10.1021/om300792b.s001
Chin Min Wong
Chin Min
Wong
Khuong
Q. Vuong
Khuong
Q.
Vuong
Mark R. D. Gatus
Mark
R. D. Gatus
Carol Hua
Carol
Hua
Mohan Bhadbhade
Mohan
Bhadbhade
Barbara A. Messerle
Barbara A.
Messerle
Catalyzed Tandem C–N/C–C
Bond Formation for the Synthesis of Tricyclic Indoles using Ir(III)
Pyrazolyl-1,2,3-Triazolyl Complexes
American Chemical Society
2012
Ir complexes
Rh
bond
formation
BArF
catalyst
NMR
TOF
indole
hydroxyalk
trend PhCH 2
2012-11-12 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Catalyzed_Tandem_C_N_C_C_Bond_Formation_for_the_Synthesis_of_Tricyclic_Indoles_using_Ir_III_Pyrazolyl_1_2_3_Triazolyl_Complexes/2470357
A series of new pyrazolyl-1,2,3-triazolyl N<i>–</i>N′ bidentate donor ligands (<b>2a</b>–<b>c</b>, <b>3a</b>–<b>d</b>) 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<sub>2</sub> < <i>p</i>-CH<sub>3</sub>Ph < Ph < <i>p</i>-CF<sub>3</sub>Ph < <i>p</i>-NO<sub>2</sub>Ph, as illustrated in the gradual downfield
shift of the 1,2,3-triazolyl-<i>C</i>4′ <sup>13</sup>C 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<sup>F</sup><sub>4</sub>, BPh<sub>4</sub>; <b>5</b>–<b>8</b>), [Rh(N–N′)Cp*Cl]X (X = BAr<sup>F</sup><sub>4</sub>, BPh<sub>4</sub>; <b>9</b>–<b>11</b>), and [Rh(N–N′)(CO)<sub>2</sub>]BAr<sup>F</sup><sub>4</sub> (<b>13</b>–<b>16</b>) (BAr<sup>F</sup><sub>4</sub> = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)
were synthesized and fully characterized. The solid-state structures
of <b>5</b>, <b>6a′</b>, <b>6b</b>, <b>7b</b>, <b>8</b>, <b>9</b>, <b>10a</b>, <b>10a′</b>, <b>11</b>, and <b>15c</b> 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 (<b>17S</b>–<b>20S</b>) was assessed. The Ir(III) catalysts were the most efficient
for the C–C bond formation step, and the Rh(I) complexes <b>13</b>–<b>16</b> were the most efficient catalysts
for C–N bond formation, where TOFs >1000 h<sup>–1</sup> were reached. However, the Ir(III) complexes <b>5</b>–<b>8</b> 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 <b>17S</b>, <b>18S</b>, and <b>20S</b>.