Redox Inactive Metal Ion Promoted CH Activation of Benzene to Phenol with Pd^II(bpym): Demonstrating New Strategies in Catalyst Designs

Abstract

Al in: A new strategy was introduced to modify the electronics and steric hindrance of the Pd(II) ion in order to change its reactivity towards benzene hydroxylation. In trifluoroacetic acid, free Pd(II) ions provide dominantly biphenyl, with phenol as minor product. Ligation of bpym to the Pd(II) ion results in its deactivation with regard to benzene functionalization. The addition of the redox inactive Al(III) ion to the Pd(II)(bpym) complex recovers its catalytic activity, and alters the reactivity of Pd(II) ion from benzene coupling to hydroxylation.

Immobilization of Molecular Catalysts for Enhanced Redox Catalysis

“…No oxidation of phenol occurred at 298 K, because the strong acid sites of Al‐MCM‐41 captured phenol to prevent further oxidation . Inhibition of phenol oxidation in the presence of a strong acid was also reported in a homogeneous hydroxylation of benzene …”

“…[177] Inhibition of phenol oxidation in the presence of as trong acid was also reported in ah omogeneous hydroxylation of benzene. [182] The kinetic study combined with the ESR detection of the intermediate indicated that the catalytic hydroxylation of benzene occurred via the Mn IV -oxo speciesg enerated by the reaction of [(tpa)Mn II ] 2 + with H 2 O 2 inside Al-MCM-41 ([(tpa)Mn IV (O)] 2 + @Al-MCM-41), as illustrated in Scheme 4. [177] The immobilized[ (tpa)Mn II ] 2 + @Al-MCM-41c atalyzed the hydroxylation of electron deficientn itrobenzene as well with H 2 O 2 at ah ighert emperature (323 K) to produce o-nitrophenol selectively.…”

Palladium-catalyzed aerobic acetoxylation of benzene using NOx-based redox mediators

“…For example, Fujiwara disclosed Pd(OAc) 2 /1,10-phenanthroline-catalyzed selective synthesis of phenol with O 2 in combination with CO as a sacrificial reductant [15 atm of each, turnover numbers (TON) = 12] [8]. Yin recently reported a Pd(OAc) 2 /2,2′-bipyrimidine-catalyzed process using 20 atm of O 2 , where selectivity was diverted from biphenyl to phenol when redox-inactive metals such as aluminum triflate were included in the reaction mixture (TON = 10.6) [9]. The most effective methods to date, however, employ Pd(OAc) 2 in combination with a heteropolyacid (HPA), H 3+x [PMo 12–x V x O 40 ], cocatalyst.…”

A General Strategy for Open‐Flask Alkene Isomerization by Ruthenium Hydride Complexes with Non‐Redox Metal Salts

“…For instance, the introduction of non‐redox metal ions promoted redox metal ions such as Fe, Mn, V, and Pd remarkably in reactions such as hydroxylation, C−C coupling, isomerization, and epoxidation . Evidenced by mechanism studies, the presence of non‐redox metal ions can change the coordination structure of reactive species substantially, which regulates their catalytic activities –. The presence of non‐redox metals may also alter the reaction pathway and control the yield distribution of different oxidative products .…”