Lionel Delaude

New In situ Generated Ruthenium Catalysts Bearing N‐Heterocyclic Carbene Ligands for the Ring‐Opening Metathesis Polymerization of Cyclooctene

New 1,3-diarylimidazol(in)ium chlorides bearing phenyl, 1-naphthyl, 4-biphenyl, 2-tolyl, 2,6-dimethylphenyl, and 3,5-dimethylphenyl substituents were synthesized. They were combined with [RuCl2(p-cymene)]2 and potassium tert-butoxide or sodium hydride to generate the corresponding ruthenium-N-heterocyclic carbene complexes in situ. Catalyst precursors derived from imidazol(in)ium salts bearing the 2,4,6-trimethylphenyl (mesityl) and the 2,6-diisopropylphenyl groups were also prepared. The catalytic activity of all these species in the photoinduced ring-opening metathesis polymerization of cyclooctene was investigated. The C4-C5 double bond in the imidazole ring of the N-heterocyclic carbene ligands was not crucial to achieve high catalytic efficiencies. The presence or the absence of alkyl groups on the ortho positions of the phenyl rings had a more pronounced influence. Blocking all the ortho positions was a requisite for obtaining efficient catalysts. Failure to do so probably results in the ortho-metallation of the carbene ligand, thereby altering the coordination sphere of the ruthenium active centers.

Synthesis and evaluation of new RuCl2(p-cymene)(ER2R′) and (η1:η6-phosphinoarene)RuCl2 complexes as ring-opening metathesis polymerization catalysts

Abstract New RuCl 2 ( p -cymene)(ER 2 R′) complexes (E=P, As, Sb; R, R′=H, alkyl, arylalkyl) have been synthesized and used as catalyst precursors for the ring-opening metathesis polymerization (ROMP) of cyclooctene, cyclopentene, and norbornene. When ER 2 R′ was a phosphinoarene, the p -cymene ligand could be displaced upon heating and tethered (η 1 :η 6 -phosphinoarene)RuCl 2 complexes were obtained. Simple thermogravimetric analysis (TGA) of the complexes provided clear-cut indication on their potential catalytic activity in ROMP.

The Use of Imidazolium-2-dithiocarboxylates in the Formation of Gold(I) Complexes and Gold Nanoparticles††Dedicated to Prof. Dr. Hubert Schmidbaur on the occasion of his 75th birthday.

The imidazolium-2-dithiocarboxylate ligands IPr.CS(2), IMes.CS(2), and IDip.CS(2) react with [AuCl(PPh(3))] to yield [(Ph(3)P)Au(S(2)C.IPr)](+), [(Ph(3)P)Au(S(2)C.IMes)](+), and [(Ph(3)P)Au(S(2)C.IDip)](+), respectively. The compounds [(L)Au(S(2)C.IMes)](+) are prepared from the reaction of IMes.CS(2) with [AuCl(L)] (L = PMe(3), PCy(3), CN(t)Bu). The carbene-containing precursor [(IDip)AuCl] reacts with IPr.CS(2) and IMes.CS(2) to afford the complexes [(IDip)Au(S(2)C.IPr)](+) and [(IDip)Au(S(2)C.IMes)](+) with two carbene units, one bound to the metal center and the other to the dithiocarboxylate unit. Treatment of the diphosphine-gold complex [(dppm)(AuCl)(2)] with 1 equiv of IMes.CS(2) yields [(dppm)Au(2)(S(2)C.IMes)](2+), while the reaction of [L(2)(AuCl)(2)] (L(2) = dppb, dppf) with 2 equiv of IMes.CS(2) results in [(L(2)){Au(S(2)C.IMes)}(2)](2+). The homoleptic complexes [Au(S(2)C.IPr)(2)](2+), [Au(S(2)C.IMes)(2)](2+), and [Au(S(2)C.IDip)(2)](2+) are obtained from the reaction of [AuCl(tht)] with 2 equiv of the appropriate imidazolium-2-dithiocarboxylate ligand. The compounds [(Ph(3)P)Au(S(2)C.NHC)](+) (NHC = IMes, IDip) and [(IDip)Au(S(2)C.NHC)](+) (NHC = IPr, IMes) are characterized crystallographically. The IMes.CS(2) ligand is also used to prepare functionalized gold nanoparticles with diameters of 11.5 (+/-1.2) and 2.6 (+/-0.3) nm.

