Group IVB Metallocenes Research Articles

Electrophilic Routes to 6F Polymers and Attempted Synthesis of Semi-fluorinated Group IVB Metallocene Polymers

Electrophilic Routes to 6F Polymers and Attempted Synthesis of Semi-fluorinated Group IVB Metallocene Polymers

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This article refers to:Group IVB Metallocene Polyesters Containing Camphoric Acid and Preliminary Cancer Cell Activity

Group IVB metallocene polyesters containing camphoric acid and preliminary cancer cell activity

ABSTRACTPolyesters were formed from the reaction of the salt of camphoric acid and Group IVB metallocene dichlorides using the interfacial polycondenzation process. The polyesters were formed in good yields with moderate chain lengths. Fourier transform infrared spectroscopy shows bands characteristic of the presence of both reactants with new bands characteristic of the formation of the M‒O and M–O(CO) linkage present. The polymers largely exist in a bridging geometry of the carbonyl groups about the metal atom. Nuclear magnetic resonance shows the presence of bands derived from both reactants. Matrix-assisted laser desorption/ionization mass spectroscopy shows ion fragments to three units for the polymers with isotopic abundance characteristic of the presence of metal atoms in the ion fragment clusters. All the polymers exhibit good ability to inhibit all the tested cancer cell lines but the zironocene and hafnocene polymers exhibit especially good inhibition of the tested cancer cell lines that included two pancreatic cancer cell lines. They represent a potential new group of anticancer drugs.

Group IVB Metallocene Polyesters Containing Camphoric Acid and Preliminary Cancer Cell Activity

Polyesters were formed from the reaction of the salt of camphoric acid and Group IVB metallocene dichlorides employing the interfacial polycondensation process. The polyesters were formed in good yields with moderate chain lengths. FTIR shows bands characteristic of the presence of both reactants with new bands characteristic of the formation of the M-O and M-O(CO) linkage present. The polymers largely exist in a bridging geometry of the carbonyl-groups about the metal atom. NMR shows the presence of bands derived from both reactants. MALDI MS shows ion fragments to three units for the polymers with isotopic abundances characteristic of the presence of metal atoms in the ion fragment clusters. All of the polymers exhibit good ability to inhibit all of the tested cancer cell lines but the zironocene and hafnocene polymers exhibit especially good inhibition of the tested cancer cell lines that included two pancreatic cancer cell lines. They represent a potential new group of anticancer drugs.Polyesters were formed from camphoric acid and Group IVB metallocene dichlorides employing the interfacial polycondensation process. IR, NMR and MLADI MS results are consistent with the proposed structure. Polymers exhibit outstanding ability to inhibit the tested cancer cell lines including two pancreatic cancer cell lines. They represent a potential new group of anticancer drugs.

Synthesis and Characterization, Including Cancer Cell Line Inhibition, of Group VA (Group 15)-Containing Polyesters from Reaction with Camphoric Acid

Polyesters were rapidly synthesized employing interfacial polymerization from reaction of the salt of camphoric acid with Group VA (Group 15) triphenylmetallic dihalides. Yields range from 25 to 46 percent with chain lengths about 250. Infrared spectroscopy shows the formation of two new bands one assigned to the symmetrical M–O stretching and the second assigned to the asymmetrical M–O stretching. The bridging structure about the metal atom increases as the metal atom size increases. MALDI MS and proton NMR are consistent with the formation of the polyester structure. Ion fragment clusters to four to six units are identified. The polymers show good inhibition of a group of cancer cell lines including two pancreatic human cancer cell lines. In comparison with other metal/camphoric acid polymers, the metallocene polymers exhibit low EC50 to the nanogram/ml range, and CI50 values greater than one thousand for the hafnocene and zirconocene products. If this trend continues, the emphasis should be on the Group IVB metallocenes with respect to efforts to create anticancer drugs.

