Molecular Rare-Earth-Metal Hydrides in Non-Cyclopentadienyl Environments

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.

Frustrated Lewis Pair-Type Reactivity of Intermolecular Rare-Earth Aryloxide and N-Heterocyclic Carbene/Olefin Combinations

This work reports the cooperative reactivity of rare-earth aryloxide complexes with N-heterocyclic carbene (NHC) or N-heterocyclic olefin (NHO), showcasing their synergistic effect on the activation of H2 and diverse organic substrates. Reactions of RE(OAr)3 (RE=La, Sm, and Y; Ar=2,6-tBu2-C6H3) with unsaturated NHC ItBu (:C[N(R)CH]2, R=tBu) isolated abnormally bound RE metal NHC complexes RE/aNHC. In contrast, no metal-NHO adducts were formed when RE(OAr)3 were treated with NHO (R2C=C[N(R)C(R)]2, R=CH3). Both RE/aNHC and RE/NHO Lewis pairs enabled cooperative H2 activation. Furthermore, RE(OAr)3 were found to catalyze the hydrogenation of the exocyclic C=C double bond of NHO under mild conditions. Moreover, treatment of the La/aNHC complex with benzaldehyde produced a La/C4 1,2-addition product. The La/NHO Lewis pair could react with (trimethylsilyl)diazomethane and α, β-conjugated imine, affording an isocyanotrimethylsilyl lanthanum amide complex and a La/C 1,4-addition product, respectively.

Reactivity of a Neutral Yttrium(III) Trimethyl Complex toward Brønsted and Lewis Acids

The present study corroborates that the neutral tridentate N-ligand 1,4,7-trimethyl-triazacyclononane (Me3TACN) qualifies as a versatile platform to study selective ligand exchange with rare-earth-metal alkyl complexes, herein [(Me3TACN)YMe3]. Treatment with Brønsted-acidic bis(dimethylsilyl)amine, HN(SiHMe2)2, gave selectively the mono-exchanged heteroleptic complex [(Me3TACN)YMe2{N(SiHMe2)2}]. Depending on the molecular ratio employed, the reaction of [(Me3TACN)YMe3] with AlMe3 resulted in the isolation/crystallization of [(Me3TACN)YMe2(AlMe4)] [1 : 1] or ion-separated [(Me3TACN)YMe(AlMe4)][AlMe4] [1 : 2] and [(Me3TACN)YMe(AlMe4)][Al2Me7] [1 : 3]. Analogous reactions with the heavier group 13 methyls GaMe3 and InMe3 generated mixed methyl/tetramethylgallato complex [(Me3TACN)YMe2(GaMe4)] and ion-separated [{(Me3TACN)YMe2}2{μ-Me}][InMe4]. Finally, dimethylalane, HAlMe2, converted [(Me3TACN)YMe3] into heteroaluminate [(Me3TACN)Y(HAlMe3)3], representing an AlMe3-supported, molecular yttrium trihydride complex. All compounds were investigated by single crystal X-ray diffraction (SC-XRD), homo- and heteronuclear (13C, 27Al, 89Y, 115In) NMR as well as IR spectroscopies and elemental analyses.

Synthesis and Reactivity of Discrete Europium(II) Hydride Complexes

The bulky β-diketiminate ligand frameworks [BDIDCHP]- and [BDIDipp/Ar]- (BDI=[HC{C(Me)2N-Dipp/Ar}2]- (Dipp=2,6-diisopropylphenyl (Dipp); Ar=2,6-dicyclohexylphyenyl (DCHP) or 2,4,6-tricyclohexylphyenyl (TCHP)) have been developed for the kinetic stabilisation of the first europium (II) hydride complexes, [(BDIDCHP)Eu(μ-H)]2, [(BDIDipp/DCHP)Eu(μ-H)]2 and [(BDIDipp/TCHP)Eu(μ-H)]2, respectively. These complexes represent the first step beyond the current lanthanide(II) hydrides that are all based on ytterbium. Tuning the steric profile of β-diketiminate ligands from a symmetrical to unsymmetrical disposition, enhanced solubility and stability in the solution-state. This provides the first opportunity to study the structure and bonding of these novel Eu(II) hydride complexes crystallographically, spectroscopically and computationally, with their preliminary reactivity investigated.

