Phosphine ligands alkyl halide carbonylation

One of the first mechanistic proposals for the hydrocarboxylation of alkenes catalyzed by nickel-carbonyl complexes came from Heck in 1963 and is shown in Scheme 24. An alternate possibility suggested by Heck was that HX could add to the alkene, producing an alkyl halide that would then undergo an oxidative addition to the metal center, analogous to the acetic acid mechanism (Scheme 19). Studies of Rh- and Ir-catalyzed hydrocarboxylation reactions have demonstrated that for these metals, the HX addition mechanism, shown in Scheme 24, dominates with ethylene or other short-chain alkene substrates. Once again, HI is the best promoter for this catalytic reaction as long as there are not any other ligands present that are susceptible to acid attack (e g. phosphines). 

The reactions have a very wide scope. Acyl halides serve as substrates for Stille couplings in addition to the usual aryl and alkenyl halides however, most alkyl halides cannot be used as substrates. Like Pd-catalyzed carbonylations, reactions proceed most quickly when X = I and rather slowly when X = Cl, although especially bulky phosphine ligands such as /-Bu3P allow even aryl chlorides to undergo coupling at room temperature. Again, triflates are also widely... 

Alkyl halides are less investigated in this protocol. a-Halo ethers, thioethers, and lactones can be used in this protocol. a-Halocarbonyl compounds react abnormally with allyl- and acetonyltins to give oxiranes via the attack at the carbonyl followed by the cyclization (Scheme 34).p°]-P3] -pjjg reaction appears to be a variation of a simple Lewis-acid-catalyzed aldol-type condensation. On the other hand, if a catalyst without phosphine ligand is used, 1,4-diketone is formed (Scheme 35). 

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