Organic triflates

Jang, S.-B, Polymer-Bound Palladium-Catalysed Cross-coupling of Organoboron Compounds with Organic Halides and Organic Triflates, Tetrahedron Lett. 1997, 38, 1793-1796. 

Jang SB, Polymer-bound palladium-catalyzed cross-coupling of organoboron compounds with organic halides and organic triflates, Tetrahedron Lett., 38 1793-1796, 1997. 

Phenylacetophenone [AsPhg is superior to PPh3 and P(2-furyl)3 for the reaction between aryltin and organic triflates] [22]. 

Oh-e, T., Miyaura, N., and Suzuki, A. (1993). Palladium-catalyzed cross-coupling reaction of organoboron compounds with organic triflates. J Org Chem 58 2201-2208. 

Stille coupling reactions of organic triflates are often facilitated by added LiCl when conducted in THF solvent. Presumably the chloride anion replaces the triflate ligand on palladium following oxidative addition, which leads to increased stability of the Pd(Ar)(X) species [35] this additive may also assist in the transmetalation step. However, LiCl is not needed when the StiUe reactions are carried out in polar solvents like NMP [36]. 

The selective formation of the arylated or vinylated allylalcohol was rationalized by assuming a cationic four-manbered intermediate, in which the hydrogen atom (H ) on the hydroxyl-bearing carbon is located unfavorably for a syn palladium hydride elimination. The cationic intermediates were generated from organic triflates, iodonium salts,or organic iodide/thallium or silver salt combinations (Scheme 28). 

This mechanistic interpretation of the StiUe reaction has been the base for the formulation of the mechanisms of other cross-coupling reactions. Model studies on the couphng of alkynes with vinyl triflates with [Pt(PPhj)4] were in overall agreement with that proposal [54], although involvement of cationic complexes in the transmetallation step was strongly suggested by this work. Farina [55] and Brown [56] also found that the intermediates formed upon oxidative addition of organic triflates to Pd(0) are cationic complexes such as [PdR (S)L2] nd [PdR L3]+. 

A variety of other leaving groups have been employed, especially triflates. There is an unusual mechanistic consequence in their reactions. In the basic Heck mechanism given above (Scheme 5.1), ligand dissociation is required prior to alkene coordination, in order to generate a palladium complex 5.5 with a vacant site for alkene coordination. While this is most commonly the dissociation of a phosphine ligand, if an organic triflate is the substrate, then the triflate anion may dissociate (Scheme 5.8). A vacant site is then opened up... 

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