Rare-Earth-Metal Methyl and Methylidene Complexes Stabilized by TpR,R'-Scorpionato Ligands─Size Matters

Homoleptic tetramethylaluminates Ln(AlMe4)3 react with KTptBu,Me (TptBu,Me = tris(3-tBu-5-Me-pyrazolyl)borato) to yield rare-earth-metal methylidene complexes (TptBu,Me)Ln(μ3-CH2)[(μ-Me)AlMe2]2 (Ln = La, Ce, Nd). The lanthanum reaction is prone to additional C-H- and B-N-bond activation, affording coproducts La[HB(pzMe,tBu)(pzCMe2,Me)2][(μ-CH2)(μ-Me)AlMe2]2 and [La(μ-pztBu,Me)(AlMe4)2]2 (pztBu,Me = 3-tBu-5-Me-pyrazolato). The protonolysis reaction of Ln(AlMe4)3 and HpztBu,Me provides more efficient access to [Ln(μ-pztBu,Me)(AlMe4)2]2 (Ln = La, Nd). Treatment of Ln(AlMe4)3 with KTpMe,Me led to methylidene complexes (TpMe,Me)Ln(μ3-CH2)[(μ-Me)AlMe2]2 (Ln = Nd, Sm) or bis(tetramethylaluminate) complexes (TpMe,Me)Ln(AlMe4)2 (Ln = Y, Lu). The neodymium reaction generated methine derivative (TpMe,Me)Nd[(μ4-CH)(AlMe2)2(μ-pz,Me,Me)][(μ-Me)AlMe2] as a minor coproduct. The reaction of Ln(GaMe4)3 (Ln = Y, La, Ce, Nd, Sm, Ho) with HTptBu,Me gave methylidene complexes (TptBu,Me)Ln(μ3-CH2)[(μ-Me)GaMe2]2 (Ln = La, Ce, Nd, Sm) and alkyl complexes (TptBu,Me)LnMe[(μ-Me)GaMe3] (Ln = Y, Ho), while competing B-N bond activation reactions produced GaMe2[BH(Me)(μ-pztBu,Me)2] and (TptBu,Me)Ln(η2-pztBu,Me)[(μ-Me)GaMe3] (Ln = Y, Ho). The steric impact of the TpR,Me ligands was examined by cone angle calculations. Rare-earth-metal methylidene complexes (TptBu,Me)Ln(μ3-CH2)[(μ-Me)EMe2]2 (E = Al, Ga) successfully promote carbonyl methylenation reactions upon addition of ketone.

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.

Rare-earth metal ethylene and ethyne complexes

Guanidinate homometallic rare-earth ethyl complexes [LLn(μ2-η1:η2-Et)(Et)]2 (Ln = Y(1-Y), Lu(1-Lu)) and heterobimetallic rare-earth ethyl complexes LLn(Et)(μ2-η1:η2-Et)(μ2-η1-Et)(AlEt2) (Ln = Y(2-Y), Lu(2-Lu)) have been synthesized by the treatment of LLn(CH2C6H4NMe2-o)2 (L = (PhCH2)2NC(NC6H3iPr2-2,6)2) with different equivalents of AlEt3 in toluene at ambient temperature. Interestingly, the unprecedented rare-earth ethyne complex [LY(μ2-η1-Et)2(AlEt)]2(μ4-η1:η1:η2:η2-C2H2) (3-Y) containing a [C2H2]4- unit was afforded from 2-Y. The formation mechanism study on 3-Y was carried out by DFT calculations. Furthermore, the nature of the bonding of 3-Y was also revealed by NBO analysis. The reactions of LLn(CH2 C6H4NMe2-o)2 (Ln = Y, Lu) with AlEt3 (4 equiv.) in toluene at 50 °C produced firstly the non-Cp rare-earth ethylene complex LY(μ3-η1:η1:η2-C2H4)[(μ2-η1-Et)(AlEt2)(μ2-η1-Et)2(AlEt)] (4-Y), and the Y/Al ethyl complex LY[(μ2-η1-Et)2(AlEt2)]2 (5-Y) as an intermediate of 4-Y was isolated from the reaction of LY(CH2C6H4NMe2-o)2 with AlEt3 (4 equiv.) in toluene at -10 °C.

A binuclear guanidinate yttrium carbyne complex: unique reactivity toward unsaturated C-N, C-O and C-S bonds

A guanidinato-stabilized binuclear yttrium carbyne complex [(PhCH2)2NC(NC6H3iPr2-2,6)2]2Y2(μ2-Me)(AlMe3)2(μ4-CH) (1) was synthesized via C-H bond activation and its versatile reactivities were investigated. Complex 1 underwent σ-bond metathesis with PhSSPh and nucleophilic addition with PhCN to form the corresponding yttrium thiolate complex 3 and aza-allyl complex 4 respectively. Additionally, the rare yttrium carbide complex 5 was also prepared by treatment of complex 1 with S8. Interestingly, in the reaction with PhNCS, the C[double bond, length as m-dash]S double bond was cleaved, followed by C-H bond activation to give the yttrium sulfide complex 7 with a ketenimine dianion ligand. Unexpectedly, the reaction of complex 1 with CO (1 atm) resulted in deoxygenative coupling of CO, to afford mono- or dioxo-yttrium complexes at different temperatures. The mechanism of the possible formation processes of complexes 3 and 9 was elucidated by DFT calculations.

