Metal groups vinyl halide reactions

Four oxidation states of palladium are encountered in organometallic chemistry see Palladium Inorganic Coordination Chemistry) In order of importance, they are Pd , Pd , Pd, and Pd . With the reduction of palladium from Pd to Pd , the metal changes its reactivity from electrophile to nucleophile. However, unlike main group nucleophiles such as thiolates or cyanide, Pd complexes react with both alkyl halides and aryl or vinyl halides. Reactions of Pd complexes with these latter sp halides generate new Pd aryl or vinyl bonds through the process of oxidative addition. 

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. 

Transition metal-catalyzed cross-coupling reactions between vinyl organometallic compounds and unactivated alkyl halides that can be usually performed with palladium, nickel and cobalt are of particular synthetic interest [37-39]. Recently, the groups of Cahiez [48] and Cossy [49] concurrently reported the first iron-catalyzed reaction of alkenyl Grignard compounds with primary and secondary alkyl halides (X=Br, I) (Scheme 5.15). The two protocols basically differ in the iron source... 

Much of the recent interest in the arylstannanes, particularly the aryltrialkylstannanes, however, derives from their use in the Stille reaction in which an aryl-C bond is generated by reaction with a halide or sulfonate RX, where R = vinyl, allyl, benzyl, or aryl, to give Ar-R under catalysis by palladium68 or another transition metal.69-72 The reactions are very tolerant of various functional groups, and are finding wide application in organic synthesis, and are considered in Section 22.2. 

Dienes containing a terminal vinyl group can be synthesized by either vinyl-alkenyl or alkenyl-vinyl coupling. The merits and demerits of the use of vinyl metals relative to that of vinyl halides are discussed in Sect. B.i. Some representative examples of Pd-catalyzed vinyl-alkenyl coupling reactions are summarized in Table 9. 

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