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.

CO, CO2 and CS2 activation by divalent ytterbium hydrido complexes

Treatment of a divalent ytterbium hydride complex [(Tp^Ad,iPr)Yb(H)(THF)] (Tp^Ad,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) (1) with CO, CO₂ and CS₂ resulted in the formation of a divalent ytterbium ethenediolate complex [(Tp^Ad,iPr)Yb]₂(cis-OCHCHO) (2), a formate complex [(Tp^Ad,iPr)Yb(κ²-O₂CH)(THF)] (3), and a trivalent ytterbium ethenetetrathiolate complex [(Tp^Ad,iPr)Yb^III]₂(C₂S₄) (4), respectively. DFT calculations were carried out to elucidate the reaction profiles of complexes 3 and 4.

Reactivity Studies on Lanthanum and Cerium Hydrido Metallocenes

The alkyl complexes [5-1,3-(Me3C)2C5H3]2Ln(CH2C6H4-o-NMe2) (Ln = La 1, Ce 2) react with 9-borabicyclo[3.3.1]nonane (9-BBN) in THF to afford the lanthanum boroxide complex [5-1,3-(Me3C)2C5H3]2La(µ-OBC8H14)(THF) (3) and cerium boroxide complex [5-1,3-(Me3C)2C5H3]2Ce(µ-OBC8H14)(THF) (4)....

A mononuclear divalent ytterbium hydrido complex supported by a super-bulky scorpionate ligand

The first mononuclear divalent ytterbium hydride complex [(Tp^Ad,iPr)Yb(H)(THF)] (Tp^Ad,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) (2) bearing a terminal hydrido ligand was obtained by hydrogenolysis of the benzyl precursor in hexane. Complex 2 exhibited two different reaction patterns towards allenes: Yb-H addition with cyclohexylallene and deprotonation of 1,1-dimethylallene.

Scandium and lanthanum hydride complexes stabilized by super-bulky penta-arylcyclopentadienyl ligands

Hydrogenolysis of the half-sandwich penta-arylcycopentadienyl-supported rare-earth metal dibenzyl complexes [(Cp^Ar5)Ln(p-CH₂-C₆H₄-Me)₂(THF)] (Cp^Ar5 = C₅Ar₅, Ar = 3,5-ⁱPr₂-C₆H₃; Ln = Sc, La) afforded a bimetallic scandium complex [(Cp^Ar5)Sc(H)(μ-OC₄H₉)]₂ (2) with two terminal hydrido ligands, and a double-sandwich bimetallic lanthanum hydride complex [(Cp^Ar5)La(μ-H)]₂ (4) bearing the reduced Cp^Ar5 ligand. DFT calculations were conducted to elucidate the reaction profiles.

Ytterbium (II) Hydride as a Powerful Multielectron Reductant

A dimeric β-diketiminato ytterbium(II) hydride affects both the two-electron aromatization of 1,3,5,7-cyclooctatetraene (COT) and the more challenging two-electron reduction of polyaromatic hydrocarbons, including naphthalene (E⁰ =-2.60 V). Confirmed by Density Functional Theory calculations, these reactions proceed via consecutive polarized Yb-H/C=C insertion and deprotonation steps to provide the respective ytterbium (II) inverse sandwich complexes and hydrogen gas. These observations highlight the ability of a simple ytterbium(II) hydride to act as a powerful two-electron reductant at room temperature without the necessity of an external electron to initiate the reaction and avoiding radicaloid intermediates.

