Victorio Cadierno

Glycerol and derived solvents: new sustainable reaction media for organic synthesis.

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 Article is to provide a comprehensive overview on the developments reached in this field.

Metal-catalyzed amide bond forming reactions in an environmentally friendly aqueous medium: nitrile hydrations and beyond

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.

Allenylidene and Higher Cumulenylidene Complexes

3.3.2. Half-Sandwich Complexes 3523 3.4. Group 9 Metals 3526 3.5. Group 10 Metals 3527 4. Preparation of Higher Cumulenylidene Complexes 3527 5. Reactivity of Allenylidene Complexes 3528 5.1. General Considerations 3528 5.2. Reactions of Allenylidene Complexes 3528 5.2.1. Group 6 Metals 3528 5.2.2. Group 7 Metals 3529 5.2.3. Group 8 Metals 3530 5.2.4. Group 9 Metals 3537 6. Reactivity of Higher Cumulenylidene Complexes 3538 6.1. Reactions of Butatrienylidene Complexes 3538 6.2. Reactions of Pentatetraenylidene Complexes 3539 7. Catalytic Reactions Involving Allenylidene Complexes 3539

Recent Developments in the Reactivity of Allenylidene and Cumulenylidene Complexes

Allenylidene and higher cumulenylidene complexes [M]=C(=C)n=CR1R2 (n = 1, 2, 3) have continuously gained significance in the context of transition metal carbene chemistry. Important developments which have been disclosed during the last two years are reviewed. These include a variety of stoichiometric and catalytic reactions of allenylidene complexes and their utility in organic synthesis. The related chemistry of butatrienylidene (n = 2) and pentatetraenylidene (n = 3) complexes as well as theoretical studies are also reviewed.

Indenyl complexes of Group 8 metals

Abstract The present review article is concerned with the state of the art of the chemistry of indenyl Group 8 metal complexes which has undergone significant progress during the last decade. It deals mainly with complexes of the types: (a) bis(indenyl) sandwich compounds [M(η5-C9H7−xRx)2] (R=H, Me); (b) half-sandwich derivatives [M(η5-C9H7−xRx)(CO)2]2 and [M(η5-C9H7−xRx)XL2] (X=halides, H, alkyl, acetylide; L=two electron donor ligands); (c) cationic complexes [M(η5-C9H7−xRx)L2L′]+ (L, L′=two electron donor ligands). A detailed account of the synthesis, structural and reactivity aspects is presented including kinetic studies and catalytic processes. A discussion of the structural features and coordination modes of the indenyl group with special attention to its distortion parameters is presented. The reactivity studies include redox (chemical and electrochemical) processes, insertion reactions, ring transformations as well as ligand exchange processes in half-sandwich derivatives [M(η5-C9H7−xRx) XL2]. In particular, a detailed discussion of the ability of the moiety [M(η5-C9H7−xRx)L2] to stabilize unsaturated carbene groups such as vinylidene (CCR2, allenylidene CCCR2 and α,β-unsaturated alkenyl carbene C(H)C(R1)CRR′ complexes is presented. The influence of the indenyl ring on the regio- and stereoselective nucleophilic additions to these carbene groups allows selective synthesis leading to either allenyl or functionalized alkynyl complexes. A large number of the latter have been synthesized some of them showing excellent non-linear optical properties.

Bis(allyl)ruthenium(IV) Complexes Containing Water‐Soluble Phosphane Ligands: Synthesis, Structure, and Application as Catalysts in the Selective Hydration of Organonitriles into Amides

The novel mononuclear ruthenium(IV) complexes [RuCl(2)(eta(3):eta(3)-C(10)H(16))(L)] [L=(meta-sulfonatophenyl)diphenylphosphane sodium salt (TPPMS) (2a), 1,3,5-triaza-7-phosphatricyclo[3.3.1.1(3, 7)]decane (PTA) (2b), 1-benzyl-3,5-diaza-1-azonia-7-phosphatricyclo[3.3.1.1(3, 7)]decane chloride (PTA-Bn) (2c), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) (2d), and 2,4,10-trimethyl-1,2,4,5,7,10-hexaaza-3-phosphatricyclo[3.3.1.1(3, 7)]decane (THPA) (2e)] have been synthesized by treatment of the dimeric precursor [{RuCl(mu-Cl)(eta(3):eta(3)-C(10)H(16))}(2)] (C(10)H(16)=2,7-dimethylocta-2,6-diene-1,8-diyl) (1) with two equivalents of the corresponding water-soluble phosphane. Reaction of 1 with one equivalent of the cage-type diphosphane ligand 2,3,5,6,7,8-hexamethyl-2,3,5,6,7,8-hexaaza-1,4-diphosphabicyclo[2.2.2]octane (THDP) allowed also the high-yield preparation of the dinuclear derivative [{RuCl(2)(eta(3):eta(3)-C(10)H(16))}(2)(mu-THDP)] (2f). All these new complexes have been analytically and spectroscopically (IR and multinuclear NMR) characterized. In addition, the structure of 2b, 2c, 2d, and 2f was unequivocally confirmed by X-ray diffraction methods. Complexes 2a-f are active catalysts for the selective hydration of nitriles to amides in pure aqueous medium under neutral conditions. The wide scope of this catalytic transformation has been evaluated by using the most active catalysts [RuCl(2)(eta(3):eta(3)-C(10)H(16))(THPA)] (2e) and [{RuCl(2)(eta(3):eta(3)-C(10)H(16))}(2)(mu-THDP)] (2f). Advantages of using MW versus conventional thermal heating are also discussed.

