Earth Bis Research Articles

Triboranate derivatives of calcium and strontium

This contribution reports the alkaline earth-mediated formation of homonuclear sigma bonding between the metalloid element, boron. The resultant triborane anions result from the formal dismutation of bis(pinacolato)diboron (B2pin2) and the generation of putative heavier group 2 boryl intermediates. Initial reactions of the heavier alkaline earth bis-(trimethylsilyl)amides, [Ae{N(SiMe3)2}2] (Ae = Ca or Sr), with an equimolar quantity of bis(pinacolato)diboron (B2pin2) provided the 4-coordinate group 2 silazide diborane adducts [Ae(B2pin2){N(SiMe3)2}2] in which the diborane acts as a bidentate ligand via κ2-O,O' coordination. Reaction of the calcium species at 60 °C with a further three molar equivalents of B2pin2 induced the elimination of pinBN(SiMe3)2 and the formation of the bis-triboranate derivative, [Ca(B3pin3)2], in which the 6-coordinate calcium centre is bound in a κ3-O,O',O''-coordination mode by the three contiguous pinacolate oxygen atoms of both catena-B(sp2)-B(sp3)-B(sp2) bonded anions. Although analogous treatment of [Ae(B2pin2){N(SiMe3)2}2] provided similar triboranate anion formation, in this case two equivalents of the strontium silazide were retained within the structure of the trimetallic species, [Sr(B3pin3)2(Sr{N(SiMe3)2}2)2]. Despite these contrasting outcomes both triboranate complexes provide rare examples of catena-boron species beyond the common diboranes, (R2B-BR2), in which the homologated unit is propagated by electron precise and otherwise unsupported B-B bonds.

Systematic Structural Elucidation for the Protonated Form of Rare Earth Bis(porphyrinato) Double-Decker Complexes: Direct Structural Evidence of the Location of the Attached Proton.

Direct structural evidence of the presence and location of the attached proton in the protonated form of rare earth bis(porphyrinato) double-decker complexes is obtained from an X-ray diffraction study of single crystals for a series of protonated forms of bis(tetraphenylporphyrinato) complexes [M(III)(tpp)(tppH)] (M = Tb, Y, Sm, Nd, and La). When CHCl3 is used as a solvent for crystallization of the complexes, their nondisordered molecular structures are obtained and the attached proton is identified on one of the eight nitrogen atoms. Use of other solvents affords another type of crystal, in which the position of the proton is disordered and thus the molecular structure is averaged. La complex also affords the disordered average structure even when CHCl3 is used for crystallization. A variable-temperature diffraction study for the Tb complex reveals that the dynamics of the proton in the nondisordered crystal is restricted.

Purification of rare earth bis(trifluoromethyl-sulfonyl)amide salts by hydrometallurgy and electrodeposition of neodymium metal using potassium bis(trifluoromethyl-sulfonyl)amide melts

This paper reports a novel bench-scale hydrometallurgical procedure and electrodeposition using potassium bis(trifluoromethyl-sulfonyl)amide (KTFSA) melts for the recovery of rare earth (RE) elements from Nd-Fe-B magnet waste. The investigations were performed at bench scale to assess the potential of a process based on leaching, deironization, and purification of RE amide salts. In the leaching process using 3.4 kg of oxidized Nd-Fe-B and 14.2 L of an aqueous solution of 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide (HTFSA), 83.0% Nd and 0.98% Fe were leached in 13 h, indicating that selective leaching of RE elements was performed at bench scale. Then, KOH or oxidized Nd-Fe-B was used as a precipitation agent in the deironization process and 100.0% Fe was successfully separated from RE components. Moreover, 4.07 kg of purified amide salts (M(TFSA)3, M = Pr, Nd, Dy, B, Al, and trace elements) were recovered from a spray dryer. The electrochemical behavior of Nd(III) in KTFSA melts containing M(TFSA)3 (molar fraction of RE components: xRE = 0.1) was investigated in this study. Electrochemical analysis revealed that the reduction peak of Nd(III) at around +1.0 V vs. K/K+ was due to the following reaction: Nd(III) + 3e− → Nd(0). The diffusion coefficient of Nd(III) was estimated to be 3.14 × 10−10 m2 s−1 at 483 K by semi-differential analysis, which is similar to that of Nd(III) in KTFSA melts containing pure Nd(TFSA)3 salts (xNd = 0.1). The electrodeposition of Nd was performed under potentiostatic conditions of +0.8 V vs. K/K+ at 483 K. The electrodeposits had a fine surface morphology with small metal particles. The electrodeposits were confirmed to be Nd metal in the middle layer analyzed by scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Finally, we demonstrated the effectiveness of the novel recovery process for practical use by estimating whole material flow.

