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

ABSTRACT: 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 ?,?'-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.

SUBMITTER: Ma W

PROVIDER: S-EPMC5632790 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Reductive Hydrogenation of Sulfido-Bridged Tantalum Alkyl Complexes: A Mechanistic Insight.

Project description:Hydrogenolysis of a series of alkyl sulfido-bridged tantalum(IV) dinuclear complexes [Ta(η5-C5Me5)R(μ-S)]2 [R = Me, nBu (1), Et, CH2SiMe3, C3H5, Ph, CH2Ph (2), p-MeC6H4CH2 (3)] has led quantitatively to the Ta(III) tetrametallic sulfide cluster [Ta(η5-C5Me5)(μ3-S)]4 (4) along with the corresponding alkane. Mechanistic information for the formation of the unique low-valent tetrametallic compound 4 was gathered by hydrogenation of the phenyl-substituted precursor [Ta(η5-C5Me5)Ph(μ-S)]2, which proceeds through a stepwise hydrogenation process, disclosing the formation of the intermediate tetranuclear hydride sulfide [Ta2(η5-C5Me5)2(H)Ph(μ-S)(μ3-S)]2 (5). Extending our studies toward tantalum alkyl precursors containing functional groups susceptible to hydrogenation, such as the allyl-and benzyl-substituted compounds [Ta(η5-C5Me5)(η3-C3H5)(μ-S)]2 and [Ta(η5-C5Me5)(CH2Ph)(μ-S)]2 (2), enables alternative reaction pathways en route to the formation of 4. In the former case, the dimetallic system undergoes selective hydrogenation of the unsaturated allyl moiety, forming the asymmetric complex [{Ta(η5-C5Me5)(η3-C3H5)}(μ-S)2{Ta(η5-C5Me5)(C3H7)}] (6) with only one propyl fragment. Species 2, in addition to the hydrogenation of one benzyl fragment and concomitant toluene release, also undergoes partial hydrogenation and dearomatization of the phenyl ring on the vicinal benzyl unity to give a η5-cyclohexadienyl complex [Ta2(η5-C5Me5)2(μ-CH2C6H6)(μ-S)2] (7). The mechanistic implications of the latter hydrogenation process are discussed by means of DFT calculations.

| S-EPMC10324320 | biostudies-literature

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Project description:It is vital to design effective nitrogen fixation systems that operate under mild conditions, and to this end we recently reported an example of the catalytic formation of ammonia using a dinitrogen-bridged dimolybdenum complex bearing a pincer ligand, where up to twenty three equivalents of ammonia were produced based on the catalyst. Here we study the origin of the catalytic behaviour of the dinitrogen-bridged dimolybdenum complex bearing the pincer ligand with density functional theory calculations, based on stoichiometric and catalytic formation of ammonia from molecular dinitrogen under ambient conditions. Comparison of di- and mono-molybdenum systems shows that the dinitrogen-bridged dimolybdenum core structure plays a critical role in the protonation of the coordinated molecular dinitrogen in the catalytic cycle.

| S-EPMC4015321 | biostudies-literature

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| S-EPMC2961348 | biostudies-literature

Diazoalkanes in Low-Coordinate Iron Chemistry: Bimetallic Diazoalkyl and Alkylidene Complexes of Iron(II).

Project description:The addition of (trimethylsilyl)diazomethane and its conjugate base to iron β-diketiminate precursors gives novel dinuclear complexes in which the bridges are either diazomethane derivatives or an alkylidene. One product is an unusual bridging alkylidene complex containing two three-coordinate iron(II) centers. On the other hand, syntheses using the deprotonated diazomethane give two bridging diazomethyl species with binding modes that have not been observed in iron complexes previously. In the presence of a coordinating tetrahydrofuran solvent, a diiron(II) compound with μ-N bridges rearranges to a more stable isomer with μ-N,C bridges, a process that is accompanied by a 1,3-shift of a silyl group.

| S-EPMC5499981 | biostudies-literature

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| S-EPMC2954233 | biostudies-literature

Fluoride as ligand: chemistry of some new terminal and bridged systems.

