C-C bond cleavage and carbonylation enabled by an NNN-pincer uranium scaffold metal-arene interaction.

Metal-arene complexes have recently attracted an increasing interest in f-element chemistry, but the functionalization of arenes mediated by uranium-arene interactions is limited to a single example. Here, we report a new uranium-biphenylene complex supported by a bulky rigid trianionic NNN-pincer ligand in which the uranium-arene interaction is able to promote C-C bond cleavage and functionalization with CO under mild conditions to yield a U-bound 9-fluorenone. Reduction of the U(iv)-pincer complex [NNN-U(THF)ClK(THF)] (1) with KC, in the presence of biphenylene, results in the terminal arene complex [NNN-U(THF)(biphenylene)][K(THF)] (3).

Reactivity Studies on Organolithium Complexes Bearing Electrophilic Carbenes toward Isonitriles.

Isonitriles, as unsaturated substrates, have rarely been reported to react with organolithium compounds containing an electrophilic carbene. The lithium compounds [::(-:)-1-(GCH)-3-(2,6-PrCHN═CH)-CHNLi] (G = 2-N-CHNCH (), CHOCH (), 2-CHO (), 2-(CH)NCH ()) have been synthesized by applying the corresponding ligands bearing an ene(amido) neighboring electrophilic carbene, which bridges the lithium centers. The reactivities of the lithium compounds toward aromatic isonitriles have been studied, revealing a novel -[4 + 1] cyclization that delivers various multifunctionalized 2,4-dihydropyrroloindoline-based lithium complexes - insertion of the isonitriles into the Li-C and Li-N bonds of the corresponding lithium compounds.

Steric Control in Low-Valent Mn Diamide Complexes: Contrasting Magnesium and Manganese in N and Benzene Activation.

Reduction of Mn precursors with bulky diamide ligands provided access to a complex with the longest known Mn-Mn bond and to a rare example of N activation at high-spin Mn centers. While some instructive parallels can thus be drawn to observations made for Mg analogues, the accessibility of filled d orbitals in the respective Mn intermediates leads to a distinct behavior toward benzene that undergoes an oxidative addition.

Facile N-C bond cleavage and arene reduction by a transient uranium(ii) complex.

Complexes of uranium(ii) remain extremely rare and their reactivity is practically unexplored. Here we report that the reduction of the heteroleptic bis-aryloxide U(iii) complex [U( -{( ArO)Me-cyclam})I], A, yields a rare and highly reactive U(ii) intermediate that enables a rare example of intramolecular uranium mediated N-C cleavage and effects arene reduction resulting in the isolation of the U(iv) complex [U{ -(( BuArO)Me-cyclam)}{ -( BuArOCH)}] (2) and of the inverse-sandwich complex [{U( -{( ArO)Me-cyclam})}( : -benzene)] (3) respectively. Moreover, the U(ii) solvent-dependent reactivity results in the formation of a putative U-N complex in diethyl ether.

Unique selectivity of rare-earth metal ambiphilic carbenes towards organic molecules and novel reactivity patterns with isonitriles.

Studies on the chemistry of highly active rare-earth (RE) metal ambiphilic carbenes face challenges due to the lack of appropriate model molecular platforms because the corresponding ambiphilic carbenes have empty p-orbitals. Here, the synthesis of novel multi-chelated amidate rare-earth metal pincer complexes bearing ambiphilic carbenes is realized by using indol-2-yl-based ligands. The ambiphilic carbene (indol-2-yl carbon) of these complexes is extremely active and shows unique selective reactivity towards various organic molecules including carbodiimides, imine, diphenyldiazomethane, aluminum alkyls, 9-BBN and isonitriles, which demonstrate a range of unprecedented reactivity patterns such as formal [2 + 2] cyclometallation, [3 + 3] annulation, and aza-[4 + 1] annulation, while unprecedented aza-[4 + 1 + 1] annulation products were isolated from the reactions of the rare-earth metal complexes bearing electrophilic carbenes and strongly polarized metallacyclopropanes with 2,6-dimethylphenylisonitrile.

Solvatochromism and Redox Multi-Switch in a Trinuclear Cobalt(II) Complex.

A trinuclear cobalt(II) complex incorporating the redox-active hexahydroxytriphenylene (HHHTP) ligand was prepared and isolated in two different redox states: [Co (sq-sq-sq)] (1) and [Co (cat-sq-sq)] (2) (sq = semiquinone; cat = catecholate), enabled by its remarkable solvatochromic behavior. The ligand field tuning of the Co(II) centers through the ancillary ligand MeTPA (tris(6-methyl-2-pyridylmethyl)amine) allowed accessing six reversible one-electron processes instead of only three with the parent TPA ligand, therefore increasing the range of redox-coupled magnetic and optical switching in this system. Upon reduction, the three redox processes are ligand-centered and involve the three sq/cat couples of hexahydroxytriphenylene (HHTP), while we hypothesize that some of the oxidation processes may involve the Co(II) metallic species.

Lanthanide(III)-dependent hydration of the methanol dehydrogenase cofactor, pyrroloquinoline quinone.