Selective Si-C(sp3) bond cleavage of a silyl-bridged amido alkyl ligand in an yttrium complex

Compared with Si-C(sp² and sp) bonds bearing neighboring π-bond hyperconjugative interactions, the activation of robust Si-C(sp³) bonds has proved to be a challenge. Herein, two distinct Si-C(sp³) bond cleavages have been realized by rare-earth-mediated and nucleophilic addition of unsaturated substrates. The reactions of Tp^Me2Y[κ²-(C,N)-CH(SiH₂Ph)SiMe₂NSiMe₃](THF) (1) with CO or CS₂ gave two endocyclic Si-C bond cleavage products, Tp^Me2Y[κ²-(O,N)-OCCH(SiH₂Ph)SiMe₂NSiMe₃](THF) (2) and Tp^Me2Y[κ²-(S,N)-SSiMe₂NSiMe₃](THF) (3), respectively. However, 1 reacted with nitriles such as PhCN and p-R'C₆H₄CH₂CN in a 1 : 1 molar ratio to yield the exocyclic Si-C bond products Tp^Me2Y[κ²-(N,N)-N(SiH₂Ph)C(R)CHSiMe₂NSiMe₃](THF) (R = Ph (4); R = C₆H₅CH₂ (6H); R = p-F-C₆H₄CH₂ (6F); and R = p-MeO-C₆H₄CH₂ (6MeO)), respectively. Moreover, complex 4 can continuously react with an excess of PhCN to form a Tp^Me2-supported yttrium complex with a novel pendant silylamido-substituted β-diketiminato ligand, Tp^Me2Y[κ³-(N,N,N)-N(SiH₂Ph)C(Ph)CHC(Ph)N-SiMe₂NSiMe₃](PhCN) (5).

Rare-earth-metal half-sandwich complexes incorporating methyl, methylidene, and hydrido ligands

Complexes Cp*₃Ln₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ (Ln = Y, Dy; Cp* = C₅Me₅) are formed via elimination of CH₄ and C₂H₄ from the respective trinuclear polymethyl complexes [Cp*Ln(μ₂-CH₃)₂]₃, involving the methyl/methylidene complex Cp*₃Ln₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-CH₃)(thf)₂ as an intermediate. Compound Cp*₃Y₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ displays "Schrock-type" nucleophilic carbene reactivity, converting ketones into the corresponding terminal alkenes. Treatment of Cp*₃Y₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ with [D₄]methanol proved accessibility of all small-group functionalities as indicated by the simultaneous formation of deuterated HD and deuterated methanes CH₃D and CH₂D₂.

Facile synthesis of a glutathione-depleting Cu(II)-half-salamo-based coordination polymer for enhanced chemodynamic therapy

Chemodynamic therapy (CDT), utilizing Fenton catalysts to convert intracellular H₂O₂ into toxic hydroxyl radicals (˙OH) to kill cancer cells, has a wide application prospect in tumor treatment because of its high selectivity. Its anticancer effect, however, is unsatisfactory due to the overexpressed glutathione (GSH). Herein, a GSH-depleting Cu(II)-half-salamo-based coordination polymer (CuCP) was prepared and validated by single crystal X-ray crystallography, Hirshfeld surface analyses and DFT calculations. The Cu(II) ions in the coordination polymer are five-coordinated bearing slightly twisted square pyramidal coordination environments and are bridged by phenoxy and alkoxy groups. After internalization by tumor cells, the CuCP could be biodegraded and reduced by GSH to generate a large amount of Cu(I), simultaneously depleting GSH. Subsequently, the Cu(I) ions interact with H₂O₂ to generate toxic ˙OH through a Fenton-like reaction to enhance their anticancer efficacy. Our study provides useful insights into designing smarter metal-based anticancer agents to improve the CDT efficiency in cancer therapy.

Bonding Nature of "Ionic Carbenes" in [M3(μ3-CH2)]-Containing Compounds: The Covalent Interaction

While a series of trinuclear rare-earth metal methylene (divalent >CH₂) complexes with the so-called "ionic carbene" have been known for decades, the nature of metal-carbene interactions in this class of compounds remains elusive. Herein, a quantum chemical investigation has been performed to reveal the bonding nature in typical trimetallic "ionic carbene" species with the [M₃(μ₃-CH₂)] (M = Sc, Y, La, and Ac) cluster core. Through various chemical bonding analyses, we have demonstrated that there exists a non-negligible covalent interaction between μ₃-CH₂ and M₃ moieties, and the chemical bonding can be accounted for with two three-center two-electron (3c-2e) bonds. The chemical bonding analyses reveal that the metal d-electron configuration plays an important role in stabilizing various μ₃-coordinated carbene complexes. The late transition metals do not favor such a μ₃-coordination geometry, thus explaining why ionic carbene complexes are usually found for rare-earth and early transition metals. A series of ionic carbene complexes with early transition metals, lanthanides, and actinides are predicted to be stable as well. These reactive ionic carbene complexes may have characteristic properties for organic synthesis and catalysis.

Reactivity of Mixed Methyl-Aminobenzyl Guanidinate Lutetium Complex towards iPrN=C=NiPr, CS2 and Ph2PH

A heteroleptic terminal alkyl lutetium complex stabilized by a bulky guanidinato ligand, LLu(CH2C6H4NMe2-o)(Me)(THF) (1) (L = (PhCH2)2NC(NC6H3iPr2-2,6)2) has been synthesized by treatment of LLu(CH2C6H4NMe2-o)2 with AlMe3 (1 equiv) via an...

Trinuclear scandium methylidyne complexes stabilized by pentamethylcyclopentadienyl ligands

The first examples of scandium methylidyne complexes [(Cp*)Sc(μ2-X)]3(μ3-CH) (Cp* = C5Me5; X = Br, Me, OMe), free of Lewis acids, can be achieved in high yields from [(Cp*)ScMe2]2 through a facile route. The chemical and geometrical flexibility to incorporate organic substrates indicates a rich chemistry of complex [(Cp*)Sc(μ2-OMe)]3(μ3-CH).