1357583-83-5Relevant academic research and scientific papers
New rhodium(I) and iridium(I) complexes containing mixed pyrazolyl-1,2,3-triazolyl ligands as catalysts for hydroamination
Hua, Carol,Vuong, Khuong Q.,Bhadbhade, Mohan,Messerle, Barbara A.
, p. 1790 - 1800 (2012/04/23)
Two new bidentate pyrazolyl-triazolyl donor ligands, 4-((1H-pyrazol-1-yl) methyl)-1-benzyl-1H-1,2,3-triazole, PyT (1a), and 4-((1H-pyrazol-1-yl)methyl)-1- phenyl-1H-1,2,3-triazole, PyS (1b), were synthesized using the copper(I)-catalyzed "click" reaction between 1-propargylpyrazole and benzyl azide or phenyl azide, respectively. Cationic rhodium(I) and iridium(I) complexes containing the new N-N′ ligands of the general formulas [M(N-N′)(COD)]X (M = Rh or Ir, N-N′ = PyT or PyS, and X = BPh 4- or BArF4- (tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) 2a-c for Rh and 3a-c for Ir) and [M(N-N′)(CO)2]X (M = Rh or Ir, N-N′ = PyT or PyS, and X = BPh4- or BArF4-4a-d for Rh and 5a-d for Ir) were successfully prepared and fully characterized. The solid-state structures of eight of these complexes were determined using single-crystal X-ray diffraction and show that the triazolyl moiety coordinates to the metal center via the N3′ atom, forming six-membered metallacycles. These metallacycles adopted a distorted boat conformation in all of the structures determined. The M-N(triazole) bonds were found to be slightly shorter than the M-N(pyrazole) bonds, illustrating the stronger donating capacity of the triazolyl donor in comparison to that of the pyrazolyl donor. All of the cationic rhodium and iridium complexes reported here are catalytically active for the intramolecular hydroamination of 4-pentyn-1-amine (6) to 2-methyl-1-pyrroline (7) at 60 °C, with TOFs > 400 h-1 in many cases. The dicarbonyl complexes [M(N-N′)(CO)2]BAr F4 (M = Rh or Ir) 4c,d and 5c,d were efficient as catalysts for the intramolecular cyclization of nonterminal alkynamines (8a,b) to cyclic imines (9a,b) via the hydroamination reaction and the cyclization of alkenamines (10a-c) to their corresponding cyclic amines (11a-c) also via the hydroamination reaction.
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.
