Bulky Ligands Research Articles

Exploring the Structure-Activity Relationships of Albumin-Targeted Picoplatin-Based Platinum(IV) Prodrugs.

Platinum(II) complexes prevail as first-line treatment for many cancers but are associated with serious side effects and resistance development. Picoplatin emerged as a promising alternative to circumvent GSH-induced tumor resistance by introducing a bulky 2-picoline ligand. Although clinical studies were encouraging, picoplatin did not receive approval. Interestingly, the anticancer potential of prodrugs based on picoplatin is widely underexplored, and even less so the respective tumor-targeting approaches. We synthesized two new "hybrid" picoplatin(II) derivatives with an oxalate or cyclobutane dicarboxylate leaving group and their corresponding platinum(IV) prodrugs with an albumin-targeting maleimide moiety or a succinimide as reference. Picoplatin(II) and its derivatives indeed reacted much slower with GSH compared to the respective analogs cisplatin, carboplatin, or oxaliplatin. While PicoCarbo(IV) and PicoOxali(IV) were reduced slowly in the presence of ascorbic acid, picoplatin(IV) was extremely unstable. All three prodrugs were widely inactive in the MTT assays. The platinum(IV)-maleimide complexes rapidly bound to albumin with stable conjugates for >25 h. Albumin-binding resulted in elevated platinum plasma levels, prolonged blood circulation, and enhanced tumor accumulation of the prodrugs in mice bearing CT26 tumors. However, only maleimide-functionalized PicoCarbo(IV) and picoplatin(II) significantly inhibited tumor growth. One possible explanation is that for albumin-binding platinum(IV) prodrugs, the bulky 2-picoline moiety prevents sufficient activation/reduction to unlock their full anticancer potential.

C2-Selective Palladium-Catalyzed C-S Cross-Coupling of 2,4-Dihalopyrimidines.

Under most conditions, 2,4-dihalopyrimidines undergo substitution reactions at C4. Here we report that Pd(II) precatalysts supported by bulky N-heterocyclic carbene ligands uniquely effect C2-selective cross-coupling of 2,4-dichloropyrimidine with thiols. The regioselectivity of this reaction stands in stark contrast to ∼1500 previously reported Pd-catalyzed cross-couplings that favor C4 in the absence of other substituents on the pyrimidine ring. Selectivity in the catalytic system reported herein is extremely sensitive to the structure of the Pd(II) precatalyst, largely due to competing C4-selective nucleophilic aromatic substitution. C2-selectivity is high with most 1° thiols and thiophenols, and a range of substituted dichloropyrimidines can be used. The atypical selectivity of this transformation may facilitate diversity-oriented synthesis, as demonstrated for derivatives of an antiviral agent. Under these conditions, C2─Cl cleavage may not take place through a typical oxidative addition pathway.

Understanding the Reactivity of "Naked" Acyclic Carbene-like Species Featuring a Group 13 Element in the [4+1] Cycloaddition with Benzene.

The chemical reactivity between benzene and the "naked" acyclic carbene-like (G13X2)- species, having two bulky N-heterocyclic boryloxy ligands at the Group 13 center, was theoretically assessed using density functional theory computations. Our theoretical studies show that (BX2)- preferentially undergoes C-H bond insertion with benzene, both kinetically and thermodynamically, whereas the (AlX2)- analogue favors a reversible [4 + 1] cycloaddition. Conversely, the heavier carbene analogues ((GaX2)-, (InX2)-, and (TlX2)-) are not expected to engage in a reaction with benzene. The activation strain model analysis suggests that the geometric deformation energy of benzene, driven by the relativistic effects of the central G13 element in the (G13X2)- molecule, is crucial in determining the chemical reactivity of the [4 + 1] cycloaddition with benzene. According to our theoretical analyses, the stronger forward bonding is specifically the sp2-σ-orbital (G13) → vacant protruding p-π* orbitals (bent benzene). In contrast, the weaker backward bonding is the empty p-π orbital (G13) ←-filled protruding p-π orbital (bent benzene). Moreover, our theoretical findings indicate that the singlet-triplet splitting of (G13X2)- can be used as a diagnostic measure to predict the barrier height and reaction energy for their [4 + 1] cycloaddition with benzene.

