Metal alkoxide group

The linearity of the plot shows that the propagation was first order with respect to lactide monomer. The absence of an induction period indicates that the initiator was reactive from the beginning and that no rearrangement of initiator aggregates was necessary to form the active species. The nature of the metal, alkoxide groups, solvent, and temperature does not generally influence the first order in monomer [71,104]. 

The putative mechanism involves coordination and activation of the lactide by the metal complex (1, Fig. 2). The lactide, once activated, is subsequently attacked by the metal alkoxide group (another way to view this is that lactide inserts into the metal alkoxide bond) (2, Fig. 2). The putative intermediate then undergoes ring opening of the lactide, by an acyl bond cleavage, and a new metal alkoxide bond is... 

The use of metal alkoxides, especially those of Ti and Mg, as active components of multicomponent Ziegler-Natta type catalysts has an established place in industry. Many patent applications have been filed over the years but they read rather like cookery recipes and will not be documented here. Anionic polymerization of styrene, butadiene, and isoprene has also received much investigation. The addition of alkali metal alkoxides MOR to alkali metal amides MNH2 gives rise to a range of complex base initiators whose properties may be modulated by the nature of the metal, alkoxide group, and solvent. Similarly the effect of lithium alkoxides on the rate of polymerization of styrene initiated by -butyl lithium has also been reported. " ... 

Metal alkoxides are compounds in which a metal is attached to one or more alkyl groups by an oxygen atom. Alkoxides are derived from alcohols by the replacement of the hydroxyl hydrogen by metal. 

Much work has been done on the structure of the metal alkoxides (49). The simple alkaU alkoxides have an ionic lattice and a layer stmcture, but alkaline earth alkoxides show more covalent character. The aluminum alkoxides have been thoroughly studied and there is no doubt as to their covalent nature the lower alkoxides are associated, even in solution and in the vapor phase. The degree of association depends on the bulkiness of the alkoxy group and can range from 2 to 4, eg, the freshly distilled isopropylate is trimeric (4) ... 

The advantages of titanium complexes over other metallic complexes is high selectivity, which can be readily adjusted by proper selection of ligands. Moreover, they are relative iaert to redox processes. The most common synthesis of chiral titanium complexes iavolves displacement of chloride or alkoxide groups on titanium with a chiral ligand, L ... 

Another group of chelants that form stable chelates at high pH because of metal—alkoxide coordination are the sugar acids, such as gluconic acid [526-95-4] (1 )- Utility for this group is found in high alkalinity botde washes and other cleansers (19). 

To complete the synthesis of keto disaccharide 16, the cyclic carbonate must be cleaved and the C-4 hydroxyl group must be oxidized selectively. With respect to the former objective, it is well known that a metal alkoxide (e. g. sodium methoxide) can easily... 

From the preceding discussion, it is easily understood that direct polyesterifications between dicarboxylic acids and aliphatic diols (Scheme 2.8, R3 = H) and polymerizations involving aliphatic or aromatic esters, acids, and alcohols (Scheme 2.8, R3 = alkyl group, and Scheme 2.9, R3 = H) are rather slow at room temperature. These reactions must be carried out in the melt at high temperature in the presence of catalysts, usually metal salts, metal oxides, or metal alkoxides. Vacuum is generally applied during the last steps of the reaction in order to eliminate the last traces of reaction by-product (water or low-molar-mass alcohol, diol, or carboxylic acid such as acetic acid) and to shift the reaction toward the... 

Sol-gel chemistry offers a unique advantage in the creation of novel organic-inorganic hybrids. The sol-gel process begins with a solution of metal alkoxide precursors [M(0/f) ] and water, where M is a network-forming element, and R is typically an alkyl group. Hydrolysis and... 

A similar steric effect was observed in the reaction of benzyl carboxylate (44). When 44a-d were treated with Bu OK under solvent-free conditions at around 100 °C for 30 min, the corresponding condensation products 45a (75%), 45b (66%), 45c (64%), and 45d (84%) were obtained in the yields indicated [9] (Scheme 6). When the same reactions of 44a-d and Bu OH were carried out in toluene under reflux for 16 h, no condensation product was obtained and 44a-d were recovered unchanged. In solution reactions, exchange of the alkoxy group occurs among the substrate, reagent, and solvent. Therefore, the alkoxy groups of the ester, metal alkoxide, and alcohol used as a solvent should be identical. 

The most common sol-gel process employs metal alkoxides of network forming elements (M(0R) where M is Si, B, Ti, Al, etc. and R is often an alkyl group) as monomeric precursors. In alcohol/water solutions the alkoxide groups are removed stepwise by hydrolysis reactions, generally employing acid or base catalysts, and are... 

Compound (6) has the structure shown in Fig. 4(d). It formally has 14-electron configurations about each metal atom and all fourteen electrons are involved in the bonds represented by lines in the structural drawing. Either the U2-CO group makes no appreciable demand for tt electron density or there may be an indirect feeding of electrons from the lone-pair orbitals of the alkoxide groups to y2-C0. Alkoxide groups are known to be 7r-electron donors. 

Metal alkoxide compounds, frequently represented as M(OR)x, where M is a metal and R is an alkyl group, are the most common precursors in sol-gel CSD processes and are also frequently used in chelate processes.3-12,30-34 Groups such as OR, which are bound to a metal center, are frequently referred to as ligands. Alkoxide compounds, including commonly used alkoxides such as... 

The alkoxide group R is chosen so that the heavier alkali metal alkoxide MOR is soluble in ether or hydrocarbon solvents and so the by-product LiOR may easily be separated from the desired heavier alkali metal phosphide/arsenide (which is often insoluble in weakly or noncoordinating solvents such as ethers and hydrocarbons). 

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