Indole-Containing Ligands

With the incredible increase in research devoted to metal-catalyzed coupling reactions, which we will encounter in subsequent chapters, and the necessity of employing specialized ligands for this chemistry, it is no surprise that numerous indole-based ligands have been invented. In this regard Bandini and Eichholzer published an excellent 

A very large number of indole-based hgands have been developed to facihtate palladium- and rhodium-catalyzed cross-coupling reactions. The research groups of Sannicolo, Benincori, Beller, Reek, Koskinen, Heo, Mino, Sarkar, Franzen, and Kwong have made enormous contributions in this area. 

Given the voluminous effort by several groups to design, synthesize, and implement ligands based on 

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Although Li[B(NHMe)4] exists,most tetraamidoborates contain ligands derived from five-membered heterocyclics such as pyrrole, indole, imidazole, pyrazole and indazole. The thermal and hydrolytic stabilities of these borates are fairly hi. When the heterocycle contains two nitrogens the borates can exist in acidic form and the tetraimidazol-l-ylborate can be used for gravimetric determination of the proton. Another type of borate containing a BN4 unit is represented by bicyclic derivatives formed with iV,iV",iV"-trimethylbiuret. ... 

Trifluoromethylated heteroarenes are widely applicable in the synthesis of pharmaceuticals. Using 10 mol% palladinm acetate as catalyst, TMSCF3 as trifluoro-methylating reagent, bidentate nitrogen-containing ligand L, and PhI(OAc)2 as oxidant, Liu and coworkers developed a novel palladium catalyzed oxidative trifluoromethylation of indoles at room temperatnre (Scheme 9.20). This reaction likely involves a palladium (II/IV) mechanism for the formation of the sp C—CF3 bond. 

Perdew GH, Babbs CF. 1991. Production of Ah receptor ligands in rat fecal suspensions containing tryptophan or indole-3-carbinol. Nutr. Cancer. 16 209-18... 

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