N-heterocyclic carbene catalyzed carba-, sulfa-, and phospha-Michael additions with NHC·CO2 adducts as precatalysts

N-heterocyclic carbene catalyzed Michael additions have been revisited with 1,3-dialkyl- or 1,3-diarylimidazol(in)ium-2-carboxylates, that is, NHC·CO2 adducts, as the source of the free NHC catalysts in solution. Using these precatalysts, a number of efficient carba-, sulfa-, and phospha-Michael additions were achieved very conveniently, without the need for an external strong base to generate the NHC by deprotonation of an azolium salt. To further expand the scope of the procedure, some NHC-catalyzed sulfa-Michael/aldol organocascades were also investigated.

Ruthenium catalysts bearing N-heterocyclic carbene ligands in atom transfer radical reactions

The catalytic activity of ruthenium-p-cymene complexes bearing N-heterocyclic carbene ligands in atom transfer radical addition (ATRA) or polymerisation (ATRP) strongly depends on the substituents of the carbene ligand, thereby providing a nice illustration of the importance of organometallic engineering and ligand fine tuning in homogeneous catalysis.

A procedure for quantitative regioselective nitration of aromatic hydrocarbons in the laboratory

Abstract Aromatic hydrocarbons are nitrated by metallic nitrates impregnated on the K10 montmorillonite in the presence of acetic anhydride (Menke conditions). The influence on this stoichiometric reaction of the conditions (metallic cation; solvent; temperature) is studied. With toluene as the test molecule, the reaction is optimized to a 100% yield combined with a 8:1 para preference (79 % para , 20% ortho , 1 % meta ).

Oxidation of organic substrates with potassium ferrate (VI) in the presence of the K10 montmorillonite

Abstract Among various aluminosilicate supports, the K10 montmorillonite clay was the best catalyst for the oxidation of organic substrates with potassium ferrate (VI) Thus, a solid mixture of K 2 FeO 4 and K10 has been used for the efficient oxidation of selected alcohols, benzylamine, thiophenol. and aniline in hydrocarbon solvents at room temperature. Somewhat humid clay performs best, and it is important to control the amount of water associated to the solid support.

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

Summary By focusing on recent developments on natural and non-natural azasugars (iminocyclitols), this review bolsters the case for the role of olefin metathesis reactions (RCM, CM) as key transformations in the multistep syntheses of pyrrolidine-, piperidine- and azepane-based iminocyclitols, as important therapeutic agents against a range of common diseases and as tools for studying metabolic disorders. Considerable improvements brought about by introduction of one or more metathesis steps are outlined, with emphasis on the exquisite steric control and atom-economical outcome of the overall process. The comparative performance of several established metathesis catalysts is also highlighted.

Retracing the evolution of monometallic ruthenium–arene catalysts for C–C bond formation

Preformed or in situ generated monometallic ruthenium-arene complexes with the generic formula RuX(2)(arene)(L) (L = phosphine or N-heterocyclic carbene) are versatile and efficient catalyst precursors for olefin metathesis and atom transfer radical reactions. Their synthesis is usually accomplished using simple and straightforward experimental procedures starting from the [RuCl(2)(p-cymene)](2) dimer. This article retraces their evolution over the past 20 years and highlights similarities and differences with the parallel development of well-defined RuX(2)(=CHR)(L(1))(L(2)) ruthenium-alkylidene catalysts.

Microwave-Assisted Ruthenium-Catalyzed Reactions

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers has been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared with conventional heating methods. The present contribution aims at illustrating the advantages of this technology in homogeneous catalysis by ruthenium complexes and, when data are available, at comparing microwave-heated and conventionally heated experiments. Selected examples refer to olefin metathesis, isomerization reactions, 1,3-dipolar cycloadditions, atom transfer radical reactions, transfer hydrogenation reactions, and H/D exchange reactions.