Dimethyl Aluminum Research Articles

Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands

This paper describes a substantial enhancement of the aminopyridinato ligand stabilized early transition metal chemistry by introducing the sterically very demanding 2,6-dialkylphenyl substituted aminopyridinato ligands derived from (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridin-2-yl]-amine ( 1a– H, ApH) and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridin-2-yl]- amine ( 1b– H, Ap ∗H). The corresponding bis aminopyridinato zirconium dichloro complexes, [Ap 2ZrCl 2] ( 3a) and [Ap 2 ∗ZrCl 2] ( 3b) and the dimethyl analogues, [Ap 2ZrMe 2] ( 4a) and [Ap 2 ∗ZrMe 2] ( 4b) (Me = methyl) were synthesized, using standard salt metathesis routes. Single-crystal X-ray diffraction was carried out for the dichloro derivatives. Both zirconium metal centers have a distorted octahedral environment with a cis-orientation of the chloride ligands in 3a and a closer to trans-arrangement in 3b. The dimethyl derivatives are proven to be highly active ethylene polymerization catalysts after activation with [R 2N(Me)H][B(C 6F 5) 4] (R = C 16H 33–C 18H 37). During attempted co-polymerizations of α-olefins (propylene) and ethylene high activity and selectivity for ethylene and nearly no co-monomer incorporation was observed. Increasing the steric bulk of the ligand going from (2,6-dimethylphenyl) to (2,4,6-triisopropylphenyl) substituted pyridines, switches the catalyst system from producing long chain α-olefins to polymerization of ethylene in a living fashion. In contrast to the dimethyl complexes only [Ap 2 ∗ZrCl 2] in the presence of MAO at elevated temperature gave decent polymerization activity. NMR investigations of the reaction of dichloro complexes with 25 equiv. of MAO or AlMe 3 at room temperature revealed, that [Ap 2ZrCl 2] decomposes under ligand transfer to aluminum and formation of [ApAlMe 2], while [Ap 2 ∗ZrCl 2] remains almost unreacted under the same conditions. The aminopyridinato dimethyl aluminum complexes, [ApAlMe 2] ( 5a) and [Ap ∗AlMe 2] ( 5b) were synthesized independently and structurally characterized. The aluminum complexes 5a and b show no catalytic activity towards ethylene, when “activated” with[R 2N(Me)H][B(C 6F 5) 4].

The synthesis and characterization of germanium dichloride and dimethyl aluminium chloride derivatives of the 2,2-dipyridylamine ligand

The reactions of germanium dichloride and dimethyl aluminium chloride with 2,2-dipyridylamine (dpa) affords germanium and organo-aluminium complexes. Structural characterization reveals that the preferential coordination site of both germanium and aluminium is within the sterically protected pyridyl, (pyridyl = C5H5N = py), pocket. Py2NGeCl, compound (1), crystallizes in the triclinic space group, P-1, with cell coordinates; a=8.2956(11), b=9.9938(13), c=12.6517(17), α=92.033(2)°, β=92.834(2)°, γ=91.685(2)°. The aluminium complex, Py2NAlMe2·Al(Me)Cl, (2), crystallizes in the orthorhombic space group, Pna2(1), with cell parameters: a=13.3707(10), b=10.8706(8), c=16.1306(12). The X-ray analysis of the side products of these reactions, the lithium halide adducts are also reported.

Investigation of ion pair formation in the triphenylmethyl chloride–trimethyl aluminium system, as a model for the activation of olefin polymerization catalyst

Triphenylmethyl chloride (“trityl chloride”, Ph 3CCl) will transfer chloride ions to aluminium alkyls and methylaluminoxane and it is thereby converted into 1,1,1-triphenylethane (“trityl methyl” Ph 3CMe) and the triphenylcarbonium ion (“trityl ion”, Ph 3C +). IR spectra of these trityl species have been recorded. Assignments are supported by quantum chemical calculations, leading to significant revisions for some of the modes that are most influenced by reactions. A bright yellow colour shown to be due to the trityl cation, makes trityl chloride a useful indicator for ion pair formation. Trimethyl aluminium (TMA) is chlorinated by trityl chloride and forms dimethyl aluminium chloride (DMAC). DMAC will form a stable ion pair with trityl chloride, probably by forming the anion Al 2Cl 3Me 4 −. Large excess of trityl chloride causes the formation of AlCl 4 −, and probably AlCl 3Me − and AlCl 2Me 2 − anions. It appears that methyl aluminium chloride anions are formed if, and only if, the anions have at least three chlorine atoms, possibly because of the need to dissipate the negative charge enough to keep the anion dissolved in the hydrocarbon solvent. Methylaluminoxane (MAO) also forms ion pair with trityl chloride, although to lesser extent and less persistent.

