Pd-catalyzed C–H bond activation of benzene in the CO2-expanded solvent

ChemInform Abstract: Highly Active Palladium‐Based Catalyst System for the Aerobic Oxidative Direct Coupling of Benzene to Biphenyl.

“…For this reason, in various previous studies some cocatalysts were introduced to help the regeneration of Pd II . [19][20][21][22][23][24][25][26] In this work, the catalytic system of Pd(OAc) 2 -TfOH leads to no observable palladiumb lack, which suggestst hat the introduction of TfOH may inhibit the aggregation of Pd 0 species and promote the regenerationo fP d II , which thusultimately advances the whole catalytic cycle.…”

“…The corresponding TON value is as high as 180, which is far superior to all of the catalytic systems reportedp reviously for the aerobic coupling of benzene to biphenyl. [19][20][21][22][23][24][25][26] Benzoic acid (BEA) and phthalic acid (PTA) lead to inferiora ctivities ( Various solvents are tried in the reaction. Only aqueous acetic acids olution is active as the solventf or the generation of biphenyl, and no activity was observed upon using aqueous solutionso fe thanol, acetonitrile, DMF,D MSO, or mixtures of ethanol/acetic acid or acetonitrile/acetic acid as solvents.…”

“…[15][16][17][18] As ar esult,v arious metal-containing cocata-lysts werea dopted to promote the efficiency of the Pd catalyst. [19][20][21][22][23][24][25][26] PdCl 2 combinedw ith Zr IV /Mn II /Co II species led to biphenyl in ah igh yield (~84 %) with aT ON of~12. [24] Pd(OAc) 2 combined with a1 :1 mixtureo fH 4 [25] The selectivity to biphenyl was 79 %b ecause of the formation of byproducts: am ixture of o-, m-, and p-terphenyls along with as mall amount of phenol.T oe nhance the solubility of oxygen in the reaction medium, CO 2 -expanded solventw as appliedi nt he Pd(OAc) 2 -Cu(OAc) 2 catalytic system to give ab iphenyl yield of 19 %.…”

“…[24] Pd(OAc) 2 combined with a1 :1 mixtureo fH 4 [25] The selectivity to biphenyl was 79 %b ecause of the formation of byproducts: am ixture of o-, m-, and p-terphenyls along with as mall amount of phenol.T oe nhance the solubility of oxygen in the reaction medium, CO 2 -expanded solventw as appliedi nt he Pd(OAc) 2 -Cu(OAc) 2 catalytic system to give ab iphenyl yield of 19 %. [26] Nevertheless, to date, the number of studies related to the direct couplingo fb enzene to biphenyl is still limited, and the efficiency of Pd catalystf or theseb iphenyl synthesesi su nsatisfactory if we considert he yield, selectivity,a nd TON. Moreover,p reviousr eactions werep erformed with the assistanceo f as toichiometrica mount of metal-containing cocatalyst, and yet no efficient system that involves metal-free additives has been reported for the Pd-catalyzed aerobic oxidative direct coupling of benzene to biphenyl.…”

Structure of the Active Platinum Cluster and Reaction Pathway of the Selective Synthesis of Phenol from Benzene and Oxygen Regulated with Ammonia on a Platinum Cluster/β‐Zeolite Catalyst Studied by DFT Calculations

“…Therefore, a direct synthesis of phenol from benzene with molecular oxygen as the sole oxidant is desired, and realization of this ideal process has long been a challenge. In previous studies, many oxidants have been used for the direct synthesis of phenol from benzene, including O 2 , H 2 O 2 , N 2 O, H 2 +O 2 , O 2 /CO, and O 2 /NH 3 . In the H 2 +O 2 , O 2 /CO and O 2 /NH 3 systems, O 2 cannot directly transform benzene into phenol, but it is activated by reduction with H 2 (to form H 2 O 2 ), CO (as a sacrificial reagent), and NH 3 (to form N 2 O).…”