1094872-17-9Relevant academic research and scientific papers
Weakly coordinating counter-ions for highly efficient catalysis of intramolecular hydroamination
Dabb, Serin L.,Ho, Joanne H. H.,Hodgson, Richard,Messerle, Barbara A.,Wagler, Joerg
, p. 634 - 642 (2009)
A series of cationic rhodium(i) and iridium(i) complexes of the type [M(L∩L)(C2)]BArF24 (where M = Rh or Ir, L∩L = bis(pyrazol-1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim) or 1-(2-(diphenylphosphino)ethyl)-3,5- diphenylpyrazole (Ph2PyP), C2 = 1,5-cyclooctadiene (COD) or (CO)2 and BArF24 = tetrakis[3,5- bis(trifluoromethyl)phenyl]borate) were synthesised in good yields. The solid-state structure of a number of complexes, including [Ir(Ph 2PyP)(COD)]BArF24, [Ir(bpm)(COD)]BAr F24 and [Ir(bim)(COD)]BArF24 was determined using X-ray crystallography. The efficiency of the complexes as catalysts for the intramolecular hydroamination of 4-phenyl-3-butyn-1-amine, 4-pentyn-1-amine and 2-(2-phenylethynyl)aniline was established. The incorporation of the BArF24- counter-ion in the Rh(i) and Ir(i) complexes was found to significantly improve the catalytic activity of the complexes, compared to the analogous Rh(i) and Ir(i) complexes containing BPh4- as the counter-ion. Excellent conversions were achieved for the cyclisation of 2-(2-phenylethynyl)aniline to 2-phenylindole using [Rh(bpm)(CO)2]BArF24 as a catalyst. The use of a microwave reactor for enhancing the catalysed reactions was also investigated. The Royal Society of Chemistry 2009.
Catalyzed tandem C-N/C-C bond formation for the synthesis of tricyclic indoles using Ir(III) pyrazolyl-1,2,3-triazolyl complexes
Wong, Chin Min,Vuong, Khuong Q.,Gatus, Mark R. D.,Hua, Carol,Bhadbhade, Mohan,Messerle, Barbara A.
, p. 7500 - 7510 (2013/01/15)
A series of new pyrazolyl-1,2,3-triazolyl N-N′ bidentate donor ligands (2a-c, 3a-d) were prepared via Cu(I)-catalyzed Huisgen cycloaddition reactions between 1-propargylpyrazoles and 4-substituted phenyl azides. The electron-withdrawing ability of the substituents follows the trend PhCH 2 3Ph 3Ph 2Ph, as illustrated in the gradual downfield shift of the 1,2,3-triazolyl-C4′ 13C NMR resonances. A series of Rh and Ir complexes containing these pyrazolyl-1,2,3-triazolyl or bis(pyrazol-1-yl)methane donor ligands of general formulae [Ir(N-N′)Cp*Cl]X (X = BAr F4, BPh4; 5-8), [Rh(N-N′)Cp*Cl]X (X = BArF4, BPh4; 9-11), and [Rh(N-N′)(CO) 2]BArF4 (13-16) (BArF4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) were synthesized and fully characterized. The solid-state structures of 5, 6a′, 6b, 7b, 8, 9, 10a, 10a′, 11, and 15c were determined by X-ray diffraction studies. As the electron-withdrawing strength of the phenylene substituent on the triazolyl ring is increased, the M-N3′(triazole) bond length becomes longer. The efficiency of these Rh and Ir complexes as catalysts for the synthesis of tricyclic indoles via tandem C-N and C-C bond formation reactions from 2-(hydroxyalk-1-ynyl)anilines (17S-20S) was assessed. The Ir(III) catalysts were the most efficient for the C-C bond formation step, and the Rh(I) complexes 13-16 were the most efficient catalysts for C-N bond formation, where TOFs >1000 h-1 were reached. However, the Ir(III) complexes 5-8 were found to be the only active catalysts for the tandem C-N and C-C bond formation, as the Rh(I) complexes were not active catalysts for the C-C bond formation step. The C-N bond formation leading to the formation of indoles was found to proceed via two reaction pathways with 2-(hydroxyalk-1-ynyl)aniline substrates: (a) hydroamination and (b) hydroalkoxylation-Lewis acid mediated isomerization. Pathway (b) is likely to be the main pathway in the formation of indoles starting with 2-(hydroxyalk-1-ynyl)aniline substrates 17S, 18S, and 20S.