Avaliação da capacidade adjuvante do cloreto de dimetildioctadecilamônio associado ao hidróxido de alumínio na indução da resposta imune humoral de bovinos vacinados com o vírus da diarréia viral bovina

The humoral immune response of cattle vaccinated with inactivated bovine viral diarrhea virus (BVDV) using the association of dimethyl dioctadecyl ammonium chloride (DDA-chloride) and aluminum hydroxide (vaccine B) as adjuvant, was compared with the same antigenic formulation adsorbed with only aluminum hydroxide (vaccine A). The neutralizing antibodies titers were assessed two weeks after the second vaccine dose. The animals that received vaccine B had better humoral responses than the calves vaccinated with vaccine A. The mean titers of neutralizing antibodies, expressed in Log2, for the calves that received vaccine B was higher to those observed in group vaccinated with vaccine A. These results show that the inclusion of DDA chloride in vaccine formulations adsorbed with aluminum hydroxide determine a better humoral immune response in cattle vaccinated with BVDV inactivated.

Synthesis and structure of four-coordinate dimethyl aluminium complexes incorporating new N,O-chelating arylamido ligands

A new type of arylamido ligands with an intramolecular coordinating ortho-ether-substituent (i.e. a O,N − chelating ligand) is introduced. The achiral and chiral 4-coordinate dimethyl aluminium complexes [2-ROC 6H 4NR′]AlMe 2 ( 4a: R=R′=Cy; 4b: R=(−)-menthyl, R′=Cy, 4c: R=(−)-menthyl, R′=CPh 3) have been prepared by reaction of the appropriate amido Li salt with ClAlMe 2. Complex 4a could also be obtained, via methane elimination, by reaction of AlMe 3 with the corresponding ligand. The presence of two rotamers in solution at room temperature for 4b and for 4c is most likely due to a restricted rotation of the (−)-menthyl group at this temperature due to severe steric interactions with the rest of the complex.

A cationic aluminum methyl complex supported by an anionic tacn ligand

Reaction of (tacn)H [(tacn)H=1,4-diisopropyl-1,4,7-triazacyclononane] with AlMe 3 leads to the formation of the thermally stable adduct [(tacn)H]·AlMe 3 ( 1). The dimeric aluminum dimethyl complex [(tacn)AlMe 2] 2 ( 2) was obtained by metathesis of (tacn)Li 2 with two equivalent of Me 2AlCl in toluene at 80 °C. In 2 the anionic nitrogen atoms bridge the two AlMe 2 units while the neutral amino atoms are free of coordination. Treatment of 2 with 2 equiv. of B(C 6F 5) 3 in CH 2Cl 2 yielded a well separated ionic aluminum methyl borate complex [((tacn)AlMe) 2][MeB(C 6F 5) 3] 2 ( 3), featuring five-coordinate aluminum centers. Molecular structures of 2 and 3 were determined by single-crystal X-ray crystallography.

Variable coordination chemistry of the phospha(III)guanidinate anion; application as a metal-functionalised phosphine ligand.

Structural investigation of Li-complexes of the phospha(III)guanidinate anion [Ph2PC[NiPr]2]- revealed variable coordination to lithium; synthesis of the dimethyl aluminium compound, (Ph2PC[NiPr]2)AlMe2, which behaves as a metal-functionalised phosphine ligand towards platinum, is reported.

Synthesis and Characterization of Organoaluminum Complexes Containing Bi- or Tridentate-Substituted Pyrrole Ligands

Reactions of AlCl3 with 1 equiv of Li{C4H2N(CH2NMe2)2-2,5} or 2 equiv of Li{C4H3N(CH2NMe2)-2} in diethyl ether at −78 °C afforded AlCl2{C4H2N(CH2NMe2)2-2,5} (1) and AlCl{C4H3N(CH2NMe2)-2} (2), respectively. Alkylation of 1 with MeLi in diethyl ether generates the aluminum dimethyl complex 3. Compound 2 is thermally unstable and was converted to uncharacterized product in CHCl3 within 2 days at 80 °C. Compounds 1, 2, and 3 were characterized by NMR spectroscopy and X-ray structure determination.