ChemInform Abstract: Group 2 Catalysis for the Atom‐Efficient Synthesis of Imidazolidine and Thiazolidine Derivatives.

AbstractAmong 3 alkaline earth bis(amide) precatalysts tested (M: Sr, Mg, Ca), the strontium compound is the most effective one.

Group 2 Catalysis for the Atom-Efficient Synthesis of Imidazolidine and Thiazolidine Derivatives.

A wide variety of functionalised imidazolidine-2-ones and -thiones, 2-imino-imidazolidines and thiazolidine-2-thiones have been synthesised under very mild reaction conditions by using simple and cost-effective alkaline earth bis(amide) precatalysts, [Ae{N(SiMe3 )2 }2 (THF)2 ] (Ae=Mg, Ca, Sr). The reactions ensue with 100 % atom efficiency as one-pot cascades from simple, commercially available terminal alkyne and heterocumulene reagents. The reactions take place through the initial assembly of propargylamidines, which are utilised in subsequent cyclisation reactions through addition of the isocyanate, isothiocyanate and, in one case, carbon disulfide reagents. This reactivity is deduced to take place through a well-defined sequence of heterocumulene hydroacetylenation and alkyne hydroamidation steps, which are all mediated at the alkaline earth centre. The rate and regioselectivity of the cyclisation reactions are, thus, found to be heavily dependent upon the identity of the catalytic alkaline earth centre employed. Similarly, the selectivity of the reactions was observed to be profoundly affected by stereoelectronic variations in the individual substrates, albeit by a similar Group 2-centred reaction mechanism in all cases studied.

Innovative Inorganic Synthesis

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Alkaline earth catalysis for the 100% atom-efficient three component assembly of imidazolidin-2-ones.

A variety of functionalised imidazolidin-2-ones may be synthesised under very mild reaction conditions using non-toxic and cost-effective alkaline earth bis(amide) pre-catalysts in a 100% atom-efficient, intermolecular one-pot assembly from inexpensive alkyne and cumulene reagents.

Alkaline Earth Catalysis of Alkynyl Alcohol Hydroalkoxylation/Cyclization

Heavier alkaline earth bis(trimethylsilyl)amides [Ae{N(SiMe3)2}2]2 (Ae = Ca, Sr, Ba) are shown to act as effective precatalysts for the regioselective intramolecular hydroalkoxylation/cyclization of a wide range of alkynyl and allenyl alcohols. In the majority of cases, cyclization of alkynyl alcohols produces mixtures of the possible endo- and exocyclic enol ether products, rationalized as a consequence of alkynylalkoxide isomerization to the corresponding allene derivatives. Cyclization rates for terminal alkynyl alcohols were found to be significantly higher than for substrates bearing internal alkynyl substituents, while the efficacy of cyclization was in general found to be determined by a combination of stereoelectronic influences and the thermochemical viability of the specific alkaline earth metal catalysis, which we suggest is determined by the individual M–O bond strengths. Kinetic studies have provided a rate law pertaining to a pronounced catalyst inhibition with increasing [substrate], indicating that turnover-limiting insertion of C–C unsaturation into the M–O bond requires the dissociation of substrate molecules away from the Lewis acidic alkaline earth center.

Homoleptic Alkaline Earth Metal Bis(trifluoromethanesulfonyl)imide Complex Compounds Obtained from an Ionic Liquid

The first homoleptic alkaline earth bis(trifluoromethanesulfonyl)imide (Tf2N) complexes [mppyr]2[Ca(Tf2N)4], [mppyr]2[Sr(Tf2N)4], and [mppyr][Ba(Tf2N)3] were crystallized from a solution of the respective alkaline earth bis(trifluoromethanesulfonyl)imide and the ionic liquid [mppyr][Tf2N] (mppyr = 1,1-N-methyl-N-propylpyrrolidinium). In the calcium and strontium compounds, the alkaline earth metal (AE) is coordinated by four bidentately chelating Tf2N ligands to form isolated (distorted) square antiprismatic [AE(Tf2N)4]2- complexes which are separated by N-methyl-N-propylpyrrolidinium cations. In contrast, the barium compound, [mppyr][Ba(Tf2N)3], forms an extended structure. Here the alkaline earth cation is surrounded by six oxygen atoms belonging to three Tf2N- anions which coordinate in a bidentate chelating fashion. Three further oxygen atoms of the same ligands are linking the Ba2+ cations to infinite (infinity)(1)[Ba(Tf2N)3] chains.

