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N-Heterocyclic carbenes (NHCs) are nowadays one of the most widely employed ligands in organometallic chemistry and homogeneous catalysis due to the inherent stability of the metal-carbene bond and the ease of modification of the backbone as well as the N-wingtips substituents of these ligands. The functionalization of NHCs with hydrophilic groups offers the possibility of using NHC-metal complexes in aqueous catalysis, a hot topic within the Green Chemistry context due to the positive implications associated with the use of water as a reaction medium. In line with the enormous interest aroused by gold complexes in catalysis, significant efforts have been directed in the last years to the design and application of hydrophilic NHC-gold catalysts. This review is aimed to summarize the research in this area. The catalytic applications of water-soluble gold nanoparticles stabilized by hydrophilic NHCs are also covered. [ABSTRACT FROM AUTHOR]

The hydration of nitriles is an important transformation because the resulting primary amides present a huge number of applications in synthetic organic chemistry, as well as industrial and pharmaceutical interest. Metallic compounds (complexes, oxides, and nanoparticles) are known to catalyze the hydration of nitriles by activating the nitrile substrate, the water molecule, or both partners, upon coordination. In this Minireview article, the application of metal‐based catalysts in the hydration of α‐ and β‐hydroxynitriles and cyanamides is comprehensively discussed. Compared to more classical organonitriles, little attention has been paid to the hydration of these particular class of substrates despite the synthetic relevance of the respective carboxamides, i. e. α‐/β‐hydroxyamides and ureas. Transfer hydration strategies, in which a water surrogate is employed to convert the C≡N group into the C(=O)NH2 one, are also covered. [ABSTRACT FROM AUTHOR]

The preparation of the tethered arene-ruthenium(II) complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] (R = Ph, n = 1 (9a), 2 (9b), 3 (9c); R = iPr, n = 1 (10a), 2 (10b), 3 (10c)) from the corresponding phosphinite ligands R2PO(CH2)nPh (R = Ph, n = 1 (1a), 2 (1b), 3 (1c); R = iPr, n = 1 (2a), 2 (2b), 3 (2c)) is presented. Thus, in a first step, the treatment at room temperature of tetrahydrofuran solutions of dimers [{RuCl(μ-Cl)(η6-arene)}2] (arene = p-cymene (3), benzene (4)) with 1-2a-c led to the clean formation of the corresponding mononuclear derivatives [RuCl2(η6-p-cymene){R2PO(CH2)nPh}] (5-6a-c) and [RuCl2(η6-benzene){R2PO(CH2)nPh}] (7-8a-c), which were isolated in 66–99% yield. The subsequent heating of 1,2-dichloroethane solutions of these compounds at 120 °C allowed the exchange of the coordinated arene. The substitution process proceeded faster with the benzene derivatives 7-8a-c, from which complexes 9-10a-c were generated in 61–82% yield after 0.5–10 h of heating. The molecular structures of [RuCl2(η6-p-cymene){iPr2PO(CH2)3Ph}] (6c) and [RuCl2{η6:κ1(P)-C6H5(CH2)nOPiPr2}] (n = 1 (10a), 2 (10b), 3 (10c)) were unequivocally confirmed by X-ray diffraction methods. In addition, complexes [RuCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] (9-10a-c) proved to be active catalysts for the dehydrogenative coupling of hydrosilanes and alcohols under mild conditions (r.t.). The best results were obtained with [RuCl2{η6:κ1(P)-C6H5(CH2)3OPiPr2}] (10c), which reached TOF and TON values up to 117 600 h−1 and 57 000, respectively. [ABSTRACT FROM AUTHOR]

A dual ruthenium/ketoreductase catalytic system has been developed for the conversion of β‐ketonitriles into optically active β‐hydroxyamides through an unprecedented hydration/bioreduction cascade process in aqueous medium working in concurrent mode. The ketoreductase‐mediated ketone reduction took place with exquisite stereoselectivity and it was simultaneous to the nitrile hydration promoted by the ruthenium catalyst. The overall transformation occurred: (i) employing commercially and readily available catalytic systems (ii) under mild reaction conditions, (iii) with high degree of conversion and excellent stereoselectivity, and (iv) without the need to isolate intermediates and with high final product yields. This genuine process demonstrates the benefits of combining metal and enzymatic catalysis to tackle the limitations arising from each field. Metals and enzymes unite! A chemoenzymatic orthogonal tandem protocol for the highly enantioselective synthesis of β‐hydroxyamides from β‐ketonitriles in water is reported, establishing a fruitful cooperation between metal catalysts and enzymes for filling in the gaps from previous methodologies. [ABSTRACT FROM AUTHOR]

