Direct Synthesis of Hydrogen Peroxide in Water by Means of a Rh-Based Catalyst

Abstract

This paper reports the synthesis, structure, and mechanistic action of a Rh-based catalyst, the monohydroxide diaqua RhIII complex 1, for the direct synthesis of H2O2 from H2 and O2. Of particular interest is the elucidation of the crystal structures of 1, the low-valent RhI complex 2, the dinuclear RhII complex 3, and the peroxide RhIII complex 4 that appear in the catalytic cycle. In order to clarify the mechanistic action of the Rh-based catalyst, the catalytic reaction was investigated with 1 in water, but the possible intermediates 2–4 were isolated in organic solvents. First, we describe the synthesis, characterization, and behavior of the functioning, Rh-based catalyst. We then describe this catalytic direct synthesis of H2O2 from H2 and O2 with 1 (turnover number (TON) = 3.8 for 3 h).

Safe, One-Pot, Homogeneous Direct Synthesis of H2O2

“…A UV–vis–NIR absorption spectrum of 1 shows a shoulder at 380 nm, which is similar to the spectrum of our previous Rh II dimer with the iMP ligand (Figure S7). The XPS spectrum of 1 exhibits Rh 3d 3/2 and 3d 5/2 peaks at 313.3 and 308.7 eV (Figure S8c), which are similar to those of our previously reported Rh II dimer complex and are lower than those of the related Rh III complex 3 . These results, taken together, indicate that complex 1 adopts a dinuclear structure with divalent Rh centers.…”

“…Inspired by this idea, we previously synthesized a complex with an iMP ligand {iMP = 2,6-bis­(2-imidazolyl-1-methyl)­pyridine} that stores electrons from H 2 and, using a mixed gas of H 2 and O 2 outside the explosion range, investigated the direct synthesis of H 2 O 2 in one flask . However, the reactivity of this electron storage complex with O 2 was very low, and H 2 O 2 was hardly produced catalytically.…”

“…The Rh–Rh distance {2.7378(4) Å} of 4 was longer than those of other unsupported Rh II dimer complexes {2.624(1)–2.7052(5) Å} (Table S3). − A 1 H NMR spectrum shows peaks in the diamagnetic region, which suggests that each Rh II metal center is linked by a metal–metal bond (Figure S4). A UV–vis–NIR absorption spectrum of 1 shows a shoulder at 380 nm, which is similar to the spectrum of our previous Rh II dimer with the iMP ligand (Figure S7).…”

Employing three-blade propeller lanthanide complexes as molecular luminescent thermometers: study of temperature sensing through a concerted experimental/theory approach

“…2,6-Bis(1-methyl-imidazol-2-yl)pyridine (L) was prepared according to the literature procedure. 56 IR spectra were recorded as Nujol mulls on a Bruker-Vertex 70 spectrophotometer. The C, H, N elemental analyses were carried out in the microanalytical laboratory of the IOMC by means of a Carlo Erba Model 1106 elemental analyzer with an accepted tolerance of 0.4 units on carbon (C), hydrogen (H), and nitrogen (N).…”

Facile synthesis of Pd–Au/BNNS bimetallic catalysts for direct generation of H2O2 from H2 and O2 under environmentally friendly conditions

“…1,2 The large increase in consumption in recent years relates to an increased demand for propylene oxide, mostly used in the production of polyurethane plastics. 3,4 Currently, over 90% of H 2 O 2 is obtained via anthraquinone oxidation (AO) (Scheme 1a). This process starts with the hydrogenation of substituted anthraquinone in the presence of palladium (Pd) catalysts to form the diol.…”