Synthesis and Characterization of 5-Coordinate Tungsten Hydride Anions: [(tBu3SiNH)(tBu3SiN=)2HWR]M

Treatment of (^tBu₃SiNH)(^tBu₃SiN=)₂WH ( 1 -H) with small alkyl anions (RM) afforded tungsten alkyl hydride anions [(^tBu₃SiNH)(^tBu₃SiN=)₂HWR)]M ( 3 -(R)M: R=CH₃, M=Li; R=ⁿBu, M=Li; R=^neoPe, M=Li; R=CH₂Ph (Bn), M=K (two isomers); R=CCH, M=Na; R=CH=CH₂ (Vy), M=Li). The saturated alkyl anions 3 -(R)M ( 3 -(R)M: R=CH₃, M=Li; R=ⁿBu, M=Li; R=^neoPe, M=Li; R=CH₂Ph (Bn), M=K) degraded via apparent 1,2-RH-elimination to produce the known [(^tBu₃SiN=)₃WH]M ( 2 -HM), but the acetylide ( 3 -(C₂H)Na) and vinyl ( 3 -(Vy)Li) anions converted to their hydrogenated isomers, [(^tBu₃SiN=)₃WVy]Na ( 2 -VyNa) and [(^tBu₃SiN=)₃WEt]Li ( 2 -EtLi), respectively. The structure of 3 -(ⁿBu)Li is reported, and a discussion of tungsten-hydride coupling constants in ^tBu₃SiX-ligated (X=O, NH, N) systems is given.     

Entry to alkynylplatinum(IV) chemistry using hypervalent iodine(III) reagents,and the synthesis of triphenyl{4,4′-bis(tert-butyl)-2,2′-bipyridine}iodoplatinum(IV)

The reaction of phenyl(alkynyl)iodine(III) triflates with diorganoplatinum(II) complexes provides a general route for the synthesis of a new class of alkynylplatinum(IV) complexes containing Pt^IVR₂(CCR²) groups, e.g., the 4,4^′-bis(tert-butyl)-2,2^′-bipyridine complexes PtIR₂(CCSiMe₃)(Bu^t₂bpy) (R=Me, Ph); IPh₂(OTf) reacts with PtPh₂(Bu^t₂bpy) to form the first archetypal triarylplatinum(IV) complex PtIPh₃(Bu^t₂bpy).     

Ethylene polymerisation by Ni–diphosphine azine complexes

The properties of [NiX(PR₂CH₂C(Bu^t)?NN?C(Bu^t)CH₂PR₂)]⁺ complexes (where X = Br, and R = cyclohexyl (Cy), isopropyl (Prⁱ), tert‐butyl (Bu^t), phenyl (Ph); X = Cl or I, and R = cyclohexyl) as catalysts for the polymerisation of ethylene were evaluated with or without the co‐catalysts methylaluminoxane (MAO), diethylaluminium chloride, trimethylaluminium or tri(isobutyl)aluminium. Their efficiency depends on the characteristics of the halogen (X) and the R group of the diphosphine azine ligand. Bromide (X) strongly enhances the catalytic properties of the complexes within the R order Cy > Prⁱ > Ph > Bu^t. Temperature, co‐catalyst ratio (Al/Ni) and complex concentration also influence the catalytic activity. The best results were obtained with [NiBr{PCy₂CH₂C(Bu^t)?NN?C(Bu^t)CH₂PCy₂}]Br activated by MAO (A = 25.8 kg (mol Ni)^?1 bar^?1 h^?1). The polymers were characterised using NMR and differential scanning calorimetry as branched polyethylenes, the number of branches increasing with the temperature of polymerisation. The molecular weights of the polymers were estimated using NMR. A proposal for the catalyst active precursor is made on the basis of experimental data and molecular orbital calculations. Copyright © 2007 Society of Chemical Industry     

The flexibility of binding modes of the supersilyl thiolate ligand SSitBu3−

The synthesis and structural characterization of [Zn(SSitBu₃)₂]₂ are described. The degradation of sulfur with [Zn(SitBu₃)₂] in tetrahydrofuran yielded the supersilyl thiolate complex [Zn(SSitBu₃)₂]₂. X-ray quality crystals of [Zn(SSitBu₃)₂]₂ were grown from a benzene solution at ambient temperature (monoclinic, C2/c). The trigonal-planar coordinate zinc atoms in [Zn(SSitBu₃)₂]₂ are surrounded by one terminal and two bridging thiolate ligands. The bonds between the Zn and S atoms of the terminal ligands are significantly shorter than those between the Zn and S atoms of the bridging ligands.     

