Metal halide, nucleophilic alkylation

These Sn/Li transmetallations involve nucleophilic attack of an alkyl anion at the tin center. Transmetallations with metal halides on the other hand involve electrophilic attack of the metal at the allylic double bond. 

Some neutral metal carbonyls, particularly coordinatively unsaturated ones, are sufficiendy nucleophilic to undergo reaction with organic halides. Sigma-alkyl species which undergo subsequent CO insertion are formed by such reactions27. Hence, carbonylations... 

The metal-centered reduction of iron and cobalt porphyrins [(por)Afn] yields metalloporphyrin anions [Eq. (13.13)]. The reduction potential for this reaction is 13, and is equivalent to the N- value for the oxidation of the metal-centered nucleophile [(por)uM-]. The one-electron reduction of alkyl halides yields the... 

Oxoalkyl- and 3-oxoalkyl-triphenylbismuthonium salts transfer the alkyl groups to various hetero nucleophiles such as piperidine, triphenylphosphane, arylsulfinates, alcohols, arylthiolates, dimethyl sulfide, and metal halides under mild conditions (Equation (132)).214 215 Methyl- and allyl-triphenylbismuthonium salts also alkylate some heteronucleophiles.216 The leaving ability of the triphenylbismuthonio group has been found to be higher than that of the triflate anion. 

The neutral complex [Fe2(CO)6S2] (65) is known to undergo reduction to form the disulfide-bridged dimeric compound [Fe4S4(CO)i2]2- (66),60 which on further reduction yields [Fe2(CO)6S2]2 (67).61-62 The nucleophilic character of the bridging sulfides in the fully reduced dianion 67 is demonstrated by its reaction with a variety of metal halides to yield metal clusters in which the butterfly unit of 67 acts as a bidentate ligand coordinated via the bridging sulfides.63-66 With alkyl halides, 67 reacts to form S-alkylated products.60-63... 

Reaction with the metal converts the alkyl halide into a compound that will react with electrophiles instead of nucleophiles. Thus, organolithium and organomagnesium compounds react as if they were carbanions. 

A more prevalent approach has been the nucleophilic alkylation of a metal halide, as in the metathesis of 344 with methyllithium to afford Tp Rh(Me) (rj -C Rs) (348). This approach was also employed to prepare the iridium complex Tp Ir(Me)Br(PMe3) (372) from the respective dibromide. Similarly, a range of alkyl halides of general formula Tp Rh(R)X(CNCH2 Bu) (374-385,... 

A constant dichotomy in the reactions of metal complexes with alkyl halides is whether the complex is truly reacting as a nucleophile or as a reductant, and a facile discrimination between the two roles has not been found as yet. 

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