- Ln(II)/Pb(II)-Ln(III)/Pb(0) Redox Approach toward Rare-Earth-Metal Half-Sandwich Complexes
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The divalent bis(trimethylsilyl)amide complexes Ln[N(SiMe3)2]2(THF)2 (Ln = Sm, Yb) react with 0.5 equiv of lead(II) pentamethylcyclopentadienide, Cp?2Pb (Cp? = C5Me5), in n-hexane to form the half-sandwich complexes Cp?Ln[N(SiMe3)2]2 (Ln = Sm, Yb) in almost quantitative yield. The same reaction performed with Eu[N(SiMe3)2]2(THF)2 resulted in the cocrystallization of the sandwich complex Cp?2Eu[N(SiMe3)2] and homoleptic Eu[N(SiMe3)2]3. The divalent bis(dimethylsilyl)amide complexes Ln{[μ-N(SiHMe2)2]2Ln[N(SiHMe2)2](THF)}2 (Ln = Sm, Yb) react with 1.5 equiv of Cp?2Pb in n-hexane/THF to form the half-sandwich complexes Cp?Ln[N(SiHMe2)2]2(THF) (Ln = Sm, Yb). The corresponding europium reaction did not provide any crystalline material. Treatment of divalent Eu[N(SiMe3)2]2(THF)2 with 2 equiv of 3-tert-butyl-5-methylpyrazole (HpztBu,Me) in THF generates [(pztBu,Me)Eu(μ-pztBu,Me)(THF)2]2. Oxidation of the europium(II) pyrazolate complex with 1 equiv of Cp?2Pb in THF afforded Cp?Eu(μ-pztBu,Me)2(THF)2. The tetramethylaluminate compounds {Ln(AlMe4)2}n (Ln = Sm, Yb) react with 0.5 equiv of PbCp?2 in n-hexane to produce mixtures of half-sandwich and metallocene complexes Cp?Ln(AlMe4)2 and [Cp?2Ln(μ-AlMe4)]2, respectively. The attempted oxidation of {Eu(AlMe4)2}n led to the formation of {Cp?Eu(AlMe4)}, which could be crystallized from THF to give polymeric {Cp?Eu(μ-AlMe4)(THF)3}n. The reaction of chloro-contaminated {Sm(AlMe4)2}n with 2 equiv of HCp? performed in THF led to the isolation of the unexpected mixed chloride methylidene complex [Cp?3Sm3(μ2-Cl)3(μ3-Cl)(μ3-CH2)(THF)3]. Reacting {Yb(AlEt4)2}n with 0.5 equiv of Cp?2Pb in n-hexane gave a mixture of products, from which Cp?2Yb(AlEt4) was identified. Performing the same reaction in toluene in the presence of diethyl ether resulted in the formation of the divalent metathesis product Cp?Yb(AlEt4)(Et2O)2.
- Bienfait, André M.,Wolf, Benjamin M.,T?rnroos, Karl W.,Anwander, Reiner
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- Monodentate coordination of the normally chelating chiral diamine (R,R)-TMCDA
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After isolating an unusual binuclear, but monosolvated NaHMDS complex [{(R,R)-TMCDA}·(NaHMDS)2]∞ which polymerises via intermolecular electrostatic Na...MeHMDS interactions, further (R,R)-TMCDA was added to produce the dis
- Ojeda-Amador, Ana I.,Martínez-Martínez, Antonio J.,Kennedy, Alan. R.,Armstrong, David R.,O'Hara, Charles T.
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- Unusual redox chemistry of ytterbium carbazole-bis(oxazoline) compounds: Oxidative coupling of primary phosphines by an ytterbium carbazole- bis(oxazoline) dialkyl
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The 1,8-bis(4′,4′-dimethyloxazolin-2′-yl)-3,6-di-tert- butylcarbazole anion (Czx) forms monomeric, six-coordinate halide complexes of Yb(II), (Czx)Yb(X)(THF)2 (X = I (2), Cl (3)), by metathesis of YbX2 with NaCzx (1) or Na/Hg reduction of (Czx)Yb(Cl) 2(THF). The crystal structure of 1 reveals a polymeric chain structure in which the oxazoline ring bridges to the Na+ of an adjacent unit. The iodo complex 2 serves as a precursor to divalent silylamide, alkyl, and phosphide complexes, (Czx)Yb(X)(THF)n (4, X = N(SiMe 3)2, n = 1; 5, X = CH(SiMe3)2, n = 1; 7a, X = 2,4,6-Me3C6H2PH, n = 2; 7b, X = 2,4,6-Pri3C6H2PH, n = 2). The X-ray structure of 4 reveals a distorted-trigonal-bipyramidal geometry with the Czx ligand occupying two axial sites and one equatorial site in a pseudo-mer coordination mode. In contrast to the typical metathesis chemistry observed with LiCH(SiMe3)2, an unusual oxidation occurs when 2 or 3 is treated with LiCH2SiMe3 to generate the previously isolated trivalent alkyl (Czx)Yb(CH2SiMe3)2. Trivalent Yb complexes with the Czx ligand also display unusual redox chemistry: rapid reduction to the Yb(II) phosphides 7a,b is observed on treatment of mer,cis-(Czx)Yb(Cl)2(THF) with ArPH- Na+ (6a,b) or, equivalently, on treatment of (Czx)Yb(CH2SiMe3) 2 with ArPH2. In both cases, oxidative coupling of the phosphide or phosphine was observed to form meso- and rac-biphosphines, ArPH-PHAr (Ar = 2,4,6-Me3C6H2 (9a), 2,4,6-Pri3C6H2 (9b)).