Synthesis and structure of the pentanuclear mixed-metal cluster [Co4MoCp(μ3-SBut)(μ3-S)(μ3-CO)(μ-CO)2(CO)6]

The pentanuclear mixed-metal cluster [Co₄MoCp(μ₃-SBu^t)(μ₃-S)(μ₃-CO)(μ-CO)₂(CO)₆] (1) has been synthesised by reaction of [CoMoCp(CO)₇] with Bu^tSSBu^t. X-ray structural analysis identified an asymmetric unit with three cobalt atoms and one molybdenum forming an irregular tetrahedron while one cobalt–molybdenum edge is bridged by a cobalt atom. Crystal data: space group P2(1)/n, a=10.162(2), b=13.722(3), c=17.69(5) Å, β=91.44(2)°, Z=4.     

Reduction of poly(vinyl chloride) with tri-n-butyltin hydride

Reduction of PVC with tributyl-tin-hydride (Bu₃SnH) was studied in order to optimize the method. The reactions were carried out in mixtures of xylene and tetrahydrofuran, chlorine content was determined by ¹H n.m.r. spectroscopy, and the melting behaviour by d.s.c. It was possible to obtain a product with less than 0.1% chlorine in less than 6 h. The ¹³C n.m.r. spectrum showed that the product contained about 4 methyl branches per 1000 monomer units and gave no evidence of chlorinated structures.     

Polymerization of styrene with diphenylzinc-water systems previously aged

Summary Diphenylzinc-water systems, Ph₂Zn-H₂O, were aged at various temperatures and for various lengths of time. These systems by themselves and those to which t-butyl chloride was added, Ph₂Zn–H₂O–Bu^tCl, were used as initiator for styrene polymerizations. For Ph₂Zn–H₂O systems, both conversion and molecular weight of the polymers were much affected by ageing. Ph₂Zn–H₂O–Bu^tCl systems, after ageing at various temperatures, did not improve their capability to induce styrene polymerization at-78°C in dichloromethane, confirming their ionic nature.Presented in part at the 2nd Ibero-American Polymer Symposium, 4th Latin-American Polymer Symposium, 6th International Macromolecular Colloquium, Gramado, Brazil, September 1994     

Chemistry of Intermolecular Frustrated Lewis Pairs in Motion: Emerging Perspectives and Prospects

This feature article describes the chemistry in motion of frustrated Lewis pairs (FLPs). With state-of-the-art ab initio molecular dynamics (AIMD) simulations supplemented by minimum energy path (MEP) and potential energy surface (PES) calculations, we examine the binding of CO₂ and the heterolytic cleavage of H₂ by a Lewis base (LB), tBu₃P, and a Lewis acid (LA), B(C₆F₅)₃. We strive to uncover and understand mechanistic implications of the physical laws that govern the behavior of a LB and a LA when they react with a third species (e.g., CO₂ or H₂) at finite temperature. The approximation that we necessarily must make at present is to forgo the quantization of the movement of atoms in favor of the Born-Oppenheimer molecular dynamics (BOMD), which unfold according to the classical (Newton’s) laws of motion. However, strict quantum chemical theory is used to compute all of the forces that govern the dynamics of the macromolecular FLP system. Using physical reasoning and innovative computer simulations, we show that multi-scale motion is the predominant mechanistic aspect in reactions of the tBu₃P/B(C₆F₅)₃ FLP, as well as, conceivably, those of other similar intermolecular FLPs. Insight achieved thus far leads to a novel activity model for intermolecular FLPs and specific predictions, which could be useful for future experimental and theoretical studies of FLP and other chemistries.     

