The synthesis and polymerization behavior of bimetallic pyridine diamide complexes containing transition metal (Ti,Zr)

Titanium and zirconium complexes with a pyridine diamide ligand, [2,6-(RNCH₂)₂NC₅H₃]²⁻ (PDMP; R = 2,6-dimethylphenyl) have been synthesized and their catalytic behaviors investigated for ethylene polymerization. It was found that the zirconium complexes, [PDMP]ZrCl₂ (7) and [PDMP][ZrCl₃ × THF]₂ (8), gave higher activities than the titanium complexes, [PDMP]TiCl₂ (5) and [PDMP][TiCl₃]₂ (6). The bimetallic complexes (6, 8) gave higher activities than the corresponding monometallic complexes (5, 7). The titanium complexes gave polymers with higher molecular weight (M_w) than the zirconium complexes. The molecular weight distribution (M_w/M_n) of the polymers obtained from the pyridine diamide complexes were much broader than that of the normal metallocene catalysts. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3756–3762, 1999     

Polymerization of styrene with chromium acetylacetonate–triisobutylaluminum catalyst system

Styrene is polymerized with chromium acetylacetonate–triisobutylaluminum catalyst at 40°C in a benzene medium. At the stoichiometric ratio of Al/Cr of 4, the activity for polymerization was found to be maximum. Further, the kinetic studies were carried out at this ratio of Al/Cr of maximum activity. The kinetics of polymerization and the total activation energy around 10.00 kcal/mole suggest a coordinate anionic mechanism.     

Ambient temperature rapid ATRP of methyl acrylate, methyl methacrylate and styrene in polar solvents with mixed transition metal catalyst system

Ambient temperature atom transfer radical polymerization (ATRP) of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (Sty) in the presence of polar solvents (dimethyl sulfoxide: DMSO, dimethylformamide: DMF and acetonitrile: MeCN) with a mixed transition metal catalyst system (Fe(0) as initial activator and CuBr₂/Me₆TREN complex as deactivator) provides a rapid synthesis of polymers with very low polydispersity (PDI) values and predetermined molecular weights. The polymethylacrylate (PMA) prepared using this novel approach contains the Br-terminated chain ends (functionality ∼100%) and can be successfully used for block copolymer synthesis (as demonstrated on the chain extension experiment performed using the PMA–Br macroinitiator). The key elementary reactions involved in this novel ATRP system and some preliminary mechanistic aspects of the process are also discussed.     

Effect of catalyst transition metal and ancillary ligand on syndiospecific polymerization of styrene

In the coordination polymerization of styrene, selected transition metal complexes of metals other than group 4 elements and non-metallocenes have been investigated in comparison to a known half-metallocene titanium complex with regard to the catalytic activity as well as to the thermal and molecular properties of the polymers synthesized. Whereas iron catalysts lead to syndiotactic polystyrenes, catalysts with nickel as the transition metal result only in atactic polymers with an enhanced isotactic content.In addition to the influence of the transition metal, the effect of a broad variation of the ancillary ligands of a specific half-sandwich titanocene, octahydrofluorenyl titanium trimethoxide, on polymerization activity and polymer properties has been investigated and discussed in detail.     

Polymerization of styrene with the VOCL3–AlEt2Br catalyst system

The rate of polymerization with the VOCl₃–AlEt₂Br catalyst system at 30°C. in n-hexane reached a maximum at an Al/V molar ratio of 1.5. At this ratio, the rate of polymerization was first-order with respect to catalyst and second-order with respect to monomer concentrations. The apparent activation energy calculated was 6.4 kcal./mole. Diethylzine was found to act as a chain transfer agent. However, the molecular weights of polymers obtained were low. The possibility of bromide-containing catalyst sites acting in the termination reaction has been investigated. The average valence of vanadium is discussed in relation to molecular weights.     

The Role of 2-(Methacryloyloxy) Ethyl Acetoacetate in the Polymerization of Hybrid Multicomponent (Si, Ti, Zr) Sols

2-(Methacryloyloxy) ethylacetoacetate (MEEAH) was used as stabilyzing agent to control the chemical reactivity of Ti and Zr monomeric alkoxides in a Si—Ti—Zr sol. The organic and inorganic polymerizations were carried out simultaneously. The organic polymerization was performed using benzoyl peroxide as the initiator. The inorganic polymerization was done via the sol-gel process. The polymerization was studied by several spectroscopic techniques, including Fourier Transform Infrared (FTIR), UV-Vis, ²⁹Si NMR, Small Angle X-ray Scattering (SAXS) and X-ray diffraction (XRD). Theoretical calculation and experimental results showed that MEEAH acted as a monodentate ligand, mainly. This led to a high condensation extent of the Si species in the sol. A short range order gel was obtained, according to the SAXS results. The Si—O—Ti and Si—O—Zr bonds were detected by FTIR. The bonds remained stable, because a sample calcined at 1173 K was amorphous according to the XRD results, indicating structural homogeneity.     

