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Development of Pd Supported Catalysts Using Thiol‐Functionalized Mesoporous Silica Frameworks: Application to the Chemo‐ and Regioselective C ‐3 Arylation of Free‐Indole
Author(s) -
Renom Carrasco Marc,
Khodja Walid,
Demarcy Clément,
Veyre Laurent,
Camp Clément,
Thieuleux Chloé
Publication year - 2021
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.202001086
Subject(s) - chemistry , catalysis , palladium , leaching (pedology) , thiol , mesoporous silica , regioselectivity , selectivity , turnover number , metal , heterogeneous catalysis , surface modification , indole test , mesoporous material , combinatorial chemistry , inorganic chemistry , nuclear chemistry , organic chemistry , environmental science , soil science , soil water
We report here the development of Pd‐supported catalysts for the selective C ‐3 arylation of free‐indole using thiol‐functionalized silica supports to anchor the palladium centers. The palladium (II) complex, Pd(OAc) 2 , was efficiently loaded into various thiol‐functionalized mesostructured silicas at room temperature. These materials exhibit different contents of surface SH groups (0.3 to 1.8 SH/nm 2 ) and various SH/Pd molar ratios from 6 to 65. It was found that the catalysts containing the most isolated surface SH groups (0.3 SH/nm 2 ) and the highest loading of Pd were the most active, reaching 70 % of conversion, 1400 as turnover numbers and 100 % selectivity in the C ‐3 arylated product using only 0.05 mol % of Pd. However, a leaching of active Pd species (1.7 ppm) was detected. The best compromise was found for a specific solid containing isolated surface thiol groups (0.3 SH/nm 2 ) and a very low loading of Pd (SH/Pd=65). It exhibited a high TON (608) with a very low Pd leaching of 0.5 ppm in the course of the catalytic reaction. These results thus illustrate that both surface SH sites isolation and concentration, as well as the SH/Pd molar ratio are key parameters to access high catalytic performances and very low leaching of metal during catalysis.