Highly Reactive Scandium Phosphinoalkylidene Complex: C-H and H-H Bonds Activation

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.

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.

Rare-Earth Metal Phosphinidene Complexes: A Trip from Bridging One to Terminal One

ConspectusAs phosphorus analogues of alkylidene (or carbene) and imido (or nitrene) complexes, phosphinidene complexes have received great attention not only for their fundamental scientific merits but also for their ability to build new phosphorus-containing molecules. A large number of phosphinidene complexes in bridging, mononuclear, or terminal coordination modes have been synthesized, and their reactivity has been extensively explored. However, the synthesis of rare-earth metal (scandium, yttrium, and lanthanide metal) phosphinidene complexes lagged behind the transition metal and actinide congeners for decades. Rare-earth metal ions are among the hardest Lewis acids, whereas phosphinidene ligands are soft Lewis bases; rare-earth metal-phosphinidene coordination is thus mismatched based on the Pearson's HSAB principle. The bridging rare-earth metal phosphinidene complexes were not reported until 2008, and the synthesis of the mononuclear and terminal species is even more challenging, which has only recently been achieved.Our group reported a bis(μ2-phosphinidene)dineodymium complex in 2008. In the following >10 years, we have been pursuing the terminal rare-earth metal phosphinidene complexes. Due to the high instability of rare-earth metal-phosphorus multiple bonds, the synthesis and stabilization of these complexes are extremely difficult. Finally, by using suitable phosphinidene ligands and supporting ligands, we obtained the first mononuclear rare-earth metal phosphinidene complex in 2018 and the first terminal rare-earth metal phosphinidene complex in 2020. In these more than ten years of research, we have also found some interesting reactivity of the rare-earth metal phosphinidene complexes. The rare-earth metal bridging phosphinidene complexes can act as two-electron reductants based on the oxidative coupling of two phosphinidene ligands into a diphosphene ligand. The mononuclear rare-earth metal phosphinidene complexes catalyze the hydrogenation of terminal alkenes under mild conditions, and the joint experimental/DFT studies indicate that the hydrogenation reaction proceeds in a 1,2-addition/elimination mechanism rather than the common σ-bond metathesis mechanism. These reactivities are new and important for the rare-earth metal complexes. In addition, the ligand design in our study may contribute to the synthesis of rare-earth metal-arsenic multiple bonding complexes and alkaline-earth metal-phosphorus multiple bonding complexes, which have not yet been realized. Herein, we present an account of our investigations into rare-earth metal phosphinidene complexes, a trip from bridging one to terminal one. To give the readers an overall image of the development of the rare-earth metal phosphinidene complexes, some findings from other researchers are also included.

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.

Cascade Nucleophilic Attack/Addition Cyclization Reactions to Synthesize Oxazolidin-2-imines via (Z)-2-Bromo-3-phenylprop-2-en-1-ols/3-phenylprop-2-yn-1-ols and Diphenyl Carbodiimides

Two concise strategies to synthesize oxazolidin-2-imines by cascade nucleophilic attack/addition cyclization reactions of (Z)-2-bromo-3-phenylprop-2-en-1-ols/3-phenylprop-2-yn-1-ols and diphenyl carbodiimides without a transition-metal catalyst have been developed. The reactions exhibited good substrate applicability tolerance, and a variety of substituted (Z)-4-((Z)-benzylidene)-N,3-diphenyloxazolidin-2-imines were synthesized in moderate to excellent yields with good stereoselectivity. The reports also provided a convenient strategy to synthesize 3-phenylprop-2-yn-1-ols by (Z)-2-bromo-3-phenylprop-2-en-1-ols. The economic and practical methods provide a great advantage for potential industrial synthesis of oxazolidin-2-imines.