- Zou, Jin,Berg, David J.,Oliver, Allen,Twamley, Brendan
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- Migration of trimethylsilyl group in the reaction of sodium bis(trimethylsilyl)amide with bromobenzene
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The reaction of sodium bis(trimethylsilyl)amide with bromobenzene gave a mixture of N,N-bis-(trimethylsilyl)aniline and N,2-bis(trimethylsilyl)aniline, the latter being a rearrangement product formed via 1,3-migration of trimethylsilyl group from the nitrogen atom to the ortho-carbon atom in the benzene ring.
- Lis,Tsyrendorzhieva,Albanov,Rakhlin,Voronkov
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- β-Oxo-δ-diimine Nickel Complexes: A Comparison of Tautomeric Active Species in Ethylene Polymerization Catalysis
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A series of mono- and bimetallic Ni alkyl complexes of a β-oxo-δ-diimine (BODDI) ligand are reported. The monometallic complexes have a second binding pocket, of which the free "arm" can exist as either an enamine (e.g., 8, BODEI, β-oxo-δ-enamineiminato) or imine (e.g., 3, BODII, β-oxo-δ-imineiminato) tautomer. The identity of the tautomer in the secondary Ni coordination sphere has a significant effect on ethylene polymerization behavior: the enamine tautomer, which hydrogen bonds to the central O atom and is in conjugation with the N,O backbone chelate, is significantly more electron rich and yields a much lower molecular weight polymer than the imine tautomer, which rotates away from Ni to a distal position and has little effect on polymerization. Deprotonation of the second binding pocket with M(HMDS) (M = Li, Na, K) yields the Ni-alkali metal heterobimetallic complexes 3Li, 3Na, and 3K. The deprotonated alkali metal enamides display ethylene polymerization behavior similar to the neutral imine complex because the enamide arm can also distally rotate to minimize interaction with the Ni coordination sphere upon activation.
- Chiu, Hsin-Chun,Pearce, Adam J.,Dunn, Peter L.,Cramer, Christopher J.,Tonks, Ian A.
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- Method of continuous variation: Characterization of alkali metal enolates using 1h and 19F NMR spectroscopies
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The method of continuous variation in conjunction with 1H and 19F NMR spectroscopies was used to characterize lithium and sodium enolates solvated by N,N,N,N-tetramethylethyldiamine (TMEDA) and tetrahydrofuran (THF). A strategy developed using lithium enolates was then applied to the more challenging sodium enolates. A number of sodium enolates solvated by TMEDA or THF afford exclusively tetramers. Evidence suggests that TMEDA chelates sodium on cubic tetramers.
- Tomasevich, Laura L.,Collum, David B.
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- Coordination of isocyanide and reduction of cyclooctatetraene by a homoleptic uranium(III) aryloxide, and characterisation of the heteroleptic uranium(III) dimer [{U(N″)2(thf)(μ-I)}2]
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[U(ODtbp)3] (ODtbp?=?O-2,6-tBu2C6H3) reacts in a 1:1 ratio with the isocyanide CN-Xyl (Xyl?=?2,6-Me2C6H3) to form the pseudo-tetrahedral 4-coordinate adduct [U(CNXyl)(ODtbp)3] with νCN24?cm?1higher compared to the free isocyanide. Uranium(III) complexes with bulky ligands UX3(X: ODtbp, N″?=?N(SiMe3)2) react with cyclooctatetraene (COT) in a 2:1 U:COT ratio to generate the half-sandwich UIV[U(COT)X2] and [UX4] (which for X?=?N″ spontaneously converts into the more stable metallacycle [U(N″)2{κ2-N(SiMe3)SiMe2CH2}] and HN″), as opposed to the other potential product, the inverse COT-sandwich [(UX2)2(μ-COT)]. The heteroleptic UIIIamido-iodide [{U(N″)2(thf)(μ-I)}2] can be isolated in a low yield (14%) from the 2:1 reaction of KN″ and [UI3(thf)4] in thf, and its molecular structure was shown to be dimeric with iodine atoms bridging the U centres.
- Mansell, Stephen M.,Arnold, Polly L.