Project description: Not available

| S-EPMC3594586 | biostudies-literature

Synthesis of Tungsten Imido Alkylidene Complexes that Contain an Electron-Withdrawing Imido Ligand.

Project description:Tungsten NArR alkylidene complexes have been prepared that contain the electron-withdrawing ArR groups 2,4,6-X3C6H2 (ArX3, X = Cl, Br), 2,6-Cl2-4-CF3C6H2 (ArCl2CF3), and 3,5-(CF3)2C6H3 (Ar(CF3)2). Reported complexes include W(NArR)2Cl2(dme) (dme = 1,2-dimethoxyethane), W(NArR)2(CH2CMe3)2, W(NArR)(CHCMe3)(OTf)2(dme), and W(NArR)(CHCMe3)(ODBMP)2 (DBMP = 4-Me-2,6-(CHPh2)C6H2). The W(NArR)(CHCMe3)(ODBMP)2 complexes were explored as initiators for the polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD).

| S-EPMC4195510 | biostudies-literature

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Project description:A triptycene-based bis(benzimidazole) ester ligand, L3, was designed to enhance the electron donating ability of the heterocyclic nitrogen atoms relative to those of the first generation bis(benzoxazole) analogs, L1 and L2. A convergent synthesis of L3 was designed and executed. Three-component titration experiments using UV-visible spectroscopy revealed that the desired diiron(II) complex could be obtained with a 1:2:1 ratio of L3:Fe(OTf)2(MeCN)2:external carboxylate reactants. X-ray crystallographic studies of two diiron complexes derived in this manner from L3 revealed their formulas to be [Fe2L3(μ-OH)(μ-O2CR)(OTf)2], where R = 2,6-bis(p-tolyl)benzoate (7) or triphenylacetate (8). The structures are similar to that of a diiron complex derived from L1, [Fe2L1(μ-OH)(μ-O2CArTol)(OTf)2] (9) with a notable difference being that, in 7 and 8, the geometry at iron more closely resembles square-pyramidal than trigonal-bipyramidal. Mössbauer spectroscopic analyses of 7 and 8 indicate the presence of high-spin diiron(II) cores. These results demonstrate the importance of substituting benzimidazole for benzoxazole for assembling biomimetic diiron complexes with syn disposition of two N-donor ligands, as found in O2-activating carboxylate-bridged diiron centers in biology.

| S-EPMC3625018 | biostudies-literature

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Project description:Alkali metal naphthalenide or anthracenide reacted with scandium(III) anilides [Sc(X){N(tBu)Xy}2 (thf)] (X=N(tBu)Xy (1); X=Cl (2); Xy=C6 H3 -3,5-Me2 ) to give scandium complexes [M(thf)n ][Sc{N(tBu)Xy}2 (RA)] (M=Li-K; n=1-6; RA=C10 H8 2- (3-Naph-K) and C14 H10 2- (3-Anth-M)) containing a reduced arene ligand. Single-crystal X-ray diffraction revealed the scandium(III) center bonded to the naphthalene dianion in a σ2 :π-coordination mode, whereas the anthracene dianion is symmetrically attached to the scandium(III) center in a σ2 -fashion. All compounds have been characterized by multinuclear, including 45 Sc NMR spectroscopy. Quantum chemical calculations of these intensely colored arene complexes confirm scandium to be in the oxidation state +3. The intense absorptions observed in the UV/Vis spectra are due to ligand-to-metal charge transfers. Whereas nitriles underwent C-C coupling reaction with the reduced arene ligand, the reaction with one equivalent of [NEt3 H][BPh4 ] led to the mono-protonation of the reduced arene ligand.

| S-EPMC7496515 | biostudies-literature

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