface coating effectively suppressed the polyselenide dissolution from the MPC/Se cathode, thus reducing the loss of Se active material and improving the overall performance of Na-Se batteries. Compared to the pristine MPC/Se, Al2O3-coated MPC/Se cathode exhibited improved discharge capacity, cycling stability, and rate capability in Na-Se batteries (figures 3 and 6). Keywords: Fluoroethylene carbonate; lithium/sodium−selenium batteries; ALD coating; carbonate-based electrolyte; microporous carbon

Reactivity of N-Phosphinoguanidines of the Formula (HNR)(Ph2PNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from N-Phosphinoguanidinates to Phosphinimine-Amidinates.

We report the reactivity of N-phosphinoguanidines of the formula (HNR)(Ph2PNR)C(NAr) (R = iPr and Ar = 2,6-iPr2C6H3 [Dipp] for 1a, R = iPr and Ar = 2,4,6-Me3C6H2 [Mes] for 1b, and R = Cy and Ar = Dipp for 1c), prepared in high yields from the corresponding trisubstituted guanidines, toward main group metal alkyls AlMe3, ZnEt2, MgnBu2, and nBuLi to obtain novel phosphinoguanidinato and phosphinimine-amidinato compounds. Reactions of 1a-c with AlMe3 at room temperature led to the kinetic phosphinoguanidinato products [Al{κ2-N,N'-(NR)C(NAr)(NRPPh2)}Me2] (2a-c), whereas the mild heating (60-80 °C) of solutions of 2a-c give the thermodynamic phosphinimine-amidinato products [Al{κ2-N,N'-(NR)C(NAr)(PPh2NR)}Me2] (3a-c) after ligand rearrangement. The reactions of equimolar amounts of 1a-c and ZnEt2 initially give solutions containing unstable phosphinoguanidinato compounds [Zn{κ2-N,P-(NR)C(NAr)(NRPPh2)}Et] (4a-c), which rearrange upon mild heating to the phosphinimine-amidinato derivatives [Zn{κ2-N,N'-(NR)C(NAr)(PPh2NR)}Et] (6a-c). Bis(phosphinoguanidinato) compounds [Zn{κ2-N,P-(NR)C(NAr)(NRPPh2)}2] (5a-c) can be obtained under mild conditions (<45 °C) in THF, whereas bis(phosphinimine-amidinato) compounds [Zn{κ2-N,N'-(NR)C(NAr)(PPh2NR)}2] (7a-c) are also accessible under more forcing conditions (55-100 °C) from (i) ZnEt2 and 1b,c (2 equiv), (ii) 6a and 1a, or (iii) 5b,c. Equimolar mixtures of MgnBu2 and 1a-c in THF at room temperature give unstable phosphinimine-amidinato monoalkyl products [Mg{κ2-N,N'-(NR)C(NAr)(PPh2NR)}nBu(THF)2] (8a-c), whereas 2 equiv of 1a,b are required to reach the bischelate compounds [Mg{κ2-N,N'-(NiPr)C(NAr)(PPh2NiPr)}2] (9a,b). Finally, phosphinoguanidinato compounds [Li{κ2-N,P-(NR)C(NDipp)(NRPPh2)}(THF)2] (10a,c) were obtained in the reactions of 1a,c with nBuLi in THF under ambient conditions. The removal of the solvent from solutions of 10a,c under partial vacuum leads to the dinuclear compounds [Li2{μ-κ2-N,N':κ1-N-(NR)C(NDipp)(NRPPh2)}2(THF)2] (11a,c) after the decoordination of one of the THF molecules in 10a,c and dimerization. Heating solutions of 10a,c at 60 °C triggers ligand rearrangement to give phosphinimine-amidinato compounds [Li{κ2-N,N'-(NR)C(NDipp)(PPh2NR)}(THF)2] (12a,c). We also propose a mechanism for the ligand rearrangement reaction from 10a to give 12a, supported by DFT calculations, which fits nicely with our experimental results. It essentially involves a carbodiimide deinsertion reaction followed by a [3 + 2] cycloaddition between the resulting lithium phosphino-amide and the carbodiimide.

