Albert Demonceau

HIGHLY EFFICIENT RUTHENIUM-BASED CATALYTIC SYSTEMS FOR THE CONTROLLED FREE-RADICAL POLYMERIZATION OF VINYL MONOMERS

A new set of ruthenium complexes such as 1 and 2 (the Grubbs ruthenium-carbene complex) has been shown to mediate the controlled atom-transfer radical polymerization (ATRP) of vinyl monomers with exceptional efficiency. Furthermore, there is a striking parallelism between the catalytic activity of these compounds in olefin metathesis and in ATRP.

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.

Ruthenium-catalysed ring-opening metathesis polymerization of cycloolefins initiated by diazoesters

Abstract Addition of catalytic amounts of diazoesters to various ruthenium complexes, including some diruthenium(II,II) tetrakis carboxylates, led to new catalyst systems that promoted the ROMP not only of norbornene (bicyclo[2.2.1]heptene) but also of cyclooctene and cyclopentene. The conversion and the cis content of the polymers varied widely and depended on the nature of the catalyst precursor.

Transition-metal-catalysed reactions of diazoesters. Insertion into C–H bonds of paraffins by carbenoids

Rhodium(II) carboxylates of perfluoroacids are very efficient catalysts for promoting the insertion of carbenes (carbenoids)(generated from diazoesters) into the C–H bonds of alkanes with selectivites which differ from those observed in typical free-crbene processes.

Targeted drugs by olefin metathesis: piperidine-based iminosugars

Examining advances in the class of natural and non-natural piperidine azasugars, important therapeutic agents and potent glycosidase inhibitors, this review looks at syntheses applying olefin metathesis as a highly efficient key step and gateway strategy for discovery of better iminosugar leads for treatment of widespread affections like viral and metabolic diseases. Amply illustrated is how ring-closing metathesis (RCM and RCEYM), promoted by commercial ruthenium alkylidene catalysts, manage to construct the common tetrahydropyridine core while cross-metathesis (CM), starting from this generic scaffold, provides general access to families of novel azasugars. Special consideration is given to high-profile iminosugar drugs of this class (1-deoxynojirimycin and congeners, adenophorine, fagomine, isofagomine and some of their N- and C-substituted analogues) stressing upon newest trends for enhancing biological activity and modulating previously unexploited targets in multispecific therapies.

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.

Olefin cyclopropanation reactions catalysed by novel ruthenacarborane clusters

Abstract Novel ruthenacarborane clusters exhibit high activity as cyclopropanation catalysts in reactions between ethyl diazoacetate and alkenes.

Transition-metal-catalyzed reaction of diazocompounds, efficient synthesis of functionalized ethers by carbene insertion into the hydroxylic bond of alcohols

Abstract An Efficient catalytic synthesis of unsaturated ethers by carbene insertion (with diazoesters as carbene precursors) into the OH bond of unsaturated alcohols is reported. The regioselectivity for the OH insertion is high. However, depending on the catalyst counter-ions and the diazoester alkoxy group, addition to the unsaturated centre can be promoted to some extent, yielding then cyclopropyl and cyclopropenyl carbinols. The mechanistic aspects of the reactions are discussed.

Radical reactions catalysed by ruthenium(II) complexes with anionic carborane phosphine ligands: Kharasch addition to olefins and controlled polymerisation

Abstract Ruthenium-carborane complexes 1 – 3 mediated the Kharasch addition of carbon tetrachloride across olefins with high yields which markedly depended on the catalyst and the substrate used. In addition, the atom transfer radical polymerisation of methyl methacrylate could be carried out in a highly controlled way.

Highly efficient Kharasch addition catalysed by RuCl(Cp*)(PPh3)2

Air-stable and readily available RuCl(Cp*)(PPh3)2 is so far the best ruthenium-based catalyst precursor for promoting the addition of CCl4 and CHCl3 across olefins at a temperature as low as 40°C.