Catalyst, Ligand and Solvents

Almost all Suzuki polycondensations published to date in the literature use 1-3 mol% of catalyst, mostly Pd[P(p-tolyl)3]3, Pd(PPh3)4 or in situ prepared Pd[P(o-tolyl)3]2. Most catalysts for the Suzuki polycondensation employ tri-arylphosphine ligands. New ligands, which include Buchwald s biaryl-based phosphines, Beller s diadamantyl phosphines, Fu s tri(tert-butyl)phos-phine, and Hartwig s pentaphenylated ferrocenyl phosphines, have been developed for Suzuki-Miyaura cross-coupling reactions. Buchwald-type ligand has been applied to polymerize dichloro monomers using Suzuki polycondensation. 

The solvent systems will affect the progress of the polycondensation. Most Suzuki polycondensation are carried out in biphasic mixtures of organic solvents such as toluene, xylene, THF, or dioxane and an aqueous medium 

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It was described that the use of the combination of Pd(OAc)2/dppp /THE resulted in the highest yield. It is not clear whether such a combination of catalyst, ligand and solvent is restricted to the hydrothiocarboxylation of conjugated enynes or also may be applied to other alkynes. Furthermore, it remains to be explored whether, in the Pt-catalyzed reaction performed in CHjCN [see Eq. (7.18)], conjugated enynes can be used. 

All the examples discussed here show that the selectivity of a homogeneously catalyzed reaction is decisively influenced by the central atom of the catalyst. Fine tuning can be made by modification of the ligands. The HSAB concept can be helpful in selecting catalysts, ligands, and solvents, as well as in planning test reactions. 

Reaction of the cyclopropyl-substituted pivalate (25) with dimethyl benzylidenema-lonate in the presence of a palladium catalyst gave a mixture of alkylidenecyclo-propane (26) and vinylcyclopropane (27). The ratio of these two adducts is found to be quite sensitive to the choice of ligand and solvent. While triisopropyl phosphite favors the formation of the methylenecyclopropane (26), this selectivity is completely reversed with the use of the bidentate phosphite ligand dptp (12). Interestingly there was no evidence for any products that would have derived from the ring opening of the cyclopropyl-TMM intermediate (Scheme 2.8) [18]. 

Certain amines, when linked to TPPTS, form ionic solvents liquid at quite low temperatures. Bahrman [33] used these ionic liquids as both ligands and solvents for the Rh catalyst for the hydroformylation of alkenes. In this otherwise interesting... 

A variety of monomers, including styrene, acrylonitrile, (meth) acrylates, (meth) acrylamides, 1,3-dienes, and 4-vinylpyridine, undergo ATRP. ATRP involves a multicomponent system of initiator, an activator catalyst (a transition metal in its lower oxidation state), a deactivator (the transition state metal in its higher oxidation state) either formed spontaneously or deliberately added, ligands, and solvent. Successful ATRP of a specific monomer requires matching the various components so that the dormant species concentration exceeds the propagating radical concentration by a factor of 106. 

Phenols such as 2.6-dimethyIphenol are converted rapidly and in high yield to high molecular weight polymers at room temperature with oxygen in the presence of amine complexes of copper salts as catalyst. Much of the work described in the literature has been performed with copper (I) chloride as catalyst and pyridine as ligand and solvent. Other amines, primary, secondary or tertiary can be used as ligands for the catalyst. Autoxidation of copper (I) chloride in pyridine results in the... 

The cobalt-catalyzed radical Kumada coupling was extended to 1-silylvinyl- and silylethynylmagnesium compounds (entry 5) [282]. Co(acac)3 in the presence of TMEDA, which served as a ligand and solvent, proved to be the catalyst of choice however, a rather high loading of 20—40 mol% was required. The reaction... 

Ligand and solvent effects on catalyst activity in propylene oligomerization... 

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