The synthesis and catalytic behavior of the osmium(II) complexes [OsCl2( η6- p-cymene)(PR2OH)] [R=Me ( 2 a), Ph ( 2 b), OMe ( 2 c), OPh ( 2 d)] in nitrile hydration reactions is presented. Among them, the best catalytic results were obtained with the phosphinous acid derivative [OsCl2( η6- p-cymene)(PMe2OH)] ( 2 a), which selectively provided the desired primary amides in excellent yields and short times at 80 °C, employing directly water as solvent, and without the assistance of any basic additive (TOF values up to 200 h−1). The process was successful with aromatic, heteroaromatic, aliphatic, and α,β-unsaturated organonitriles, and showed a high functional group tolerance. Indeed, complex 2 a represents the most active and versatile osmium-based catalyst for the hydration of nitriles reported so far in the literature. In addition, it exhibits a catalytic performance similar to that of its ruthenium analogue [RuCl2( η6- p-cymene)(PMe2OH)] ( 4). However, when compared to 4, the osmium complex 2 a turned out to be faster in the hydration of less-reactive aliphatic nitriles, whereas the opposite trend was generally observed with aromatic substrates. DFT calculations suggest that these differences in reactivity are mainly related to the ring strain associated with the key intermediate in the catalytic cycle, that is, a five-membered metallacyclic species generated by intramolecular addition of the hydroxyl group of the phosphinous acid ligand to the metal-coordinated nitrile. [ABSTRACT FROM AUTHOR]

The novel guanidinate-osmium(II) complexes [OsCl{κ2-( N, N′)-C(NR)(N iPr)NH iPr}(η6- p-cymene)] [R = Ph ( 3a), 4-C6H4F ( 3b), 4-C6H4Cl ( 3c), 4-C6H4CF3 ( 3d), 3-C6H4CF3 ( 3e), 3,5-C6H3(CF3)2 ( 3f), 4-C6H4CN ( 3g), 4-C6H4Me ( 3h), 3-C6H4Me ( 3i), 2-C6H4Me ( 3j), 4-C6H4 tBu ( 3k), 2,6-C6H3 iPr2 ( 3l), 2,4,6-C6H2Me3 ( 3m)] have been synthesized in high yields (70-88 %) by treatment of THF solutions of the dimeric precursor [{OsCl(µ-Cl)(η6- p-cymene)}2] ( 1) with 4 equivalents of the corresponding guanidine ( iPrHN)2C=NR ( 2a-m) at room temperature. The easily separable guanidinium chloride salts [( iPrHN)2C(NHR)]Cl ( 4a-m) were also formed in these reactions. The structures of 3a, 3d, and 3h were unequivocally confirmed by X-ray diffraction methods. Complexes 3a- m proved to be active in the catalytic dehydration of aldoximes. The best results were obtained with [OsCl{κ2-( N, N′)-C(N-4-C6H4CF3)(N iPr)NH iPr}(η6- p-cymene)] ( 3d; 5 mol-%), which, in acetonitrile at 80 °C, was able to convert selectively a large variety of aromatic, heteroaromatic, α,β-unsaturated, and aliphatic aldoximes into the corresponding nitriles in high yields and short reaction times. [ABSTRACT FROM AUTHOR]

Amide bond formation reactions are among the most important transformations in organic chemistry because of the widespread occurrence of amides in pharmaceuticals, natural products and biologically active compounds. The Beckmann rearrangement is a well-known method to generate secondary amides from ketoximes. However, under the acidic conditions commonly employed, aldoximes RHC=NOH rarely rearrange into the corresponding primary amides RC(=O)NH2. In recent years, it was demonstrated that this atom-economical transformation can be carried out efficiently and selectively with the help of metal catalysts. Several homogeneous and heterogenous systems have been described. In addition, protocols offering the option to generate the aldoximes in situ from the corresponding aldehydes and hydroxylamine, or even from alcohols, have also been developed, as well as a series of tandem processes allowing the access to N-substituted amide products. In this Feature article a comprehensive overview of the advances achieved in this particular research area is presented. [ABSTRACT FROM AUTHOR]