Migratory functionalization of unactivated alkyl bromides for construction of all-carbon quaternary centers via transposed tert-C-radicals

Despite remarkable recent advances in transition-metal-catalyzed C(sp3)−C cross-coupling reactions, there remain challenging bond formations. One class of such reactions include the formation of tertiary-C(sp3)−C bonds, presumably due to unfavorable steric interactions and competing isomerizations of tertiary alkyl metal intermediates. Reported herein is a Ni-catalyzed migratory 3,3-difluoroallylation of unactivated alkyl bromides at remote tertiary centers. This approach enables the facile construction of otherwise difficult to prepare all-carbon quaternary centers. Key to the success of this transformation is an unusual remote functionalization via chain walking to the most sterically hindered tertiary C(sp3) center of the substrate. Preliminary mechanistic and radical trapping studies with primary alkyl bromides suggest a unique mode of tertiary C-radical generation through chain-walking followed by Ni–C bond homolysis. This strategy is complementary to the existing coupling protocols with tert-alkyl organometallic or -alkyl halide reagents, and it enables the expedient formation of quaternary centers from easily available starting materials.

Dehydrogenative Coupling of Terminal Alkynes with O/N-Based Monohydrosilanes Catalyzed by Rare-Earth Metal Complexes.

Newly synthesized rare-earth metal alkyl complexes bearing a tripyrrolyl ligand act as excellent precatalysts for the cross-dehydrogenative coupling between various terminal alkynes and O/N-based monohydrosilanes of HSi(OEt)3/HSi(NMe2)3, leading to the formation of a variety of alkoxysilylalkyne and aminosilylalkyne derivatives in good to high yields. The precatalysts LRE(CH2SiMe3)(thf)2 (RE = Y(1a), Er(1b), Yb(1c), L = 2,5-[(2-C4H3N)CPh2]2(C4H2NMe), thf = tetrahydrofuran) were easily prepared in high yields via the reactions of RE(CH2SiMe3)3(thf)2 with the proligand H2L in a single step. Mechanistic studies reveal that treatment of 1 with phenylacetylene could generate the active catalytic species: dinuclear rare-earth metal alkynides (L(thf)n[RE(μ-C≡CPh)]2L) (RE = Y(5a), n = 1; Yb(5c), n = 0), which could react with HSi(OEt)3 to produce the coupling product 4aa and the dinuclear rare-earth metal hydrides (L (thf)[RE(μ-H)]2L) (RE = Y(6a); Yb(6c)). By contrast, prior treatment of 1c with HSi(OEt)3 proceeds via cleavage of the Si-O bond to produce the dinuclear ytterbium alkoxide (LYb(μ-OEt))2 7c, which is inert in the dehydrogenative coupling reaction. The results of the mechanistic studies are consistent with the observation that the reaction is greatly influenced by the addition sequence of precatalyst/alkynes/silanes.

Magnesium tetraorganyl derivatives of group 13 metals as intermediate products in the synthesis of group 13 metal alkyls and aryls

Reactions of organomagnesium halides with group 13 metal halides lead to the formation of R3M type compounds (R = alkyl, aryl; M = Al, Ga, In) and are considered as the simplest methods of R3M compound syntheses. These seemingly simple reactions reveal a much more complex chemistry involving mixed magnesium‐group 13 metal compounds. To elucidate the reaction course of reactions of organomagnesium halides with group 13 metal halides, we have studied reactions of R3M with organomagnesium halides. The interaction of Et3M with R1MgX led to the formation of following products being mixtures of crystalline ionic complexes with the general composition of [Et4‐nR1nM]−[XMg (thf)5]+·(thf): [Et2.2Al(CH=CH2)1.8]−[BrMg (thf)5]+·(thf) (1), [Et3Ga(CH=CH2)]−[BrMg (thf)5]+·(thf) (2), [Et4Al]−[BrMg (thf)5]+·(thf) (3), [Et4Ga]−[BrMg (thf)5]+·(thf) (4), [Et2.9Al(C6H5)1.1]−[BrMg (thf)5]+·(thf) (5), [Et2.9Ga(C6H5)1.1]−[BrMg (thf)5]+·(thf) (6), [Et3.4GaMe0.6]−[IMg (thf)5]+·(thf) (7) and [Et4In]−[BrMg (thf)5]+·(thf) (8). A comparison of the production course of group 13 metal trialkyls R3M with a thermal decomposition of 1–8 products showed that reactions of MX3 with RMgX (X = Br, I; R = alkyl, aryl) yield initially intermediate ionic compounds, which must then be thermally decomposed to obtain pure R3M compounds. If group 13 metal bromides and iodides, and alkyl (aryl)magnesium bromides and iodides in thf are used, only intermediate products with the [R4M]−[XMg (thf)5]+·(thf) structure are formed.

