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The amount of free ions, ion pairs, and higher aggregate of the possible species present in a solution during the gold(I)-catalyzed alkoxylation of unsaturated hydrocarbon, i.e., ISIP (inner sphere ion pair) [(NHC)AuX] and OSIP (outer sphere ion pairs) [(NHC)Au(TME)X] [NHC 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; TME = tetramethylethylene (2,3-bis methyl-butene); X− = Cl−, BF4−, OTf−; and OTs− BArF4− (ArF = 3,5-(CF3)2C6H3)], has been determined. The 1H and 19F DOSY NMR measurements conducted in catalytic conditions indicate that the dissociation degree (α) of the equilibrium ion pair/free ions {[(NHC)Au(TME)X] [(NHC)Au(TME)]+ + X−} depends on the nature of the counterion (X−) when chloroform is the catalytic solvent: while the compounds containing OTs− and OTf− as the counterion gave a low α (which means a high number of ion pairs) of 0.13 and 0.24, respectively, the compounds containing BF4− and BArF4− showed higher α values of 0.36 and 0.32, respectively. These results experimentally confirm previous deductions based on catalytic and theoretical data: the lower the α value, the greater the catalytic activity because the anion that can activate methanol during a nucleophilic attack, although the lower propensity to activate methanol of BF4− and BArF4−, as suggested by the DFT calculations, cannot be completely overlooked. As for the effect of the solvent, α increases as the dielectric constant increases, as expected, and in particular, green solvents with high dielectric constants show a very high α (0.90, 0.84, 0.80, and 0.70 for propylene carbonate, γ-valerolactone, acetone, and methanol, respectively), thus confirming that the moderately high activity of NHC-Au-OTf in these solvents is due to the specific effect of polar functionalities (O-H, C=O, O-R) in activating methanol. Finally, the DOSY measurements conducted in p-Cymene show the formation of quadrupole species: under these conditions, the anion can better exercise its ‘template’ and ‘activating’ roles, giving the highest TOF.

The cyclometalated terpyridine complexes [Ru(η2-OAc)(NC-tpy)(PP)] (PP = dppb 1, (R,R)-Skewphos 4, (S,S)-Skewphos 5) are easily obtained from the acetate derivatives [Ru(η2-OAc)2(PP)] (PP = dppb, (R,R)-Skewphos 2, (S,S)-Skewphos 3) and tpy in methanol by elimination of AcOH. The precursors 2, 3 are prepared from [Ru(η2-OAc)2(PPh3)2] and Skewphos in cyclohexane. Conversely, the NNN complexes [Ru(η1-OAc)(NNN-tpy)(PP)]OAc (PP = (R,R)-Skewphos 6, (S,S)-Skewphos 7) are synthesized in a one pot reaction from [Ru(η2-OAc)2(PPh3)2], PP and tpy in methanol. The neutral NC-tpy 1, 4, 5 and cationic NNN-tpy 6, 7 complexes catalyze the transfer hydrogenation of acetophenone (S/C = 1000) in 2-propanol with NaOiPr under light irradiation at 30 °C. Formation of (S)-1-phenylethanol has been observed with 4, 6 in a MeOH/iPrOH mixture, whereas the R-enantiomer is obtained with 5, 7 (50–52% ee). The tpy complexes show cytotoxic activity against the anaplastic thyroid cancer 8505C and SW1736 cell lines (ED50 = 0.31–8.53 µM), with the cationic 7 displaying an ED50 of 0.31 µM, four times lower compared to the enantiomer 6.

The qualitative impact of pollutants on water quality is mainly related to their nature and their concentration, but in any case, they determine a strong impact on the involved ecosystems. In particular, refractory organic compounds represent a critical challenge, and several degradation processes have been studied and developed for their removal. Among them, heterogeneous Fenton treatment is a promising technology for wastewater and liquid waste remediation. Here, we have developed mono- and bimetallic formulations based on Co, Cu, Fe, and Mn, which were investigated for the degradation of three model organic dyes (methylene blue, rhodamine B, and malachite green). The treated samples were then analyzed by means of UV-vis spectrophotometry techniques. Bimetallic iron-based materials achieved almost complete degradation of all three model molecules in very short time. The Mn-Fe catalyst resulted in the best formulation with an almost complete degradation of methylene blue and malachite green at pH 5 in 5 min and of rhodamine B at pH 3 in 30 min. The results suggest that these formulations can be applied for the treatment of a broad range of liquid wastes comprising complex and variable organic pollutants. The investigated catalysts are extremely promising when compared to other systems reported in the literature.