Recent Progress in the Chemistry of Rare Earth Metal Alkyl and Hydrido Complexes Bearing Mono(cyclopentadienyl) Ligands

AbstractFor Abstract see ChemInform Abstract in Full Text.

Recent Progress in the Chemistry of Rare Earth Metal Alkyl and Hydrido Complexes Bearing Mono(cyclopentadienyl) Ligands

Abstract The acid–base reactions between rare earth tris(alkyl) complexes and silylene-linked cyclopentadiene–amines and –phosphines afford straightforwardly the corresponding cyclopentadienyl–amido and –phosphido rare earth alkyl complexes, respectively. This method can also be utilized for the synthesis of rare earth bis(alkyl) complexes bearing mono(cyclopentadienyl) ligands such as C5Me4SiMe3. The reaction of the alkyl complexes with H2 or PhSiH3 readily gives the corresponding hydrido complexes; in the case of the bis(alkyl) complexes bearing the C5Me4SiMe3 ligand, a novel type of rare earth polyhydrido cluster has been isolated and structurally characterized. The silylene-linked cyclopentadienyl–arylamido and –phosphido rare earth alkyl complexes act as excellent catalyst precursors for the dimerization of terminal alkynes and hydrosilylation of olefins, respectively. The rare earth polyhydrido clusters exhibit unique reactivities toward unsaturated organic substrates such as lactones, nitriles, and olefins.

Electronic Structure, Molecular Geometry, and Bonding Energetics in Zerovalent Yttrium and Gadolinium Bis(arene) Sandwich Complexes. A Theoretical ab Initio Study

The first ab initio study of bonding and bonding energetics in zerovalent rare earth bis(arene) sandwich complexes is presented. The d3 ground state and d2s1 first excited state [(e2g)3 and (e2g)2(...

ChemInform Abstract: Condensation and Decomposition of Hydrated Alkaline Earth Bis(hydrogenphosphoramidates) with Acids.

AbstractThe alkaline earth bis(hydrogenphosphoramidates) (I), prepared from alkaline hydrogenphosphoramidates, are treated with acids such as gaseous HCl to form the orthophosphates (II) and polyphosphates (III) ‐ (V).

CONDENSATION AND DECOMPOSITION OF HYDRATED ALKALINE EARTH BIS(HYDROGENPHOSPHORAMIDATES) WITH ACIDS

Abstract Alkaline earth bis(hydrogenphosphoramidates) were made by the wet process. The phosphoramidates reacted with hydrogen chloride, acetic acid, and oxalic acid to form ortho- and polyphosphates without producing imidopolyphosphates. For the degradation and polymerization, water was considered to play a very important role and the following reaction seemed to be the first step: where M stands for an alkaline earth cation.

Nuclear magnetic resonance studies of rare earths polyaminocarboxylates. IV. Nitrilotriacetates [1, 2

Abstract 1 H-NMR has been used to study the rare earth bis(nitrilotriacetates) (M = La, Ce, Pr, Nd, Sm, Eu, Tm, Yb, Lu, Y) in the presence of an excess ligand as a function of pH. Three kinetic pathways are observed for the intermolecular ligand exchange reaction: The rate constants −o , for the formation of the bis complexes, are in agreement with a mechanism involving outer-sphere complex formation, followed by a dissociative interchange of the outer-sphere NTA 3− with an inner-sphere water molecule. along the rare earth series, the rate constants k −3 are nearly constant (2 × 10 3 to 6 × 10 3 s −1 M −1 ) and 0.7 × 10 4 to 1.0 ¢ 10 4 smaller than k −σ . Two mechanisms may be invoked for the formation of M(NTA) 3− 2 . In the first one, the rate determining step is again the rate of loss of a water molecule from the inner-sphere, with HNTA 2− protonated on a carboxylate group as the reacting species. In the second one, it is proposed that the decrease in rate is due to the relatively slow rate of proton migration from the nitrogen atom in a partially bonded reaction intermediate. The symmetry ligand exhange occurs through a progressive chelation of the entering ligand and simultaneous dechelation of the leaving ligand. The rate constants k 1 decrease strongly along the series, whereas the stability constants K ML 2 increase.