Methylation metal imine complexes

Because of the relative rates of chain propagation versus chain walking, polymers from the bis(imine) catalysts can be quite different depending on the metal. Nickel complexes form polymers with mostly shorter-chain branches and more crystallinity while polyethylene from the palladium analogs is more highly branched, to the point it can be amorphous. The palladium complexes also have the abihty to incorporate remarkably high (1 10 mole percent) amounts of polar monomers such as methyl acrylate and methyl vinyl ketone, though at considerable loss in activity. ... 

Some years ago, Malmstrom etal. synthesized water-soluble metal phosphine complexes based on water-soluble polymers [41], In order to have solubility in both an acidic and a basic medium, they prepared two different water-soluble polymers. For the first, they made methyl [4-(diphenylphosphino)benzyl]amine (PNH) react with poly(acrylic acid) (PAA) using dicydocarbodiimide (DCC) as the coupling agent, under strict exclusion of oxygen (25). For the second, they reacted (4-carboxy-phenyl)diphenylphosphine with polyethylene imine (PEI) at room temperature (26). The reduction by sodium borohydride was made in situ, followed by the addition of methanesulfonic add and diethyl ether. Then, the methanesulfonic salt of phosphinated polyethylenimine was predpitated. 

The combined reaction thus involves initial formation of the iminium ion from the carbonyl compound and amine at pH 6, and this intermediate is then reduced by the complex metal hydride to give the amine. This can also he a way of making methyl-suhstituted amines via intermediate imines with formaldehyde. 

The use of organomagnesium reagents as bases leads to complexation of the nitrile imines (e.g., 141), which has been found to have a strong effect in promoting syn selectivity in reactions with methyl 2-(l-hydroxyalkyl)acrylates via coordination of the metal atom with the alcoholic oxygen (e.g., leading to the formation of 142). Lithium complexation had little effect (78). 

Grigg and co-workers (383) found that chiral cobalt and manganese complexes are capable of inducing enantioselectivity in 1,3-dipolar cycloadditions of azomethine ylides derived from arylidene imines of glycine (Scheme 12.91). This work was published in 1991 and is the first example of a metal-catalyzed asymmetric 1,3-dipolar cycloaddition. The reaction of the azomethine yhde 284a with methyl acrylate 285 required a stoichiometric amount of cobalt and 2 equiv of the chiral ephedrine ligand. Up to 96% ee was obtained for the 1,3-dipolar cycloaddition product 286a. 

In 1997, the first truly catalytic enantioselective Mannich reactions of imines with silicon enolates using a novel zirconium catalyst was reported [9, 10]. To solve the above problems, various metal salts were first screened in achiral reactions of imines with silylated nucleophiles, and then, a chiral Lewis acid based on Zr(IV) was designed. On the other hand, as for the problem of the conformation of the imine-Lewis acid complex, utilization of a bidentate chelation was planned imines prepared from 2-aminophenol were used [(Eq. (1)]. This moiety was readily removed after reactions under oxidative conditions. Imines derived from heterocyclic aldehydes worked well in this reaction, and good to high yields and enantiomeric excesses were attained. As for aliphatic aldehydes, similarly high levels of enantiomeric excesses were also obtained by using the imines prepared from the aldehydes and 2-amino-3-methylphenol. The present Mannich reactions were applied to the synthesis of chiral (3-amino alcohols from a-alkoxy enolates and imines [11], and anti-cc-methyl-p-amino acid derivatives from propionate enolates and imines [12] via diastereo- and enantioselective processes [(Eq. (2)]. Moreover, this catalyst system can be utilized in Mannich reactions using hydrazone derivatives [13] [(Eq. (3)] as well as the aza-Diels-Alder reaction [14-16], Strecker reaction [17-19], allylation of imines [20], etc. 

Photolysis of diethylthallium bromide in cyclohexane is a radical process involving cleavage of the thallium-carbon bond, which yields ethylcyclohexane and dicyclohexyl, as well as other products. Photoelectron transfer from benzyltributylstannanes to 10-methylacridinium ion results in cleavage of the metal-carbon bond, to give the corresponding benzyl radicals, rather than benzyl cations. Photochemical homolysis of Re- and Ru-alkyl bonds in Re(alkyl)-(CO)3(diimine) and Ru(I)(alkyl)(CO)2(diimine) complexes has been studied by Fourier transform ESR. In related manganese complexes, Mn(R)(CO)3(di-imine), elimination of CO is the predominant pathway when R = methyl, but Mn-alkyl homolysis occurs when R = benzyl. 

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