In the last few years there has been increasing interest in the use of water as a reaction medium for catalysis, and therefore in designing water-soluble transition-metal catalysts. Half-sandwich (ή6-arene)-ruthenium(II) complexes are a versatile and well-known family of ruthenium compounds that exhibit a rich catalytic and coordination chemistry. This Perspective article focuses on the catalytic applications in aqueous media of (ή6-arene)-ruthenium(II) complexes containing water-soluble phosphines, and related hydrophilic P-donor ligands. [ABSTRACT FROM AUTHOR]

A series of water-soluble N-protonated thiazolyl-phosphine hydrochloride salts have been synthesized and coordinated to the ruthenium(ii) fragment [RuCl2(η6-p-cymene)]. The resulting complexes were evaluated as potential catalysts for the selective hydration of nitriles to primary amides in environmentally friendly aqueous medium. The best results in terms of activity were achieved when tris(5-(2-aminothiazolyl))phosphine trihydrochloride was used as ligand. Using the Ru(ii) complex 9 derived from this salt (3 mol%), the catalytic reactions proceeded cleanly in pure water at 100 °C without the assistance of any additive, affording the desired amides in high yields (＞78%) after short reaction periods (0.5–7 h). The process was operative with both aromatic, heteroaromatic, α,β-unsaturated and aliphatic nitriles, and tolerated several functional groups. The utility of 9 in promoting the formation of primary amides in water by catalytic rearrangement of aldoximes and direct coupling of aldehydes with NH2OH·HCl has also been demonstrated. [ABSTRACT FROM AUTHOR]

Amides are versatile building blocks in synthetic organic chemistry, presenting a wide range of pharmacological applications, and are used as raw materials in industry for the large-scale production of engineering plastics, detergents and lubricants. The development of green procedures for the synthesis of this relevant class of compounds from various starting materials, which replace antiquated methods using carboxylic acid derivatives and amines, is therefore of prime interest in modern chemistry. In this review article, a survey of metal-catalyzed synthetic approaches of amides conducted in an environmentally friendly aqueous medium is given. [ABSTRACT FROM AUTHOR]

Neutral arene-ruthenium(II) complexes [RuCl2(η6-arene){κ1-( P)-PPh2py}] and [RuCl2(η6-arene){κ1-( P)-PPh2(py-4-NMe2)}] (arene = benzene, p-cymene, mesitylene, hexamethylbenzene) have been synthesized and studied as potential catalysts for the selective hydration of nitriles to amides using benzonitrile as a model substrate. The effectiveness of these complexes was low due to the high tendency of the 2-(diphenylphosphanyl)pyridine ligands to form stable κ2-( P, N)-chelate rings, as demonstrated by NMR spectroscopy and catalytic experiments performed with the isolated cationic derivatives [RuCl(η6-arene){κ2-( P, N)-P N}][SbF6] [P N = PPh2py, PPh2(py-4-NMe2)]. Despite its reluctance to adopt a chelating κ2-( P, N) coordination mode, cooperative effects of the bulky 2-(diphenylphosphanyl)pyridine ligand PPh2(py-6- tert-amyl) were not observed in complexes [RuCl2(η6-arene){κ1-( P)-PPh2(py-6- tert-amyl)}] (arene = benzene, p-cymene). The novel bis(allyl)-ruthenium(IV) derivatives [RuCl(η3:η3-C10H16){κ2-( P, N)-P N}][SbF6] [P N = PPh2py, PPh2(py-4-NMe2)] and [RuCl2(η3:η3-C10H16){κ1-( P)-PPh2(py-6- tert-amyl)}] (C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl) were also synthesized and fully characterized, and again led to modest conversions in the benzonitrile hydration reaction. Improvements in the catalytic activities of complexes [RuCl2(η6- p-cymene){κ1-( P)-PPh2py}], [RuCl(η6- p-cymene){κ2-( P, N)-PPh2py}][SbF6] and [RuCl(η3:η3-C10H16){κ2-( P, N)-PPh2py}][SbF6] were observed in the presence of excess PPh2py due to the in situ formation of the catalytically more active dication [Ru{κ2-( P, N)-PPh2py}3]2+. [ABSTRACT FROM AUTHOR]

The rapid growth of the biodiesel industry has led to a large surplus of its major byproduct, i.e.glycerol, for which new applications need to be found. Research efforts in this area have focused mainly on the development of processes for converting glycerol into value-added chemicals and its reforming for hydrogen production, but recently, in line with the increasing interest in the use of alternative greener solvents, an innovative way to revalorize glycerol and some of its derivatives has seen the light, i.e.their use as environmentally friendly reaction media for synthetic organic chemistry. The aim of the present Feature Articleis to provide a comprehensive overview on the developments reached in this field. [ABSTRACT FROM AUTHOR]

