Correction for 'Adipic acid formation from cyclohexanediol using platinum and vanadium catalysts: elucidating the role of homogeneous vanadium species' by Owen Rogers et al., Catal. Sci. Technol., 2020, 10, 4210-4218, https://doi.org/10.1039/D0CY00914H

Correction for ‘Adipic acid formation from cyclohexanediol using platinum and vanadium catalysts: elucidating the role of homogeneous vanadium species’ by Owen Rogers et al., Catal. Sci. Technol., 2020, 10, 4210–4218, https://doi.org/10.1039/D0CY00914H

Selectivity in the oxidation of alkylated polynuclear aromatic hydrocarbon can be specifically controlled by the choice solvent.

The applicability of platinum and vanadium catalysts for the production of adipic acid from cyclohexanediol is severely limited by the instability of the latter species in liquid phase reactions.

With the aim of exploiting new organometallic species for cross‐coupling reactions, we report here on the Au III ‐mediated C aryl −P bond formation occurring upon reaction of C^N cyclometalated Au III complexes with phosphines. The [Au(C^N)Cl 2 ] complex 1 featuring the bidentate 2‐benzoylpyridine (C CO N) scaffold was found to react with PTA (1,3,5‐triaza‐7‐phosphaadamantane) under mild conditions, including in water, to afford the corresponding phosphonium 5 through C−P reductive elimination. A mechanism is proposed for the title reaction based on in situ 31 P{ 1 H} NMR and HR‐ESI‐MS analyses combined with DFT calculations. The C−P coupling has been generalized to other C^N cyclometalated Au III complexes and other tertiary phosphines. Overall, this work provides new insights into the reactivity of cyclometalated Au III compounds and establishes initial structure–activity relationships to develop Au III ‐mediated C−P cross‐coupling reactions.

With the aim of exploiting new organometallic species for cross-coupling reactions, we report here on the AuIII -mediated Caryl -P bond formation occurring upon reaction of C^N cyclometalated AuIII complexes with phosphines. The [Au(C^N)Cl2 ] complex 1 featuring the bidentate 2-benzoylpyridine (CCO N) scaffold was found to react with PTA (1,3,5-triaza-7-phosphaadamantane) under mild conditions, including in water, to afford the corresponding phosphonium 5 through C-P reductive elimination. A mechanism is proposed for the title reaction based on in situ 31 P{1 H} NMR and HR-ESI-MS analyses combined with DFT calculations. The C-P coupling has been generalized to other C^N cyclometalated AuIII complexes and other tertiary phosphines. Overall, this work provides new insights into the reactivity of cyclometalated AuIII compounds and establishes initial structure-activity relationships to develop AuIII -mediated C-P cross-coupling reactions.

With the aim of exploiting new organometallic species for cross-coupling reactions, we report here on the Au-III-mediated C-aryl-P bond formation occurring upon reaction of C<^>N cyclometalated Au-III complexes with phosphines. The [Au(C<^>N)Cl-2] complex 1 featuring the bidentate 2-benzoylpyridine ((CN)-N-CO) scaffold was found to react with PTA (1,3,5-triaza-7-phosphaadamantane) under mild conditions, including in water, to afford the corresponding phosphonium 5 through C-P reductive elimination. A mechanism is proposed for the title reaction based on in situ P-31{H-1} NMR and HR-ESI-MS analyses combined with DFT calculations. The C-P coupling has been generalized to other C<^>N cyclometalated Au-III complexes and other tertiary phosphines. Overall, this work provides new insights into the reactivity of cyclometalated Au-III compounds and establishes initial structure-activity relationships to develop Au-III-mediated C-P cross-coupling reactions.

Within the framework of designing new self-assembled metallosupramolecular architectures for drug delivery, seven [Pd2L4]4+ metallacages (L = 2,6-bis(pyridine-3-ylethynyl)pyridine) featuring different groups in exo-position, selected to enhance the cage solubility in aqueous environment, were synthesized. Thus, carboxylic acids, sugars, and PEG groups were tethered to the bispyridyl ligands directly or via disulfide bond formation, as well as via click chemistry. The ligands and respective cages were characterized by different methods, including NMR spectroscopy and high-resolution electrospray mass spectrometry (HR-ESI-MS). While the two ligands featuring carboxylic acid-functionalized groups showed improved solubility in water, the other ligands were soluble only in organic solvents. Unfortunately, all the respective self-assembled cages were also insoluble in water. Afterwards, the encapsulation properties of the anticancer drug cisplatin in selected [Pd2L4]X4 cages (X = NO3-, BF4-) were studied by 1H, 1H DOSY, and 195Pt NMR spectroscopy. The effect of the counter ions as well as of the polarity of the solvent in the drug encapsulation process were also investigated, and provided useful information on the host-guest properties of these experimental drug delivery systems. Our results provide further experimental support for previous studies that suggest the desolvation of guests from surrounding solvent molecules and the resulting solvent rearrangement may actually be the primary driving force for determining guest binding affinities in metallacages, in the absence of specific functional group interactions.

