Alfred F. Noels

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.

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.

Toward a novel metal based chemotherapy against tropical diseases 4. Synthesis and characterization of new metal-clotrimazole complexes and evaluation of their activity against Trypanosoma cruzi

Abstract The syntheses and characterization of metal imidazole complexes showing activity against Trypanosoma cruzi, the causative agent of Chagas disease, are presented, RuCl2(CTZ)2 (2) and RuCl2(BTZ)2 (4) were prepared by reaction of RuCl2(NCCH3)4 (1) with the appropriate ligand (CTZ, clotrimazole = 1-[(2-chlorophenyl)diphenylmethyl]-1H-imidazole; BTZ = 1-[(2-bromophenyl)diphenylmethyl]-1H-imidazole) [Ru(bipy)(CTZ)2](PF6)2 (3) (bipy=2,2′-bipyridyl) was obtained by reaction of 2 with bipy and NH4PF6 in MeCN. Reaction of [RhCl(COD)]2 with CTZ yielded RhCl(COD)(CTZ) (5) (COD=1,5-cyclooctadiene), while AuCl1CTZ (6), K2[PtCl4(CTZ)2] (7) and [Cu(CTZ)2]PF6 (8) were obtained by interaction of CTZ with AuCl1·HCl, K2PtCl4 and [Cu(CH3CN)4]PF6, respectively. All the new complexes were characterized by NMR and other appropriate techniques, X-ray diffraction studies of 4·3H2O, 5 and 6 were also carried out. The structure of 4·3H2O consists of a distorted tetrahedral arrangement of two N atoms from the BTZ ligands and two Cl atoms around the Ru(II) ion; 4·3H2O crystallizes in the orthorhombic space group Puma (No. 62) with a=12.818(5), b=29.115(5), c=12.040(5) A , V=4493.2(8) A and Z=4. Complex 5 displayed a square planar structure typical for Rh(1) bound to N from CTZ, Cl, and the two CC bonds of COD; 5 crystallized in the triclinic space group (P(= l) (No. 2) with a=12.407(3), b=12.876(4), c=10.069(3) A , α=111.59(2)°, β=107.80(2)°, γ=103.28(2)°, V=1313.4(8) A 3 and Z=2. Complex 6 also displayed a square arrangement of N from CTZ, plus three Cl atoms around the Au(III) ion; 6 crystallized in the monoclinic space group P21/n (No. 14) with a=9.507(1), b=18.280(4), c=12.877(1) A , β=100.59(1)°, V=2199.7(5) A 3 and Z=4. All the new compounds were found to be active against in vitro cultures of Trypanosoma cruzi, following the trend 3 = 7

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.