Functionalized Grignard reagents functional group tolerance

Another feature of the Pd—C bonds is the excellent functional group tolerance. They are inert to many functional groups, except alkenes and alkynes and iodides and bromides attached to sp carbons, and not sensitive to H2O, ROH, and even RCO H. In this sense, they are very different from Grignard reagents, which react with carbonyl groups and are easily protonated. 

The transition metal catalyzed carbon-carbon bond formation between organomagnesium reagents and aryl (vinyl) halides has been one of the pioneering entries into cross-coupling chemistry. The reaction has been widely utilized since than in azine chemistry,22 with the limitation that the functional group tolerance of Grignard reagents is only moderate. Here only some of the more recent developments will be mentioned. 

Grignard reagents are least tolerant of common organic electrophilic functional groups, such as carbonyl and nitro groups, while organoboron compounds tolerate most such electrophiles. 

Another important feature of the Grignard reagents is the Lewis acidity of magnesium salts thaL in many cases, can help activate the electrophilic partner, thereby often enhancing the variety of electrophiles suitable for coupling. This enhanced reactivity is, however, responsible for the major drawback associated with the use of organomagnesiums, namely, the reduced functional group tolerance. 

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