C–Cl Oxidative Addition and C–C Reductive Elimination Reactions in the Context of the Rhodium-Promoted Direct Arylation

A cycle of stoichiometric elemental reactions defining the direct arylation promoted by a redox-pair Rh(I)–Rh(III) is reported. Starting from the rhodium(I)-aryl complex RhPh{κ³-P,O,P-[xant(PⁱPr₂)₂]} (xant(PⁱPr₂)₂ = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene), the reactions include C–Cl oxidative addition of organic chlorides, halide abstraction from the resulting six-coordinate rhodium(III) derivatives, C–C reductive coupling between the initial aryl ligand and the added organic group, oxidative addition of a C–H bond of a new arene, and deprotonation of the generated hydride-rhodium(III)-aryl species to form a new rhodium(I)-aryl derivative. In this context, the kinetics of the oxidative additions of 2-chloropyridine, chlorobenzene, benzyl chloride, and dichloromethane to RhPh{κ³-P,O,P-[xant(PⁱPr₂)₂]} and the C–C reductive eliminations of biphenyl and benzylbenzene from [RhPh₂{κ³-P,O,P-[xant(PⁱPr₂)₂]}]BF₄ and [RhPh(CH₂Ph){κ³-P,O,P-[xant(PⁱPr₂)₂]}]BF₄, respectively, have been studied. The oxidative additions generally involve the cis addition of the C–Cl bond of the organic chloride to the rhodium(I) complex, being kinetically controlled by the C–Cl bond dissociation energy; the weakest C–Cl bond is faster added. The C–C reductive elimination is kinetically governed by the dissociation energy of the formed bond. The C(sp³)–C(sp²) coupling to give benzylbenzene is faster than the C(sp²)–C(sp²) bond formation to afford biphenyl. In spite of that a most demanding orientation requirement is needed for the C(sp³)–C(sp²) coupling than for the C(sp²)–C(sp²) bond formation, the energetic effort for the pregeneration of the C(sp³)–C(sp²) bond is lower. As a result, the weakest C–C bond is formed faster.

Transformation of the sp2 Carbanion to Carbene with Subsequent 1,1-Migratory Insertion and Nucleophilic Substitution in Rare-Earth Metal Chemistry

The development of Fischer-type electrophilic carbene chemistry with early transition metals has been a great challenge due to the fact that such metals in their high oxidation states lack the d electrons to stabilize the electrophilic carbene. Herein, we disclose the first experimental and theoretical findings of in situ transformation of an sp² carbanion to a Fischer-type electrophilic carbene with rare-earth metals in their high oxidation state with a d⁰ electron via electron transfer. The carbene may undergo 1,1-migratory insertion into an adjacent RE-C(sp³) bond, and an unprecedented ring opening of the indole ring of the ligand occurs when the carbenes undergo nucleophilic substitution with a special organolithium reagent o-Me₂NC₆H₄CH₂Li. The key to success is the uniquely tailored novel ligand systems featuring a suitable conjugate building block (^-C═C-C═N) bearing an sp² carbanion connected to the rare-earth metal center.

Phosphorus-Atom Transfer from Phosphaethynolate to an Alkylidyne

A low-spin and mononuclear vanadium complex, (Me nacnac)V(CO)(η2 -P≡Ct Bu) (2) (Me nacnac- =[ArNC(CH3 )]2 CH, Ar=2,6-i Pr2 C6 H3 ), was prepared upon treatment of the vanadium neopentylidyne complex (Me nacnac)V≡Ct Bu(OTf) (1) with Na(OCP)(diox)2.5 (diox=1,4-dioxane), while the isoelectronic ate-complex [Na(15-crown-5)]{([ArNC(CH2 )]CH[C(CH3 )NAr])V(CO)(η2 -P≡Ct Bu)} (4), was obtained via the reaction of Na(OCP)(diox)2.5 and ([ArNC(CH2 )]CH[C(CH3 )NAr])V≡Ct Bu(OEt2 ) (3) in the presence of crown-ether. Computational studies suggest that the P-atom transfer proceeds by [2+2]-cycloaddition of the P≡C bond across the V≡Ct Bu moiety, followed by a reductive decarbonylation to form the V-C≡O linkage. The nature of the electronic ground state in diamagnetic complexes, 2 and 4, was further investigated both theoretically and experimentally, using a combination of density functional theory (DFT) calculations, UV/Vis and NMR spectroscopies, cyclic voltammetry, X-ray absorption spectroscopy (XAS) measurements, and comparison of salient bond metrics derived from X-ray single-crystal structural characterization. In combination, these data are consistent with a low-valent vanadium ion in complexes 2 and 4. This study represents the first example of a metathesis reaction between the P-atom of [PCO]- and an alkylidyne ligand.

