Enantiopure Amidinate Complexes of the Rare-Earth Elements

Synthetic Access to α-Oxoketene Aminals by the Nucleophilic Addition of Enol Silane-Derived Palladium(II) Enolates to Carbodiimides

Synthetically important α-oxoketene aminal intermediates can now be accessed from readily available and inexpensive carbodiimides as starting materials via the nucleophilic addition of palladium enolates derived from enol silane precursors. This operationally simple method features mild reaction conditions, including open air atmosphere, ligand-free metal catalysis, broad substrate scope, and multi-gram scalability. Select synthetic applications that take advantage of the enamine character of α-oxoketene aminals and involve C-nucleophilic additions to electrophilic systems, including an α,β-unsaturated ester, an azo dicarboxylate, an aralkyl halide, and an aldehyde, are demonstrated.

Rare-earth metal complexes with redox-active formazanate ligands

The synthesis and characterisation of rare-earth metal complexes with redox-active formazanate ligands are described. Deprotonation of the neutral formazan ligand L¹H (L¹ = PhNNC(Ph)NNPh) with [Ln{N(SiMe₃)₂}₃] (Ln = Y, Sm, Dy) resulted in homoleptic tris(formazanate) complexes with the general formula [(L¹)₃Ln] (Ln = Y (1), Sm (2), Dy (3)), in which the central metal atom is coordinated by six N atoms, revealing a propeller-type structure. To generate heteroleptic complexes, a novel formazan ligand L²H (L² = {PhNNC(4-tBuPh)NNPh}) was employed. Salt metathesis by using the trivalent precursors [SmCp*₂(μ-Cl)₂K(thf)] (Cp* = η⁵-C₅Me₅) or [LnCp₂Cl]₂ (Cp = η⁵-C₅H₅, Ln = Dy, Yb) and [L²K(thf)] formed mono(formazanate) complexes, [L²SmCp*₂] (4) and [L²LnCp₂] (Ln = Dy (5), Yb (6)), respectively. Unexpectedly, a redox reaction occurred between [L²K(thf)] and the divalent ytterbium precursor, [YbI₂(thf)₂], generating the trivalent ytterbium complex [(L²)₃Yb] (7). When the neutral formazan ligand (L2H) reacted with [SmCp*₂(thf)₂], the oxidised samarium complex 4 was formed. These novel compounds were fully characterised and their electrochemical properties were explored by cyclic voltammetry.

Hetero-bimetallic Lanthanide-Coinage Metal Compounds Featuring Possible Metal-Metal Interactions in the Excited State

Heterometallic complexes, combining metals of the outer rims of the d-block, for example lanthanides(III) (Ln) and coinage metals(I) (M) are scarcely reported, synthetically challenging and highly interesting in terms of their interactions. In this context, we synthesized hetero-bimetallic Ln-M compounds ligated by the phosphine functionalized amidinate system (N,N'-bis[(2-diphenylphosphino)phenyl]formamidinate, "dpfam"). The resulting compounds [dpfam3 LnM][OTf] (Ln = La, Nd and M = Ag, Au) feature a close proximity of the two metal centres and were investigated experimentally by photoluminescence spectroscopy and quantum chemical calculations. The latter showed rare La-Au interactions for the first excited state.

Alkali Metal Complexes of a Bis(diphenylphosphino)methane Functionalized Amidinate Ligand: Synthesis and Luminescence

A novel bis(diphenylphosphino)methane (DPPM) functionalized amidine ligand (DPPM-C(N-Dipp)2 H) (Dipp=2,6-diisopropylphenyl) was synthesized. Subsequent deprotonation with suitable alkali metal bases resulted in the corresponding complexes [M{DPPM-C(N-Dipp)2 }(Ln )] (M=Li, Na, K, Rb, Cs; L=thf, Et2 O). The alkali metal complexes form monomeric species in the solid state, exhibiting intramolecular metal-π-interactions. In addition, a caesium derivative [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 was obtained by cleavage of a diphenylphosphino moiety, forming an unusual six-membered ring structure in the solid state. All complexes were fully characterized by single crystal X-ray diffraction, NMR spectroscopy, IR spectroscopy as well as elemental analysis. Furthermore, the photoluminescent properties of the complexes were thoroughly investigated, revealing differences in emission with regards to the respective alkali metal. Interestingly, the hexanuclear [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 metallocycle exhibits a blue emission in the solid state, which is significantly red-shifted at low temperatures. The bifunctional design of the ligand, featuring orthogonal donor atoms (N vs. P) and a high steric demand, is highly promising for the construction of advanced metal and main group complexes.

Organometallic complexes of neodymium: an overview of synthetic methodologies based on coordinating elements

Organometallic complexes of neodymium have unique coordinating ability to form both micro and macromolecules as well as metal-based polymers. These complexes have been reported in different fields and play a tremendous role in luminescence, catalytic, biological and magnetic applications. So, the current study will comprise all possible routes for the synthesis of organometallic complexes of neodymium. Neodymium complexes have been synthesized of single, double, triple and tetra linkages with H, C, N, O as well as S, B, and X. The detailed synthetic routes have been classified into four categories but in brief, neodymium forms complexes by reacting metal chloride, nitrate or oxide (hydrated or dehydrated) as precursor along with appropriate ligand. Most applied solvents for neodymium complexes were Toluene and THF. These complexes required a range of temperature based on the nature of complexes as well as linkages. The authors have surveyed the research work published through 2011–2020 and provide a comprehensive overview to understand the synthetic routes of organometallic complexes of neodymium.