Cycloisomerization versus Hydration Reactions in Aqueous Media: A Au(III)-NHC Catalyst That Makes the Difference

A novel water-soluble Au(III)-NHC complex has been synthesized and successfully applied in the intramolecular cyclization of γ-alkynoic acids into enol-lactones under biphasic toluene/water conditions, thus representing a rare example of an active and selective catalyst for this transformation in aqueous media. Remarkably, competing alkyne hydration processes were not observed, even during the desymmetrization reaction of challenging 1,6-diyne substrates. In addition, after phase separation, the water-soluble Au(III) catalyst could be recycled 10 times without loss of activity or selectivity.

Ruthenium-catalyzed redox isomerization/transfer hydrogenation in organic and aqueous media: A one-pot tandem process for the reduction of allylic alcohols

The hexamethylbenzene-ruthenium(II) dimer [{RuCl(μ-Cl)(η6-C6Me6)}2] 1 and the mononuclear bis(allyl)-ruthenium(IV) complex [RuCl2(η3:η2:η3-C12H18)] 2, associated with base and a hydrogen donor, were found to be active catalysts for the selective reduction of the CC bond of allylic alcohols both in organic and aqueous media. The process, which proceeds in a one-pot manner, involves a sequence of two independent reactions: (i) the initial redox-isomerization of the allylic alcohol, and (ii) subsequent transfer hydrogenation of the resulting carbonyl compound. The highly efficient transformation reported herein represents, not only an illustrative example of auto-tandem catalysis, but also an appealing alternative to the classical transition-metal catalyzed CC hydrogenations of allylic alcohols. The process has been successfully applied to aromatic as well as aliphatic substrates affording the corresponding saturated alcohols in 45–100% yields after 1.5–24 h. The best performances were reached using (i) 1–5 mol% of 1 or 2, 2–10 mol% of Cs2CO3, and propan-2-ol or (ii) 1–5 mol% of 1 or 2, 10–15 equivalents of NaO2CH, and water. The catalytic efficiency is strongly related to the structure of the allylic alcohol employed. Thus, in propan-2-ol, the reaction rate essentially depends on the steric requirement around the CC bond, therefore decreasing with the increasing number of substituents. On other hand, in water the transformation is favoured for primary allylic alcohols vs. secondary ones.

Water-soluble ruthenium(II) catalysts [RuCl2(η6-arene)-{P(CH2OH)3}] for isomerization of allylic alcohols and alkyne hydration

The novel water-soluble ruthenium(II) complexes [RuCl(2)(eta(6)-arene)[P(CH(2)OH)(3)]]2a-c and [RuCl(eta(6)-arene)[P(CH(2)OH)(3)](2)][Cl]3a-c have been prepared in high yields by reaction of dimers [[Ru(eta(6)-arene)(micro-Cl)Cl](2)](arene = C(6)H(6)1a, p-cymene 1b, C(6)Me(6)1c) with two or four equivalents of P(CH(2)OH)(3), respectively. Complexes 2/3a-c are active catalysts in the redox isomerization of several allylic alcohols into the corresponding saturated carbonyl compounds under water/n-heptane biphasic conditions. Among them, the neutral derivatives [RuCl(2)(eta(6)-C(6)H(6))[P(CH(2)OH)(3)]]2a and [RuCl(2)(eta(6)-p-cymene)[P(CH(2)OH)(3)]]2b show the highest activities (TOF values up to 600 h(-1); TON values up to 782). Complexes 2/3a-c also catalyze the hydration of terminal alkynes.

Dichloro(dodeca-2,6,10-triene-1,12-diyl)ruthenium(IV): a highly efficient catalyst for the isomerization of allylic alcohols into carbonyl compounds in organic and aqueous media

The catalytic activity of the bis(allyl)-ruthenium(iv) complex [Ru([small eta](3):[small eta](2):[small eta](3)-C(12)H(18))Cl(2)] in the transposition of allylic alcohols into carbonyl compounds, both in THF and H(2)O as solvent, is reported.