Highly Efficient Hydrogenation Ruthenium and Osmium Catalysts based on Ampy type Ligands

Ruthenium phosphine complexes have been widely examined in homogeneous hydrogenation (HY) and transfer hydrogenation reactions (TH), which are cost-effective and environmentally benign ways accepted in the industry for the reduction of carbonyl compounds. On account of the reversibility of the C-H bond activation, ruthenium catalysts have attracted a great deal of interest for a number of organic transformations, including borrowing hydrogen reactions. In this context, the design of efficient chelating and non-innocent ligands is crucial to achieve high activity and retard catalyst deactivation. Highly efficient Ru and Os catalysts for both TH and HY reactions were obtained by our group with ligands based on the 2-(aminomethyl)pyridine motif (A). More productive catalysts were subsequently developed by employment of pincer terdentate CNN ligands showing a metal-carbon \u3c3-bond (B).1 These complexes allow fast reduction of ketones and aldehydes, including some biomass derivatives (5-HMF, ethyl levulinate), with H2, 2-propanol or ammonium formate at S/C up to 105. Employment of chiral catalysts in the ketone reduction afforded alcohols with up to 99% ee. The Ru and Os derivatives A and B can also catalyze the acceptorless DHY of alcohols to ketones and other transformations involving alcohol C-H activation, namely alcohol racemization, deuteration and ketone \u3b1-alkylation. Evidence has been provided that the catalytically active Ru hydride species are in rapid equilibrium with metal-amino alkoxides

Pincer and Carbonyl Ruthenium Complexes for Transfer Hydrogenation Reactions

The transfer hydrogenation (TH) catalyzed by ruthenium complexes is a cost-effective and environmentally benign way for the reduction of carbonyl compounds. On account of the reversibility of the TH process, ruthenium catalysts have attracted a great deal of interest for a number of C-H activation organic transformations. To improve the catalytic activity and to retard decomposition, the design of suitable chelating and non-innocent ligands appears crucial. We report here the preparation of pincer, carbonyl and acetate ruthenium complexes, displaying high productivity for the TH of carbonyl compounds, including flavanones and biomass-derived molecules (5-HMF, ethyl levulinate). The alkylation of amines with alcohols and the preliminary results on the photochemical TH of carbonyl compounds are also presented

Terpyridine Diphosphine Ruthenium Complexes as Efficient Photocatalysts for the Transfer Hydrogenation of Carbonyl Compounds

Over the past decade, visible-light photoredox catalysis or photocatalysis has grown to become a commonly employed powerful tool in organic synthesis leading to new unique and valuable molecular transformations, inaccessible from thermally activated processes.[1] Photocatalysis can be conducted in homogeneous conditions as well as employing heterogeneous transition metal or solid semiconductors.[2] The commonly employed homogeneous visible-light photocatalysts are homoleptic Ru and Ir polypyridyl complexes, like [Ru(bpy)3]2+ and [Ir(ppy)3] (bpy = 2,2’-bipyridine; ppy = 2-phenylpyridine). These compounds, when excited by visible light undergo a metal-to-ligand-charge transfer (MLCT) transitions from HOMO and LUMO orbitals of the ligand.[3] The 2,2’:6’,2”- terpyridine (tpy) is an NNN-type Pincer ligand, which can give tight chelation of various metal cations in a nearly planar geometry. The presence of the electron-deficient pyridine cycles make it a strong σ-donor and also as a very good π-receptor, moreover the presence of low energetic LUMO levels allows it to participate in the redox reactions as a non-innocent ligand.[4] Among the catalytical reactions, the transfer hydrogenation (TH) of carbonyl compounds promoted by Ru complexes is a core process for the synthesis of alcohols in an environmentally friendly and widely accepted method in industry.[5] We report herein a practical and innovative procedure for the synthesis of a new class of ruthenium cationic [RuX(PP)(tpy)]Y (PP = diphosphine; X = Cl, OAc; Y = Cl, OAc, PF6) complexes containing tpy and a suitable diphosphine (Figure 1). These cationic complexes are active visible-light photocatalysts for the TH of carbonyl compounds at 30 °C in 2- propanol