Catalytic hydrogenation of levulinic acid to form gamma-valerolactone was studied over Cu-ZrO2 catalysts doped with metal oxides from the first-row transition metals. The Cu-ZrO2 material was prepared by oxalate gel coprecipitation, and dopants were added by an incipient wetness approach. The addition of 1% Mn into Cu ZrO2 significantly increases the yield of y-valerolactone, and the catalytic activity of Mn/Cu-ZrO2 was found to be 1.6 times higher than that of the undoped Cu ZrO2 catalyst. Catalyst characterization suggests that the Mn dopant improves the dispersion of Cu on the surface of ZrO2. Kinetic studies show that the reaction order with respect to the substrate concentration is approximately zero. However, the order of reaction with respect to the partial pressure of H-2 is different for the Mn/Cu-ZrO2 and Cu-ZrO2 catalysts. Comparison of reaction products from reactions carried out in H2O and D2O solvents using H-1 NMR and C-13 NMR show that there is a pre equilibrium keto enol isomerization step under our reaction conditions. DFT calculations show that the enol isomers have a higher affinity for the Cu surface, which may improve the substrate in the hydrogenation step of the reaction.

Terpene synthases catalyse the first step in the conversion of prenyl diphosphates to terpenoids. They act as templates for their substrates to generate a reactive conformation, from which a Mg2+-dependent reaction creates a carbocation-PP, ion pair that undergoes a series of rearrangements and (de)-protonations to give the final terpene product. This tight conformational control was exploited for the (R)-germacrene A synthase- and germacradien-4-ol synthase-catalysed formation of a medium-sized cyclic terpenoid ether from substrates containing nucleophilic functional groups. Farnesyl diphosphate analogues with a 10,11-epoxide or an allylic alcohol were efficiently converted to a 11-membered cyclic terpenoid ether that was characterised by HRMS and NMR spectroscopic analyses. Further experiments showed that other sesquiterpene synthases, including aristolochene synthase, delta-cadinene synthase and amorphadiene synthase, yielded this novel terpenoid from the same substrate analogues. This work illustrates the potential of terpene synthases for the efficient generation of structurally and functionally novel medium-sized terpene ethers.

Inline, real time NMR and temperature measurements have been used to optimise the continuous flow synthesis of difluoromethyltrimethylsilane (TMSCF2H) by the reduction of the Ruppert-Prakash reagent (TMSCF3). These measurements were used to maximise the space-time-yield, while ensuring this exothermic process remains safe. In this way, a three-fold increase in space-time-yield was achieved compared to the reported batch procedure, isolating 25 g of pure TMSCF2H after 105 min. (C) 2018 Published by Elsevier Ltd.

Ruthenium-ion-catalyzed oxidation (RICO) of polyaromatic hydrocarbons (PAHs) has been studied in detail using experimental and computational approaches to explore the reaction mechanism. DFT calculations show that regioselectivity in these reactions can be understood in terms of the preservation of aromaticity in the initial formation of a [3+2] metallocycle intermediate at the most-isolated double bond. We identify two competing pathways: C-C bond cleavage leading to a dialdehyde and C-H activation followed by H migration to the RuOx complex to give diketones. Experimentally, the oxidation of pyrene and phenanthrene has been carried out in monophasic and biphasic solvent systems. Our results show that diketones are the major product for both phenanthrene and pyrene substrates. These diketone products are shown to be stable under our reaction conditions so that higher oxidation products (acids and their derivatives) are assigned to the competing pathway through the dialdehyde. Experiments using 18 O-labelled water do show incorporation of oxygen from the solvents into products, but this may take place during the formation of the reactive RuO4 species rather than directly during PAH oxidation. When the oxidation of pyrene is carried out using D2 O, a kinetic isotope effect (KIE) is observed implying that water is involved in the rate-determining step leading to the diketone products.