Ring‐opening polymerization of trimethylenecarbonate by the bridged diphenoxo ytterbium (II) complex

A novel ytterbium (II) complex 2 supporting by a bridged bisphenolate ligand H₂L^OC4H7 (L = C₄H₇OCH₂N(CH₂‐2‐OC₆H₂‐3,5‐Bu)₂) with a tetrahydrofuran donor on side‐arm was synthesized in high yield and characterized by elementary analysis, IR, ¹H‐NMR, and ¹³C‐NMR. Ring‐opening polymerization of 1,3‐trimethylenecarbonate (TMC) was carried out using complex 2 and a known complex [Me₂NCH₂CH₂N(CH₂‐2‐O‐3,5‐C₆H₂(Bu^t)₂)₂]Yb 1 as the initiators, respectively. It was found that both complexes 1 and 2 can alone initiate the ring‐opening polymerization of TMC, and complex 1 showed higher activity than complex 2 . The activity of both complexes 1 and 2 was found to be higher than that of monodentate phenoxo ytterbium (II) complex (2,6‐Bu‐C₆H₃O)₂Yb(THF)₃. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ethylene/α‐olefin copolymerization by nonbridged (cyclopentadienyl)(aryloxy)titanium(IV) dichloride/AliBu3/Ph3CB(C6F5)4 catalyst systems

A series of nonbridged (cyclopentadienyl) (aryloxy)titanium(IV) complexes of the type, (η⁵‐Cp′)(OAr)TiCl₂ [OAr = O‐2,4,6‐^tBu₃C₆H₂ and Cp′ = Me₅C₅ ( 1 ), Me₄PhC₅ ( 2 ), and 1,2‐Ph₂‐4‐MeC₅H₂ ( 3 )], were prepared and used for the copolymerization of ethylene with α‐olefins (e.g., 1‐hexene, 1‐octene, and 1‐octadecene) in presence of AlⁱBu₃ and Ph₃CB(C₆F₅)₄ (TIBA/B). The effect of the catalyst structure, comonomer, and reaction conditions on the catalytic activity, comonomer incorporation, and molecular weight of the produced copolymers was examined. The substituents on the cyclopentadienyl group of the ligand in 1 – 3 play an important role in the catalytic activity and comonomer incorporation. The 1 /TIBA/B catalyst system exhibits the highest catalytic activity, while the 3 /TIBA/B catalyst system yields copolymers with the highest comonomer incorporation under the same conditions. The reactivity ratio product values are smaller than those by ordinary metallocene type, which indicates that the copolymerization of ethylene with 1‐hexene, 1‐octene, and 1‐octadecene by the 1–3/ TIBA/B catalyst systems does not proceed in a random manner. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

New family of quadruply-bonded ditungsten(II,II) species with chloride and amine ligands

The first ditungsten(II,II) complexes with amine ligands of the formula W₂Cl₄(NH₂R)₄ (R=Prⁿ (1), Bu^t (2), Cy (3)) have been prepared by reduction of a tungsten(IV) compound with potassium graphite in the presence of the appropriate amine. The X-ray crystal structure determination of 3 revealed a quadruply-bonded ditungsten molecule having D_2d geometry and a trans arrangement of the amine ligands on each metal atom.     

Homopolymerization of styrenic monomers and their copolymerization with ethylene using group 4 non-metallocene catalysts

Homopolymerization of styrenic monomers (St, p-Me-St, p-tBu-St, p-tBuO-St) and their copolymerization with ethylene, with the use of [(^tBu2O₂NN′)ZrCl]₂(μ-O) ( 1 ) and (^tBu2O₂NN′)TiCl₂ ( 2 ), where ^tBu2O₂NN′ = Me₂N(CH₂)₂N(CH₂-2-O⁻-3,5-tBu₂-C₆H₂)₂, is explored in the presence of MMAO and (iBu)₃Al/Ph₃CB(C₆F₅)₄. The ethylene/styrenic monomers copolymerization with 1 /MMAO produces exclusively copolymers with high activity and good comonomer incorporation whereas the other catalytic systems yield mixtures of copolymers and homopolymers. The use of p-alkyl styrene derivatives instead of styrene raises the catalytic activity, comonomer incorporation and molecular weights of the copolymers. Complex 2 exhibits higher activity in homopolymerization of styrenic monomers than 1 irrespective of the kind of the activator employed. A clear dependence is observed for the molecular weight and catalyst activity against the kind of the styrenic monomer. The obtained polymers were atactic and only the complex 2 , when activated by MMAO, promoted the highly syndiospecific polymerization of p-Me-St and p-tBu-St. Poly(p-tBuO-St) exhibits fiber-forming properties.     