Ru–Ag and Ru–Au dicarbene complexes from an abnormal carbene ruthenium system

The first complexes containing an anionic dicarbene connected to two different d-block elements are reported. The synthetic pathway entails metalation and transmetalation reactions, starting from a cationic abnormal Ru-NHC complex

Sustainable solvent-free selective oxidation of benzyl alcohol using Ru(0) supported on alumina

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.Peer ReviewedPostprint (published version

Mild N-Alkylation of Amines with Alcohols Catalyzed by Acetate Ruthenium Complexes

The formation of C-N bonds for the preparation of amines compounds is a reaction of high relevance for the synthesis of bulk and fine chemicals (1). The preparation of several drug molecules involves N-substitution transformations that are usually performed by reaction of amines with alkylating agents or via reductive amination. In this context, the catalytic Nalkylation of amines using environmentally friendly alcohols as alkylating reagents and affording water as only byproduct, is an attractive atom-economic way for the C-N bond formation (2,3). We report here the straightforward synthesis of the carboxylate ruthenium complexes of formula Ru(OAc)2(diphosphane)(CO)n (n = 0, 1). These compounds are efficient catalysts for the N-alkylation of amines using primary alcohols under mild reaction conditions, with an alcohol / amine molar ratio of 10-100. Evidence has been provided that in catalysis a monohydride species is formed through an equilibrium reaction

New frontiers of cognitive rehabilitation in geriatric age: the Mozart effect (ME)

The ME was described for the first time in 1993. Subsequently other studies with similar designs were performed. The present study, therefore, proposes: (i) to verify the existence of the benefits of exposure to music in elderly subjects with mild cognitive impairment (MCI), (ii) to explore whether it is possible to find any lasting improvement after training, conducted for a long period of time, with such musical pieces, in the measurable cognitive performances. The study we conducted showed that the ME is present in geriatric patients with MCI; the influence on spatial–temporal abilities remains constant in time if the stimulation is maintained. The continuation of our study will consist of increasing the number of individuals examined and in having them listen to music during the study of ECG rhythms and during the acquisition of cerebral functional magnetic resonance imaging (fMRI), and, at the same time, testing them by neuropsychometric methods

Enantioselective Cytotoxicity of Chiral Diphosphine Ruthenium(II) Complexes Against Cancer Cells

The chiral cationic complex [Ru(η1-OAc)(CO)((R,R)-Skewphos)(phen)]OAc (2R), isolated from reaction of [Ru(η1-OAc)(η2-OAc)(R,R)-Skewphos)(CO)] (1R) with phen, reacts with NaOPiv and KSAc affording [RuX(CO)((R,R)-Skewphos)(phen)]Y (X=Y=OPiv 3R; X=SAc, Y=OAc 4R). The corresponding enantiomers 2S-4S have been obtained from 1S containing (S,S)-Skewphos. Reaction of 2R and 2S with (S)-cysteine and NaPF6 at pH=9 gives the diastereoisomers [Ru((S)-Cys)(CO)(PP)(phen)]PF6 (PP=(R,R)-Skewphos 2R-Cys; (S,S)-Skewphos 2S-Cys). The DFT energetic profile for 2R with (S)-cysteine in H2O indicates that aquo and hydroxo species are involved in formation of 2R-Cys. The stability of the ruthenium complexes in 0.9 % w/v NaCl solution, PBS and complete DMEM medium, as well as their n-octanol/water partition coefficient (logP), have been evaluated. The chiral complexes show high cytotoxic activity against SW1736, 8505 C, HCT-116 and A549 cell lines with EC50 values of 2.8–0.04 μM. The (R,R)-Skewphos derivatives show higher cytotoxicity compared to their enantiomers, 4R (EC50=0.04 μM) being 14 times more cytotoxic than 4S against the anaplastic thyroid cancer 8505 C cell line