Synthesis of poly(ether esters) from reaction of alpha-cyano-4-hydroxycinnamic acid and group IVB metallocenes

ABSTRACTPoly(ether esters) are rapidly synthesized in moderate yield employing the interfacial polycondensation reaction system from the reaction of alpha-cyano-4-hydroxycinnamic acid and Group IVB metallocenes. The products are high polymers. Infrared spectroscopy shows the formation of new bands derived from the M-O and M-O(CO) linkages. It also shows that the products exist as alternating M-O and M-O(CO) linkages. The products show outstanding inhibition of a variety of cancer cell lines including two pancreatic cancer cell lines. EC50 values for the polymers are in the nanogram/mL range. The ability to inhibit the cancer cell lines is generally Hf>Zr>Ti. Thus, future synthesis and testing might consider using compounds containing hafnocene and zirconocene in addition to the titanocene moiety.

Group IVB metallocene poly(ether ester) polymers containing alpha-cyano-4-hydroxycinnamic acid that act as self-matrix materials in MALDI MS

ABSTRACTPolymers derived from reacting Group IVB metallocene dihalides and the matrix alpha-cyano-4-hydroxycinnamic acid act as their own matrix agent when performing MALDI MS. Ion fragments containing two repeat units and greater are formed. The results are similar to those obtained employing graphite as the matrix material. The advantage of employing graphite as a comparative standard is that non-interfering ion fragment clusters are not produced by graphite. This is the second report of the inclusion of alpha-cyano-4-hydroxycinnamic acid into a condensation polymer and the use of the polymer itself as a matrix material indicating that this approach can be successfully applied to other systems. The addition of graphite as a matrix material allows the mass range to increase for the reflective mode.

The Mechanism of Ethylene Polymerization Reaction Catalyzed by Group IVB Metallocenes. A Rational Analysis Through the Use of Reaction Force

A density functional theory study of the ethylene polymerization mechanism catalyzed by metallocene methyl cations based on group IVB (Ti, Zr, and Hf) is presented. The concept called reaction force was applied in order to decompose the activation energy into two parts with the aim of distinguishing the predominance of structural or electronic effects within intervals along the reaction coordinate on each step of the polymerization process. This has implied an alternative rational analysis of elementary chemical reactions associated with the polymerization mechanism under the assumption that the Cossée–Arlman’s mechanism is operating along the whole process. Three reaction models representing elementary chemical reactions of the polymerization process (initiation, propagation, and termination) were used through molecular quantum mechanical calculations. The simplest of metallocene methyl cations (built up by two cyclopentadienyl groups and one methyl group linked to the metal) was used as a catalytic molecular model. Since the main goal was focused on getting information of intrinsic global reactivity of catalytic systems, both solvent and co-catalyst were not modeled in the present work. As a result, energy profiles indicate that ethylene polymerization reactions are better catalyzed by the respective metallocene cation based on Ti, whereas the catalysts based on Zr and Hf present similar characteristics among them, thus supporting experimental results where the molecular weight of polyethylene obtained by means of metallocene cation based on Ti approximately doubles the molecular weights of polyethylene catalyzed by metallocenes based on Zr and Hf. However propagation and termination steps are better catalyzed by metallocene complexes based on Zr and Hf, thus masking the influence of initiation step upon the molecular weight of the obtained polymer and providing more importance to termination step rather than propagation step. This would help to better understand differences presented in the average molecular weight of a same polymer obtained with each of these catalytic systems. As some key steps of the polymerization process would be more favored with one type of metallocene rather than other one, the use of reaction force would help to better understand how to modify energetic barriers and or global changes in energy by perturbating geometrical or electronic structure of catalytic systems. The latter suggests that the ideal polymerization process should be carried out with different catalytic systems depending on the step of polymerization and not with a unique catalyst as has been commonly performed up to now. That might lead to the obtention of a more wide range of new polymeric materials.

Ability of Group IVB metallocene polyethers containing dienestrol to arrest the growth of selected cancer cell lines.