Novel Metal Complexes Containing 1-Azaallyl and β-Diketiminato Ligands

The bis[β-diketiminato(dimethyl)aluminium] complex {Me2Al[N(R)C(Ar)]2CH}2CH2 (Ar = C6H4Me-4, R = SiMe3) 1 and the bis[lithium β-diketiminate]s {Li[N(R)C(Ar)]2CH}2CH2 2(Ar = C6H5) and 3 (Ar = C6H4Me-4) were prepared and fully characterised. The X-ray structures of 1 and 2 are reported, showing different features; 2 has the unexpected fused bicyclic structure of two 8-membered rings. The adamantyl-substituted lithium 1-azaallyl complex {Li[N(R)C(Ad)C(H)R]}2 4 and the lithium β-diketiminates {Li[N(R)C(Ad)C(H)R]}2 5 (Ar = C6H5) and 6 (Ar = C6H4Me-4) were synthesised. Each was reacted either with AlMeCl2 (for 4) or AlMe2Cl (for 5), yielding the aluminium derivatives MeAl[N(R)C(Ad)C(H)R][N(R)C(Ad)=C(H)R] 7 and Me2Al[N(R)C(Ad)C(H)C(Ar)N(R)] 8, respectively.

An Alternative Approach to Al2O2 Ring Systems by Unexpected Cleavage of Stable Al−F− and Si−O− Bonds

The reaction of dimethyl aluminum fluoride (Me2AlF, DMAF) with 2,6-diisopropylphenol and triethylcitrate, respectively, leads to the products (RO)6Al4F2Me4 (R = 2,6-i-Pr2C6H3) (1) and (ROAlFMe)2 (R = C(CH2COOEt)2(COOEt)) (2), containing Al2O2 ring systems. Both aluminum-μ-oxo fluorides have been structurally characterized. Fluorine exchange in the reaction of 2,6-diisopropylphenol with DMAF has been monitored using 19F NMR spectroscopy. The proposed processes in solution are confirmed by the solid-state structure of 1. Compound 1 contains four aluminum centers forming three four-membered ring systems. The two outer cycles consist of bridging −OR groups, whereas the aluminum atoms in the central cycle are connected via fluorine atoms. Two of the aluminum atoms are 4-fold coordinated, and two are 5-fold coordinated. Compound 1 contains a rare four-membered Al2F2 ring system. Compound 2 exhibits a dimeric structure, with oxygen rather than fluorine atoms bridging the aluminum atoms. A further carboxy oxygen atom binds coordinatively to one aluminum atom in 2. The aluminum atoms are 5-fold coordinated. In search of an alternative approach to synthesizing Al2O2 ring systems, it has been found that neither DMAF nor trimethyl aluminum (Me3Al, TMA) reacts with (Me3Si)2O, whereas the reaction of diisobutyl aluminum hydride (i-Bu2AlH, DIBAH) with (Me3Si)2O leads to (i-Bu2AlOSiMe3)2 (3). In compound 3 the aluminum centers in the four-membered Al2O2 ring system are only 4-fold coordinated. This is the first example of a structurally characterized aluminum product obtained from (Me3Si)2O under cleavage of the Si−O bond.

Orientation of aluminum nuclei on Si(100) and Si(111)

Aluminum has been deposited by chemical vapor deposition from dimethyl aluminum hydride onto silicon. Deposition conditions were chosen such that the deposition was selective onto silicon with respect to silicon dioxide. The crystal orientation of the nuclei has been studied. It is shown that on Si(100) the preferred mode of growth for the aluminum nuclei is Al(111).

Synthesis, Structure, and Reactivity of β-Diketiminato Aluminum Complexes

The preparation and reaction chemistry of β-diketiminato aluminum complexes are described. (TTP)AlCl2 (1) (TTPH = 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene) is formed by the treatment of AlCl3 with LiTTP. Sequential alkylation of 1 with CH3Li results in the formation of the mono- and dimethyl aluminum complexes (TTP)AlMeCl (2) and (TTP)AlMe2 (3), respectively. Only monoalkyl complexes are produced when more hindered alkyllithium reagents are used. Compounds 2 and 3 are more conveniently prepared by treating Al(CH3)3 with TTPH·HCl and TTPH, respectively. The more sterically hindered β-diketimine ligand 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene (DDPH) also reacts smoothly with Al(CH3)3 to yield (DDP)Al(CH3)2 (4). Compound 3 undergoes methyl abstraction reactions upon addition of B(C6F5)3 or AgOTf. Cationic species formed from 3 and B(C6F5)3 are unstable and decompose to (TTP)Al(CH3)(C6F5) and MeB(C6F5)2. In contrast, (TTP)Al(CH3)(OTf) (6) is thermally stable, but the trif...