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).

Insertion of Metal-Substituted Silylene into Naphthalene's Aromatic Ring and Subsequent Rearrangement for Silaspiro-Benzocycloheptenyl and Cyclobutenosilaindan Derivatives

Synthesis of silacycle compounds are of fundamental and application importance. Herein we report the first example of insertion of metal-substituted silylene fragment into naphthalene's aromatic ring. More significantly, this insertion is followed by interesting rearrangements to yield silaspiro-benzocycloheptenyl and cyclobutenosilaindan derivatives. The formation of cyclobutenosilaindan derivative includes the C-C bond cleavage and 4π electrocyclization steps; the formation of silaspiro-benzocycloheptenyl derivative is more complicated, including the C-C bond cleavage, reversible 4π electrocyclization, C-H bond activation and C-Si bond cleavage. DFT investigations were carried out to shed light on the mechanistic aspects of these two rearrangements. The formed cyclobutenosilaindan potassium can readily react with PhOH, MeOTf, EtOTf, PhCH₂ Cl or PhCOCl at room temperature to afford the hydrogen, alkyl, benzyl or benzoyl substituted cyclobutenosilaindans in high yields.

Cyclic Bis-alkylidene Complexes of Titanium and Zirconium: Synthesis, Characterization, and Reaction

Transition-metal alkylidenes have exhibited wide applications in organometallic chemistry and synthetic organic chemistry, however, cyclic Schrock-carbene-like bis-alkylidenes of group 4 metals with a four-electron donor from an alkylidene have not been reported. Herein, the synthesis and characterization of five-membered cyclic bis-alkylidenes of titanium (4 a,b) and zirconium (5 a,b) are reported, as the first well-defined group 4 metallacyclopentatrienes, by two-electron reduction of their corresponding titana- and zirconacyclopentadienes. DFT analyses of 4 a show a four-electron donor (σ-donation and π-donation) from an alkylidene carbon to the metal center. The reaction of 4 a with N,N'-diisopropylcarbodiimide (DIC) leads to the [2+2]-cycloaddition product 6. Compound 4 a reacted with CO, affording the oxycyclopentadienyl titanium complex 7. These reactivities demonstrate the multiple metal-carbon bond character. The reactions of 4 a or 5 a with cyclooctatetraene (COT) or azobenzene afforded sandwich titanium complex 8 or diphenylhydrazine-coordinated zirconacyclopentadiene 9, respectively, which exhibit two-electron reductive ability.

2-Butene Tetraanion Bridged Dinuclear Samarium(III) Complexes via Sm(II)-Mediated Reduction of Electron-Rich Olefins