Isobutylaluminum aryloxides as metallocene activators in Homo‐ and copolymerization of olefins

The article describes that sterically hindered isobutylaluminum aryloxides with bulky ^tBu substituents at 2,6‐ positions of aryl fragment, i.e. (2,6‐di‐^tBu,4‐R‐C₆H₂O)AlⁱBu₂ (R = H ( 1‐DTBP ), Me ( 1‐BHT ), ^tBu ( 1‐TTBP )) and (2,6‐di‐^tBu,4‐R‐C₆H₂O)₂AlⁱBu (R=H( 2‐DTBP ), Me( 2‐BHT )) can serve as cocatalysts for metallocene complexes. Isobutylaluminum aryloxides have been applied for activation of rac‐Et(2‐MeInd)₂ZrMe₂ in homopolymerization of ethylene, propylene, copolymerization of ethylene and propylene, and terpolymerization of ethylene, propylene, and 5‐ethylidene‐2‐norbornene at Al/Zr = 300 mol/mol. The type of R substituent at 4‐position has a significant effect on catalyst activity. The catalytic system with 1‐TTBP showed the highest activity in all homo‐ and copolymerization processes. Diisobutylaluminum aryloxides provide much higher activity to the systems in all polymerization processes and stronger ability for propylene incorporation in copolymer than diaryloxides. The activities of the systems with isobutylaluminum aryloxides are similar or exceed that of the system with MAO as activator as have shown for propylene polymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43276.     

Thermodynamics of hydrobromic acid in t-butanol + water mixtures from electromotive force measurements

The standard potentials of AgAgBr electrode have been determined in eighteen t-butanol + water mixtures containing up to 90 wt% t-butanol from the emf measurements of the cell Pt, H₂ (g, 1 atm): HBr (m), X% Bu^tOH, Y% H₂O: AgBr, Ag at nine different temperatures from 15 to 55°C at five intervals. The standard molal potential in each solvent has been expressed as a function of temperature. The standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr, and the standard thermodynamic quantities for the transfer of one mole of HBr from water to t-butanol + water media have been computed and discussed.     

Quaternary salts as solubilization site modifiers of organic compounds in anionic micellar solutions

The effects of the addition of different salts (quaternary bromides or NaBr) on the viscosity (measured under Newtonian flow conditions) of sodium dodecylbenzenesulfonate (SDBS) micellar solutions were studied at 30°C. Tetra-n-butylammonium bromide (Bu₄NBr) was found most effective in increasing the viscosity (due to possible change in micellar shape) at fairly low SDBS concentration (50 mM). The effectiveness of Bu₄NBr may be due to the presence of four butyl chains and to the positive charge on its counterion (Bu₄N⁺) which can subsequently interact with anionic SDBS micelles electrostatically as well as hydrophobically; owing to solubility/steric problems, other salts were ineffective. Organic additives such as cyclohexylamine and cyclohexanol had marginal effects on viscosity when added to 50 mM SDBS solutions having no Bu₄NBr. However, in the presence of Bu₄NBr, the effect was dependent on salt concentration and the nature of the additive. The overall effect is discussed on the basis of change in the solubilization site of the additive in the presence of Bu₄NBr.     

Direct Transesterification/Isomerization/Methoxycarbonylation of Various Plant Oils

A selection of plant oils was catalytically transferred into 1,19-nonadecanedioate by a direct transesterification, isomerization and methoxycarbonylation under mild conditions using Pd/o-C₆H₄(CH₂P ^t Bu₂)₂. Additionally, sulfuric acid was demonstrated as being able to substitute methane sulfonic acid as co-catalyst without any significant loss of activity and selectivity.     

