Bulky Ytterbium Formamidinates Stabilise Complexes with Radical Ligands, and Related Samarium “Tetracyclone” Chemistry

Synthesis and Reactivity of Bis-tris(pyrazolyl)borate Lanthanide/Aluminum Heterobimetallic Trihydride Complexes

Molecular heterobimetallic hydride complexes of lanthanide (Ln) and main-group (MG) metals exhibit chemical properties unique from their monometallic counterparts and are highly reactive species, making their synthesis and isolation challenging. Herein, molecular Ln/Al heterobimetallic trihydrides [Ln(Tp)2(μ-H)2Al(H)(N″)] [2-Ln; Ln = Y, Sm, Dy, Yb; Tp = hydrotris(1-pyrazolyl)borate; N″ = N(SiMe3)2] have been synthesized by facile insertion of aminoalane [Me3N·AlH3] into the Ln-N amide bonds of [Ln(Tp)2(N″)] (1-Ln). Thus, this is a simple synthetic strategy to access a range of Ln/Al hydrides. Reactivity studies demonstrate that 2-Ln is a heterobimetallic hydride, with evidence for the cooperative nature of 2-Ln shown by the catalytic amine-borane dehydrocoupling under ambient conditions in contrast to its monomeric counterparts.

Dinuclear ytterbium(III) benzamidinate complexes with bridging S32-, Se22- and Te22- ligands: synthesis, structure and magnetic properties

Treatment of Yb(II) complex [L2Yb(THF)2] (L = PhC(NSiMe3)2) with elemental sulfur, selenium or tellurium resulted in the isolation of a series of dinuclear Yb(III) complexes featuring side-on bound S32- (1), Se22- (2) or Te22- (3) moieties, respectively. Magnetic study on these complexes revealed that 3 is a rare lanthanide telluride single-molecule magnet (SMM).

A 2,2'-bipyridyl calcium complex: synthesis, structure and reactivity studies

A 2,2'-bipyridyl calcium complex based on a tridentate ligand [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca(bipy)(THF) (1) was prepared by the reduction of {[CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]CaI(THF)}₂ with potassium graphite in the presence of 2,2'-bipyridine (bipy). Complex 1 is a good Ca(I)synthon, as shown by its reactivity with I₂, PhCH₂SSCH₂Ph, PhCH₂SeSeCH₂Ph and 9-fluorenone, yielding the calcium iodide complex [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]CaI(bipy) (2), calcium thiolate [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca(SCH₂Ph)(bipy) (3), calcium selenolate [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca(SeCH₂Ph)(bipy) (4), and calcium ketyl complex [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca[O-(9-C₁₃H₈˙)](bipy)·2THF (5·2THF), respectively. In addition, reactions of complex 5 with CS₂, CH₂CHCH₂Br and PhCH₂Br give the corresponding dimeric bis(thiolate) complex {[S₂CC(CMe(NAr))C(Me)NCH₂CH₂NMe₂]Ca(DME)}₂ (6), dimeric calcium bromide complex {[(9-CH₂CHCH₂-C₁₃H₈-9)-O]CaBr(THF)(bipy)}₂ (7) and {[(9-C₆H₅CH₂-C₁₃H₈-9)-O]CaBr[O-(9-C₁₃H₈)](bipy)}₂ (8). These results demonstrated that the calcium ketyl complex 5 can also be employed as a single-electron transfer reagent. All the new compounds were characterized by various spectroscopic methods, and their solid-state structures were further confirmed by single-crystal X-ray diffraction analyses.

On the usability of salt metathesis reactions for the synthesis of sterically crowded tris-formamidinate Ln(iii) complexes: success and limits. Spontaneous reduction of Eu(iii) to Eu(ii)

New homoleptic complexes of Eu3+ and Nd3+ bearing three bulky N,N′-bis(diisopropylphenyl)formamidinates were prepared using salt metathesis in a toluene medium. In the presence of THF, the sterically-induced reduction of Eu3+ to Eu2+ was observed.

A simple one-pot route to stable formamidinatoiodidolanthanoid(III) complexes from lanthanoid metals

A number of formamidinatoiodidolanthanoid(III) complexes, [Ln(DFForm)₂I(thf)₂] and [Ln(DFForm)I₂(thf)₃] (DFFormH = N,N'-bis(2,6-difluorophenyl)formamidine) and [Ln(DippForm)I₂(thf)₃] (DippFormH = N,N'-bis(2,6-diisopropylphenyl)formamidine) have been synthesized in good yields by one-pot direct reactions of the corresponding free metals with iodine and DFFormH or DippFormH in suitable ratios and are stable to rearrangement.

