Presence Of AlMe3 Research Articles

Synthesis of N-substituted amidinoheteroles and their reactivity towards Burgess reagent

N-Substituted amidinoimidazoles and amidinopyrroles were synthesized by the reaction of 2-cyanoimidazole and 2-cyanopyrrole with the corresponding ammonium salts in the presence of AlMe3 in toluene under reflux conditions. With the aim to investigate the transformation of the N-substituted amidino group to isonitrilium ion, N-mesitylamidinoimidazole and N-diisopropylphenylamidinopyrrole were allowed to react with the Burgess reagent. Instead of the desired deamination product, 1,2,4,6-thiatriazinone 1,1-dioxides were produced, which are heterocycles containing a part of the Burgess reagent and the K-area of amidinoheteroles.

Effect of AlR3 (R = Me, Et, iBu) addition on the composition and microstructure of ethylene/1-olefin copolymers made with post-metallocene complexes of group 4 elements

The effect of trialkylaluminum compound (AlR3, where R = Me, Et, iBu) addition on the performance of the [LigZrCl]2(μ-O)/AliBu3/Ph3CB(C6F5)4 and LigTiCl2/AliBu3/Ph3CB(C6F5)4 (Lig = Me2N(CH2)2N(CH2-2-O-3,5-tBu2-C6H2)2) catalysts in ethylene/1-olefin copolymerization was investigated. The presence of AlMe3 in the feed during the copolymerization process catalyzed by the diamine-bis(phenolate) zirconium catalyst greatly increases the amount of incorporated comonomer and leads to microstructural changes, e.g., the formation of blocky and alternating sequences of 1-olefin units. Moreover, the use of AlMe3 limits the reaction yield and decreases the molecular weight of the produced copolymers. The catalytic properties of the diamine-bis(phenolate) titanium catalyst were much less affected by trimethylaluminum; its use slightly decreased the catalyst activity and copolymer molecular weight. A lower molecular weight was also detected for the copolymers produced by catalysts in the presence of both AlEt3 and AliBu3, whereas they did not cause any important changes in the catalytic activity, overall composition or microstructure of the produced copolymers. Copolymerization tests with other catalytic systems, (LigFI)2ZrCl2/AliBu3/Ph3CB(C6F5)4 (LigFI = (C6H5)N = CH(2-O-3,5-tBu2-C6H2)) and Et(Ind)2ZrCl2/MMAO, in the presence of AlMe3, were also carried out for the purpose of comparison. The effect of trialkylaluminium compound (AlR3, where R = Me, Et, iBu) addition on the performance of the transition metal complex/AliBu3/Ph3CB(C6F5)4 catalysts in ethylene/1-olefin copolymerization was investigated. It was shown that AlR3 may affect the catalytic properties of the system (activity, comonomer incorporation, and copolymer microstructure). This influence is dependent on the type of organoaluminum compound and on the structure of the complex, i.e., on the structure of the ligand and on the type of transition metal.

Isoprene Regioblock Copolymerization: Switching the Regioselectivity by the in Situ Ancillary Ligand Transmetalation of Active Yttrium Species

Regioblock copolymers of single alkenes hold great promise for modifying the properties of polymer materials but remain scarce due to the lack of viable synthetic methodologies. Here we describe a method for switching the regioselectivity of the cationic yttrium-catalyzed polymerization of conjugated dienes during chain growth, which leads to the formation of a series of di- and multiregioblock homo/mixed-copolymers with different properties from isoprene and myrcene. Mechanistic data demonstrate that the amidinate yttrium active species [LbYPIP3,4]+ (Lb = [PhC(NC6H4iPr2-2,6)2]−) changes to the tetramethylaluminate yttrium active center {LsYPIP3,4}+ (Ls = [AlMe4]−) in situ by amidinate ligand transfer in the presence of AlMe3. The transformation of active species switches the regioselectivity from 3,4- to cis-1,4 polymerization while the polymer chain keeps propagating. AliBu3 not only functions as a chain transfer agent but also plays a key role in preventing the chain termination during the amidinate tr...