Direct enantioseparation of axially chiral 1,1′-biaryl-2,2′-diols using amidine-based resolving agents

Amidine-based optically active resolving agents for enantiomer separation of axially chiral 1,1′-biaryl-2,2′-diols have been developed. A strongly basic amidine bearing no substituents on its nitrogen atoms enables the formation of their diastereomeric salts upon being mixed with weakly acidic phenol derivatives. Enantiopure 1,1′-biaryl-2,2′-diols can be obtained in high yields after only one crystallization of their salts with the chiral amidine derived from dehydroabietic acid. X-ray crystallography revealed that the amidine moiety forms a salt with the phenol group and additional intermolecular NH/π interactions contribute to the efficient chiral recognition process.

Enantioseparation of atropisomeric biphenols using a chiral amidine derived from dehydroabietic acid was reported. Only one crystallization of their mixture gave pure diastereomeric salts of biphenols from racemate.

Computational Study of spx (x=1-3)-Hybridized Be-Be Bonds Stabilized by Amidinate Ligands

Complexes containing odd-electron Be-Be bonds are still rare until now. Hereby, a series of neutral di-beryllium amidinate complexes containing a Be-Be bond were explored theoretically. The complexes with direct chelation with the Be₂ dimer by the bidentate amidinate (AMD) ligands are always corresponding to their global minimum structures. The detailed bonding analyses reveal that the localized electrons of the Be-Be fragment can be adjusted by the amount of AMD ligands because each AMD ligand only takes one electron from the Be₂ fragment. Meanwhile, the hybridization of the central Be atom also changes as the number of AMD ligands increases. In particular, the sp³ -hybridized single-electron Be-Be bond is firstly identified in the tri-AMD-ligands-chelated neutral D_3h -Be₂ (AMD)₃ complex, which also possesses the higher stability compared to its monoanionic D_3h -Be₂ (AMD)₃ ^- and monocationic C₃ -Be₂ (AMD)₃ ⁺ analogues. Importantly, our study provides a new approach to obtain a neutral odd-electron Be-Be bond, namely by the use of radical ligands through side-on chelation.

Enantiomerically Pure Tetravalent Neptunium Amidinates: Synthesis and Characterization

The synthesis of a tetravalent neptunium amidinate [NpCl((S)-PEBA)3 ] (1) ((S)-PEBA=(S,S)-N,N'-bis-(1-phenylethyl)-benzamidinate) is reported. This complex represents the first structurally characterized enantiopure transuranic compound. Reactivity studies with halide/pseudohalides yielding [NpX((S)-PEBA)3 ] (X=F (2), Br (3), N3 (4)) have shown that the chirality-at-metal is preserved for all compounds in the solid state. Furthermore, they represent an unprecedented example of a structurally characterized metal-organic Np complex featuring a Np-Br (3) bond. In addition, 4 is the only reported tetravalent transuranic azide. All compounds were additionally characterized in solution using para-magnetic NMR spectroscopy showing an expected C3 -symmetry at low temperatures.

Neutral and cationic enantiopure group 13 iminophosphonamide complexes

Synthesis and reactivity of enantiopure iminophosphonamide ligand L-H (L = [Ph2P{N(R)CH(CH3)Ph}2]) with group 13 metal compounds has been investigated. The reaction of L-H with LiAlH4 afforded the aluminium monohydride complex [L2AlH]. The monochloride complexes [L2MCl] (M = Al, Ga) were accessed by reacting corresponding MCl3 (M = Al, Ga) with L-Li. Furthermore, the tetracoordinated aluminium cation [L2Al]+[GaCl4]- and gallium cation [L2Ga]+[AlCl4]- were obtained by chloride abstraction from [L2MCl] (M = Al, Ga), respectively. The title complexes represent the first examples of enantiopure group 13 metal complexes coordinated by chiral iminophosphonamides. All complexes have been characterized by single crystal X-ray diffraction, multinuclear NMR, EA and IR studies.

Multinuclear Cu(I) Clusters Featuring a New Triply Bridging Coordination Mode of Phosphaamidinate Ligands

Phosphabenzamidine [mes-NH-C(Ph)═P-mes) (1) and phosphaformamidine (mes-NH-CH═P-mes) (4) ligands have been synthesized and characterized. The conjugate bases of 1 and 4 coordinate by each bridging three Cu(I) ions, forming hexa- and tetranuclear clusters Cu₆[mes-N═C(Ph)-P-mes]₃Cl₄Li(THF)₂ (3) and Cu₄[mes-N═CH-P-mes]₄ (5), respectively. Both clusters have been fully characterized using ¹H NMR, ³¹P NMR, and X-ray crystallography. Complexes 3 and 5 exhibit a previously unknown coordination mode of phosphaamidinates, which are far less studied than their well-known amidinate counterparts.

Rigid NON-donor pincer ligand complexes of lutetium and lanthanum: synthesis and hydroamination catalysis

A rigid NON-donor pincer ligand was employed for the synthesis of neutral lutetium and anionic lanthanum alkyl complexes; the former is highly active for both intra- and inter-molecular hydroamination.

Di- and octa-nuclear dysprosium clusters derived from pyridyl-triazole based ligand: {Dy2} showing single molecule magnetic behaviour

Dy^III-based two complexes, {Dy₂} (1) and {Dy₈} (2), were successfully isolated with H₂bpte ligand. In 1, H₂bpte bears trans,trans- while in 2 has cis,cis- coordination modes. {Dy₂} displays the single-molecule magnet behaviour with an energy barrier U_eff = 59(4) K.