Coordination compounds derived from transition metal salts and bis(3,5-dimethylpyrazolyl)methane

Summary The preparation of transition metal complexes containing the sterically hindered ligand, bis(3,5-dimethylpyrazolyl)methane (LL) is described. Compounds of formula M(LL)X₂ (M = Co^II, Ni^II or Zn^II and X = Cl^– or Br^–) or M(LL)₂X₂ (M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II, Zn^II or Cd^II and X = ClO ₄ ^– ; M = Co^II, Ni^II, Cu^II or Zn^II and X = NO ₃ ^– ; M = Ni^II or Cu^II and X = Cl^– or Br^–) have been isolated. In addition, an apparently trimeric Cu₃(LL)₄Cl₆ · EtOH compound is reported. For Ni(LL)Cl₂ a five-coordinated chloro-bridged dimer is found. The perchlorato compounds, M(LL)₂(ClO₄)₂, appear to have one bidentate ClO ₄ ^– and one ionic ClO ₄ ^– group. The M(LL)₂ species appears to occur either in octahedral geometry, leaving twocis-positions free, or in a tetrahedral geometry without space for other ligands, and probably also in a five-coordinate geometry with one free ligand position.Structural conclusions are drawn from i.r., far-i.r. and ligand-field spectra, x-ray powder patterns, magnetic susceptibility data, e.s.r. spectra and conductivity data.     

Polymerization of 1-aryl-2-trimethylsilylacetylenes by transition metal catalysts(II)

Polymerization of 1-aryl-2-trimethylsilylacetylene (aryl = thienyl, furyl, and pyridyl) was carried out by transition metal catalysts. The polymer yield was generally low due to the steric hindrance. R₄Sn (R = Me, n-Bu, Ph) exhibits some cocatalytic activities with respect to polymer yield and molecular weight. On the other hand, the polymerization was decelerated when organoaluminum compounds were used as cocatalysts. The polymer yield increased in the following order: phenyl > thienyl > furyl > pyridyl, according to the aryl substituents. The NMR (¹H- and ¹³C-), IR, and UV-visible spectra indicated that the resulting polymers have a linear conjugated polyene structure each containing the aromatic substituent and trimethylsilyl group. From ¹H-NMR integration, it was found that the resulting polymers are partially desilylated depending on the substituents of monomer and the polymerization conditions. The solubility behavior, stability and fluoride-ion induced desilylation reaction of the polymers were also studied.     

Preparation and physical properties of early-late heterobimetallic compounds featuring Ir-M bonds (M = Ti, Zr, Hf)

Treatment of Cp*Ir N(t)Bu (1) with the appropriate metallocene equivalent is an effective route for the preparation of the heterobimetallic complexes Cp*Ir(μ-N(t)Bu)MCp(2) (2-M, M = Ti, Zr, Hf). The electronic structures of the isostructural series of compounds, 2-M, are described with reference to single-crystal X-ray, Raman, UV-vis, and cyclic voltammetry data. Density functional theory (DFT) calculations were used to aid in the interpretation of this experimental work. Treatment of the zirconium or hafnium congeners with 2,6-lutidinium triflate leads to protonation of the Ir-M bond, to afford Cp*Ir(μ-N(t)Bu)(μ-H)MCp(2)OTf (3-M, M = Zr, Hf). Compound 3-Zr was characterized by single-crystal X-ray diffraction and independently prepared by the reaction of 1 and Cp(2)Zr(H)Cl in the presence of Me(3)SiOTf. In reactions analogous to those for 2-Zr, 2-Hf reacts with S(8) and aryl azides to insert an S-atom or aryl azide fragment into the metal-metal bond, yielding Cp*Ir(μ-N(t)Bu)(μ-S)HfCp(2) (6-Hf) and Cp*Ir(μ-N(t)Bu)(N(3)Ph)HfCp(2) (4-Hf), respectively. Heating 4-Hf results in N(2) extrusion to form Cp*Ir(μ-N(t)Bu)(NPh)HfCp(2) (5-Hf). The kinetics of the latter reaction were studied to obtain activation parameters and a Hammett trend; these data are compared to those for the analogous reaction involving Ir-Zr heterobimetallics.     

