A Remote ‘Imidazole’‐Based Ruthenium(II) Para‐Cymene Pre‐catalyst for the Selective Oxidation Reaction of Alkyl Arenes and Alcohols

Abstract

Herein we disclosed the use of a remote ‘imidazole’‐based precatalyst [(para‐cymene)RuII(L)Cl]+, C‐1 where L=2‐(4‐substituted‐phenyl)‐1H‐imidazo[4,5‐f][1,10] phenanthroline) for the selective oxidation of a variety of alkyl arenes/heteroarenes and alcohols to their corresponding aldehydes or ketones in presence of tert‐butyl hydroperoxide (TBHP). The remote ‘imidazole’ moiety present in the complex facilitates the activation of oxidant and subsequent generation of active species via the release of para‐cymene from C‐1, which in‐turn was less effective without the ‘imidazole’ moiety. The mechanistic features of C‐1 promoted oxidation of alkyl arenes were also assessed from spectroscopic, kinetic, and few control experiments. The substrate scope for C‐1 promoted oxidation reaction was assessed based on the selective oxidation of 27‐different alkyl arenes/heteroarenes and 25 different alcohols to their corresponding aldehydes/ketones in moderate to good yields.

p-Xylene Oxidation to Terephthalic Acid: New Trends

“…al. [ 56 ] reported, in 2020, that the use of a ruthenium(II) complex achieved interesting results at 60 °C in the presence of TBHP. While oxidizing 4-methyl benzyl alcohol, it was possible to oxidize the methyl group to an aldehyde (with a yield of 65% after 3 h), maintaining the alcohol in the aromatic ring and avoiding the formation of p-toluic acid.…”

Design and synthesis of dinuclear cobalt(ii) complexes derived from strong π-acidic ligands: crystal structure and studies on the oxidation of sp3 C–H bonds

“…1 H NMR (400 MHz, CDCl 3 ) d 7.60-7.58 (m, 2H), 7.45-7.39 (m, 4H), 7.24-7.20 (m, 2H). 13 63 . Light yellow liquid.…”

Selective Oxidation of Alkylarene in H2O Catalyzed by the Polyoxometalate Supported Chromium Catalyst

“…[17] The peak of À OH and À CH 2 on benzyl alcohol (H 2 , H 3 ) around 3.5 ppm and 4.6 ppm appeared shortly when the reaction started, which indicated the formation of benzyl alcohol. In the third step, benzyl alcohol interacts with intermediate C. [17] Among C, one of the MoÀ O bonds breaks, forming a MoÀ OÀ Ph bond to generate intermediate D. [13,15] Through the transfer of α-H from the benzyl position of intermediate D to the cleaved peroxy group, benzaldehyde is generated, and catalyst 1 is released, thus completing the catalytic cycle process. [34] Correspondingly, we can see on the 1 H NMR that the peak of À CHO on benzaldehyde (H 4 ) around 10 ppm appeared gradually (Figure 1).…”

“…[8][9][10] Endeavors to address the drawbacks have promoted tremendous progresses in the past years and gradually the efficient catalytic systems towards selective oxidation of methylarene CÀ H bonds established (Scheme 1). [11][12][13][14][15][16][17][18][19][20][21][22] Pappo and coworkers set out the pioneering work by adopting Co(OAc) 2 or Mn(OAc) 2 /N-hydroxyphthalimide (NHPI) in hexafluoropropan-2ol (HFIP) and achieved high efficiency in the synthesis of a variety of benzaldehydes. [12] In 2019, Pratihar team reported using a ruthenium (II) precatalyst and TBHP as oxidant to get the controlled and predictably selective oxidation of methyl-arenes/alkylarenes and aliphatic alkanes.…”

“…Endeavors to address the drawbacks have promoted tremendous progresses in the past years and gradually the efficient catalytic systems towards selective oxidation of methylarene C−H bonds established (Scheme 1). [11–22] Pappo and coworkers set out the pioneering work by adopting Co(OAc) 2 or Mn(OAc) 2 /N‐hydroxyphthalimide (NHPI) in hexafluoropropan‐2‐ol (HFIP) and achieved high efficiency in the synthesis of a variety of benzaldehydes [12] …”