Divalent Ytterbium Hydrido Complex Supported by a β-Diketiminato-Based Tetradentate Ligand: Synthesis, Structure, and Reactivity

While the chemistry of trivalent rare-earth metal hydrido complexes has been well developed in the past 40 years, that of the divalent rare-earth metal hydrido complexes remains in its infancy because of the synthetic challenge of such complexes. In this paper, we report the synthesis and structural characterization of a divalent ytterbium hydrido complex supported by a bulky β-diketiminato-based tetradentate ligand. This hydrido complex is a dimer containing two μ-hydrogen ligands, and it easily undergoes a hydrido shift reaction to form a new divalent ytterbium hydrido complex that contains only one hydrido bridge. Furthermore, this hydrido complex reacts with pyridine and pyridine derivatives, showing versatile reactivity [Yb-H addition to pyridine, hydrido shift to ancillary ligand, and ytterbium(II)-center-induced redox reaction with bipyridine]. This hydrido complex reacts with Ph₃P═O, resulting in a P-C^Ph cleavage of Ph₃P═O and an elimination of C₆H₆; on the other hand, the reaction with Ph₃P═S is a hydrido coupling-based redox reaction. The reactions of this hydrido complex with 1 and 2 equiv of PhSSPh clearly indicate that the hydrido coupling-based redox reaction is prior to the ytterbium(II) oxidation-based redox reaction.

A dinuclear Mo2H8 complex supported by bulky C5H2tBu3 ligands

Hydride-bridged transition metal complexes have been found to serve as suitable precursors for the activation of small molecules without the use of reducing agents. In this study, we synthesized a dinuclear Mo2H8 complex supported by bulky C5H2tBu3 (Cp‡) ligands, Cp‡2Mo2H8 (1), from the reaction of Cp‡MoCl4 with KC8 under H2. The hydrides of complex 1 can be replaced with benzene at 60 °C to afford a μ-benzene complex Cp‡2Mo2H2(μ-C6H6) (2).

Monomeric thorium dihydrido complexes: versatile precursors to actinide metallacycles

The monomeric actinide dihydrido complex [(Cp^Ar*)(Cp*)ThH₂(THF)] (2) and actinide metallacyclopentyne [(Cp^Ar*)(Cp*)Th(PhCH–CC–CHPh)] (4) were obtained for the first time.

Direct imaging of how lanthanides break the normal evolution of plants

After rare earth elements [REE(III)] are anchored outside of the plasma membrane, REE(III) break plant evolution to initiate leaf cell endocytosis, which finally affects plant growth. However, the molecule for anchoring REE(III) in the acidic environment outside of the plasma membrane is not clear, which is crucial for exploring the mechanism of REE(III) breaking plant evolution. Here, lanthanum(III) [La(III)] and terbium(III) [Tb(III)] were respectively served as a representative of REE(III) without and with f electrons, and Arabidopsis was served as a representative of plants, cellular and molecular basis for arabinogalactan proteins (AGP) anchoring REE(III) outside of the plasma membrane was investigated. By using interdisciplinary methods, when REE(III) initiated leaf cell phagocytosis, we observed the increase in the expression of AGP and their migration to the outside of the plasma membrane. In the acidic environment outside of the plasma membrane, Tb(III) formed more stable Lewis acid-base [REE(III)-AGP] complexes with a higher apparent binding constant (1.51 × 10^-6) than La(III) (1.24 × 10^-6). In REE(III)-AGP complexes, the bond lengths of REE(III)-O were in normal range and H-bonds were strong H-bonds. The formation of REE(III)-AGP complexes sequentially disturbed the secondary and tertiary structure of AGP, which were enhanced with increasing the concentration of REE(III), and Tb(III) caused stronger structural changes than La(III). Hence, AGP could be molecules for anchoring REE(III) outside of the plasma membrane. The results of this study are direct imaging of how lanthanides break the normal evolution of plants, and can serve as an important guidance for investigating mechanism of lanthanides in organisms.

Scandium alkyl and hydride complexes supported by a pentadentate diborate ligand: reactions with CO2 and N2O

Alkyl and hydrido scandium complexes of the dianionic pentadentate ligand B2Pz4Py are reported.

Molecular hydrides of divalent ytterbium supported by a macrocyclic ligand: synthesis, structure and olefin hydrofunctionalization catalysis

Cationic ytterbium hydrides [(Me₄TACD)₂Yb₂H_(2+n)]⁽²⁻ⁿ⁾⁺ (n = 0, 1) catalyzed the H₂/D₂ isotope exchange as well as hydrogenation and hydrosilylation of 1-hexene.

