Solvents as ligands

Attempts have been made to treat selective ion solvation in mixed solvents as ligand exchange reactions [36 e]. We express ion X (cation or anion) existing in solvent A by XA and in solvent B by XB,-. Here, nf=ri if the molecular size of A is very different from that of B or if A is unidentate and B is bidentate (e.g. PC and DME in the solvation of Li+). Otherwise, it is usual that n=n. Then, the ligand exchange reaction in the mixture of A and B will proceed as follows with the increase in the concentration of B ... 

The problem with aryl chlorides seems to be that they do not compete effectively with reactant alkenes or even many solvents as ligands or reactants at palladium(0). Even if the arylpalladium chloride is formed its equilibrium concentration under the usual reaction conditions is probably very low. 

Depending on the coordinative properties of the anion and on the degree of the cation s reactivity, the ionic liquid can be regarded as iimocent solvent, as ligand (or ligand precursor), as co-catalyst or as the catalyst itself... 

Oxidative addition of trimethyloxonium tetrafluoroborate to a Pt(0) complex containing dimethylfumarate and phen ligands 108 leads to the corresponding cationic methylplatinum(ii) complex 109, and substitution of the coordinated olefin by dimethyl acetylenedicarboxylate 110 leads to insertion of the coordinated alkyne into the Pt-Me bond in MeCN, giving the complex having an alkenyl group and the solvent as ligands 111 (Scheme 16). 

COi is another molecule which reacts with conjugated dienes[10,95,96], COt undergoes cyclization with butadiene to give the five- and six-membered lactones 101. 102. and 103, accompanied by the carboxylic esters 104 and 105[97.98], Alkylphosphines such as tricyclohcxyl- and triisopropylphosphine are recommended as ligands. MeCN is a good solvent[99],... 

The solvent used plays an important role, since it can stabilize the organomag-nesium species through complexation. Nucleophilic solvents such as ethers—e.g. diethyl ether or tetrahydrofuran—are especially useful. The magnesium center gets coordinated by two ether molecules as ligands. 

Ionic liquid as solvent and ligand/ligand precursor... 

For the installation of the pyrrolidinylethanol moiety 10 on the aryl group, we first tested Buchwald s Cu-catalyzed conditions with 10, aryl iodide 12, Cs2C03, Cul and 1,10-phenanthroline at 110°C in toluene to prepare the penultimate 49 [14a], The reaction was very slow, giving only 5-10% conversion even after 2 days. The reaction was faster at higher temperatures but two impurities 50 and 51 were observed (Scheme 5.14). To find the optimal conditions, xylene and diglyme were tested as solvents, lithium, potassium and cesium carbonates were screened as bases and 2,2 -bipyridy], TMEDA and l-(2-dimethylaminoethyl)-4-methylpiperazine were examined as ligands. The optimized protocol was identified as 10mol% of... 

Sterically demanding, water-soluble alkylphosphines 6.10 and 6.11 as ligands have been found to have a high activity for the Suzuki coupling of aryl bromides in aqueous solvents (Eq. 6.35).115 Turnover numbers up to 734,000 mmol/mmol Pd have been achieved under such conditions. Glucosamine-based phosphines were found to be efficient ligands for Suzuki cross-coupling reactions in water.116... 

Indium(I) iodide serves as a two electron reducing agent to promote a Ni-catalyzed allylation of benzaldehyde with 1,3-dienes [23]. In the presence of a catalytic amount of Ni(acac)2 and a stoichiometric amount of Ini, 1,3-butadiene reacts with 2 equiv. of benzaldehyde to provide a mixture of a 1,4-diol 28 and 1,6-diol 29 and/or with 1 equiv. of benzaldehyde to give 27 (Eq. 8). The product distribution of 27-29 markedly depends on the solvent, the ligand, and the additive employed (Table 2). The combination of Ni(acac)2, PPI13, and 3 equiv. of water in DMI provides the 1,4-diol 28 as the major product (run 1). Under similar conditions, dppb dramatically changed the reaction course and the mono-allylation product 27 is produced exclusively (run 2). In contrast to these, the reaction in dry THF provides the 1,6-diol 29 in excellent yield (rim 3). 

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