Grignard reagent, transition metals

Acylation at carbon with Grignard and organo-lithium reagents Transition Metal Complexes... 

The synthesis involves the nickel-catalyzed coupling of the mono-Grignard reagent derived from 3-alkyl-2,5-diiodothiophene (82,83). Also in that year, transition-metal hahdes, ie, FeCl, MoCl, and RuCl, were used for the chemical oxidative polymerization of 3-substituted thiophenes (84). Substantial decreases in conductivity were noted when branched side chains were present in the polymer stmcture (85). 

The high diastereoselectivity which is found in the nucleophilic addition of Grignard reagents to chiral 2-0x0 acetals can be explained by a chelation-controlled mechanism. Thus, coordination of the magnesium metal with the carbonyl oxygen and the acetal moiety leads to a rigid structure 3A in the transition state with preferred attack of the nucleophile occurring from the S/-side. 

The diastereoselectivity of the reaction may be rationalized by assuming a chelation model, which has been developed in the addition of Grignard reagents to enantiomerically pure a-keto acetals7,8. Cerium metal is fixed by chelation between the N-atom, the methoxy O-atom and one of the acetal O-atoms leading to a rigid structure in the transition state of the reaction (see below). Hence, nucleophilic attack from the Si-face of the C-N double bond is favored4. 

The work on vinyl sulphones and their reactions with Grignard reagents, in the presence of transition metal catalysts, all emanates from Julia s laboratory191-195, with the exception of a note196 that presents evidence for SET processes in the alkylation of vinyl sulphones by organometallic reagents. 

Among others, alkyls of Be, Cd, Hg, Al, Sn, Pb, Co, Pt, and Au have been prepared by treatment of Grignard reagents with the appropriate halide. The reaction has been used to prepare alkyls of almost all non-transition metals and even of some transition metals. Alkyls of metalloids and of nonmetals, including Si,... 

The only other known transition metal terphenyl derivative is the blue, crystalline cobalt species Co(ju.-Br)C6H3-2,6-Mes2(THF) 239 (Fig. 12). It is isostructural to the corresponding magnesium derivative discussed earlier. It was synthesized via the reaction of CoCl2 with the Grignard reagent,... 

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