Rare-earth metal hydrides supported by silicon-bridged boratabenzene fluorenyl ligands: synthesis, structure and reactivity

The first boratabenzene derivatives of rare-earth metal hydrides were synthesized, and their reactivity was studied.

Synthesis and structure of the first discrete dinuclear cationic aluminum complexes

The preparation of discrete mono- and dicationic dinuclear aluminum complexes from the parent charge neutral dinuclear precursors has been studied. The first crystal structure of a dicationic dialuminum complex is reported.

Homo- and Heteropolynuclear Clusters of Phosphine Triphenolates

The synthesis and structural characterization of a series of homo- and heteropolynuclear clusters constructed with a potentially tetradentate phosphine triphenolate ligand are presented. Treatment of tris(3,5-di-tert-butyl-2-hydroxyphenyl)phosphine (H3[O3P]) with 3 equiv of nBuLi in diethyl ether at -35 °C affords hexanuclear Li6[O3P]2(OEt2)2 (1) as colorless crystals. In situ lithiation of H3[O3P] with 3 equiv of nBuLi in THF at -35 °C followed by metathetical reactions with MnCl2 or NiCl2(DME) gives crystals of forest green pentanuclear MnLi4[O3P]2(THF)3 (2) or dark brown tetranuclear Ni2Li2[O3P]2(THF)2 (3), respectively. Alkane elimination of ZnR2 (R = Me, Et) with H3[O3P] in THF at 25 °C generates high yields of colorless crystalline trinuclear Zn3[O3P]2(THF)2 (4). The cluster structures of 1-4 were all determined by single crystal X-ray diffraction studies. These molecules represent the first examples of metal complexes supported by phosphine triphenolate derivatives. The cluster 2 contains a paramagnetic core of high spin Mn(II) (S = 5/2) as indicated by solution and solid state magnetic susceptibility measurements.

Synthesis and reactivity of cyclometalated triamidophosphine complexes of niobium and tantalum

The triamidophosphine protioligand 1 reacts with the homoleptic pentakis(dimethylamido) precursors of niobium and tantalum [M(NMe2)5, where M = Nb, Ta] to form cyclometalated complexes of the type [N2PCN-κ(5)-N,N,P,C,N]M(NMe2) (2-M). Apart from the three amido donors, one benzylic position of the ligand backbone is deprotonated over the course of this reaction, resulting in the formation of a new M-C bond. As a consequence, a metallaziridine substructure is formed, and the triamidophosphine moiety thus serves as a tetraanionic pentadentate ligand. The dimethylamido complexes 2-M can be converted into the corresponding triflates [N2PCN-κ(5)-N,N,P,C,N]M(OTf) (3-M) and alkyl complexes [N2PCN-κ(5)-N,N,P,C,N]M(CH2SiMe3) (4-M) by treatment with triethylsilyl triflate (Et3SiO3SCF3) followed by (trimethylsilyl)methyllithium (LiCH2SiMe3). The alkyl complexes exhibit interesting reactivities, including a second cyclometalative backbone activation affording the trimethylphosphine-stabilized complexes [NP(CN)2-κ(6)-N,P,C,N,C,N]M(PMe3) (5-M). In the case of tantalum, the formation of a dinuclear hydrido complex (6) is observed upon hydrogenation of 4-Ta. In the case of niobium, the metallaziridine substructure in 4-Nb is prone to ring opening via protonation with triphenylsilylamine (Ph3SiNH2), resulting in formation of the corresponding imido complex [PN3-κ(4)-P,N,N,N]Nb=NSiPh3 (7).

Reactivity of functionalized indoles with rare-earth metal amides. Synthesis, characterization and catalytic activity of rare-earth metal complexes incorporating indolyl ligands

The synthesized rare-earth metal amido complexes displayed different catalytic activity for intramolecular hydroamination of aminoalkenes.