The selective oxidation of primary alcohols into their corresponding carbonyl compounds is challenging because of the easy over oxidization to acids and esters. The traditional reaction requires large amounts of solvent and oxidant, causing serious environmental issues. Recently, several efforts have been made to transform the reaction into a more sustainable process. Here, we investigated the solvent-free oxidation of benzyl alcohol using air as a green oxidant in the presence of ruthenium supported on alumina and zirconia, thereby meeting atom economy and environmental requirements. The materials were extensively characterized and, in addition to their activity, selectivity, and reusability, the environmental sustainability of the process was assessed according to green chemistry metrics. XRD, TEM, and XPS analyses suggest that the formation of metallic Ru on the support plays a key role in the catalytic activity. Ru supported on alumina, after a reduction treatment, achieves good activity (62% conversion) and a complete selectivity in a very sustainable process (without a solvent and with air as oxidant), as indicated by the very low E-factor value. The formulation is very stable and maintains high activity after recycling.

The pincer complexes [MX(CNN)(PP)] (M = Ru, Os; X = Cl, OTf; HCNN = 1-(6-arylpyridin-2-yl)methanamine; PP = diphosphine) have proven to efficiently catalyze both racemization and deuteration of alcohols in the presence of a base. Chiral alcohols have been racemized at 30–50 °C using 1 mol% of Ru or Os pincer complexes and 5 mol% of KOtBu in 2-propanol. Primary and secondary alcohols are efficiently deuterated at the α position, with respect to the OH group, using 2-propanol-d8as solvent with Ru or Os pincer complexes and KOtBu at 30–50 °C. For secondary alcohols incorporation of deuterium at the β position has also been observed. In 2-propanol-d8the pincer complexes catalyze the simultaneous deuteration and racemization of (S)-1-phenylethanol, the two processes being strictly correlated. For both reactions much the same activity has been observed with the Ru and Os complexes. The pincer complexes display a superior activity with respect to the related compounds [MCl2(NN)(PP)] (NN = bidentate amine or pyridine ligand). The synthesis of the new complexes [MCl(CNN)(PP)] (M = Ru, 2, 4and Os, 6, 7; PP = dppb, dppf) and [Ru(OTf)(CNN)(dppb)] (3) is also reported. [ABSTRACT FROM AUTHOR]

A series of chiral HCNN ligands ((S)-1b−g) (S)-2-(1-aminoethyl)-6-(aryl)pyridine (aryl = 4-MeO-phenyl, 1b; 4-CF3-phenyl, 1c; 3,5-di-Me-phenyl, 1d; 3,5-di-CF3-phenyl, 1e; 1-naphthyl, 1f; 2-naphthyl, 1g) were synthesized starting from commercial 2-acetyl-6-bromopyridine (2), by a chemoenzymatic method involving the dynamic kinetic resolution of the corresponding secondary alcohol (rac-3). The conversion of the resulting (R)-3, obtained in 98% ee, into the homochiral amine ((S)-6), followed by Suzuki coupling with the appropriate arylboronic acids 7b−g, gave access to (S)-1b−g, isolated in 97% ee, with an overall yield up to 50%. The in situ generated pincer complexes [MCl(CNN)(PP)] (M = Ru, Os; PP = Josiphos diphosphine), prepared from [MCl2(PPh3)3], (R,S)-Josiphos diphosphines, and the ligands (S)-1b−g, were found to efficiently catalyze the asymmetric transfer hydrogenation of acetophenone in 2-propanol at 60 °C and in the presence of NaOiPr. On the basis of these data, the 2-naphthyl ruthenium and osmium derivatives [RuCl(CNN)((R,S)-Josiphos*)] (8) (HCNN = (S)-1g) and [OsCl(CNN)(PP)] (PP = (R,S)-Josiphos, 9, and (R,S)-Josiphos*, 10) were isolated from [MCl2(PPh3)3], (R,S)-Josiphos diphosphines, and the ligand (S)-1g. Complexes 8and 10, displaying the correctly matched chiral PP and CNN−ligands, are highly active and productive catalysts for the transfer hydrogenation of alkyl aryl ketones and methyl pyridyl ketones with TOF = 105−106h−1, using 0.005 mol % of catalysts and achieving up to 99% ee. The comparison of the catalytic activity of these pincer complexes shows that Ru and Os derivatives display similar rate and enantioselectivity. [ABSTRACT FROM AUTHOR]