Yttrium and Aluminum Alkyl Complexes of a Rigid Bis-Anilido NON-Donor Ligand: Synthesis and Hydroamination Catalysis

The palladium-catalyzed coupling of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene (XBr2) with 2 equiv of 2,4,6-triisopropylaniline afforded the proligand 4,5-bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H2XN2), and reaction of H2XN2 with [Y(CH2SiMe2R)3(THF)2] (R = Me, Ph) produced the monoalkyl yttrium complexes [(XN2)Y(CH2SiMe2R)(THF)] (R = Me (1a), Ph (1b)). Neutral 1a showed near-zero ethylene polymerization activity (1 atm, 20 and 80 °C), and in the presence of AlMe3, 1a converted to [(XN2)Y{(μ-Me)2AlMe2}(THF)] (2). Compound 2 is thermally robust, and transfer of the XN2 ligand from yttrium to aluminum was not observed even at elevated temperatures. However, [(XN2)AlMe] (3) was accessible via the reaction of H2XN2 with AlMe3, demonstrating the ability of the wide-bite-angle XN2 ligand to coordinate to much smaller aluminum(III). Neutral 1a proved to be highly active for both intra- and intermolecular hydroamination with various substrates, yielding Markovnikov products i...

Trimethylaluminium‐Mediated Reaction of Primary Carboxamides with Amines and Indoles: A Convenient Synthesis of Amidines and Indole‐3‐acylimines

AbstractA simple, convenient and general method, exhibiting good functional group tolerance, is described for the synthesis of N‐ and N,N‐disubstituted amidines by the reaction of primary carboxamides with amines mediated by trimethylaluminium (AlMe3). Subsequent reaction of the indole systems with primary carboxamides in the presence of AlMe3 gives exclusively the C‐3 substituted imine product.

ChemInform Abstract: Unsymmetrical Tetrasubstituted Ureas from Tertiary Carbamoylimidazole: Activation by AlMe3.

AbstractA general and efficient access towards unsymmetrical urea derivatives is presented, involving the amination of carbamoylimidazoles in the presence of AlMe3.

Cationic Alkylaluminum-Complexed Zirconocene Hydrides as Participants in Olefin Polymerization Catalysis

The alkylaluminum-complexed zirconocene trihydride cation [(SBI)Zr(μ-H)(3)(Al(i)Bu(2))(2)](+), which is obtained by reaction of (SBI)ZrCl(2) with [Ph(3)C][B(C(6)F(5))(4)] and excess HAl(i)Bu(2) in toluene solution, catalyzes the formation of isotactic polypropene when exposed to propene at -30 °C. This cation remains the sole observable species in catalyst systems free of AlMe compounds. In the presence of AlMe(3), however, exposure to propene causes the trihydride cation to be completely converted, under concurrent consumption of all hydride species by propene hydroalumination, to the doubly Me-bridged cation [(SBI)Zr(μ-Me)(2)AlMe(2)](+). The latter then becomes the resting state for further propene polymerization, which produces, by chain transfer to Al, mainly AlMe(2)-capped isotactic polypropene.

Synthesis of novel 5-hydroxyalkenylphosphonates by addition of aromatic aldehydes to zirconacyclopentenylphosphonates

Novel 5-hydroxyvinylphosphonates were obtained in a regio- and stereoselective manner, by addition of aromatic aldehydes to zirconacyclopentenylphosphonates in the presence of AlMe3, in 68–82% isolated yields. The reaction is specific for aromatic aldehydes.

Monotitanocene catalysts: an ESR study of Ti(III) derivatives formed in presence of MAO and other organoaluminium compounds

Mixtures of monocyclopentadienyltitaniumtrichloride derivatives [Cp′TiCl3, Cp′=C5H5=Cp (1), C5Me5=Cp∗ (2), Me=CH3] and methyl-aluminoxane (MAO), well known catalytic systems for olefins, styrene and dienes polymerisation, were characterised by ESR spectroscopy. The assignment of the observed signals to defined structures was carried out by comparison with the systems: 1, 2/AlMe3; 1/Al(iso-butyl)2hydride, 2/AlEt3, 2/AlMe3/[CPh3][B(C6F5)4]. In all the analysed mixtures titanium is partially reduced to the trivalent state and, generally, 1 shows a higher tendency to reduction than 2. At low Al/Ti ratio (R=10) both in the presence of AlMe3 or MAO, 1 and 2 produce similar Ti(III) compounds: the bimetallic trinuclear complex Cp′Ti[(μ-Cl)2AlMe2]2 (A and A∗ for 1 and 2, respectively). At higher ratio (R=300, 500), new species are observed, at higher g-values, compatible with a alkylation of the metal centre. In the system 1/MAO a rather unstable new species C appears initially at g=1.977, and is progressively converted to a stable titanium hydride compound (D). In the system 2/MAO (R=300, 500) the species C∗ (g=1.975) and C1∗ (g=1.977) are observed. C∗ and C1∗ form in the system Cp∗TiCl3/AlMe3/[CPh3][B(C6F5)4] as well, i.e. in the presence of the ionising agent [CPh3][B(C6F5)4], which is also employed to activate the half-metallocene precursors for styrene polymerisation, pointing to the formation of common species in the two catalytic systems.