Low-coordinate bis-phosphine and monophosphine Ni(0) complexes: synthesis and reactivity in C-S cross-coupling.

Preformed Ni(0) complexes are rarely used as precatalysts in cross-coupling reactions, although they can incorporate catalytically active nickel directly into the reaction. In this work, we focus on the preparation and the catalytic application of low-coordinate Ni(0) complexes supported by bulky monophosphine ligands in C-S cross-coupling reactions. We have prepared two families of Ni(0) complexes, bis-phosphine aducts of the type [Ni(PR2Ar')2] (Ar' = m-terphenyl group) and monophosphine derivatives of the type [Ni(PR2Ar')(DVDS)] (DVDS = divinyltetramethyldisiloxane). DFT calculations were used to account for the atypical bent structures displayed by the bis-phosphine Ni(0) complexes. Monophosphine-Ni(0) complexes display catalytic activity superior to bis-phosphine Ni(0) adducts, which suggests that the former facilitate the generation of highly reactive monoligated PNi(0) species. Furthermore, the reactivity of monophosphine-Ni(0) precatalysts outperform that observed with Ni(II) precatalysts with the same phosphine ligands, supporting a more facile activation step to the same catalytic species. This enhanced reactivity allows for the use of lower catalyst loadings (1-5 mol%) and for carrying out the challenging coupling between aryl chlorides and alkylthiols.

Synthesis and structure of trinuclear yttrium(III) dihydrido cluster stabilized by bulky amidinate ligand

A new yttrium dihydride complex [(Amd<sup>But</sup>)Y]<sub>3</sub>(μ-H)<sub>6</sub>(THF)<sub>2</sub> (Amd<sup>But</sup> = [Bu<sup>t</sup>C(NC<sub>6</sub>H<sub>3</sub>Pr<sup>i</sup><sub>2</sub>-2,6)<sub>2</sub>]<sup>−</sup>) was synthesized by the reaction of (Amd<sup>But</sup>)Y(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(THF) with two molar equivalents of PhSiH<sub>3</sub>. This complex adopts a trinuclear structure both in crystalline state and in C<sub>6</sub>D<sub>6</sub> solution due to five μ<sup>2</sup>- and one μ<sup>3</sup>-bridging hydride ligands. The complex was found to be active in hydrosilylation of terminal alkenes with PhSiH<sub>3</sub>.</p> <p>

Dinuclear Rare-Earth β-Diketiminates with Bridging 3,5-Ditert-butyl-catecholates: Synthesis, Structure, and Single-Molecule Magnet Properties.

The dinuclear β-diketiminato complex [L1ClDy(μ-Cl)3DyL1(THF)] (1) (L1 = {2,6-iPr2C6H3-NC(Me)CHC(Me)N-2,6-iPr2C6H3}-) was obtained by reaction of DyCl3 with KL1 in a molar ratio of 1:1 and used for the preparation of the mixed-ligand complex [L1Dy(μ-3,5-Cat)]2 (2) by salt metathesis reaction with 3,5-CatK2 (3,5-Cat -3,5-di-tert-butyl-catecholate). Reactions of 3,5-CatNa2 with [L2LnCl2(THF)2] (Ln3+ = Dy, Y) ligated with the less bulky ligand L2 = {2,4,6-Me3C6H2-NC(Me)CHC(Me)N-2,4,6-Me3C6H2}- afforded the mixed-ligand THF-containing complexes [L2Ln(μ-3,5-Cat)(THF)]2 (Ln3+ = Dy (3a), Y (3b)). All new complexes were fully characterized, and the solid-state structures were determined by single-crystal X-ray diffraction. Magnetic measurements revealed single-molecule magnet behavior for the dysprosium complexes. Sub-Kelvin μSQUID studies confirm the SMM character of the systems, while CASSCF calculation along with simulation of the experimental data yields an antiferromagnetic interaction operating between the Dy3+ ions.