The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O2) as an oxidant in the presence of hydrogen peroxide (H2O2), we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O2 More oxygenated products were formed than the amount of H2O2 consumed, suggesting that the controlled breakdown of H2O2 activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.

Oxidation of aromatic hydrocarbons with differing numbers of fused aromatic rings (2-5), have been studied in two solvent environments (monophasic and biphasic) using ruthenium-ion-catalyzed oxidation (RICO). RICO reduces the aromaticity of the polyaromatic core of the molecule in a controlled manner by selective oxidative ring opening. Moreover, the nature of the solvent system determines the product type and distribution, for molecules with more than two aromatic rings. Competitive oxidation between substrates with different numbers of aromatic rings has been studied in detail. It was found that the rate of polyaromatic hydrocarbon oxidation increases with the number of fused aromatic rings. A similar trend was also identified for alkylated aromatic hydrocarbons. The proof-of-concept investigation provides new insight into selective oxidation chemistry for upgrading of polyaromatic molecules.

Graphitic oxide has potential as a carbocatalyst for a wide range of reactions. Interest in this material has risen enormously due to it being a precursor to graphene via the chemical oxidation of graphite. Despite some studies suggesting that the chosen method of graphite oxidation can influence the physical properties of the graphitic oxide, the preparation method and extent of oxidation remain unresolved for catalytic applications. Here we show that tuning the graphitic oxide surface can be achieved by varying the amount and type of oxidant. The resulting materials differ in level of oxidation, surface oxygen content and functionality. Most importantly, we show that these graphitic oxide materials are active as unique carbocatalysts for low-temperature aerobic epoxidation of linear alkenes in the absence of initiator or metal. An optimum level of oxidation is necessary and materials produced via conventional permanganate-based methods are far from optimal.

The coordination chemistry of scandium supported by bis(oxazolinylphenyl)amide (R-BOPA) ligands is reported. The R-BOPA ligand is too sterically demanding to afford bis(amide) complexes [Sc(R-BOPA){N(SiMe3)2}2], but reaction of the protio-ligand with [Sc{N(SiMe3)2}2Cl(THF)] (1) afforded the mixed amido-chloride complexes [Sc(R-BOPA){N(SiMe3)2}Cl] (2). The selective reaction of the amido and chloride co-ligands in 2 has been investigated; whilst the chloride ligand can be removed cleanly by metathesis, protonation of the N(SiMe3)2 ligand results in competitive protonation of the R-BOPA ligand. The complexes [Sc(R-BOPA)(CH2SiMe2Ph)2] (5) have been synthesised. Each R-BOPA-containing complex exists in two isomeric forms. The equilibrium has been investigated both experimentally and computationally, and the data suggest that a concerted rotation of the phenyl rings interconverts the two diastereomeric isomers. All of the R-BOPA complexes were found to be luminescent; an analysis of the photophysics, aided by TD-DFT calculations, suggests ligand-centred luminescence with distinct emission lifetimes for each isomer.

We report the oxidation of propane under mild aqueous conditions using H2O2 as the oxidant.

Fe-containing ZSM-5 catalysts are reported to be efficient catalysts for the partial oxidation of propane to oxygenated products at reaction temperatures as low as 50 degrees C in an aqueous phase reaction when using the green oxidant H2O2. It was previously proposed that extra framework Fe species at the exchange sites of the zeolite are responsible for activation of both the alkane and hydrogen peroxide. Through a systematic study of the influence of framework topology and exchange properties, it is now shown that this high catalytic activity is specific to the MFI-type BrOnsted acidic zeolite ZSM-5. Furthermore, through a simple aqueous acid washing treatment, leaching of approximately 77% of iron present within a Fe/ZSM-5 catalyst only caused the relative propane conversion to decrease by 17%; implying that most of the initially loaded Fe does not actually contribute to the catalytic activity. This small change in conversion after excess' Fe removal, amounts to a three-fold increase in turnover frequency (TOF) (Fe) from 66h(-1) to 232h(-1) compared with the parent Fe/ZSM-5 catalyst. By comparing these samples, it is shown by NH3 temperature-programmed desorption, Al-27 magic angle spinning NMR spectroscopy, X-ray photoelectron spectroscopy and TEM analysis that surface iron oxide species are effectively spectators in the oxidation of propane with H2O2. This provides further insight as to the location and true nature of the catalytically active Fe species.