The first now-named Stille reaction was published 38 years ago, and the last comprehensive revision of this catalysis was in 2004. Since then, the knowledge of the different steps of the three possible (and sometimes competing) reaction pathways (cyclic, open, and ionic) has been almost completed by synergistic experimental and theoretical studies: the Stille reaction is perhaps the best characterized catalytic process if we consider the number of intermediates that have been detected. This review concentrates on the mechanistic new knowledge and on important aspects such as the revolution with the use of bulky phosphines, the bimetallic alternative of the Stille reaction, the enantioselectivity in Stille and palladium-free Stille processes, the meaning of copper effect, or the possible approaches to make Stille coupling a greener process.
12 July 2018 in ACS Applied Materials & Interfaces
A new generation of porous polymer networks, PPNs, has been obtained in quantitative yield by reacting in superacidic media two rigid trifunctional aromatic monomers (1,3,5-triphenylbenzene and triptycene) with two ketones having electron-withdrawing groups (trifluoroacetophenone and isatin). The resulting amorphous networks are microporous materials, with moderate BET surface areas (from 580 to 790 m2 g-1) and have high thermal stability. In particular, isatin yields networks with a very high narrow microporosity contribution, 82% for triptycene and 64% for 1,3,5-triphenylbenzene. The existence of favorable interactions between lactams and CO2 molecules has been stated. The materials show excellent CO2 uptakes (up to 207 mg g-1 at 0 ºC/1 bar) and can be regenerated by vacuum, without heating. Under post-combustion conditions, their CO2/N2 selectivities are comparable to those of other organic porous networks. Because of the easily scalable synthetic method and their favorable characteristics, these materials are very promising as industrial adsorbents.
The main sequential intermediates involved in a real catalytic cycle of the Stille reaction (the coupling of ROTf with CH2 CHSnBu3 catalyzed by [PdR(OTf)(dppe)]; R = aryl) are observed and characterized unequivocally before the coupling product is released.