Rare-Earth-Metal-Catalyzed Addition of Terminal Monoalkynes and Dialkynes with Aryl-Substituted Symmetrical or Unsymmetrical Carbodiimides

Boron Complexes with Propiolamidinato Ligands: Synthesis, Structure, and Photophysical Properties

Two series of boron derivatives with propiolamidinato ligands, [BPh2{C(C≡CAr)(NR)2}] (Ar = Ph, p-MeOPh, p-FPh, p-Me2NPh, or phen; R = iPr or p-tolyl), were synthesized and structurally characterized. The corresponding propiolamidine (or propargylamidine) proligands have been obtained through sustainable methods. One is the catalytic hydroalkynylation of diisopropylcarbodiimide with different terminal alkynes, using simple ZnEt2 as a precatalyst. Alternatively, to obtain propiolamidines with aromatic groups on the nitrogen atoms, the formation of lithiated derivatives of terminal alkynes by reaction with n-BuLi in air and at room temperature, and subsequent addition to the di-p-tolylcarbodiimide, under the same conditions and using 2-MeTHF as a sustainable solvent, has been used for the first time. After reaction with BPh3, the corresponding boron amidinates were obtained, which are emissive in the solution state. The influence of the different substituents introduced into the ligands on the photophysical properties of the boron compounds has been studied. One of the obtained compounds can be used as a ratiometric fluorescent pH sensor in the acidic range.

Dipolar Coupling as a Mechanism for Fine Control of Magnetic States in ErCOT-Alkyl Molecular Magnets

The design of molecular magnets has progressed greatly by taking advantage of the ability to impart successive perturbations and control vibronic transitions in 4fn systems through the careful manipulation of the crystal field. Herein, we control the orientation and rigidity of two dinuclear ErCOT-based molecular magnets: the inversion-symmetric bridged [ErCOT(μ-Me)(THF)]2 (2) and the nearly linear Li[(ErCOT)2(μ-Me)3] (3). The conserved anisotropy of the ErCOT synthetic unit facilitates the direction of the arrangement of its magnetic anisotropy for the purposes of generating controlled internal magnetic fields, improving control of the energetics and transition probabilities of the electronic angular momentum states with exchange biasing via dipolar coupling. This control is evidenced through the introduction of a second thermal barrier to relaxation operant at low temperatures that is twice as large in 3 as in 2. This barrier acts to suppress through-barrier relaxation by protecting the ground state from interacting with stray local fields while operating at an energy scale an order of magnitude smaller than the crystal field term. These properties are highlighted when contrasted against the mononuclear structure ErCOT(Bn)(THF)2 (1), in which quantum tunneling of the magnetization processes dominate, as demonstrated by magnetometry and ab initio computational methods. Furthermore, far-infrared magnetospectroscopy measurements reveal that the increased rigidity imparted by successive removal of solvent ligands when adding bridging methyl groups, along with the increased excited state purity, severely limits local spin-vibrational interactions that facilitate magnetic relaxation, manifesting as longer relaxation times in 3 relative to those in 2 as temperature is increased.

Utility of all-pyrazole heteroscorpionates in f-element chemistry

Since their discovery in 1966, scorpionate ligands have been utilized to make coordination compounds for a variety of applications such as: studying organometallic reactions, biomimetic complexes, light-emitting materials and single-ion magnets. The recent development of a solvent-free pyrazole substitution chemistry has yielded the quantitative synthesis of asymmetrically functionalized all-pyrazole heteroscorpionate ligands. In this frontier article, we highlight the utility of all-pyrazole heteroscorpionates, specifically, nitro-trispyrazolylborates, in f-element chemistry. They offer great versatility in coordinating ability, donor strength, steric bulk and even optical charge transfer properties, all of which can be used to tune the properties of resultant complexes with metal ions. We show how they can impart structural diversity, sensitize Ln3+ luminescence and engender magnetic anisotropy and slow magnetic relaxation in the ion they coordinate. Additionally, we comment on the future of functionalized trispyrazolyl scorpionates, which includes enabling post-synthetic modifications of f-element complexes and becoming a platform to study the electronic properties of low oxidation state actinides.

Structural Diversity of Lanthanide 3-Nitrotrispyrazolylborates: Tunable Nuclearity and Intra-Ligand Charge Transfer Sensitization of Visible and NIR Ln3+ Emission

Reported are the syntheses, crystal structures, and photophysical properties of 28, novel lanthanide compounds across five structural types, [Ln(3-NO₂Tp)₂(NO₃)] (1-Ln, Ln = La-Tm, except Pm), [Bu₄N][Ln(3-NO₂Tp)(NO₃)₃] (2-Ln, Ln = Yb, Lu), [Eu(3-NO₂Tp)₂Cl(H₂O)]·2ⁱPrOH (3-Eu), [{Ln(3-NO₂Tp)₂}₂(μ₂-CO₃)]·MeOH (4-Ln, Ln = La-Gd, except Pm), and [{Ln(3-NO₂Tp)}₄(μ₂-OMe)₆(μ₄-O)] (5-Ln, Ln = Pr-Tb, except Pm) with the 3-nitrotrispyrazolylborate (3-NO₂Tp^-) ligand. The reaction of methanol or isopropanol solutions of LnX₃ (X = Cl, NO₃) with the tetrabutyl ammonium salt of the flexidentate 3-NO₂Tp^- ([Bu₄N][3-NO₂Tp]) yields Ln(3-NO₂Tp)_x complexes of various nuclearities as either monomers (1-Ln, 2-Ln, 3-Eu), dimers (4-Ln), or tetramers (5-Ln) owing to the efficient conversion of atmospheric CO₂ to CO₃^2- (dimers) or ligand controlled solvolysis of lanthanide ions (tetramers). 3-NO₂Tp^- is an efficient sensitizer for both the visible and near-IR (NIR) emissions of most of the lanthanide series, except thulium. Optical measurements, supported by density functional theory calculations, indicate that the dual visible and NIR Ln³⁺ emission arises from two intraligand charge transfer (ILCT) transitions of 3-NO₂Tp^-. This is the first report of lanthanide complexes with a nitro-functionalized pyrazolylborate ligand. The derivatization of the known Tp^- ligand results in new coordination chemistry governed by the increased denticity of 3-NO₂Tp^-, imparting remarkable structural diversity and charge transfer properties to resultant lanthanide complexes.

