Phosphine complexes reactivity

A potentially interesting development is the microwave-assisted transition-metal-free Sonogashira-type coupling reaction (Eq. 4.10). The reactions were performed in water without the use of copper(I) or a transition metal-phosphine complex. A variety of different aryl and hetero-aryl halides were reactive in water.25a The amount of palladium or copper present in the reaction system was determined to be less than 1 ppm by AAS-MS technique. However, in view of the recent reassessment of a similarly claimed transition-metal-free Suzuki-type coupling reaction, the possibility of a sub-ppm level of palladium contaminants found in commercially available sodium carbonate needs to be ruled out by a more sensitive analytical method.25 ... 

The reactivity of (367) and (368) towards phosphine complexes of Ni11 has been investigated. Depending on the nature of the phosphine and the dithiocarbamate used, different complexes were obtained 974 The stability constants for the Ni11 complexes of (369), (370), and (371) have been determined in aqueous solution. Both 1 1 and 1 2 complexes were observed.975... 

Efforts to tune the reactivity of rhodium catalysts by altering structure, solvent, and other factors have been pursued.49,493 50 Although there is (justifiably) much attention given to catalysts which provide /raor-addition processes, it is probably underappreciated that appropriate rhodium complexes, especially cationic phosphine complexes, can be very good and reliable catalysts for the formation of ( )-/3-silane products from a air-addition process. The possibilities and range of substrate tolerance are demonstrated by the two examples in Scheme 9. A very bulky tertiary propargylic alcohol as well as a simple linear alkyne provide excellent access to the CE)-/3-vinylsilane products.4 a 1 In order to achieve clean air-addition, cationic complexes have provided consistent results, since vinylmetal isomerization becomes less competitive for a cationic intermediate. Thus, halide-free systems with... 

For this complex, molecular chemistry does not adequately model the surface reactivity and the latter is strongly influenced by the presence of surface hydroxyl groups [22]. The organometallic fragments immobilized on silica have been reacted with trimethylphosphine to afford different silica-supported phosphine complexes of rhodium. The course of the reaction depends strongly on the hydroxyl content of the silica surface [23] (Scheme 7.2). 

The investigation of phosphine complexes of rhodium(I) as catalysts (or catalyst precursors) for the hydroformylation reaction continues both to better elucidate the reaction mechanism and to improve catalyst activity. The presence of dioxygen often decreases the catalytic activity (139), but can also, surprisingly, reactivate hydroformylation catalysts... 

Phosphine-complexed cuprates, formed from copper(I) iodide, 1 mol equiv. of RtLi, and 2-5 mol equiv. of tri-n-butylphosphine, show good reactivity in conjugate addition reactions with enones (Table l).39 The hazards surrounding the use of excess Bun3P, and the availability of other methodologies lower the popularity of this method, but efficiency can be realized with this methodology. 

The reactivity of -Tr-allylpalladium-phosphine complexes generated stoichiometrically or from alkenes allylically substituted with a leaving group, is essentially identical and, as a result, allyl species will be generally considered in this section without distinction as to the origin of the palladium complex. 

Normally, the most practical vinyl substitutions are achieved by use of the oxidative additions of organic bromides, iodides, diazonium salts or triflates to palladium(0)-phosphine complexes in situ. The organic halide, diazonium salt or triflate, an alkene, a base to neutralize the acid formed and a catalytic amount of a palladium(II) salt, usually in conjunction with a triarylphosphine, are the usual reactants at about 25-100 C. This method is useful for reactions of aryl, heterocyclic and vinyl derviatives. Acid chlorides also react, usually yielding decarbonylated products, although there are a few exceptions. Likewise, arylsulfonyl chlorides lose sulfur dioxide and form arylated alkenes. Aryl chlorides have been reacted successfully in a few instances but only with the most reactive alkenes and usually under more vigorous conditions. Benzyl iodide, bromide and chloride will benzylate alkenes but other alkyl halides generally do not alkylate alkenes by this procedure. 

Terao and Kambe showed a dichotomy in the reactivity of nickel complexes (review [102]). While nickel diene complexes reacted primarily via two-electron pathways [34—37], nickel phosphine complexes promote radical addition reactions [103],... 

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