The mechanism by which pyrroloquinoline quinone (PQQ)-dependent methanol dehydrogenases (MDH), bearing either a Ca or a lanthanide (Ln ion in their active site, oxidize methanol has been intensely debated. In particular, the Ln-dependent activity of Ln-MDH remains poorly understood. The lack of experimental evidence represents a significant limitation to improve our understanding of these enzymes.

Amphoteric Zinc(II) Hydride Cations [ZnH]: Effect of a Bipyridyl Ligand.

Terminal zinc hydride cations [(Mebpy)ZnH(L)][BAr] (Mebpy = 6,6'-dimethyl-2,2'-dipyridyl; Ar = 3,5-(CF)CH; L = THF, ; 4-(dimethylamino)pyridine, DMAP, ; pyridine, ; 4-(trifluoromethyl)pyridine, ) show Zn-H distances in the expected range, as exemplified by single-crystal X-ray diffraction for the THF adduct and the pyridine adduct . With the exception of labile , the ν(ZnH) stretching frequencies correlate with the electron donating character of the L ligand. The Zn-H bond shows amphoteric behavior.

Titanium-Mediated Rearrangement of Bis(alkynyl)boranes: B─C Activation versus C─H Activation.

Reactions between Rosenthal's titanocene (CpTi) and decamethyltitanocene (Cp*Ti) synthons with various bis(alkynyl)boranes were investigated. A series of titanium-fused boracyclobutenes were obtained through the reaction of the Cp*Ti synthon with (MeSi)NB(CCR) or PhB(CCPh). This represents the first realization of approaching this structural motif via the rearrangement of bis(alkynyl)boranes within the coordination sphere of a d-block metal.

Vinyl polymers with fully degradable carbon backbones enabled by aromatization-driven C-C bond cleavage.

Degradation of carbon-backbone polymers, which make up most plastics, remains a formidable challenge owing to strong and inert main-chain C-C bonds. While incorporation of comonomers that generate backbone radicals under certain conditions can induce degradation of the polymer chain, such strategies yield complex oligomer mixtures. Here we report aromatization-driven C-C bond cleavage as a viable and powerful strategy to endow the degradability into carbon backbones using acrylic polymers as a model example.

Synthesis and Catalytic Activity of Thorium Nitride Complex from Dinitrogen Reduction.

Metal nitride species are recognized as key intermediates in the conversion of dinitrogen (N) to ammonia (NH). In this work, we report the isolation of a multimetallic nitride-bridged thorium complex () by completely cleaving the N≡N triple bond of N. The complex was synthesized through the reduction of a thorium precursor, {N[CHCHN-PPr]ThCl} () and chromium dichloride (CrCl) using potassium graphite (KC) under an N atmosphere.

Nickel-Catalyzed Selective Reduction of Carbon Monoxide with Magnesium Alkyl Compounds.

Research on CO activation and homologation is pivotal for promoting sustainable chemistry and the construction of C molecular blocks. This work reports the nickel-catalyzed reduction of CO by magnesium alkyl compounds utilizing a bimetallic Mg/Ni synergistic strategy. The exposure of β-diketiminato ligand-supported magnesium monoalkyl compounds LMgR (L=[(DippNCMe)CH], Dipp=2,6-PrCH; R=Bu, CH, CH) to 1 bar of CO in the presence of 10 mol % Ni(COD) (COD: 1,5-cyclooctadiene) selectively afforded the CO single-insertion product [LMg(CHO)CH], the dimerization product [(LMg)(μ-CO)(CH)], and the linear trimerization product [(LMg)(μ-CO)(Bu)], respectively, depending on the R group.

Ligand-Directed Actinide Oxo-Bond Manipulation in Actinyl Thiacalix[4]arene Complexes.

Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An=U, Np, Pu). The thioether calixarene TC4A (4-tert-butyltetrathiacalix[4]arene) binds equatorially to the actinyl cation forming a conical pocket that differentiates the two trans-oxo groups. The 'ate' complexes, [A][UO(TC4A)] (A=[Li(DME)], HNEt) and [HNEt][AnO(TC4A)] (An=U, Np, Pu), enable selective oxo chemistry.

Nucleophilic and Electrophilic Molybdenum Terminal Oxo Complexes by Coordination-Induced Bond Weakening of Hydroxo O-H Bonds.

The extent of coordination-induced bond weakening in aquo and hydroxo ligands bonded to a molybdenum(III) center complexed by a dianionic, pentadentate ligand system was probed by reacting the known complex (BPzPy)Mo(III)-NTf, , with degassed water or dry lithium hydroxide. The aquo adduct was not observed, but two LiNTf-stabilized hydroxo complexes were fully characterized. Computational and experimental work showed that the O-H bond in these complexes was significantly weakened (to ≈57 kcal mol), such that these compounds could be used to form the diamagnetic, neutral terminal molybdenum oxo complex (BPzPy)Mo(IV)O, , by hydrogen atom abstraction using the aryl oxyl reagent ArO• (Ar = 2,4,6-tri--butylphenyl).

Four-electron reduction of benzene by a samarium(II)-alkyl without the addition of external reducing agents.