BackgroundMonomeric Group IVB (Ti, Zr and Hf) metallocenes represent a new class of antitumor compounds. There is literature on the general biological activities of some organotin compounds. Unfortunately, there is little information with respect to the molecular level activity of these organotin compounds. We recently started focusing on the anti-cancer activity of organotin polymers that we had made for other purposes and as part of our platinum anti-cancer effort.MethodsFor this study, we synthesized a new series of metallocene-containing compounds coupling the metallocene unit with dienestrol, a synthetic, nonsteroidal estrogen. This is part of our effort to couple known moieties that offer antitumor activity with biologically active units hoping to increase the biological activity of the combination. The materials were confirmed to be polymeric using light scattering photometry and the structural repeat unit was verified employing matrix assisted laser desorption ionization mass spectrometry and infrared spectroscopy results.ResultsThe polymers demonstrated the ability to suppress the growth of a series of tumor cell lines originating from breast, colon, prostrate, and lung cancers at concentrations generally lower than those required for inhibition of cell growth by the commonly used antitumor drug cisplatin.ConclusionThese drugs show great promise in vitro against a number of cancer cell lines and due to their polymeric nature will most likely be less toxic than currently used metal-containing drugs such as cisplatin. These drugs also offer several addition positive aspects. First, the reactants are commercially available so that additional synthetic steps are not needed. Second, synthesis of the polymer is rapid, occurring within about 15 seconds. Third, the interfacial synthetic system is already industrially employed in the synthesis of aromatic nylons and polycarbonates. Thus, the ability to synthesize large amounts of the drugs is straight forward.

On the Triplet Nature of Excited States of Group IVB Metallocenes

On the Triplet Nature of Excited States of Group IVB Metallocenes

Condensation Metallocene Polymers

The synthesis, characterization, and application of a wide variety of metallocene and metallocene-like polymers and oligomers is described. Much of this effort involves the Group IVB metallocenes, but the work of vanadium and ruthenium are also included. The use of these materials as analytical reagents, laser modifiers, and in solar energy conversion is described.

Phosphorescent ligand-to-metal charge-transfer excited states in the group IVB metallocene triad

Long-lived ligand-to-metal charge transfer (LMCT) excited states based on a zirconium complex (ca. 2000 μs) and a hafnium complex (ca. 300 μs) are first characterised with use of the Cp 2Zr(IV)Cl 2 and Cp 2Hf(IV)Cl 2. The tendency in the observed photophysics (absorption and phosphorescence spectra, lifetimes, and quantum yields) in the homologous group IVB metallocenes Cp 2M(IV)Cl 2 is discussed in view of the nature of the unique metal (Ti, Zr or Hf)–ligand π-bonding character.

Porphyrazinediols: Synthesis, Characterization, and Complexation to Group IVB Metallocenes.

The first metalated porphyrazinediols 11 have been prepared from (L)-(+)-dimethyl tartrate via conversion into the corresponding dispoke or 2,3-dimethoxy-2,3-butanediyl protected 2,3-dihydroxymaleonitrile, Linstead macrocyclization, transmetalation, and deprotection. Their stability is very dependent on the nature of the metal ion in the cavity of the porphyrazine. Reaction of these porphyrazinediols with metallocene dichlorides led to new solitaire porphyrazines 12 while DDQ oxidation followed by trapping with diaminomaleonitrile afforded new porphyrazine dinitriles 14.

Detection of B(C6F5)4 anions in polyethylenes made with ionic metallocene catalysts