Integrated CVD–PVD Al plug processing for sub-half micron features

We have successfully integrated Al plugs into a 0.25- μm CMOS flow using two different chemical vapor deposition (CVD) Al metallization process schemes. Both process schemes utilized CVD Al grown from dimethyl aluminum hydride (DMAH) followed by physical vapor deposition (PVD) Al–Cu deposition at a wafer temperature of less than 400°C. One process consisted of a 600-Å CVD Al liner followed by PVD Al–Cu and in situ reflow. The second process involved deposition of 2000 Å of CVD Al to fill the vias and blanket PVD Al–Cu to provide copper doping. Analysis of morphology, texture, and grain size revealed a strong dependence on the nucleation layer, with Ti nucleation layers demonstrating the smoothest Al morphology and strongest Al(111) preferred orientation. While the CVD TiN layers yielded a larger grain size than the PVD layers, Al films on CVD TiN had a random grain orientation with no preferred texture. While the reflow process produced repeatable void-free fill on contacts and vias with aspect ratios >3:1, the blanket process was prone to occasional voiding. Mean via and contact resistances for wafers processed through a 0.25- μm CMOS flow using the CVD–PVD reflow process were 1.91 Ω and 1.56 Ω, respectively, with lower resistance and tighter distributions than W in both cases. For the contact level process, reverse bias diode leakage was comparable to W. Based on the blanket film properties, robust fill, and electrical performance, the CVD Al/PVD Al–Cu reflow process is a potential replacement for the current W plug process.

Quantum chemical study on aluminum selective CVD reaction mechanism

Recently, aluminum (Al) selective chemical vapour deposition (CVD) on the silicon (Si) surface has received much attention as promising technology for ULSI metallization. The key issue is using a dimethyl aluminum hydride (DMA1H) over the Si surface terminated by hydrogen (H). In this quantum chemical study, we discuss the reaction mechanism. The reaction of AlAl bond formation occurs prior to AlSi bond formation. The methyl group has an effect which suppresses the reactivity between Al and Si. Moreover, H 2 carrier gas increases the reactivity. These results are qualitatively in agreement with the experimental observations.

Adjuvant modulation of immune responses to tuberculosis subunit vaccines.

Mice were immunized with experimental subunit vaccines based on secreted antigens from Mycobacterium tuberculosis in a series of adjuvants, comprising incomplete Freund's adjuvant (IFA), dimethyl dioctadecyl ammoniumbromide (DDA), RIBI adjuvant, Quil-A saponin, and aluminum hydroxide. Immune responses induced by these vaccines were characterized by in vitro culture of primed cells, PCR analysis for cytokine mRNA, detection of specific immunoglobulin G isotypes induced, and monitoring of protective immunity to tuberculosis (TB). The study demonstrated marked differences in the immune responses induced by the different adjuvants and identified both IFA and DDA as efficient adjuvants for a TB subunit vaccine. Aluminum hydroxide, on the other hand, induced a Th2 response which increased the susceptibility of the animals to a subsequent TB challenge. DDA was further coadjuvanted with either the Th1-stimulating polymer poly(I-C) or the cytokines gamma interferon, interleukin 2 (IL-2), and IL-12. The addition of IL-12 was found to amplify a Th1 response in a dose-dependent manner and promoted a protective immune response against a virulent challenge. However, if the initial priming in the presence of IL-12 was followed by two booster injections of vaccine without IL-12, no improvement in long-term efficacy was found. This demonstrates the efficacy of DDA to promote an efficient immune response and suggests that IL-12 may accelerate this development, but not change the final outcome of a full vaccination regime.

Potential of site specific photochemical processing using synchrotron radiation

An absorption spectrum in the vacuum ultra violet region and a photoelectron spectrum for the valence-electron-states of the gas phase dimethyl aluminum hydride (DMAH) were measured and the energy levels of the DMAH electronic states were determined. Using this result, it was concluded that the difference of the carbon contamination in photo-stimulated Al deposition between white beam synchrotron radiation and MgK α line irradiations is due to the difference of the reaction channels induced. The MgK α line irradiation excites valence electron-states, mainly π CH 3 states, and breaks the CH bond. On the other hand, in the case of SR irradiation, not only valence-electron-states, but also Al2p and Al2s core-electron states are excited and the AlC bond is broken. This indicates the usefulness of the photochemical site-specific processing.