While reduction reactions are ubiquitous in chemistry, it is very challenging to further reduce electron-rich compounds, especially the anionic ones. In this work, the reduction of 1,3-butadienyl dianion, the anionic conjugated olefin, has been realized by divalent rare-earth metal compounds (SmI₂), resulting in the formation of novel 2-butene tetraanion bridged disamarium(III) complexes. Density functional theory (DFT) analyses reveal two features: (i) the single electron transfer (SET) from 4f atomic orbitals (AOs) of each Sm center to the antibonding π*-orbitals of 1,3-butadienyl dianion is feasible and the new HOMO formed by the bonding interaction between Sm 5d orbitals (AOs) and the π*-orbitals of 1,3-butadienyl dianion can accept favorably 2e^- from 4f AOs of Sm(II); (ii) the 2-butene tetraanionic ligand serves as a unique 10e^- donating system, in which 4e^- act as two σ-donation bonding interactions while the rest 6e^- as three π-donation bonding interactions. The disamarium(III) complexes represent a unique class of the bridged bis-alkylidene rare-earth organometallic complexes. The ligand-based reductive reactivity of 2-butene tetraanion bridged disamarium(III) complexes demonstrates that 2-butene tetraanionic ligand serves as a 3e^- reductant toward cyclooctatetraene (COT) to provide doubly COT-supported disamarabutadiene complexes. The reaction of the disamarium(III) complexes with Cp*Li produces the doubly Cp*-coordinated Sm(III) complexes via salt metathesis. In addition, the reaction with Mo(CO)₆ affords the oxycyclopentadienyl dinuclear complex via CO insertion.

Three new coordination polymers based on bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane: syntheses, structures, multiresponsive luminescent sensitive detection for antibiotics and pesticides, and antitumor activities

Three novel coordination polymers (CPs), namely, {[Ag2(L)2(Mo4O13)·(CH3CN)]} n (1), {[Zn(L)(1,4-bdc)2·2(1,4-H2bdc)]} n (2), {[Cd(L)(1,4-bdc)0.5]} n (3) have been synthesized under solvothermal conditions by the reaction of bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane (L) and varied metal salts. Their structures are determined by single X-ray crystal diffraction, and further characterized by elemental analysis, IR, TGA and PXRD. CP 1 with ammonium molybdate as a secondary ligand displays a 2D network with (2,3,3,3,4)-connected net topology and the point symbol of {4·82}6{4·84·10}2{8}, CP 2 and CP 3 with 1,4-H2bdc as a secondary ligand demonstrate 3D structures with different topologies. CP 2 exhibits high sensibility and low detection limit in the recognition of antibiotics (NZF, NFT and FZD) and pesticide (DCN) identification. CP 1 demonstrates good anti-tumor activity toward the tested glioma cells. The possible luminescent sensitivity and anti-tumor mechanisms are also discussed.

Potential Precursors for Terminal Methylidene Rare-Earth-Metal Complexes Supported by a Superbulky Tris(pyrazolyl)borato Ligand

A series of solvent-free heteroleptic terminal rare-earth-metal alkyl complexes stabilized by a superbulky tris(pyrazolyl)borato ligand with the general formula [TptBu,Me LnMeR] have been synthesized and fully characterized. Treatment of the heterobimetallic mixed methyl/tetramethylaluminate compounds [TptBu,Me LnMe(AlMe4 )] (Ln=Y, Lu) with two equivalents of the mild halogenido transfer reagents SiMe3 X (X=Cl, I) gave [TptBu,Me LnX2 ] in high yields. The addition of only one equivalent of SiMe3 Cl to [TptBu,Me LuMe(AlMe4 )] selectively afforded the desired mixed methyl/chloride complex [TptBu,Me LuMeCl]. Further reactivity studies of [TptBu,Me LuMeCl] with LiR or KR (R=CH2 Ph, CH2 SiMe3 ) through salt metathesis led to the monomeric mixed-alkyl derivatives [TptBu,Me LuMe(CH2 SiMe3 )] and [TptBu,Me LuMe(CH2 Ph)], respectively, in good yields. The SiMe4 elimination protocols were also applicable when using SiMe3 X featuring more weakly coordinating moieties (here X=OTf, NTf2 ). X-ray structure analyses of this diverse set of new [TptBu,Me LnMeR/X] compounds were performed to reveal any electronic and steric effects of the varying monoanionic ligands R and X, including exact cone-angle calculations of the tridentate tris(pyrazolyl)borato ligand. Deeper insights into the reactivity of these potential precursors for terminal alkylidene rare-earth-metal complexes were gained through NMR spectroscopic studies.