Lanthanoid Complexes as Molecular Materials: The Redox Approach

The development of molecular materials with novel functionality offers promise for technological innovation. Switchable molecules that incorporate redox-active components are enticing candidate compounds due to their potential for electronic manipulation. Lanthanoid metals are most prevalent in their trivalent state and usually redox-activity in lanthanoid complexes is restricted to the ligand. The unique electronic and physical properties of lanthanoid ions have been exploited for various applications, including in magnetic and luminescent materials as well as in catalysis. Lanthanoid complexes are also promising for applications reliant on switchability, where the physical properties can be modulated by varying the oxidation state of a coordinated ligand. Lanthanoid-based redox activity is also possible, encompassing both divalent and tetravalent metal oxidation states. Thus, utilization of redox-active lanthanoid metals offers an attractive opportunity to further expand the capabilities of molecular materials. This review surveys both ligand and lanthanoid centered redox-activity in pre-existing molecular systems, including tuning of lanthanoid magnetic and photophysical properties by modulating the redox states of coordinated ligands. Ultimately the combination of redox-activity at both ligands and metal centers in the same molecule can afford novel electronic structures and physical properties, including multiconfigurational electronic states and valence tautomerism. Further targeted exploration of these features is clearly warranted, both to enhance understanding of the underlying fundamental chemistry, and for the generation of a potentially important new class of molecular material.

Selective oxo ligand functionalisation and substitution reactivity in an oxo/catecholate-bridged UIV/UIV Pacman complex

The oxo- and catecholate-bridged U^IV/U^IV Pacman complex [{(py)U^IVOU^IV(μ-O₂C₆H₄)(py)}(L^A)] A (L^A = a macrocyclic "Pacman" ligand; anthracenylene hinge between N₄-donor pockets, ethyl substituents on meso-carbon atom of each N₄-donor pocket) featuring a bent U^IV-O-U^IV oxo bridge readily reacts with small molecule substrates to undergo either oxo-atom functionalisation or substitution. Complex A reacts with H₂O or MeOH to afford [{(py)U^IV(μ-OH)₂U^IV(μ-O₂C₆H₄)(py)}(L^A)] (1) and [{(py)U^IV(μ-OH)(μ-OMe)U^IV(μ-O₂C₆H₄)(py)}(L^A)] (2), respectively, in which the bridging oxo ligand in A is substituted for two bridging hydroxo ligands or one bridging hydroxo and one bridging methoxy ligand, respectively. Alternatively, A reacts with either 0.5 equiv. of S₈ or 4 equiv. of Se to provide [{(py)U^IV(μ-η²:η²-E₂)U^IV(μ-O₂C₆H₄)(py)}(L^A)] (E = S (3), Se (4)) respectively, in which the [E₂]^2- ion bridges the two U^IV centres. To the best of our knowledge, complex A is the first example of either a d- or f-block bimetallic μ-oxo complex that activates elemental chalcogens. Complex A also reacts with XeF₂ or 2 equiv. of Me₃SiCl to provide [{(py)U^IV(μ-X)₂U^IV(μ-O₂C₆H₄)(py)}(L^A)] (X = F (5), Cl (6)), in which the oxo ligand has been substituted for two bridging halido ligands. Reacting A with either XeF₂ or Me₃SiCl in the presence of O(Bcat)₂ at room temperature forms [{(py)U^IV(μ-X)(μ-OBcat)U^IV(μ-O₂C₆H₄)(py)}(L^A)] (X = F (5A), Cl (6A)), which upon heating to 80 °C is converted to 5 and 6, respectively. In order to probe the importance of the bent U^IV-O-U^IV motif in A on the observed reactivity, the bis(boroxido)-U^IV/U^IV complex, [{(py)(pinBO)U^IVOU^IV(OBpin)(py)}(L^A)] (B), featuring a linear U^IV-O-U^IV bond angle was treated with H₂O and Me₃SiCl. Complex B reacts with two equiv. of either H₂O or Me₃SiCl to provide [{(py)HOU^IVOU^IVOH(py)}(L^A)] (7) and [{(py)ClU^IVOU^IVCl(py)}(L^A)] (8), respectively, in which reactions occur preferentially at the boroxido ligands, with the μ-oxo ligand unchanged. The formal U^IV oxidation state is retained in all of the products 1-8, and selective reactions at the bridging oxo ligand in A is facilitated by: (1) its highly nucleophilic character which is a result of a non-linear U^IV-O-U^IV bond angle causing an increase in U-O bond covalency and localisation of the lone pairs of electrons on the μ-oxo group, and (2) the presence of the bridging catecholate ligand, which destabilises a linear oxo-bridging geometry and stabilises the resulting products.

A stable dysprosium(iii) complex with a terminal fluoride ligand showing high resolution luminescence and slow magnetic relaxation

An air-stable dysprosium(iii) complex, [C(NH₂)₃]₄[DyF(piv)₄](piv)₂ (piv = pivalate), with a terminal fluoride ligand protected by forming extensive hydrogen bonds with peripheral guanidiniums has been isolated. Though the magnetic data failed to determine the energy barrier for the magnetic reversal (U_eff) accurately, the fine emission spectrum of the ⁴F_9/2→⁶H_15/2 transition at 4.2 K and ab initio calculations reveal that the U_eff is about 376(20) K, which is among the highest for high-coordinate (coordination numbers ≥ 9) lanthanide mononuclear magnets.