Colorimetric Detection of Small Molecules by a Frustrated Lewis Pair Containing a Phosphorus-Functionalized Cycloheptatrienyl?Cyclopentadienyl Titanium Sandwich Complex

The phosphorus-functionalized cycloheptatrienyl cyclopentadienyl (Cht Cp) titanium sandwich complex [(η⁷-C₇H₇)Ti(η⁵-C₅H₄PtBu₂)] ( 7 ) forms a frustrated Lewis pair (FLP) in combination with the borane B(C₆F₅)₃, and this FLP undergoes heterolytic cleavage of dihydrogen and fixation of carbon dioxide and nitrous oxide with a noticeable colorimetric response, which is visible to the naked eye. In their UV/Vis spectra, the H₂, CO₂ and N₂O fixation products exhibit a bathochromic shift of the absorption band that can be assigned to a HOMO LUMO excitation of the Cht Cp titanium (troticene) moiety.     

Über die Verwendung von Glyoxal-bis(tert.-butylnitron) als Spin-Trap

On the Use of Glyoxal Bis (t-Butyl Nitron) as a Spin Trap Nitroxides derived from glyoxal bis(t-butyl nitrone), GBBN , have been studied by e.s.r. spectroscopy. Well resolved e.s.r. spectra exhibiting extra hyperfine splitting by magnetic active nuclei in γ-position have been recorded for the spin adducts of alkyl, as well as ^.N₃ and ^.CH₂Cl radicals. Enhanced stability was found for the spin adducts of halogen atoms. However, a wider application of this spin trap is limited by the strong superposition of the e.s.r. signals of different radical spin adducts which is directly related to almost identical conformations of these nitroxides.     

Conductance measurements of some electrolytes in N,N-dimethyformamide and its binary mixtures witth other organic solvents—II

Equivalent conductances of Bu₄NBPh₄, Bu₄NNO₃, Bu₄NI,KClO₄, Kl, NaI, NaBPh₄, Ph₄PCl, LiCl, AgNO₃ and CuClO₄. 4AN have been measured at 25°C in binary mixtures of N,N-dimethylformamide (DMF) containing 1 mol % of 1, 1, 3, 3-tetramethylurea (TMU), dimethylsulphoxide (DMSO) and hexamethylphosphotriamide (HMPT). Such measurements for LiCl, NaI, KClO₄ and CuClO₄. 4AN have also been carried out in DMF and in binary mixtures of DMF containing 1 mol % pyridine (Py), α-picoline (α-Pic), β-picoline (β-Pic), γ-picoline (γ-Pic) and acetonitrile (AN). The conductance data in all the cases have been analyzed by the Shedlovsky equation. Limiting ion conductances have been obtained by the method of Fuoss et al. The actual solvated radii of ions, evaluated using limiting ion conductances show that Ag⁺ and Cu₊ have strong preferential solvation by all solvents which have been used to prepare the binary mixtures with DMF and the preferential solvation for both Ag⁺ and Cu⁺ with HMPT, DMSO and TMU is relatively stronger than with AN and is practically of similar magnitude as with the organic bases.     

Ethylene polymerization catalyzed by group 4 metal complexes of tridentate heteroscorpionate ligands

Considerable attention has been recently devoted to group 4 metal complexes of N,O polydentate ligands exhibiting electronic properties comparable to those of the cyclopentadienyl ligand: among these the heteroscorpionates are attractive candidates. Herein we review the results reached in olefin polymerization catalysis promoted by group 4 metals complexes of heteroscorpionate ligands, with particular reference to the work carried out in our research group. The ethylene polymerization catalyzed by titanium and zirconium complexes of the (3,5-^tBu₂-2-phenoxo)bis(3,5-Me₂-pyrazol-1-yl)methane ligand has been investigated in great detail. A solution structure of the active species was proposed on the basis of variable temperature ¹H NMR spectroscopic evidences. Kinetic mechanisms accounting for the formation of linear and branched polyethylenes obtained by the zirconium complexes have been proposed in the light of the ionic interactions of the active species and steric hindrance at metal centre determined by the heteroscorpionate ligands.