Recent developments in highly basic N-heterocyclic iminato ligands in actinide chemistry

In the last decade, major conceptual advances in the chemistry of actinide molecules and materials have been made to demonstrate their distinct reactivity profiles as compared to lanthanide and transition metal compounds, but some difficult questions remain concerning the intriguing stability of low-valent actinide complexes, and the importance of the 5f-orbitals in reactivity and bonding. The imidazolin-2-iminato moiety has been extensively used in ligands for the advancement of actinide chemistry owing to its unique capability of stabilizing the reactive and highly electrophilic metal ions by virtue of its strong electron donation and steric tunability. The current review article describes recent developments in the chemistry of light actinide metal ions (thorium and uranium) bearing these N-heterocyclic iminato moieties as supporting ligands. In addition, the effect of ring expansion of the N-heterocycle on the catalytic aptitude of the organoactinides is also described herein. The synthesis and reactivity of actinide complexes bearing N-heterocyclic iminato ligands are presented, and promising apposite applications are also presented. The current review focuses on addressing the catalytic behavior of actinide complexes with oxygen-containing substrates such as in the Tishchenko reaction, hydroelementation processes, and polymerization reactions. Actinide complexes have also found new catalytic applications, as demonstrated by the potent chemoselective carbonyl hydroboration and tandem proton-transfer esterification (TPTE) reaction, featuring coupling between an aldehyde and alcohol.

Synthesis and characterization of 2-t-butylimino-functionalized indolyl rare-earth metal amido complexes for the catalytic addition of terminal alkynes to carbodiimides: the dimeric complexes with the alkynide species in the μ–η1:η2 bonding modes

Dimeric complexes [(μ–η¹:η²-RCC)REL2]₂ (L = 2-(^tBuNCH)C₈H₅N), with alkynyl in the μ–η¹:η² modes, were isolated in the study of the catalytic reaction.

Intramolecular alkene hydroamination and degradation of amidines: divergent behavior of rare earth metal amidinate intermediates

The methods for catalytic intramolecular alkene hydroamination and degradation of amidines have been established. Furthermore, a tandem reconstruction/cyclization of amidines has also been developed.

Simple ZnEt2as a catalyst in carbodiimide hydroalkynylation: structural and mechanistic studies

Simple ZnEt₂is an efficient catalyst for the addition of terminal alkynes to carbodiimides, through amidinate complexes, and consecutive isocyanate addition and intramolecular cyclohydroamination.

Side-on coordination mode of a pyrazolyl group in the structure of a divalent [Sm{B(3-Mepz)4}2] complex (3-Mepz is 3-methylpyrazol-1-yl)

The discovery of polypyrazolylborate ligands allowed the development of various chemical fields and these ligands are an alternative to cyclopentadienyl, because both ligands have the same charge and donate the same number of electrons, as well as adopting the same facial geometry. Easy control of the bulkiness of polypyrazolylborate ligands is possible by modification of the substituents in the 3- and 5-positions of the pyrazolyl rings. The title complex, bis[tetrakis(3-methyl-1H-pyrazol-1-yl)borato]samarium(II), [Sm(C₁₆H₂₀BN₈)₂], was synthesized from the reaction of SmI₂ with potassium tetrakis(3-methyl-1H-pyrazol-1-yl)borate, denoted K[B(3-Mepz)₄], in tetrahydrofuran. The X-ray structure analysis revealed an unusual side-on coordination mode of a 3-methylpyrazolyl group through an N=N group in the B(3-Mepz)₄ ligand. The distortion is defined by the B-N-N-Sm torsion angle [85.5 (4)°]. This is in contrast to the structure of the similar divalent samarium complex [Sm(Tp^Me2 is tris(3,5-dimethylpyrazol-1-yl)borate], which displays normal κ³-bonding modes of the Tp^Me2 ligands.

Metal-free access of bulky N,N′-diarylcarbodiimides and their reduction: bulky N,N′-diarylformamidines

A facile synthetic protocol for the preparation of N,N′-diarylcarbodiimides and their reduction with sodium borohydride in ethanol to obtain N,N′-diarylformamidines has been demonstrated.

Five different types of η8-cyclooctatetraenyl-lanthanide half-sandwich complexes from one ligand set, including a “giant neodymium wheel”

Using one ligand set, five different types of η⁸-cyclooctatetraenyl-lanthanide half-sandwich complexes, including a “giant neodymium wheel”, have been prepared and structurally characterized.

Synthesis and catalytic activity of homoleptic lanthanide-tris(cyclopropylethinyl)amidinates

New unsolvated, homoleptic lanthanide(iii) tris(cyclopropylethinylamidinate) complexes of the type [c-C₃H₅–CC–C(NR)₂]₃Ln (R = ⁱPr, cyclohexyl; Ln = Nd, Sm, Ho) have been prepared and the crystal structure of the holmium derivative [c-C₃H₅–CC–C(NⁱPr)₂]₃Ho has been confirmed by X-ray diffraction.