Dimerized p-Semiquinone Radical Anions Stabilized by a Pair of Rare-Earth Metal Ions

Here we report stable p-quinone-radical-bridged rare-earth complexes involving the ligand tetramethylquinone (QMe₄^•-). The complexes, {Y[(QMe₄)^•-Cl₂(THF)₃]}₂ (1) and {Gd[(QMe₄)^•-Cl₂(THF)₃]}₂ (2), where THF = tetrahydrofuran, are sufficiently stable that we can measure the single-crystal structures and perform magnetic and electron paramagnetic resonance measurements. These studies show the presence of a semiquinone form and that the magnetic interaction between the radicals in the dimer is strong and antiferromagnetic.

Atom economical coupling of benzophenone and N-heterocyclic aromatics with SmI2

The mechanism of the direct coupling of benzophenone with N-heteroaromatics leading to pyridinemethanols using SmI₂ as a unique reagent is unraveled.

Carbonyl group and carbon dioxide activation by rare-earth-metal complexes

The rare-earth elements (Ln = Sc, Y, La-Lu) are widely used in stoichiometric and catalytic carbonyl group transformations. Sufficient availability, non-toxicity, high oxophilicity, tunable ion size/Lewis acidity and enhanced ligand exchangeability have been major driving factors for their successful implementation. Routinely employed reagents for stoichiometric carbonyl group transformations are divalent ytterbium and samarium compounds (e.g., ketone reduction), bimetallic CeCl3/LiR (C-C coupling), or ceric ammonium nitrate CAN (cyclic ketone oxidation). Rare-earth-metal triflates, and in particular Sc(OTf)3, are prominent examples of Lewis acid catalysts for versatile use in organic synthesis (e.g., Aldol and Michael reactions). Moreover, Ln(ii) and Ln(iii) complexes efficiently catalyze the (co)polymerization of carbonyl group-containing monomers including lactones, lactides, acrylates, and carbon dioxide. Featuring the most notorious greenhouse gas, CO2 is currently assessed as a cheap, abundant, and non-toxic C1 building block. Ln(iii) complexes are not only capable of efficient CO2 capture via reversible insertion but also of CO2 activation for catalytic conversions (copolymerization/cycloaddition with epoxides). This perspective focuses on structurally elucidated Ln complexes resulting from ketone or carbonyl derivative activation/insertion as well as carbon dioxide insertion products. The respective compounds will be sorted by structural motifs and, if applicable, details on reactivity and feasibility of catalytic reactions are presented. The article is subdivided in three parts: (i) donor and insertion products of ketones and aldehydes, (ii) redox-enhanced activation of carbonyl derivatives, and (iii) CO2 insertion/redox products and homogeneous catalytic conversion.

Reactivity of a β-diketiminate-supported magnesium alkyl complex toward small molecules

The reactivity of the magnesium alkyl {[HC(C(Me)N-2,6-iPr2C6H3)2]Mg(nBu)}2 (1) toward various small molecules provides access to a variety of magnesium derivatives. For example, the insertion of elemental chalcogens (S8 and Se8) into the Mg-C bond of complex 1 gives the dimeric magnesium thiolate {[HC(C(Me)N-2,6-iPr2C6H3)2]Mg(μ-SnBu)}2 (2), magnesium selenolate [HC(C(Me)N-2,6-iPr2C6H3)2]Mg(SenBu)(THF) (3), and magnesium diselenolate [HC(C(Me)N-2,6-iPr2C6H3)2]Mg(Se2nBu)(THF) (4). Meanwhile, compound 4 can be readily obtained by further insertion of one selenium atom into complex 3. Moreover, the reactions of complex 1 with diphenyl dichalcogenides (PhSSPh and PhSeSePh) by σ bond metathesis afford the corresponding magnesium phenyl chalcogenolates [HC(C(Me)N-2,6-iPr2C6H3)2]Mg(EPh)(THF) (E = S 5, Se 6) concomitant with PhEnBu release. Furthermore, the treatment of complex 1 with benzonitrile and phenyl isothiocyanate produces the serendipitous magnesium-1-azaallyl complex [HC(C(Me)N-2,6-iPr2C6H3)2]Mg(N(H)C(Ph)[double bond, length as m-dash]CHC3H7)(DME) (7) and the diimino-thioamidato magnesium compound {κ3-N,N',N''-(ArNCMe)2[N(Ph)CS]CH}Mg[(Ph)NC(nBu)S] (8) (Ar = 2,6-iPr2C6H3). In addition, deprotonation occurs between compound 1 and 1-methylimidazole to generate the imidazolyl complex {[HC(C(Me)N-2,6-iPr2C6H3)2]Mg(μ-Im)}2 (9) (Im = 2-N-methylimidazolyl). These results indicated that the butylmagnesium complex 1 possesses high activity toward small molecules and revealed several unusual transformations. All the new compounds were characterized by various spectroscopic methods, and their solid-state structures were further confirmed by single-crystal X-ray diffraction analyses.