Alkoxy Aluminum Catalyst

The alkoxy aluminum complexes 64-68 were utiHzed as the initiators for PLA synthesis with relatively controlled values and low polydisper-sity indexes (PDIs) (Table 6.10) [56]. 

Aluminum complexes 69-74 were synthesized easily in high yields under mild conditions by combining 1.0 equivalent of trimethylaluminum and the 

Conditions monomeninitiater ratio 100 1( 1 BnOH if required) solvent toluene, temperature 80°C. Determined from H NMR analysis. Determined from GPC analysis using THF as the solvent and reference to polystyrene standards. Determined from the analysis of the methane region of the H homonuclear decoupled NMR spectrum. 

All aluminum complexes were investigated as catalysts for the ROP of l-LA and rac-LA (Table 6.11). These aluminum complexes showed moderate to high activities (81.6-93.0% conversion) with the cocatalysts 2-propanol at 70°C. It is worth noting that the activities of these complexes decreased with the increase in substituent size on the benzene rings, while electron-withdrawing substituents raising the polymerization rate [66]. 

All the complexes are significant initiators in the presence of benzyl alcohol for the ROP of rac-LA and follow the same mechanism as described 

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The aluminiun complexes bearing nitrogen-based bidentate or tridentate ligands have recently attracted much attention in fine chemical synthesis and even more in polymerization reactions [57-64]. The synthesis of polyesters by alkoxy aluminum catalyst is attracting a considerable ciu-rent interest. The salalen aluminum complexes 59-63 were prepared (Scheme 6.12) and used for ROP of LA (Table 6.9) [65]. 

The optimum catalyst for the reaction of 175 and cyclopentadiene was generated in-situ from one equivalent of the diol and two equivalents of ethyl aluminum dichloride. Presumably this generates a Lewis acid with two dichloroalkoxy aluminum groups per molecule of catalyst. The catalyst generated from diol 181 and one equivalent of diethylaluminum chloride is not very active, possibly because here the catalyst is a di-alkoxy aluminum chloride. The highest induction was observed for a catalyst generated from the diamino substituted diol 187, which was prepared from tartaric acid. 

LLDPE was polymerized in solution with a coordination catalyst at T = 180-320 °C and P = 4-20 MPa. The new modification relates to a method for activating Z-N coordination catalysts using an alkoxy aluminum alkyl compound prepared by mixing an alcohol and alkyl aluminum. The activator retains its activity and is easy to prepare simplifying the polymerization process. Small amount of H2 may be used for MW control (see Elston CA Patent 703704 of 1965 to DuPont of Canada Ltd.)... 

A solution copolymerization of C2 with C3-12 into high-MW LLDPE was carried out using a coordination catalyst at T = 105-320 °C and P = 4-20 MPa in a tubular reactor or in a system of reactors each operating under different conditions, in an inert solvent at T >105 °C. The catalyst was activated with a solution of aluminum alkyl and alkoxy aluminum... 

Reduction of l,2,4-triazin-3-ones (84) with Raney nickel, zinc and acetic acid, lithium aluminum hydride, sodium borohydride, titanium(III) chloride, p-toluenethiol, hydrogen and a palladium catalyst, or electrochemically, produces 4,5-dihydro-l,2,4-triazin-3-ones (268) (78HC(33)189, p. 246, 80JHC1237), which may be further reduced to 1,4,5,6-tetrahydro-l,2,4-triazin-3-ones (269). l,2,4-Triazin-3-ones (84) with hydriodic acid and phosphorus yielded imidazoles (05LA(339)243). 3-Alkoxy-l,2,4-triazines (126) and sodium borohydride gave the 2,5-dihydro derivatives (270) (80JOC4594). 

The first high-activity catalyst for ethylene polymerization which avoided the necessity of washing was derived from titanium(III)alkoxy chloride and triisohexylaluminum (92) [for the patent literature, see (25)1. Another route starts with titanium trichloride. Thus, excellent results as regards activity are obtained with the so-called Stauffer TiCls which contains 30 mol% of aluminum, obtained according to the following reaction. 