Superatomic Stabilization of Dinuclear Platinum(III) through Iodide-Bridged Five-Center Ten-Electron Bonding.

One of the goals in synthetic chemistry is to obtain compounds featuring unusual valence states that are stable under ambient conditions. At present, stabilizing unusual Pt(III) states is considered difficult, except through direct Pt-Pt bonding such as that in platinum-blues or organometallization using bulky ligands. Pt(III) stabilization is also very difficult in halogen-bridged metal complex chains (MX-Chains). Herein, the iodide-bridged Pt(III) dimer compound [Pt2(en)4I3]I3 (en = ethylenediamine), which is prepared by the iodine oxidation of [PtII(en)2]I2, has been successfully synthesized and characterized. This compound is stable and is obtained as diamond-shaped single crystals with a lustrous emerald-green color under reflected light and a red color under transmitted light. The Pt(III) state is stabilized by the five-center ten-electron (5c-10e) bonding in the I-Pt-I-Pt-I core, in addition to the very strong antiferromagnetic state. The stabilization mechanism of Pt(III) through a 5c-10e bonding is considered a superatom complex; thus, this work provides new insight for stabilizing the unusual Pt(III) state.

Palladium-Catalyzed Ortho-Alkylation of Iodoarenes Enabled by a Cooperative Cycloolefin Ligand and a Bulky Trialkylphosphine

We recently achieved ortho-alkylation of iodoarenes utilizing a dual-ligand catalytic system that effectively combines palladium/olefin ligand cooperative catalysis with reversible C(sp²)−I reductive elimination enabled by a bulky trialkylphosphine ligand. Through careful mechanistic investigations, we confirmed the compatibility of the crucial steps involved in this process by isolating key organometallic intermediates and studying their stoichiometry transformations. Utilizing this protocol, we successfully achieved the ortho-alkylation of a variety of iodoarene substrates, thereby expanding the scope of applications for Catellani-type reactions. This study showcases the synthetic potential of the Pd/olefin ligand cooperative system as an innovative complement to established Pd/NBE catalysis. In this Synpacts article, we present the conceptual framework underpinning this reaction and detail the key aspects of its development. 1Introduction 2Research Background 2.1The Catellani Reaction: Pd/Norbornene Catalysis 2.2Cooperative Cycloolefin Ligands for the Catellani-Type Reactions 2.3C-X Reductive Elimination on Pd Center 3Development of the Reaction 3.1Proof-of-Concept by Stoichiometric Reactions 3.2Substrate Scope and Synthetic Applications 4Conclusion

Suppression of Interfacial Oxidation in Core/Shell InP Quantum Dots through Solvent Assisted Core-Etching Strategy for Efficient Green Light-Emitting Diodes.

Indium phosphide (InP) quantum dots (QDs) are promising alternative heavy-metal CdSe QDs for light-emitting diode (LED) application. However, their highly reactive core surface is prone to oxidation, which reduces the photoluminescence quantum yield (PL QY) and impedes subsequent shell growth. Traditional etching methods using HF aqueous solution are problematic as water can induce reoxidation during or after etching. Herein, we present HF pyridine solution as a more effective etching reagent to enhance luminous properties of InP QDs. Pyridine molecules replace the bulky carboxyl ligand, reducing steric hindrance and allowing HF easier access to the core for removing surface oxides. This ligand exchange promotes rapid shell growth, minimizing core exposure to the reaction environment and thereby reoxidation risk. Consequently, the as-prepared core/shell QDs exhibit a high PL QY of ∼90%, and the corresponding LEDs achieve an external quantum efficiency of 15.4% along with a long operational lifetime of 6819 h, outperforming the control devices.