Polymerization of olefins with Group IVB metallocenes (Ti, Zr, Hf) activated with ionic activators such as [dimethylanilinium] [B(C6F5)4] or neutral Lewis acids such as B(C6F5)3 is widely accepted to proceed via ionic catalysts, wherein the coordinatively unsaturated cation—with metal in the+4 oxidation state—is stabilized by a weakly coordinating anion [1, 2]. Evidence for the presence of the anion(s) following metallocene activation, but prior to polymerization, is abundant [3– 6]. Theoretical calculations regarding the Group IVB active site and the olefin insertion process are invariably based on cationic structures [7, 8]. However, the fate of the anions and cations throughout any given polymerization is not generally known. This is an important question because changes in anion structure, or loss of anion during polymerization could contribute to the activity profile, depressing polymerization over time, account for time and temperature dependent changes in polymer product structure (eg. molecular weight, comonomer response), and affect product properties. In this study, the fate of a key weakly coordinating anion—[B(C6F5)4]−—following commercial production of ethylene copolymers at high temperature and pressure has been determined independently by ToFSIMS [9] and LDMS [10]. The polymers selected have narrow melting distributions, narrow composition distributions, and narrow molecular weight distributions (MWD∼2.0). These three properties lend credence to the term “single site catalyst”, and suggest that the catalyst—and anions—persist, essentially unchanged, during the time each ethylene copolymer is produced. There are notable precedents to this work. Erker and coworkers have shown that reaction of (Cp)2Zr(1,3 butadiene) (Cp=C5H5 ) with one equivalent of B(C6F5)3 generates an active olefin polymerization catalyst. These workers used laser desorption mass spectrometry (LDMS), to identify oligomer anions [R-B(C6F5)3]−, where R is (C4H6)(C3H6)n(C3H7) (n∼5–26 in the example published), in the propylene polymerization product (toluene diluent, 50 ◦C and one atm) [11]. The mass spectral signature of these anions in the polypropylene product is striking and unique. On the other hand, it is well known that these ionic catalysts are readily poisoned by trace impurities. Aluminum alkyls are commonly added to “scavenge” such impurities and so protect the active site. Bochmann and Sarsfield have shown [12] that [B(C6F5)4]− anions can react with trimethylaluminum and AlBu3 to generate Al-C6F5 species. Such reactions can lead to new catalyst species with different anions or to loss of catalytic activity. In many cases, addition of larger quantities of these alkyls can have an adverse impact on metallocene catalyzed polymerizations. The polyethylenes analyzed are produced using metallocene activated with a [dimethylanilinium][tetrakis (perfluorophenyl)borate] salt. A list of the five commercial products used for this study is provided in Table I. All mass spectra were recorded using a PHI-Evans triple sector electrostatic analyzer time-of-flight mass spectrometer equipped with a pulsed liquid metal ion source (115In) for time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis and a nitrogen laser (λ= 337 nm) for laser desorption mass spectrometry (LDMS) analysis. ToF-SIMS were obtained operating the ion gun at 15 keV and 600 pA. For LDMS, 100– 300 laser shots were used to acquire the spectrum. Laser power was ∼1011 W/m2. Mass calibration was carried out using a variety of known standards. With this instrument configuration, both ToF-SIMS and LDMS can be obtained on the same sample. Analysis results from these two measurements can be compared directly. The resin samples were prepared using two different sample preparation protocols: 1) one polymer pellet (∼30 mg) was placed in a glass vial containing 10−5 m3 (10 ml) of toluene and the mixture heated to 90 ◦C. After extraction for 3 min, approximately 10−9 m3 (1μl) of the solution is deposited on a sample substrate (clean Si wafer). The solvent was evaporated in air and the wafer with extracted material was then inserted into the instrument for mass spectral analysis. 2) The pellet is cross-sectioned to expose the interior of the pellet. A slice of the pellet cross-section is inserted into the instrument and the freshly exposed surface analyzed directly.

Polymerizations of Alkenylsilanes Using Early Transition Metal Catalysts

ABSTRACTOxidative coupling of primary alkylsilanes catalyzed by Group IVB metallocene complexes leads predominantly to linear polysilanes, as first reported by Harrod. We have investigated the polymerization of ethylsilane and vinylsilane using dimethyltitanocene in order to determine the suitability of such polymers as precursors to Si-C based ceramics for application as coatings or composite matrices. A photochemical procedure for initiation of polymerization is described. Ethylsilane forms polysilanes (which contain a -Si-Si-Si-Si- backbone) by a step growth mechanism. Vinylsilane shows some Si-Si formation; however, polymerization by several different routes, including formation of polycarbosilanes (which contain a -Si-C-SI-C- backbone) by hydrosilation reactions and crosslinking via metathesis, predominate. The carbosilane polymer has high char yield (60-75%) and appears advantageous for conversion into silicon carbide, as determined by X-ray diffraction.