Alain Dormond

Anionic Monosubstituted Cyclopentadienylsamarium Derivatives: Catalysts for a Stereospecific Isoprene Polymerization

New alkyl and allyl complexes 1–3 {1: [Cp′2Sm(C3H5)]n, Cp′ = Me3CC5H4; 2: [Me4C2(C5H4)2]Sm(C3H5)2Li(dme),dme = (CH3OCH2CH2OCH3); 3: Cp′2SmMe2Li(dioxane)} were synthesized from (Cp′2SmCl)2and from the magnesium derivative [Me4C2(C5H4)2]SmCl · MgCl2(THF)4 (4). The ansa anionic complex 2 exhibited good activity for the stereospecific 1,4-trans polymerization of isoprene, whereas the neutral derivative 1 was inactive. In the same way, the anionic complex [Cp′2SmMe2]Li(dioxane) (3) was found to be an ethylene polymerization catalyst of very short lifetime. The lack of reactivity of 1 is related to the associated structure of this coordinatively unsaturated complex: this fact was established by the formation of the carbene adduct Cp′2Sm(C3H5)[C(NiPr)2(CMe)2] (1′). Crystals of 1′ were isolated but this new compound undergoes a partial rearrangement into a tris-Cp′ species in solution. Similar behaviour is observed for the analogous complex Cp′2SmCl[C(NiPr)2(CMe)2] (1′′). The X-ray crystal structure revealed the formation of the adduct, as a toluene solvate, which exists in benzene solution in equilibrium with Cp′3Sm and Cp′SmCl2[C(NiPr)2(CMe)2]2. The catalytic behaviour of 2 is compared with that of other early lanthanide derivatives.

Non-hindered ansasamarocenes, versatile catalysts for diene/olefin/polar monomer copolymerisations. What is really the active species?

Abstract Catalytic systems containing an ansabiscyclopentadienyllanthanide core and lithium and/or magnesium salts are obtained by reaction of the chloride precursors with allyllithium. These allyl complexes lead to the same active species which polymerises 1,3-dienes, copolymerises 1,3-dienes and α-olefin or α,ω-dienes or allows the controlled diblock polyisoprene/polycaprolactone copolymerisation. The exact nature of this active species and of the allyl precursors is investigated here.

Lanthanide bis(trifluoromethanesulfonyl)amides, synthesis, characterization and catalytic activity

Abstract The synthesis of lanthanum, neodymium and ytterbium bis(trifluoromethanesulfonyl)amides, named triflimidates, from acetates, carbonates and oxides is investigated. When the synthesis is performed in water, all the salts contain one molecule of water and the lanthanum and neodymium salts synthesized from the acetates also contain one molecule of acetic acid. After removal of the water and acetic acid in refluxing ethanol, the salts are obtained anhydrous but associated for lanthanum and neodymium, whereas the ytterbium salt is monomeric and volatile. When the synthesis is performed directly in ethanol, the neodymium salt contains two molecules of coordinated ethanol. In non-hazardous solvents, these triflimidates are better catalysts than the analogous triflates toward either Friedel–Crafts acylations, or Fries transpositions or Baeyer–Villiger oxidations. Unexpectedly, the cerium(IV) triflimidate catalyzes the oxidation of aromatic ketones to give the corresponding acids.

New Viscoelastic Materials Obtained by Insertion of an α-Olefin in a trans-Polyisoprene Chain with a Single-Component Organolanthanide Catalyst

Copolymerisation of isoprene with C 6 -C 18 a-olefins by a single component organolanthanide catalyst affords poly(trans-1,4-isoprene) containing 6-10% of inserted olefin. The mechanical properties of highly crystalline transpolyisoprene are dratically modified after insertion of the alkyl chains, leading to quasi-amorphous viscoelastic materials.

Early lanthanide organometallic hydrides: electronic and steric control of the stability

Abstract Steric and electronic effects on the stability of early lanthanide, neodymium and samarium, organometallic hydrides are discussed. The instability of (tmp)2SmH (tmp=tetramethylphospholyl) is attributed to electronic factors and the low stability of (tBuC5H4)2SmH is related to steric reasons. The analogous neodymium hydride (tBuC5H4)2NdH, could not be obtained, whereas the more hindered triethylborohydride was formed. Access to bisphospholyl bridged heterobimetallic ruthenium–lanthanide hydrides is also related to the size of the lanthanide atom. The bimetallic structures are accessible for lanthanides of ionic radii smaller than 1 A. The role of organometallic hydrides versus alkyls as catalysts for olefin or diene polymerization is discussed, a first and unique example of hex-1-ene and isoprene copolymerization is presented.

Catalytic activity of solvated and unsolvated lanthanide halides in Friedel–Crafts acylations

Abstract Anhydrous lanthanide halides — chlorides and bromides — can act as homogeneous catalysts of Friedel–Crafts acylations. The catalytic activity is related to the solubility of these anhydrous salts. More soluble THF or dioxane (Diox.) neodymium and samarium adducts are more active catalysts.

New aromatic diamines containing a multiring flexible skeleton for the synthesis of thermally stable polyimides

Abstract Multi-ring aromatic diamines bearing a long alkyl chain (C 6 , C 8 or C 16 ) were obtained from the corresponding dinitro compounds synthesized by a Friedel–Crafts alkylation of substituted mesitylenes by paranitrobenzyl chloride. The bismaleimide synthesized from the diamine bearing a C 16 chain formed a thermostable polyimide.

Complexes aryloxy derives du dicyclopentadienyltitane(III)

Abstract Aryloxy complexes of dicyclopentadienyltitanium(III) derivatives were prepared through the action of a phenoxide ion on the corresponding CpCp′TiCl chlorides or by reduction of the chloroaryloxydicyclopentadienyltitanium(IV) compounds. These complexes were identified by their physical properties and their reaction products with CCl4 or (SR)2. Oxidative addition (d1 → d0) of (SR)2 gave mixed complexes [η5-Cp-η5-Cp′Ti(OAr)SR] which were isolated in two diastereoisomeric forms when Cp′ is a chiral ligand.

Organolanthanides, catalysts for specific olefin-diene copolymerization : access to new materials

Abstract Non-hindered ansa dicyclopentadienylallyl complexes of samarium, [(CMe2C5H4)2Sm(allyl)]n, and (CMe2C5H4)2Sm(allyl)L (L=THF or allylLi) polymerize isoprene without an aluminum cocatalyst. The polymerizations are highly stereospecific, affording nearly quantitatively 1–4 trans polyisoprene. In the presence of linear 1-olefins, copolymers are formed, with 6–10% of olefin inserted; the 1–4 trans structure of the polyisoprene chain is not altered, and only one olefin molecule is inserted between two polyisoprene fragments. In the common initiator of these three catalytic systems, the (CMe2C5H4)2Sm(allyl) moiety, only one vacant site would be available. As a consequence of the presence of the alkyl aliphatic chain, the viscoelastic behaviour of the branched copolymers markedly differs from that of trans 1–4 polyisoprene: an important loss of crystallinity and a dramatic decrease of the Young modulus are observed; the copolymers show elastomeric properties.

Catalytic activity of rare-earth-supported catalysts in Friedel–Crafts acylations

Abstract Friedel–Crafts acylations are catalysed by rare-earth-supported catalysts. The preparation, characterization and performance of these solid catalysts in a test acylation reaction and in a variety of syntheses of aromatic ketones are reported. In contrast to the reactions using AlCl3, the experimental conditions are non-polluting and the final work-up does not require any aqueous treatment.