Cerium-carbon dative interactions supported by carbodiphosphorane

A set of complexes containing dative interactions between a rare-earth metal and carbon are reported. Complex 2, Br₃Ce(CDP)(THF), with a Ce←C bond was synthesized by the reaction of CeBr₃ with a carbon(0) ligand, carbodiphosphorane (CDP). More significantly, a trivalent cerium complex 3, [BrCe(CDP)₂](BPh₄)₂, with two σ dative interactions C→Ce←C was also isolated, which represents an unusual example of two dative interactions formed with the same atom in a molecule. Furthermore, π donation by the second lone-pair electrons of the CDP ligand is rather weak. Single-crystal X-ray diffraction shows that the Ce-C bond lengths in these complexes are comparable with those in cerium(iii)-carbene species. Density functional theory calculations support the dative interaction formation in these complexes and the strength of σ-donation in 3 is stronger than that in 2.

Scandium Phosphonioketene: Synthesis, Bonding and Reactivity

Reaction of a scandium phosphoniomethylidene with carbon monoxide provides the first scandium phosphonioketene (1). X-ray diffraction analysis shows that the complex has a very short Sc-C bond (2.138(2) Å), and DFT calculations indicate that this unusual short bond length is due to the significant contribution of ionic coulomb interaction between carbon and scandium and the η² -O,C coordination fashion. Complex 1 is thermally stable, albeit shows high reactivity towards a series of unsaturated substrates, including carbon dioxide, ketone, imine, nitrile and isocyanide. In the reaction with tert-butyl isocyanide, not only an insertion of tert-butyl isocyanide into the Sc-C bond occur, but also a C-H activation on the phenyl ring. DFT calculations show that the reactivity of 1 operated by nucleophilic properties, and therefore the reaction mechanism favors the nucleophilic attack to isocyanide as a rate-determining step, followed by the stepwise C-H activation through an interesting C-H deprotonation.

Geminal Dianions Stabilized by Main Group Elements

This review is dedicated to the chemistry of stable and isolable species that bear two lone pairs at the same C center, i.e., geminal dianions, stabilized by main group elements. Three cases can thus be considered: the geminal-dilithio derivative, for which the two substituents at C are neutral, the yldiide derivatives, for which one substituent is neutral while the other is charged, and finally the geminal bisylides, for which the two substituents are positively charged. In this review, the syntheses and electronic structures of the geminal dianions are presented, followed by the studies dedicated to their reactivity toward organic substrates and finally to their coordination chemistry and applications.

Dihydrogen activation by intermolecular rare-earth aryloxide/N-heterocyclic carbene Lewis pairs

Cooperative H₂ activation can be readily achieved by combination of homoleptic rare-earth aryloxides with N-heterocyclic carbenes under mild conditions.

A Very Short Uranium(IV)-Rhodium(I) Bond with Net Double-Dative Bonding Character

Reaction of [U{C(SiMe3 )(PPh2 )}(BIPM)(μ-Cl)Li(TMEDA)(μ-TMEDA)0.5 ]2 (BIPM=C(PPh2 NSiMe3 )2 ; TMEDA=Me2 NCH2 CH2 NMe2 ) with [Rh(μ-Cl)(COD)]2 (COD=cyclooctadiene) affords the heterotrimetallic UIV -RhI2 complex [U(Cl)2 {C(PPh2 NSiMe3 )(PPh[C6 H4 ]NSiMe3 )}{Rh(COD)}{Rh(CH(SiMe3 )(PPh2 )}]. This complex has a very short uranium-rhodium distance, the shortest uranium-rhodium bond on record and the shortest actinide-transition metal bond in terms of formal shortness ratio. Quantum-chemical calculations reveal a remarkable RhI→→ UIV net double dative bond interaction, involving RhI 4dz2 - and 4dxy/xz -type donation into vacant UIV 5f orbitals, resulting in a Wiberg/Nalewajski-Mrozek U-Rh bond order of 1.30/1.44, respectively. Despite being, formally, purely dative, the uranium-rhodium bonding interaction is the most substantial actinide-metal multiple bond yet prepared under conventional experimental conditions, as confirmed by structural, magnetic, and computational analyses.

