Indole metal complexes

Methylthiophene is metallated in the 5-position whereas 3-methoxy-, 3-methylthio-, 3-carboxy- and 3-bromo-thiophenes are metallated in the 2-position (80TL5051). Lithiation of tricarbonyl(i7 -N-protected indole)chromium complexes occurs initially at C-2. If this position is trimethylsilylated, subsequent lithiation is at C-7 with minor amounts at C-4 (81CC1260). Tricarbonyl(Tj -l-triisopropylsilylindole)chromium(0) is selectively lithiated at C-4 by n-butyllithium-TMEDA. This offers an attractive intermediate for the preparation of 4-substituted indoles by reaction with electrophiles and deprotection by irradiation (82CC467). 

The (5)-tryptophan-derived oxazaborolidenes utilized in this aldol study have been previously examined by Corey as effective catalysts for enantioselective Diels-Alder cycloaddition reactions [6]. Corey has documented unique physical properties of the complex and has proposed that the electron-rich indole participates in stabilizing a donor-acceptor interaction with the metal-bound polarized aldehyde. More recently, Corey has formulated a model exemplified by 7 in which binding by the aldehyde to the metal is rigidified through the formation of a hydrogen-bond between the polarized formyl C-H and an oxyanionic ligand [7], The model illustrates the sophisticated design elements that can be incorporated into the preparation of transition-metal complexes that lead to exquisite control in aldehyde enantiofacial differentiation. 

The potential for transition metal complexes to provide new reactivity patterns continues to be explored by the preparation of complexes and the study of their reactivity patterns. The aminoalkyl substituents of gramine, tryptamine and methyl tryptophanate promoted metalation at C2 of the indole ring by Pt(DMSO)2Cl2. The crystal structure of the gramine product was determined. 

The enantioselective alkylation of indoles catalyzed by C2-symmetric chiral bisoxazoline-metal complexes 90 encouraged many groups to develop superior asymmetric catalysts which are cheap, accessible, air-stable and water-tolerant. Other analogs of the bisoxazoline-metal complex 90 as chiral catalysts and new Michael acceptors have also been studied. The enantioselective alkylations of indole derivatives with of-hydroxy enones using Cu(II)-bis(oxazoline) catalysts 93 and 94 provided the adducts in good yields... 

Arylamines are commonplace. They are part of molecules with medicinally important properties, of molecules with structurally interesting properties, of materials with important electronic properties, and of transition metal complexes with catalytic activity. An aryl-nitrogen linkage is present in nitrogen heterocydes such as indoles [1, 2] and benzopyr-azoles, conjugated polymers such as polyanilines [3-9], and readily oxidizable triarylamines used in electronic applications [10-13]. The ability of aryl halides and triflates to form arylamines allows a single group to be used as a synthetic intermediate in aromatic carbon-... 

Chiral 2-(3-oxoalkyl)pyrroles and 3-(3-oxoalkyl)indoles can also be accessed by reaction in the presence of 10 mol% of chiral bis(oxazoline)/metal complexes in CH2C12 in very high yields and with ee values over 90% <2005JA4154>. Alkylation of pyrrole and of substituted indoles with, -unsaturated acyl phosphonates <2003JA10780> or 2-acyl N-methylimidazoles catalyzed by a chiral bis(oxazolinyl)pyridine (pybox)/scandium(III) triflate complex also exhibits good enantioselectivity over a broad range of substrates <2005JA8942>. 

Initial screening reactions carried out with enone 460 and A -methyl pyrrole in the presence of 10mol% of a series of chiral bis(oxazoline)/metal complexes in CH2CI2 as solvent, revealed complexes 458 and 459 as the most effective (Equation 110) <2005JA4154>. Using these catalysts Eriedel-Crafts adduct 461 (R = BnCH2) was formed in yields of 86% and 80% and most notably, with ee 92% and 91%, respectively. Indole derivatives 462 worked as efficiently as pyrroles and provided adducts 463 in good to excellent yields and enantiomeric excess (Equation 111). 

The HDN of aliphatic amines (equation 25) is relevant to the HDN of indoles (equation 26), pyridine (equation 27), and quinoline (equation 28) because these heterocycles are first hydrogenated to the aliphatic amines. A general mechanism proposed for the HDN of aliphatic amines is based on metal cluster catalysis of the transalkylation reaction in equation (33) and on metal complex catalyzed exchange of deuterimn for hydrogen in tertiary aliphatic amines (equation 34). There are other examples of amine activation in metal complexes. 

Almost aU of the pyrrole-, indole-, and carbazole-containing systems afforded stable Fe(ll) and Co(II) complexes. The only exceptions are hgands 44 and 47 which contain only aryl substituents. This indicates that two pairs of o-phenyl groups on the N-pyrrolyl substituents impose too much of a steric hindrance and/ or are too electron-withdrawing for the corresponding [N,N,N] metal complex to form. The two Fe(lII) precatalysts 54c, 55c were synthesized to evaluate the dependence of the polymerization performance on the oxidation state of the metal center. In total, twenty-one different N-azolyl complexes were prepared aiming at a thorough structure-activity evaluation (vide infra). 

J. Known bonding modes of indole and some of its derivatives in metal complexes. 

TABLE 6,2. Metal complexes of indole, indolyl and indoline ligands. 

Flavoquinone-metal complexes of Ag, Cu, Ni , Co , and Fe have been detected in aprotic solvents using n.m.r. and optical absorption spectroscopy. The stoicheiometry and formation constants were determined by metal ion titration in acetone. l,4-Di-N-butoxy-6//-indole[2,3-h]quinoxaline in CHCI3 extracts Ag from HNO3 solution, with formation of complex (61) indicated from i.r. spectra. On the other hand, the 2,3-dibutoxy-isomer shows no ability to extract. 

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