Several ruthenium(iv) complexes have been tested as potential catalysts for the isomerization of estragole into anethole using water and glycerol as alternative green reaction media. Best results in terms of activity and E-selectivity were obtained with the dimeric species [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (C10H16= 2,7-dimethylocta-2,6-diene-1,8-diyl) and the mononuclear derivative [RuCl2(η3:η3-C10H16){P(OMe)3}]. In particular, using a ruthenium loading of 1 mol%, almost quantitative and stereoselective formation of trans-anethole (trans/cisratios = 99 : 1) could be reached at 80 °C in short times (5–30 min) employing water–MeOH (EtOH) or glycerol–MeOH (EtOH) mixtures (1 : 1 v/v) as solvent. Recyclability issues have also been addressed. [ABSTRACT FROM AUTHOR]

Complexes [RuCl2(η6-C6H5OCH2CH2OH)(L)] (L = P(OMe)3(1a), P(OEt)3(1b), P(OiPr)3(1c), P(OPh)3(1d), PPh3(1e)) have shown to be efficient catalysts for the isomerization of estragole into anethole, the best activities being obtained in polar solvents (water, methanol, ethanol). Interestingly, a complete selectivity toward trans-anethole could be reached under smooth conditions (80 °C) and in very short times (5–15 min). The catalytic experiments have been performed both under conventional and microwave heating, reaction rates being significantly enhanced under the latter conditions. [ABSTRACT FROM AUTHOR]

Recent research work on ruthenium-catalyzed isomerizations of allylic and propargylic alcohols into carbonyl compounds is reviewed. Tandem processes based on these isomerization reactions are also included. 1 Introduction 2 Isomerizations of Allylic Alcohols 2.1 Redox Isomerization 2.2 The 1,3-Rearrangement 2.3 Tandem Processes 3 Isomerizations of Propargylic Alcohols 3.1 Meyer-Schuster and Rupe Rearrangements 3.2 Redox Isomerization 3.3 Tandem Processes 4 Conclusions and Outlook [ABSTRACT FROM AUTHOR]

Although the application of arene-osmium(II) complexes in homogeneous catalysis has been much less studied than that of their ruthenium analogues, different works have shown that, in some instances, a comparable or even superior effectiveness can be achieved with this particular class of compounds. This review article focuses on the catalytic applications of arene-osmium(II) complexes. Among others, transfer hydrogenation, hydrogenation, oxidation, and nitrile hydration reactions, as well as different C-C bond forming processes, are comprehensively discussed. [ABSTRACT FROM AUTHOR]

The title compound, i.e., [RuCl2(η6-p-cymene)(PPh2NHnPr)] (2), was obtained in a 71% yield by reacting a toluene solution of the chlorophosphine complex [RuCl2(η6-p-cymene)(PPh2Cl)] (1) with two equivalents of n-propylamine at room temperature. The aminophosphine complex 2 was characterized by elemental analysis, multinuclear NMR (31P{1H}, 1H and 13C{1H}) and IR spectroscopy. In addition, its catalytic behavior in the hydration of benzonitrile was briefly explored. [ABSTRACT FROM AUTHOR]

The title compound was synthesized by electrophilic cyanation of commercially available (R)-4-chloro-α-methylbenzylamine with cyanogen bromide in diethyl ether, and isolated as a yellow oil in 84% yield. It was characterized by 1H and 13C{1H] NMR, IR, HRMS, and specific rotation measurements. [ABSTRACT FROM AUTHOR]

The synthesis of a series of arene-osmium(II) complexes containing phosphinite-type ligands, namely, [OsCl2(η6-p-cymene){R2PO(CH2)nPh}] (R = Ph, n = 1 (4a), 2 (4b), 3 (4c); R = iPr, n = 1 (5a), 2 (5b), 3 (5c)) and [OsCl2(η6-benzene){iPr2PO(CH2)2Ph}] (7), is presented. All these compounds were characterized by elemental analysis and multinuclear NMR spectroscopy (31P{1H}, 1H and 13C{1H}), and the structure of [OsCl2(η6-p-cymene){Ph2PO(CH2)3Ph}] (4c) unequivocally confirmed through a single-crystal X-ray diffraction study. Attempts to generate the tethered species [OsCl2{η6:κ1(P)-C6H5(CH2)nOPR2}] by intramolecular exchange of the coordinated arene in 4-5a-c or 7, upon thermal or MW heating, failed. [ABSTRACT FROM AUTHOR]