Fe(II) spin-crossover in 2-D Hofmann-like coordination polymers with different sized pyridine derivatives: syntheses, crystal structures, and magnetic properties

The syntheses, crystal structures, and magnetic properties of 2-D Hofmann-like motif {FeII(alkyl-pyridine)2[AuI(CN)2]2} (alkyl = 3,4-dimethyl (1), 4-ethyl (2), 4-isopropyl (3)), {FeII(alkyl-pyridine)2[AuI(CN)2]2}∙1/2(alkyl-pyridine) (alkyl = 3,5-dimethyl (4)), and {FeII(X-Isonicotinate)2[AuI(CN)2]2} (X = allyl (5), phenyl (6)) have been investigated. In spite of a wide range of substituent sizes, the structures of 1-3, 5, and 6 are almost crystallographically identical. The 2-D layer consists of an octahedral FeII ion coordinated with the nitrogen atoms in [AuI(CN)2] linear units at equatorial positions and monodentate py derivatives at axial positions. The adjacent two layers interact via intermetallic Au–Au interactions, forming a bilayer structure. The distance between stacking bilayers is associated with bulky substituent ligands. With increasing bulkiness, the interlayer distance expands without any transformation in the crystal structure. Compound 4 possesses guest space where uncoordinated 3,5-dimethyl-pyridine is present. Compounds 1-4 and 6 undergo spin transitions. Only 5 retains the high-spin state characteristic. These constant structures are similar to formerly reported Ag derivatives {FeII(alkyl-pyridine)2[AgI(CN)2]2}. The related Ag and Au families are compared and discussed.

Ligand-enabled Ni-catalysed dicarbofunctionalisation of alkenes with diverse native functional groups

The transition metal-catalysed dicarbofunctionalisation of unactivated alkenes normally requires exogenous strong coordinated directing groups, thus reducing the overall reaction efficiency. Here, we report a ligand-enabled Ni(II)-catalysed dicarbofunctionalisation of unactivated alkenes with aryl/alkenyl boronic acids and alkyl halides as the coupling partners with a diverse range of native functional groups as the directing group. This dicarbofunctionalisation protocol provides an efficient and direct route towards vicinal 1,2-disubstituted alkanes using primary, secondary, tertiary amides, sulfonamides, as well as secondary and tertiary amines under redox-neutral conditions that are challenging to access through conventional methods. The key to the success of this reaction is the use of a bulky β-diketone ligand, which could enable the insertion of alkene to aryl-Ni(II) species, stabilize the alkyl-Ni(II) species and inhibit the homolytic alkyl-Ni(II) cleavage, supporting by both experimental and computational studies. This dicarbofunctionalisation reaction features the use of native directing group, a broad substrate scope, and excellent scalability.

Fabrications of Au–Pt Bimetallic Heterostructure Electrodes By Ligand-Exchange Assisted Layer-By-Layer Self-Assembly for Hydrogen Evolution Reaction

