Organometallic compounds electrophilic substitution

One equivalent of LiHBEt3 or LiHB(sec-butyl)3 in THF at -80° consumed the phosphine substituted a,8-dialkoxyethylidene salts 9a, b and delivered 73% yields of the formylmethyl complex CpFe(CO)PPh3(CH2CHO) (21) as the only isolable organometallic compound. The product 21 can be accounted for by an electrophile... 

In contrast to direct electrophilic substitution in which the astatine attacks one of the C—H bonds, astatination through demetalation can be used to label a substrate at a preferred site in a regiospecific manner not affecting other sensitive sites of the molecule. Since the C—M bond is more sensitive to electrophilic attack than C—H, higher yields can be obtained in short reaction times under milder experimental conditions56. Organometallic compounds of mercury, thallium and tin have been used so far for astatination via demetalation. 

The second mechanism which cannot always be strictly differentiated from the first one 41) should be considered as a typical electrophilic substitution of the arene by the iiigh valent metal compound. The latter is still more electrophilic with tri-fluoroacetate than with acetate anions. The organometallic arene intermediates were isolable in some cases 43). In the second step, the metallic residue is substituted by the acetate or trifluoroacetate ion. 

We prepared numerous new organosilicon polymers using the described a,co-bis[(trifluoromethyl)-sulfonyloxy]-substituted organosilicon derivatives as electrophilic starting materials [13, 14]. The dinucleophilic reactants were either organic or organometallic compounds. The reactions of [phenylene-1,4-bis(dimethylsilanediyl)]bis(trifluoromethanesulfonate) with six dinucleophiles in Scheme 1 illustrate the potential of this method. We could confirm the formation of the polymers at low temperature, in short reaction times, and with high yields. 

Mechanism of electrophilic displacements of metals at saturated carbon On the importance of coordination in electrophilic substitution reactions of organometallic compounds... 

The substitution reactions of organometallic compounds, in which heterolytic attack at the carbon is usually by electrophiles, are not susceptible to the simple mechanistic classification (SnI, Sn2, and S i) which is so useful in discussing nucleophilic reactions of organo-nonmetallic compounds. The situation is complicated by the propensity of the metal to increase its coordination number, and a spectrum of mechanisms has to be considered in which electrophilic attack at carbon is accompanied by or preceded by nucleophilic attack at the metal. 

In most cases, treatment of allylic halides containing one ASG with a nucleophile does not result in formation of electrophilic cyclopropanes (MIRC product) instead, other reaction pathways are followed, e.g. addition, substitution, rearrangement and elimination reactions.However, with certain alkenes or nucleophiles or under the appropriate conditions a conjugate addition-nucleophilic substitution pathway is favored, resulting in cyclopropanes substituted with one ASG. Representative examples are compiled in Tables 20 and 21 where organometallic compounds or active methylene compounds are used as the nucleophilic species in combination with allyl bromides containing an ester or a sulfone as ASG. 

Heterocyclic aromatic compounds such as pyrrole are readily metallated with Grignard reagents. The resulting compounds have N"Mg bonds and are, therefore, not organometallic compounds, but on reaction with electrophiles give 2-substituted pyrroles [14] (eq (4)). The reaction of chloroform or bromoform with PrMgCl at -78 °C in THF-HMPA (4 1) is mild and convenient method for the generation of an unstable carbenoid in the solution [15] (eq (5)). 

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