Magnesium alkyl complex catalyst

Hydroboration of aldehydes and ketones by pinacolborane is aided by a pre-catalyst cycle involving a heteroleptic magnesium alkyl complex and the ketone. ... 

The detail of the structure of the polymerisation centre present in suppported Ziegler-Natta catalysts for a-olefin polymerisation has been the subject of much research effort (e.g./-/2) The catalyst consists of a solid catalyst MgC /TiC /electron donor and a co-catalyst, an aluminium alkyl complexed with an electron donor. Proposed mechanisms for the polymerisation involve a titanium species attached to magnesium chloride with the olefin coordinated to titanium. The detail of the site at which the titanium species is attached is an important area of study in understanding the mechanism of catalysis and several recent papers 10-12) have investigated the surface structure of magnesium chloride and the attachment of TiCl4, in particular the interaction of titanium species with the 100 and 110 planes of a and (3- magnesium chloride. 

Standard Nd-based catalysts comprise binary and ternary systems. Binary systems consist of Nd chloride and an aluminum alkyl or a magnesium alkyl compound. In ternary catalyst systems a halide free Nd-precursor such as a Nd-carboxylate is combined with an Al- or Mg-alkyl plus a halide donor. By the addition of halide donors to halide-free catalyst systems catalyst activities and cis- 1,4-contents are significantly increased. In quaternary catalyst systems a solubilizing agent for either the Nd-salt or for the halide donor is used in addition to the components used in ternary systems. There are even more complex catalyst systems which are described in the patent literature. These systems comprise up to eight different catalyst components. 

Additives are also used to improve the solubility of halide donors [382, 383]. Metal(II) halides such as magnesium chloride, calcium chloride, barium chloride, manganese chloride, zinc chloride and copper chloride etc. are used as halide sources. In order to increase the solubility of the halides they are reacted with electron donors which have been previously described for the increase of solubility of Nd-components [338,339]. The number of catalyst components is further increased if two Al-compounds (alumoxane + aluminum (hydrido) alkyl) are used. In addition, a small amount of diene can also be present during the preformation of the different catalyst components as described by JSR. In some catalyst systems the total number of components reaches up to eight [338,339]. Such complex catalyst systems are also referred to in other JSR patents [384,385] (Sect. 2.2.6). 

Strong evidence for this model is provided by an elegant substrate-catalyzed single-turnover experiment presented by Sadow and coworkers [81]. The four-coordinate Cs-symmetric magnesium tris(oxazoline)borate alkyl complex [To MgMe] (To = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) excludes additional ligands from the coordination sphere and is a competent precatalyst for the hydroamination of l-aminopent-4-enes. In line with the expectations furnished by the aforementioned systems, the reaction of l-amino-2,2-diphenylpent-4-ene follows the empirical rate law v = / obs[aminoalkene] [catalyst], with a KIE of... 

This type of catalysts also offers access to low-molecular-weight SPS by chain transfer to magnesium compounds. Starting from a dimeric neodymium complex, the addition of dibutyl magnesium leads to the formation of a bimetallic alkyl complex in equilibrium with the monomeric active species and free magnesium alkyl [13] (Scheme 7.2). 

It may be interesting, in connection with the ethylene/propylene copolymers mentioned above, to present here some homogeneous Ziegler-Natta catalysts formed by soluble complexes of titanium and magnesium chlorides with alkyl phosphates as catalyst precursors and alkylaluminium compounds as activators (TiCl4)x.(MgCl2)r [0=P(0Bu)3]3-A1(/-Bu)3 and Cl3TiOMgCl-[0 = P(0Bu)3]3- A1(z -Bu)3 (Al/Ti molar ratio of ca 10 1). These catalysts have been used for random ethylene/propylene copolymerisation [73],... 

When lithium alkyl catalysts are used in non-solvating media such as aliphatic hydrocarbons, the polymer-lithium bond is not sufficiently ionic to initiate anionic polymerization so that the monomer must first complex with vacant orbitals in the lithium. A partial positive charge is induced on the monomer in the complex, and this facilitates migration of the polymer anion to the most electrophilic carbon of the complexed monomer. This type of polymerization is more appropriately termed coordinated anionic and will be discussed in the next section. There does not appear to be any evidence that alkyl derivatives of metals which are less electropositive than lithium and magnesium can initiate simple anionic polymerization. 

Organophosphorus compounds find wide use in the chemical industry as catalysts, intermediates, complexes, and end-use products. Arylphosphines and phosphine oxides are often produced by the reaction of a preformed Grignard reagent with a halophosphine or phosphine oxide. Yields are reduced by the production of unwanted side-reaction products such as biaryls. These unwanted products are reduced when the reaction is conducted under Barbier conditions. When alkyl and aryl halides are reacted with magnesium metal, a trihalophosphine or phosphine oxide, a metal halide or amine catalyst, in THE benzene mixtures, at reflux, good yields of phosphines or phosphine oxides are obtained [74]. For example, triphenylphosphine can be prepared in a 97.2% yield from the reaction of bromobenzene, trichlorophosphine, magnesium metal, aluminum chloride, and sodium chloride in THF-benzene at 70 80 C. 

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