Platinum (Pt) is a widely utilized electrocatalyst for hydrogen evolution reaction (HER) for water splitting, since the Pt–H bond strength is optimal for hydrogen adsorption and desorption for HER. In order to improve its catalytic activity and stability, previous research reported various types of preparation methods for Pt-containing bimetallic catalysts with noble metals (Ru, Pd, Ag, and Au) or transition metals (Cr, Mn, Fe, Co, Ni, Cu, and Zn) with exhibitions of electronic and bifunctional effects. Among such examples, Au–Pt bimetallic electrocatalysts indicated several advantages, such as d-band shift of active element of Pt lowering binding strength of protons, shifting Pt oxidation potential for improved stability, and increased electron transfer. These catalysts were synthesized by seeded growth, galvanostatic deposition, surface dealloying, and electrodeposition methods. Nevertheless, a facile and effortless synthesis approach must be established to realize large-scale production of multicomponent catalysts.In this study, ligand-exchange assisted layer-by-layer (LbL) self-assembly method was utilized to prepare Au–Pt nanocomposite films for HER electrocatalyst. The ligand-exchange assisted LbL self-assembly technique was used to fabricate metallic nanoparticle (NP) thin films to reduce the amount of insulating organic components, and improves electrical conductivity through metal fusion between metal NPs. Tetraoctylammonium bromide (TOA-Br) ligands on the surface of Au and Pt nanoparticles (NPs) are alternately deposited onto Ti electrodes paired with diethylenetriamine (DETA), a short alkyl amine. This process is accompanied by the removal of the pre-attached bulky surface ligands of TOA-Br. The resulting Au and Pt NP LbL nanocomposite films are characterized by uniform thin-film depositions with a metal-level electrical conductivity (8.7 × 104 S cm-1), which is similar to the bulk metal conductivity. The Au–Pt NP nanocomposite films exhibited 80 mV at a current density of 10 mA cm-2 of HER overpotential under an acidic condition of 0.5 M H2SO4, which corresponds to one-third of that of the control sample of only Pt NP LbL film. The Au–Pt LbL film indicates competitive overpotential (less than 100 mV) despite the ultra-small amount of Pt contents (0.73 wt%), which is suggestive of enhanced catalytic activity. Higher activity could be ascribed to the synergistic effect of bimetallic heterostructure films with the d-band shift, superb electrical conductivity, rapid charge transfer, and increased electrochemical surface area. The suggested synthesis approach is expected to be effective for the fabrications of various electocatalystic thin films for various energy conversion devices.

Isolation and characterization of a triplet nitrene.

Nitrene radical compounds are short-lived intermediates in a variety of nitrogen-involved transformations. They feature either a singlet or a triplet ground state, depending on the electronic properties of the substituents. Triplet nitrenes are highly reactive and their isolation in the condensed phase under ambient conditions is challenging. Here we report the synthesis and isolation of a triplet arylnitrene supported by a bulky hydrindacene ligand. The arylnitrene is fully characterized by various spectroscopic and structural techniques including electron paramagnetic resonance spectroscopy and single-crystal X-ray diffraction. Its high stability is largely attributed to the steric hindrance and effective electron delocalization provided by the supporting ligand. Electron paramagnetic resonance spectroscopy in conjunction with highly correlated wavefunction-based ab initio calculations provides support for a triplet ground state nitrene with axial zero-field splitting D = 0.92 cm-1 and vanishing rhombicity E/D = 0.002.

Synthetic studies on fusicoccin A: Enantioselective synthesis of the C-ring fragment

The enantioselective synthesis of the C-ring fragment of fusicoccin A is described. The TBS ether of hydroxyketone prepared by baker’s yeast reduction was converted to the α-ethylidene ketone by aldol condensation with propionaldehyde, followed by Michael reaction with divinylcopper reagent and conversion to enol triflate to afford a single diastereomer. X-ray crystallographic analysis of the crystalline derivative of the single diastereomer showed that the asymmetric carbon formed by the Michael reaction was consistent with the configuration of the C15 asymmetric carbon of fusicoccin A. The vinyl group of the enol triflate was converted to a hydroxymethyl group by selective dihydroxylation with a bulky ligand, oxidative cleavage of the resultant 1,2-diol with lead tetraacetate, and DIBAL-H reduction. The hydroxymethyl group was subsequently converted to TBS ether, followed by the hydrogenolysis of the benzyl group and Dess–Martin oxidation, accomplishing the enantioselective synthesis of the desired C-ring fragment of fusicoccin A.

Impact of the P‐Ligand Concentration on the Formation of Hydroformylation Catalysts: An in situ FTIR Spectroscopic Study

AbstractThe formation of hydrido rhodium(I) complexes of the type [HRh(CO)3L] and [HRh(CO)2L2] from [Rh(acac)(CO)2]/L (L: bulky monophosphite ligand) requires a ligand‐to‐rhodium ratio [L]/[Rh] > 10 to prevent the possible partial generation of [Rh6(CO)16] under typical hydroformylation conditions. Significant fractions of formed [Rh6(CO)16] at lower ratios of [L]/[Rh] can be reactivated towards the hydrido complexes after the addition of the monophosphite ligand in the presence of synthesis gas. It was also found that [Rh6(CO)16] can be transformed by treatment with an excess of monophosphite ligand under inert gas to form a mononuclear complex of the type [L`Rh(CO)L] with an ortho‐metallated ligand.