CVD AL for advanced interconnect applications

A method for depositing low resistivity, high purity aluminum films by Chemical Vapor Deposition (CVD) is introduced. Pyrolysis of Dimethyl Aluminum Hydride (DMAH) using either H 2 or an inert gas as a carrier is shown to yield films with less than 0.01 at.% carbon and oxygen and resistivities of 3.0 μΩcm. The kinetics are exponentially temperature dependent with E act ∼ 0.5 eV independent of substrate. Introduction of some possible byproducts indicate that the deposition mechanism may be self reduction of DMAH. The morphology, wettability, and step coverage of the films are shown to depend strongly on the nature of the substrate and how it is integrated with the CVD Al process. Clustering of CVD Al with the deposition of the underlying liner is shown to be critical in achieving the highest quality films. Smooth, highly 〈111〉 oriented films with excellent reflectivity may be obtained. Some methods for Cu doping are discussed including a novel form of in situ deposition. Complete via fill is obtained with blanket depositions with one or two grains filling the vias in most cases. Vias as high as 3.5:1 aspect ratio are filled—sometimes with a single grain of Al. Electrical results indicate that the via resistances and electromigration resistance of the Al plugs are excellent.

Low Pressure CVD Growth of AlxTi1-xN Films with Tetrakis- (Dimethylamido)Titanium (Tdmat) and Dimethyl Aluminum Hydride (DMAH) Precursors

ABSTRACTAlxTi1-xN film growth has been studied by a organometallic chemical vapor deposition andin-situX-ray photoelectron spectroscopy. Terakis(dimethylamido)titanium (TDMAT) and dimethyl aluminum hydride (DMAH) were used as the Ti, N and Al precursors. AlTiN film growth was observed on SiO2/Si(100) with substrate temperatures between 200 and 400 °C. The Al content in the film is controlled by the ratio of partial pressures of the two precursors in the gas phase. The metal to C to N ratio is approximately constant at 1:1:1 for most conditions studied. The chemical states of Ti, C, and N in AlxTi1-xN and titanium-carbo-nitride (TiCN) films are identical, while the Al chemical state is nitride at low, but increasingly carbidic at high Al concentration. The initial growth rate on SiO2was significantly suppressed by the presence of DMAH. At lower growth temperatures, the DMAH effect is more severe. Good step coverage was observed for AlxTi1-xN on 0.3 μm vias with a 3:1 aspect ratio.

Carbon Contamination in Synchrotron-Radiation-Stimulated Al Deposition Using a Low Temperature Condensed Layer of Dimethyl Aluminum Hydride

The carbon contamination in photochemically deposited Al films fabricated using non-monochromatized synchrotron radiation (SR) and Mg Kα line (1253.6 eV) irradiation were compared by X-ray photoelectron spectroscopy (XPS) analysis. The excitation energy dependence of the carbon contamination, especially the effects of core electron excitations, in the photo-CVD of Al using a low-temperature condensed layer of dimethyl aluminum hydride was determined using XPS spectra and gas-phase photo absorption cross section spectra. A significant decrease of the carbon contaminations was observed in the films fabricated using SR irradiation, which can excite Al 2s and Al 2p core electrons as well as the valence electrons, while no change was observed in the films fabricated using Mg Kα line irradiation. This is explained by the fact that core electron excitation breaks the Al–C bonds site-specifically.

Photon energy dependence of synchrotron radiation induced growth suppression and initiation in Al chemical vapor deposition II. Surface analysis by Auger electron spectroscopy

We analyzed the photochemical reaction of dimethyl aluminum hydride on Si and SiO 2 surfaces as a function of photon energy using synchrotron radiation. Al LVV chemical shifts in the Auger electron spectra were clearly different, depending on whether core or valence electrons were excited. When high-energy photons were used to excite the core electrons, aluminum carbide was formed on the Si surface. On the other hand, when low energy photons, which can only excite valence electrons, were utilized, metallic aluminum was formed on the Si and SiO 2 surfaces. These results were consistent with the previously reported photon energy dependence of CVD characteristics. That is, when AlC was formed with core electron excitation, growth was suppressed, and negative projection patterning was achieved. On the other hand, when Al was formed with valence electron excitation, growth was initiated and positive patterning was performed on the SiO 2 surface. We proposed a model which explained how the Al growth was controlled by the surface layers formed by photochemical reaction, and why growth suppression and initiation changed with the excitation photon energy.