883149-67-5Relevant academic research and scientific papers
Effects of bulky ligands and water in Pd-catalyzed oxidative carbonylation of phenol
Yasuda, Hiroyuki,Watarai, Keiji,Choi, Jun-Chul,Sakakura, Toshiyasu
, p. 149 - 155 (2005)
A diaryloxy Pd complex with a bulky 6,6′-dimethyl-2,2′-bipyridyl (6,6′-Me2bpy) ligand reacted with pressurized CO (5 MPa) at 25 °C to produce a diaryl carbonate, whereas a diaryloxy Pd complex with an unsubstituted 2,2′-bipyridyl (bpy) ligand hardly reacted. 1H and 13C NMR studies revealed that CO inserts into one of the Pd-O bonds in the latter complex to form a Pd aryloxycarbonyl complex, but that the subsequent reductive elimination of diaryl carbonate is slow. This is consistent with the much higher catalytic activity of the Pd-(6,6′-Me2bpy) system for the oxidative carbonylation of phenol compared to the Pd-bpy system. To verify the steric effects of the ligands, the catalytic performance was also examined using 2,2′-bioxazolyl ligands with various substituents. Introducing bulky substituents at the 4,4′-position effectively promoted the catalytic reaction. The TONs of DPC increased in the following order: methyl 2bpy ligand. The addition of molecular sieve 3A to the reaction system further improved the TON and suppressed phenyl salicylate formation. The addition of the molecular sieve also prevented CO2 formation, probably due to suppression of the reaction between CO and water, in addition to suppression of the hydrolysis of DPC.