Overcoming the Limitations of Transition-Metal Catalysis in the Chemoenzymatic Dynamic Kinetic Resolution (DKR) of Atropisomeric Bisnaphthols.

Chemoenzymatic dynamic kinetic resolution (DKR), combining a metal racemization catalyst with an enzyme, has emerged as an elegant solution to transform racemic substrates into enantiopure products, while compatibility of dual catalysis is the key issue. Conventional solutions have utilized presynthesized metal complexes with a fixed and bulky ligand to protect the metal from the enzyme system; however, this has been generally limited to anionic ligands. Herein, we report our strategy to solve the compatibility issue by employing a reliable ligand that firmly coordinates in situ to the metal. Such a reliable ligand offers π* orbitals, allowing additional metal-to-ligand d-π* back-donation, which can significantly enhance coordination effects between the ligand and metal. Therefore, we developed an efficient DKR method to access chiral BINOLs from racemic derivatives under dual copper and enzyme catalysis. In cooperation with lipase LPL-311-Celite, the DKR of BINOLs was successfully realized with a copper catalyst via in situ coordination of BCP (L8) to CuCl. A series of functionalized C 2- and C 1-symmetric chiral biaryls could be synthesized in high yields with good enantioselectivity. The racemization mechanism was proposed to involve a radical-anion intermediate, which allows the axial rotation with a dramatic decrease of the rotation barrier.

A Crystalline Mesoionic Diazasilole Featuring Low-Valent Silicon.

A 1,4,2-diazasilole containing a low-valent silicon atom has been synthesized employing a bulky imino N-heterocyclic carbene ligand. This molecular structure is characterized by a mesoionic C2N2Si five-membered ring, notable for its delocalized π electrons, intrinsic charge-separated zwitterionic properties, and a distinctly nucleophilic silicon center, culminating in 6π aromaticity. This compound manifests either mesoionic silylene or silylone characteristics upon coordination with transition metals. Demonstrating extraordinary versatility, this compound engages in diverse reactions such as coordination with iron or iridium, oxidation by S8, intramolecular ring saturation under the coordination influence of iridium, silicon atom transfer facilitated by Ph2Se2, ring contraction induced by Ph2Te2, and skeletal rearrangement triggered by Et3N•HCl. These reactions culminate in the formation of a variety of unprecedented silicon-based heterocycles, which are typically formidable to achieve using conventional methods. This study unveils previously unexplored facets of low-valent 1,4,2-diazasilole, positioning it as a promising foundational building block for future innovations in unique silicon compounds.

Single-Step Synthesis of An Ideal Chain Antiferromagnet [H2(4,4'-bipyridyl)](H3O)2Fe2F10 with Spin S=5/2.

One-dimensional (1D) magnets are of great interest owing to their intriguing quantum phenomena and potential application in quantum computing. We successfully synthesized an ideal antiferromagnetic spin S=5/2 chain compound [H2(4,4'-bpy)](H3O)2Fe2F10 (4,4'-bpy=4,4'-bipyridyl) 1, using a single-step low-temperature hydrothermal method under conditions that favors the protonation of the bulky bidentate ligand 4,4'-bpy. Compound 1 consists of well-separated (Fe3+-F-)∞ chains with a large Fe-F-Fe angle of 174.8°. Both magnetic susceptibility and specific heat measurements show that 1 does not undergo a magnetic long-range ordering down to 0.5 K, despite the strong Fe-F-Fe intrachain spin exchange J with J/kB=-16.2(1) K. This indicates a negligibly weak interchain spin exchange J'. The J'/J value estimated for 1 is extremely small (<2.8×10-6), smaller than those reported for all other S=5/2 chain magnets. Our hydrothermal synthesis incorporates both [H2(4,4'-bpy)]2+ and (H3O)+ cations into the crystal lattice with numerous hydrogen bonds, hence effectively separating the (Fe3+-F-)∞ spin chains. This single-step hydrothermal synthesis under conditions favoring the protonation of bulky bidentate ligands offers an effective synthetic strategy to prepare well-separated 1D spin chain systems of magnetic ions with various spin values.