Silyl-Phosphino-Carbene Complexes of Uranium(IV)

Unprecedented silyl-phosphino-carbene complexes of uranium(IV) are presented, where before all covalent actinide-carbon double bonds were stabilised by phosphorus(V) substituents or restricted to matrix isolation experiments. Conversion of [U(BIPMTMS )(Cl)(μ-Cl)2 Li(THF)2 ] (1, BIPMTMS =C(PPh2 NSiMe3 )2 ) into [U(BIPMTMS )(Cl){CH(Ph)(SiMe3 )}] (2), and addition of [Li{CH(SiMe3 )(PPh2 )}(THF)]/Me2 NCH2 CH2 NMe2 (TMEDA) gave [U{C(SiMe3 )(PPh2 )}(BIPMTMS )(μ-Cl)Li(TMEDA)(μ-TMEDA)0.5 ]2 (3) by α-hydrogen abstraction. Addition of 2,2,2-cryptand or two equivalents of 4-N,N-dimethylaminopyridine (DMAP) to 3 gave [U{C(SiMe3 )(PPh2 )}(BIPMTMS )(Cl)][Li(2,2,2-cryptand)] (4) or [U{C(SiMe3 )(PPh2 )}(BIPMTMS )(DMAP)2 ] (5). The characterisation data for 3-5 suggest that whilst there is evidence for 3-centre P-C-U π-bonding character, the U=C double bond component is dominant in each case. These U=C bonds are the closest to a true uranium alkylidene yet outside of matrix isolation experiments.

Versatile reactivities of rare-earth metal dialkyl complexes supported by a neutral pyrrolyl-functionalized β-diketiminato ligand

The first unprecedented examples of S-β-diketiminato species were disclosed in the reactions of rare-earth dialkyl complexes with S₈.

Perfectly isoselective polymerization of 2-vinylpyridine promoted by β-diketiminato rare-earth metal cationic complexes

Highly isotactic poly(2-vinylpyridine)s were produced with rare-earth metal complexes supported by a symmetric β-diketiminate ligand in the presence of borate.

Formation and ligand-based reductive chemistry of bridged bis-alkylidene scandium(iii) complexes

Bridged bis-alkylidene Sc(iii) complexes featuring a 2-butene-1,1,4,4-tetraanion are synthesized and show unexpected ligand-based two-electron or four-electron reduction reactivity towards different oxidants.

The chemistry of rare-earth carbene and alkylidene complexes including their synthesis, structure and reaction is a challenging issue because of their high reactivity (or instability) and the lack of synthetic methods. In this work, we report the first synthesis of the bridged bis-alkylidene complexes which feature a 2-butene-1,1,4,4-tetraanion and four Sc–C(sp³) bonds by the reaction of 1,4-dilithio-1,3-butadienes with ScCl₃. This reaction proceeds via two key intermediates: an isolable scandacyclopentadiene and a proposed scandacyclopropene. The scandacyclopentadiene undergoes β,β′-C–C bond cleavage to generate the scandacyclopropene, which then dimerizes to afford the bridged bis-alkylidene complex via a cooperative double metathesis reaction. Reaction chemistry study of the bridged bis-alkylidene complex reveals their ligand-based reduction reactivity towards different oxidants such as hexachloroethane, disulfide and cyclooctatetraene.

Synthesis, characterization and catalytic activity of rare-earth metal amides incorporating cyclohexyl bridged bis(β-diketiminato) ligands

The bridged bis(β-diketiminato) ligands supported rare-earth amides exhibited high catalytic activity towards the hydrophosphination of β-nitroalkene and α,β-unsaturated carbonyl derivatives with an excellent regioselectivity.