The use of aluminum isopropylate as a catalyst for this alkylation is apparently advantageous (128, 180). The resulting 18-ethers are formulated as 18-/3-alkoxy compounds, since it has been demonstrated in the steroid series that this alkylation proceeds with retention of the configuration (181). 

The mono- and poly-alkylated benzenes are treated using modifications of the above procedure. Monoalkylbenzenes are added to a preformed complex of acyl halides and aluminum chloride in carbon tetrachloride (Perrier modification). In this manner, the manipulation is easier, no tars are encountered, and the yields are improved (85-90%). The procedure shows no advantage, however, in the acylation of alkoxy- or chloro-aromatic compounds. The addition of benzoyl chloride to p-alkylbenzenes in the presence of aluminum chloride in cold carbon disulfide is a good procedure for making p-alkylbenzophenones (67-87%). The condensation of homologs of benzene with oxalyl chloride under similar conditions yields p,p -di alkylbenzophenones (30-55%). Polyalkylbenzenes have been acylated with acetic anhydride and aluminum chloride (2.1 1 molar ratio) in carbon disulfide in 54-80% yields. Ferric chloride catalyst has been used under similar conditions. Acetylation of p-cymene with acetyl chloride and aluminum chloride in carbon disulfide yields 2-methyl-5-isopropylaceto-phenone (55%). ... 

For group IV metals, the ease of redistribution parallels the size of the central atom. Thus for systems in which M = Sn and X and Y are alkyl, aryl, hydrogen, or electronegative groups such as halogens or alkoxy groups, equilibration can often be reached under very mild conditions, that is, <200 °C in the absence of a catalyst. The redistribution of groups on silicon, however, is a feasible process only in the presence of a catalyst, normally a Lewis acid such as aluminum chloride, and at elevated temperatures. 

As with methanol ammoxidation, yield and selectivity to the nitrile product are relatively high compared to ammoxidation of an alkene or alkane substrate. Using alumina-supported V-P-Sb-0 catalysts, selectivity to acetonitrile of 96% is obtained at 84% conversion of ethanol (81% acetonitrile yield) at 400°C (101), whereas a silicoaluminophosphate molecular sieve gives a reported 99% yield of acetonitrile at complete conversion of acetonitrile at 350°C (102). Both catalysts possess a relatively high level of surface acidity, mainly because of the presence of phosphorus and aluminum oxide moieties. These are expected to promote the initial step of the reaction—surface alkoxy formation by, for example, an equilibrium with surface hydroxyl groups. 

The catalyst was a typical modem supported Zie er-Natta catalyst of type MgCl2/TiCl4/DIBP-AlEt3/ext.donor (DIBPsdiisobutylphthalate). Titanium content of the catalyst was 2.6% b.w. The alkoxy silanes tested, with their abbreviations, are listed in Table 1. Aluminum alkyl was 10% b.w. triethylaluminum (TEA) in heptane firom Schering AG. Propylene was grade 2.5 from Messer Griesheim. 

An unoccupied coordination site and titanium alkyl bond in the titanium complex are fundamental requirements for its catalytic activity in olefin oligomerization. The titanium-alkyl bond is formed in the reaction of a titanium compound with alkyl or alkylchloroaluminum compounds when, for example, halide atoms or alkoxy groups of titanium compounds are replaced by alkyl groups of aluminum derivatives. There are many proposals concerning the structure of the Ziegler-Natta catalyst active centers. These are presented in structural formulas (16)-(21) [291. 

In addition to their use with the traditional enoxysilanes derived from ketones and esters, the bisoxazoline catalysts have been shown to mediate aldol-like additions between chelating aldehydes and 5-alkoxy-substituted ox-azoles to afford adducts such as 328 (Scheme 4.46) [165], Interestingly, the identification of aluminum salen complexes 330 as a viable catalyst expands the scope of the process to include aromatic aldehydes (Equation 31). The products are isolated as isoxazolines (cf. 331) with a high degree of relative and absolute stereocontrol. 

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