Single‐Step Synthesis of An Ideal Chain Antiferromagnet [H2(4,4′‐bipyridyl)](H3O)2Fe2F10 with Spin S=5/2

AbstractOne‐dimensional (1D) magnets are of great interest owing to their intriguing quantum phenomena and potential application in quantum computing. We successfully synthesized an ideal antiferromagnetic spin S=5/2 chain compound [H2(4,4′‐bpy)](H3O)2Fe2F10 (4,4′‐bpy=4,4′‐bipyridyl) 1, using a single‐step low‐temperature hydrothermal method under conditions that favors the protonation of the bulky bidentate ligand 4,4′‐bpy. Compound 1 consists of well‐separated (Fe3+−F−)∞ chains with a large Fe−F−Fe angle of 174.8°. Both magnetic susceptibility and specific heat measurements show that 1 does not undergo a magnetic long‐range ordering down to 0.5 K, despite the strong Fe−F−Fe intrachain spin exchange J with J/kB=−16.2(1) K. This indicates a negligibly weak interchain spin exchange J′. The J′/J value estimated for 1 is extremely small (&lt;2.8×10−6), smaller than those reported for all other S=5/2 chain magnets. Our hydrothermal synthesis incorporates both [H2(4,4′‐bpy)]2+ and (H3O)+ cations into the crystal lattice with numerous hydrogen bonds, hence effectively separating the (Fe3+−F−)∞ spin chains. This single‐step hydrothermal synthesis under conditions favoring the protonation of bulky bidentate ligands offers an effective synthetic strategy to prepare well‐separated 1D spin chain systems of magnetic ions with various spin values.

Synthesis of Bis(2,6-Diadamantyl Aryloxide) Ln(II) Complexes of Samarium, Europium, and Ytterbium and Their Ln(III) Precursors.

The syntheses of Ln(II) bis(aryloxide) complexes of Sm, Eu, and Yb have been examined with the bulky aryloxide ligand (OC6H2-2,6-Ad2-4-tBu)1- [(OAr*)1-; Ad = 1-adamantyl]. These LnII(OAr*)2(THF)2 complexes were pursued for comparison with the tris(aryloxide) Ln(II) complexes [LnII(OAr*)3]1- (Ln = La, Ce, Nd, Gd, Dy, and Lu), which have 4fn5d1 electron configurations, and with 4f14 [YbII(OAr*)3]1-. Although the Ln(II) chemistry of Sm, Eu, and Yb is often similar since they all adopt 4fn+1 electron configurations, their chemistry is surprisingly diverse with (OAr*)1-. Reactions of LnIII2(THF)2 with KOAr* in THF form the bis(aryloxide) Ln(II) complexes LnII(OAr*)2(THF)2, 1-Ln, that were characterized by X-ray diffraction for 1-Sm and 1-Yb, but crystals of 1-Eu have been elusive. Reduction of the tris(aryloxide) Sm(III) complex, SmIII(OAr*)3, 2-Sm, prepared from SmIII(NR2)3 (R = SiMe3) and HOAr* in refluxing toluene, generated the bis(aryloxide) complex, 1-Sm, and KOAr* rather than a Sm analogue of [YbII(OAr*)3]1-. Reduction of EuIII(OAr*)3, 2-Eu, prepared from EuCl3 with KOAr* in THF, caused an immediate dark blue-purple to bright red-orange color change, but crystals of the product were elusive. Neither reduction of TmIII(OAr*)3, 2-Tm, nor the reaction of TmIII2(DME)3 with KOAr* provided crystalline Tm(II) complexes.