The pincer complexes [RuX(CNN)(dppb)] (5−11: X = carboxylate, phenoxide, alkoxide, silanolate, triflate; HCNN = 1-[6-(4′-methylphenyl)pyridin-2-yl]methanamine; dppb = Ph2P(CH2)4PPh2), containing the Ru−NH2functionality and a monodentate oxygen donor ligand, have been prepared in high yield starting from [RuCl(CNN)(dppb)] (1) via substitution of the chloride with sodium or thallium compounds or protonation of the alkoxide [Ru(OiPr)(CNN)(dppb)]·n(iPrOH) (3). In the solid state the formate 5shows intermolecular NH···O hydrogen bonds, whereas the acetate 6displays an intramolecular interaction, as inferred from X-ray studies. Addition of phenol and alcohol compounds to the phenoxide and alkoxide complexes leads to fast ligand exchange through hydrogen bond interactions. The corresponding pincer complexes [RuX(CNN′)(dppb)] (12,13b: X = phenoxide, alkoxide; HCNN′ = N,N-dimethyl-1-[6-(4′-methylphenyl)pyridin-2-yl]methanamine), containing the Ru−NMe2moiety, have been obtained from [RuCl(CNN′)(dppb)] (4) and sodium phenoxide or alkoxide. All the NH2complexes 5−11are highly active catalysts in the transfer hydrogenation of ketones in 2-propanol with NaOiPr, affording complete conversion in a few minutes and achieving TOF values of up to 3.8 × 106h−1with 0.005 mol % of catalyst. [ABSTRACT FROM AUTHOR]

Ruthenium complexes of the general formula RuCl2(PPh3)(PNN‘) have been obtained from tridentate PNN‘ ligands containing phosphine (P), amine or imine (N), and pyridyl donor groups (N‘). The imino ligand Ph2P(o,o‘-C6H4CHNCH2C5H4N) (a) has been synthesized from Ph2P(2-C6H4CHO) and 2-(aminomethyl)pyridine, whereas amino Ph2P(o,o‘-C6H4CH2NHCH2C5H4N) (b) is prepared by the reduction of awith NaBH4. The complexes trans-RuCl2(PPh3)(PNN‘) PNN‘ b, (1); a, (2) containing a five-membered NN‘ cycle have been isolated in high yield by the reaction of RuCl2(PPh3)3with band a, respectively. By the same route and using the ligand Ph2P(o,o‘-C6H4CHNCH2CH2C5H4N) (c), the complex cis-RuCl2(PPh3)(c) (3) was isolated, and it displays a different stereochemistry as a result of the different size of the tridentate ligand. For the amino derivative 1, an X-ray diffraction experiment was carried out. Treatment of RuHCl(PPh3)3with the ligands aor bleads to the monohydride complexes trans-RuHCl(PPh3)(PNN‘) PNN‘ b, (4); a, (5). Complexes 1−5have been proven to catalyze the transfer hydrogenation of linear, cyclic, and aromatic ketones to secondary alcohols in 2-propanol at reflux and in the presence of (CH3)2CHONa with a very high rate (TOF values up to 250 000 h-1). The trans derivatives 1and 2containing the amino and imino functions catalyze the reduction of acetophenone with the same activity (TOF 190 000 and 185 000 h-1, respectively), suggesting that the CN group is reduced during catalysis. A lower activity has been observed for complexes 3−5. [ABSTRACT FROM AUTHOR]