Benzene reduction by molecular complexes remains an important synthetic challenge, requiring harsh reaction conditions involving group I metals. Reductions of benzene, to date, typically result in a loss of aromaticity, although the benzene tetra-anion, a 10π-electron system, has been calculated to be stable and aromatic. Due to the lack of sufficiently potent reductants, four-electron reduction of benzene usually requires the use of group I metals.

Multielectron Redox Chemistry of Ytterbium Complexes Reaching the +1 and Zero Formal Oxidation States.

Lanthanide redox reactivity remains limited to one-electron transfer reactions due to their inability to access a broad range of oxidation states. Here, we show that multielectron reductive chemistry is achieved for ytterbium by using the tripodal tris(siloxide)arene redox-active ligand, which can store two electrons in the arene anchor. Reduction of the Yb(III) complex of the tris(siloxide)arene tripodal ligand affords the Yb(II) analogue by metal-centered reduction.

Rare-earth metal complexes bearing electrophilic and nucleophilic carbon centres and their unique reactivity patterns towards pyridine derivatives.

The rare-earth metal dialkyl complexes (κ-L)RE(CHSiMe)·(THF) [RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e)] (L = 1-(2--CHNCHCH)-3-(2,6-PrCHN[double bond, length as m-dash]CH)-CHN) and the rare-earth metal monoalkyl complexes (κ-L)RE(CHSiMe)·(THF) [ = 0, RE = Lu(2a), Yb(2b); = 1, Er(2c), Y(2d), Dy(2e)], (κ-L)RE(CHSiMe)·THF [RE = Yb(3a), Er(3b), Y(3c), Dy(3d), Gd(3e)] (L = 1-(2--CHNCHCH)-3-(AdN[double bond, length as m-dash]CH)-CHN) (Ad = adamantyl, CH) have been synthesized and fully characterized. These complexes feature chelate ligands having a conjugated system (-C[double bond, length as m-dash]C-C[double bond, length as m-dash]N) with an sp carbon, which enables both electrophilic and nucleophilic carbon centres to be directly connected to the highly electrophilic rare-earth metal ions. The reactions of these complexes with different pyridine derivatives have been systematically investigated with the discovery of reactivity patterns distinct from those of previously reported transition metal complexes.

The photo-isomerization of the cyclononatetraenyl ligand and related rare earth complexes.

The cyclononatetraenyl (Cnt) ligand is a large monoanionic ligand. It is easily synthesized by ring expansion after cyclopropanation of the cyclooctatetraenyl (Cot) ligand. The Cnt ligand can be reported as the --- () isomer, where the aromatic ring is flat, and all carbon atoms form a homogenous ring, and as the --- () isomer, where one carbon places itself inside the ring.

Dinitrogen Reduction and Functionalization by a Siloxide Supported Thulium-Potassium Complex for the Formation of Ammonia or Hydrazine Derivatives.

The dinitrogen (N) chemistry of lanthanides remains less developed compared to the d-block metals and lanthanide-promoted N functionalization chemistry in well-defined lanthanide complexes remains elusive. Here we report the synthesis and characterization (SQUID, EPR, DFT, X-Ray) of the siloxide supported heterobimetallic (Tm/K) complexes [{KTm(OSi(OBu))}(μ-η : η-N)] (1) and [K{Tm(OSi(OBu))}(μ-η : η-N)] (2). Complex 2 provides a rare example of a metal complex of the triply reduced N radical.

Homoleptic Organolanthanum-Catalyzed Carbohalogenation.

Metal-halogen exchange reactions are fundamental processes in chemistry that transform organic halides into organometallic reagents. However, using these reactions to build intricate structures in a cascade manner, especially in a catalytic mode, has been a challenge. In this study, we introduce a homoleptic organolanthanum catalyst to initiate lanthanum-halogen exchange and intramolecular carbohalogenation.

Multi-electron redox reactivity of a samarium(ii) hydrido complex.

Well-defined low-valent molecular rare-earth metal hydrides are rare, and limited to Yb and Eu centers. Here, we report the first example of the divalent samarium(ii) hydrido complex [(Cp)Sm(μ-H)(DABCO)] (4) (Cp = CAr, Ar = 3,5-Pr-CH; DABCO = 1,4-diazabicyclooctane) supported by a super-bulky penta-arylcyclopentadienyl ligand, resulting from the hydrogenolysis of the samarium(ii) alkyl complex [(Cp)Sm{CH(SiMe)}(DABCO)] (3). Complex 4 exhibits multi-electron redox reactivity toward a variety of substrates.

Synthesis, structure and redox properties of single-atom bridged diuranium complexes supported by aryloxides.

Single-atom (group 15 and group 16 anions) bridged dimetallic complexes of low oxidation state uranium provide a convenient route to implement multielectron transfer and promote magnetic communication in uranium chemistry, but remain extremely rare. Here we report the synthesis, redox and magnetic properties of N, O, and S bridged diuranium complexes supported by bulky aryloxide ligands. The U(IV)/U(IV) nitride [Cs(THF)][(U(OAr))(μ-N)], 1 could be prepared and characterized but could not be reduced.