Synthesis, structural characterization, and theoretical investigation of compounds containing an Al-O-M-O-Al (M=Ti, Zr) core

We report a facile route to the first molecular compounds with the Al-O-M-O-Al (M=Ti, Zr) structural motif. Synthesis of L(Me)Al(mu-O)M(NMe2)2(mu-O)Al(Me)L [L=CH{N(Ar)(CMe)}2, Ar=2,6-iPr2C6H3; M=Ti (7), Zr (8)] was accomplished by reacting the monometallic hydroxide precursor L(Me)Al(OH) (1) with Ti(NMe2)4 or Zr(NMe2)4 under elimination of Me2NH in good yield. The crystal structural data confirm the trimetallic Al-O-M-O-Al core in both 7 and 8. Preliminary investigation on catalytic activity of these complexes reveals low activity of these complexes in ethylene polymerization as compared to the related oxygen-bridged metallocene-based heterobimetallic complexes L(Me)Al(mu-O)M(Me)Cp2 (M=Ti, Zr) which could be attributed to the relatively lower stability of the supposed cationic intermediate as revealed by DFT calculations.     

Polymerization by alkaline earth metal compounds—II Polymerization of 2- and 4-vinylpyridine,styrene and butadiene by triphenylmethyl derivatives of calcium,strontium and barium

Investigations are reported on polymerizations of 2- and 4- vinylpyridine, styrene and butadiene by a series of related alkaline earth metal initiators, Ph₃CMX(THF)_n (M = Ca, Ba, X = Cl, n = 2; M = Ca, X = Br, n = 4; M = Sr, X = Cl, n = 4; M = Sr, X = Br, n = 5) in tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME) at various temperatures and in the absence of solvent. The polymers have been examined by GPC and aspects of their microstructures determined by ¹³C and/or ¹H NMR spectroscopy and, for polybutadiene, i.r. spectroscopy. Poly-2-vinylpyridine produced by Ph₃CMX(THF)_n is rich in isotactic content; the isotacticity is higher for polymer formed in THF than DME solution, falls with change of initiator in the order M = Ca > Sr > Ba and, in DME, is greater when X = Br. The tacticities of poly-4-vinylpyridine and polystyrene are similar to those obtained from related organometallic initiators. The 1,4-content of polybutadiene decreases with initiator Ph₃CMX(THF)_n in the order M = Ba > Sr > Ca; the trans-1,4 structure generally predominates except when M = Ba from which cis-1,4 links are formed in comparable amounts.     

Polymerization of vinyl monomers with chlorosilane compounds and metal halides

It was found that styrene was polymerized with chlorosilane compounds and metal halides in 1,2-dichloroethane. The rate of polymerization of styrene was proportional to the concentration of styrene, trimethylchlorosilane, and mercuric chloride. The overall activation energy of polymerization was ?2.9 kcal/mole. The polymer yield decreased markedly on addition of ether into the polymerization system, and the infrared spectrum showed evidence of silicone fragments in the polymer. From the results, it was considered that the polymerization was initiated by a siliconium cation. The formation of a complex between trimethylchlorosilane and metal halides (i.e., ferric chloride) was confirmed by the continuous variation method of ultraviolet and visible absorption spectra.     

Polymerization of vinyl chloride by the Ti(O-n-Bu)4–AlEt3–epichlorohydrin catalyst system

The polymerization of vinyl chloride was carried out by using a catalyst system consisting of Ti(O-n-Bu)₄, AlEt₃, and epichlorohydrin. The polymerization rate and the reduced viscosity of polymer were influenced by the polymerization temperature, AlEt₃/Ti(O-n-Bu)₄ molar ratios, and epichlorohydrin/Ti(O-n-Bu)₄ molar ratios. The reduced viscosity of polymer obtained in the virtual absence of n-heptane as solvent was two to three times as high as that of polymer obtained in the presence of n-heptane. The crystallinity of poly(vinyl chloride) thus obtained was similar to that of poly(vinyl chloride) produced by a radical catalyst. It was concluded that the polymerization of vinyl chloride by the present catalyst system obeys a radical mechanism rather than a coordinated anionic mechanism.     