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- New UIII and UIV silylamides and an improved synthesis of NaN(SiMe2R)2 (R = Me, Ph)
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It is shown that the deprotonation of bulky amides such as HN(SiMe 2Ph)2 may be accelerated by the use of catalytic quantities of an alkali metal tert-butoxide salt, affording, for example, overnight syntheses of NaN(SiMe2Ph)2. The new uranium(IV) and uranium(III) complexes [U{N(SiMe2H)2}4] and [U{N(SiMe2Ph)2}3] are both accessible from the Group 1 salts of the amides and UI3(thf)4 in thf. The choice of sodium or potassium salt made no difference to the reaction outcome. Both exhibit Weak interactions between uranium and with silyl-H or silyl-Ph groups in the solid-state.
- Mansell, Stephen M.,Perandones, Bernabé Fernandez,Arnold, Polly L.
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- Ketone Enolization with Sodium Hexamethyldisilazide: Solvent- And Substrate-Dependent E- Z Selectivity and Affiliated Mechanisms
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Ketone enolization by sodium hexamethyldisilazide (NaHMDS) shows a marked solvent and substrate dependence. Enolization of 2-methyl-3-pentanone reveals E-Z selectivities in Et3N/toluene (20:1), methyl-t-butyl ether (MTBE, 10:1), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDTA)/toluene (8:1), TMEDA/toluene (4:1), diglyme (1:1), DME (1:22), and tetrahydrofuran (THF) (1:90). Control experiments show slow or nonexistent stereochemical equilibration in all solvents except THF. Enolate trapping with Me3SiCl/Et3N requires warming to -40 °C whereas Me3SiOTf reacts within seconds. In situ enolate trapping at -78 °C using preformed NaHMDS/Me3SiCl mixtures is effective in Et3N/toluene yet fails in THF by forming (Me3Si)3N. Rate studies show enolization via mono- and disolvated dimers in Et3N/toluene, disolvated dimers in TMEDA, trisolvated monomers in THF/toluene, and free ions with PMDTA. Density functional theory computations explore the selectivities via the E- and Z-based transition structures. Failures of theory-experiment correlations of ionic fragments were considerable even when isodesmic comparisons could have canceled electron correlation errors. Swapping 2-methyl-3-pentanone with a close isostere, 2-methylcyclohexanone, causes a fundamental change in the mechanism to a trisolvated-monomer-based enolization in THF.
- Collum, David B.,Woltornist, Ryan A.
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p. 17452 - 17464
(2021/11/04)
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- Extended 2,5-diazaphosphole oxides: Promising electron-acceptor building blocks for π-conjugated organic materials
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(Chemical equation presented) BTD makeover-phosphorus edition: Replacing the sulfur atom in πextended 2,1,3-benzo[c]thiadiazoles (BTD) by a phosphoryl group affords the materials with improved electronacceptor properties. The significantly lower reduction potentials and competitive electron-transfer rates make the new diazaphosphole oxides excellent candidates for application in π-conjugated organic materials (see figure).
- Linder, Thomas,Sutherland, Todd C.,Baumgartner, Thomas
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supporting information; experimental part
p. 7101 - 7105
(2010/09/14)
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- Crystalline 10,10-Bis((2-fluoro-4-pyridinyl)methyl)-9(10H)-Anthracenone and an improved process for preparing the same
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The present invention relates to processes for the synthesis of a crystalline polymorph of 10,10-Bis((2-fluoro-4-pyridinyl)methyl)-9(10H)-Anthracenone in high purity. The product is useful in the synthesis of pharmaceutical compounds for the reduction of cholinergic system dysfunction.
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- Tetrasubstituted Tetrazenes (Me3E)2N-N=N-N(EMe3)2 (E = Si, Ge, Sn): Reactivity
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By substitution of the silyl, germyl, or stannyl groups, (Me3Si)2N-N=N-N(SiMe3)2 (1) reacts with variable amounts of trifluoroacetic acid to form (Me3Si)4-nN4Hn, (Me3Ge)2N-N=N-N(GeMe)2 (2) with variable amounts of methanol to form (Me3Ge)4-nN4Hn, and (Me3Sn)2N-N=N-N(SnMe3)2 (3) with variable amounts of trimethylchlorosilane to give (Me3Sn)4-nN4(SiMe3)n (n = 1-4).The reaction of 1 with benzenesulfonyl isocyanate leads by substitution and cyclization to silylated 5-hydroxytetrazole 12.Substitution in connection with thermolysis of the substitution products formed is found in the reaction of 1 with methanol, aluminium chloride, or nitrosyl chloride and in the reaction of 3 with trimethylstannane, acetone, or nitrosobenzene.By oxidation of 1 with chlorine, bromine, or p-benzoquinone and of 3 with p-benzoquinone or oxygen, all tetrazene nitrogen is envolved.The reduction of 1 with hydrogen or alkali metals leads to nitrogen and (Me3Si)2NH or (Me3Si)2NM.
- Wiberg, Nils,Bayer, Heiner,Vasisht, Sham Kumar,Meyers, Rene
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p. 2916 - 2927
(2007/10/02)
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