Multimetallic Rare Earth and Group 4 Transition Metal Hydrides for Novel Transformations of Small Molecules

Hydrogenolysis of mono(cyclopentadienyl (Cp))-ligated rare earth metal alkyl complexes with H2 affords a variety of multimetallic rare earth hydride complexes, which can serve as a unique platform ...

Group 4 Organometallics Supported by Sterically Hindered β‐Diketonates

The synthesis, characterization, and reactivity of group 4 organometallics supported by β‐diketonates is reported. Sterically hindered β‐diketonates, such as 2,6‐dimesitylbenzoyl pinacolone (L1) and 2,6‐dimesitylbenzoyl acetylmesitylene (L2), preclude the formation of tetrakis‐ and tris‐chelates, halting at cis‐octahedrally coordinated M(Ln)2Cl2 (M = Ti, Zr, Hf; Ln = L1, L2). Metathesis with benzylmagnesium chloride affords M(Ln)2Bn2 (M = Zr, Hf) and the reduced Ti(L1)2Bn(THF) species. These are the first structurally‐characterized metal alkyl complexes exclusively supported by β‐diketonates among the group 4 metals. Thermolysis of Zr(Ln)2Bn2 complexes results in unimolecular migratory insertion reaction, forming an enone by‐product and ZrO2. Combined Eyring analyses and computational investigations suggest the bond rearrangements are initiated by an initial benzyl migration reaction to the less hindered carbonyl group on the ligand. Activation of M(Ln)2Bn2 (M = Zr, Hf) in the presence of olefins resulted in similar oxygen abstraction. Implications and prospects for β‐diketonate‐supported catalysis are discussed.

Electrode and Interface Design for High-Performance Lithium/Sodium-Selenium Batteries

Lithium/sodium-selenium (Li/Na-Se) batteries are promising energy storage systems due to their relatively low cost and high volumetric energy density of Se cathode. Rechargeable lithium-ion batteries (LIBs) play a critical role in portable devices, electric vehicles and large-scale stationary energy storage, due to their relatively high energy density and low cost among available technologies [1]. Sodium-selenium (Na-Se) batteries have also drawn much attention, because of the large abundance and low cost of sodium and decent energy density of Se [2]. As a cathode material, Se provides a moderate gravimetric capacity of 678 mAh g−1, a high volumetric capacity of 3270 mAh cm−3, and possesses a high electronic conductivity of 1 ×10 −3 S m−1 [3, 4]. These advantages of Se have stimulated growing research in developing Li-Se and Na-Se batteries over the past years. However, the practical application of these batteries has been hindered by the polyselenides dissolution (or shuttle effect phenomena), which could cause low Coulombic efficiency and poor cycling lifetime. Microporous carbon (MPC) has been fabricated through a facile carbonization method from polyvinylidene fluoride (PVDF) and used without any further activation as selenium host to produce MPC/Se composite employed as cathode in rechargeable lithium/sodium-selenium (Li/Na-Se) batteries and the electrochemical properties of the prepared cell have been investigated in Li-Se batteries. (figures 1 and 4).Basically, in linear carbonate-containing electrolytes, the metal readily decomposes at the anode side, causing capacity drop over cycling. To address this problem, electrolyte design should accompany manifested cathode structure. Hence, fluoroethylene carbonate (FEC) has been used as an additive in the electrolyte solution for stabilizing the capacity in Na-Se batteries. Our investigation showed that exceptional cell stability could be reached by using the FEC in carbonate-based electrolyte. In lithium/sodium-selenium batteries, diethyl carbonate (DEC) electrolyte decomposes in contact with metal, producing some radicals and metal alkyl carbonates. These radicals start a chain reaction, causing the destruction of over cycles. By adding the FEC to the electrolyte solution, this side reaction will be prohibited. [5] FEC readily decomposes on the surface of the metal prior to any reduction of linear carbonates, making the protective and stable surface film on the metal. This layer makes the capacity much more stable for the cell contains FEC in the electrolyte. For the cell without FEC in the electrolyte, the capacity starts to fade from initial cycles and continue fading during the cycling. In sodium/selenium batteries, at the current rate of 0.1 C, the cell contains no FEC in the electrolyte, showed a capacity of 317 and 245 mAh g-1 after 100 and 200 cycles, respectively. However, the cell with an electrolyte solution containing 3% FEC, showing excellent cyclability by way of delivering 382 and 350 mAh g-1 capacity at those above-mentioned cycles, respectively (figures 2 and 5). Another important finding was that the use of FEC additive could prevent the corrosion of metal anode from soluble polyselenides, and preserve the structural integrity of metal anode, contributing to the enhanced cycling stability and specific capacity of Na-Se batteries.The utilization of nanoscale Al2O3 surface coating by atomic layer deposition (ALD) to protect a MPC/Se cathode and reduce polyselenide dissolution was also investigated in another stage. It was found that Al2O3 surface coating effectively suppressed the polyselenide dissolution from the MPC/Se cathode, thus reducing the loss of Se active material and improving the overall performance of Na-Se batteries. Compared to the pristine MPC/Se, Al2O3-coated MPC/Se cathode exhibited improved discharge capacity, cycling stability, and rate capability in Na-Se batteries (figures 3 and 6). Keywords: Fluoroethylene carbonate; lithium/sodium−selenium batteries; ALD coating; carbonate-based electrolyte; microporous carbon