Polymerization of oil (styrene and methylmethacrylate)-in-water microemulsions

 The polymerization of styrene-in-water and methylmeth-acrylate-in-water microemulsions stabilized by nonionic surfactants was investigated using different initiation techniques. Thermally induced initiation was carried out using potassium persulfate (water soluble) and azobisiso-butyronitrile (AIBN) (oil soluble) at 60° and 50°C, respectively. When the monomer concentration was kept below a certain limit, the particle size of the nanolatex was similar to the droplet size of the microemulsion precursor. At higher monomer concentrations, the latex produced was significantly larger than the microemulsion droplets, as a result of the possible coalescence of the microemulsion droplets during polymerization. By using chemically induced polymerization (hydrogen peroxide+ascorbic acid) at temperatures below the cloud point temperature of the microemulsion or by photochemically induced initiation at room temperature, it was possible to obtain nanolatex particles with similar size to the droplets up to 10% monomer content. In all cases, the particle size was determined using photon correlation spectroscopy (PCS). Electron micrographs of the microlatex particles were taken and these confirmed the measurements obtained by PCS. The molecular weight of the polymers produced was determined by gel permeation chromatography. The average number of polymer molecules per particle was calculated. It was shown in some cases that the nanolatex contained one polymer chain per particle. A mechanism was suggested for polymerization and particle growth. Received: 29 May 1997 Accepted: 28 May 1998     

Intercalation compounds of TIS2 with lithium and transition metals LixMyTiS2 (M=Ti,Fe, Ni)

Conclusions The titanium disulfide intercalation compounds obtained that contained both lithium and transition metals with the composition Li_xMyTiS₂ (M=Ti, Fe, Ni) had an interlayer distance that was greater than in the original MyTiS₂, but less than in Li_xTiS₂ with the same lithium content.Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 478–483, March, 1987.     

Activation of transition metalalkyl bonds in methyl titanium,trichloride, dialkyl(bipyridine)nickel and other transition metal alkyls by interaction with organoaluminum compounds

Metalcarbon bonds of various alkyl-transition metal compounds including TiCH₃Cl₃, NiR₂Bipy, Cr(C₂H₅)Cl₂Py₃, FeR₂Bipy₂, CuCH₃(PPh₃)₃(C₆H₅CH₃) are activated and split on interaction with organoaluminum compounds [AlR′₃ and AlR′₂(OC₂H₅), where R′ = CH₃, C₂H₅, and n-C₃H₇]. Kinetics of the cleavage of the TiCH₃ bond in TiCH₃Cl₃ and NiR bonds in NiR₂Bipy in solutions containing the organoaluminum compounds were studied by volumetric and spectroscopic methods, respectively. In both cases the reactions were first order with respect to the concentrations of the alkyltransition metal compounds. The pseudo first order rate constants for the decomposition of NiR₂Bipy in THF solution on addition of AlR′₃ were proportional to [AlR′₃] for low concentrations of AlR′₃ and to 1/[AlR′₃] for high concentrations. Based on the kinetics, a mechanism is proposed which involves coordination of AlR′₃ with NiR₂Bipy, and splitting the NiR bonds of the binuclear adduct thus formed. The decrease of the rate constants at higher concentrations of AlR′₃ is attributed to displacement of the complexed organoaluminum component by interaction wit AlR′₃·THF.     

On the quest for new mixed-metal mu-oxo-bridged complexes: synthesis of compounds containing transition metal-oxygen-main group metal motifs M-O-M1 (M = Ti, Zr; M1 = Al, Ga) without cyclopentadienyl ligands

The reaction of TiBz4 (Bz = benzyl) with LAlMe(OH), L = (2,6-iPr2C6H3NC(Me))2CH, afforded LAlMe(mu-O)TiBz3 (1) and [LAlMe(mu-O)]2TiBz2 (2), whereas the corresponding reaction with ZrBz4 resulted only in the formation of the trinuclear species [LAlMe(mu-O)]2ZrBz2 (3). The reaction of (Mes 2Ga(OH))2 x THF (Mes = 2,4,6-Me3C6H2) with Ti(NEt2)4 yielded the cluster compound TiGa6O7(NEt2)2(Mes)6 (4). All compounds have been characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Additionally, single crystal X-ray structure data of 1, 3, and 4 are reported. Compounds 1-4 show low catalytic activities in the polymerization of ethylene. Revisiting known mu-oxo-bridged complexes containing the M-O-M(1) (M = Ti, Zr, Hf; M(1) = Al, Ga) skeleton revealed that the application of polynuclear group 13 hydroxides and oxo bridged complexes possesses a potential for the preparation of new polyoxometal clusters.