Samarium(II) Monoalkyl Complex Supported by a β-Diketiminato-Based Tetradentate Ligand: Synthesis, Structure, and Catalytic Hydrosilylation of Internal Alkynes.

The synthesis and catalytic applications of trivalent rare-earth metal alkyl complexes have been well developed, but the chemistry of divalent rare-earth metal alkyl complexes lagged much behind. Herein, we report the synthesis, structure, and catalytic applications of a samarium(II) monoalkyl complex supported by a β-diketiminato-based tetradentate ligand, [LSmCH(SiMe3 )2 ] (L=[MeC(NDipp)CHC(Me)NCH2 CH2 N(Me)CH2 CH2 NMe2 ]- , Dipp=2,6-(iPr)2 C6 H3 ). This complex is synthesized by the salt metathesis reaction of samarium iodide [LSm(μ-I)]2 and KCH(SiMe3 )2 in 63 % yield. Its structure is characterized by single-crystal X-ray diffraction, showing a distorted square-pyramid coordination geometry. This samarium(II) monoalkyl complex exhibits high catalytic activity in the hydrosilylation of aryl and methyl-substituted unsymmetrical internal alkynes with secondary hydrosilanes, selectively providing the α-(E) products in high yields.

Rare‐Earth Metal Alkyl Complexes with 3‐Arylamido‐Functionalized Indolyl Ligands: Synthesis, Characterization and Reactivity†

Summary of main observation and conclusionA series of dinuclear rare‐earth metal alkyl complexes {[μ‐η2:η1:η1‐3‐(LNCH)(CH2SiMe3)Ind]RE(CH2SiMe3)(THF)}2 (L1 = 2‐tBuC6H4, RE = Y, Gd, Dy, Er, Yb; L2 = 2,4,6‐Me3C6H2, RE = Dy, Er; Ind = indolyl) and {[μ‐η2:η1:η1‐3‐(LNCH2)Ind]RE(CH2SiMe3)(THF)}2 (L1, RE = Y, Dy, Er, Yb; L2, RE = Er, Yb) bearing 3‐arylamido functionalized indolyl ligands having diverse bonding modes with metal ions were synthesized either by the insertion reaction of the imino group to the RE—C bond or by the alkane elimination reaction. In the preparation of above complexes, rare‐earth metal alkyl complexes [μ‐η5:η1:η1‐3‐(L2NCH)(CH2SiMe3)Ind]Gd(CH2SiMe3)(THF)}2 with a μ‐η5:η1:η1 coordination mode to the gadolinium ion and {[μ‐η3:η1:η1‐3‐(L2NCH2)Ind]Dy(CH2SiMe3)(THF)}2 with a μ‐η3:η1:η1 coordination mode to the dysprosium ion were unexpectedly isolated. The reactions of 3‐(L2N=CH)Ind with Er(CH2SiMe3)3(THF)2 at room temperature, generated a tetranuclear imino‐indolyl erbium intermediate {[μ‐η1:η1‐3‐(L2N=CH)Ind]Er(CH2SiMe3)2(THF)}4, which can transform into the amido functionalized indolyl erbium complex in hot toluene. Moreover, the reactivities of the newly synthesized ytterbium complex with N‐heterocyclic compounds were investigated, affording the corresponding products of the mixed pyridyl‐indolyl, imidazolyl‐indolyl, and ortho‐metalated complexes. The yttrium complexes showed a high regioselectivity and steroselectivity for the isoprene polymerization with 1,4‐trans selectivity up to 91.7% and 1,4‐cis selectivity up to 96.1% in the presence of cocatalysts, respectively.