We became aware, in the course of our ongoing research, that the number-average molecular weight ... more We became aware, in the course of our ongoing research, that the number-average molecular weight of poly(1,4-trans isoprene) determined by conventional gel permeation chromatography (GPC) in tetrahydrofuran (THF) using polystyrene standards differs from its true value by a factor 2. As far as we know, the Mark-Houwink coefficients of this polymer in a widespread GPC eluent such as THF have never been determined. We provide in this contribution a simple relationship between the number-average molecular weight of poly(1,4-trans isoprene) determined by GPC in THF using polystyrene standards and its true value.
We present in this study a new and one-step method allowing the preparation of an unprecedented f... more We present in this study a new and one-step method allowing the preparation of an unprecedented family of stable half-lanthanidocenes. X Ray analysis shows that the isolated compounds all display the same ionic Ln-Mg bimetallic structure consisting of
New mixed allyl−borohydrido lanthanide complexes Ln(BH 4) 2 (C 3 H 5)(THF) 3 (Ln = Nd (1), Sm (2)... more New mixed allyl−borohydrido lanthanide complexes Ln(BH 4) 2 (C 3 H 5)(THF) 3 (Ln = Nd (1), Sm (2)) could be prepared in good yield by reacting Ln(BH 4) 3 (THF) 3 (Ln = Sm, Nd) with 1/2 equiv of Mg(C 3 H 5) 2 (THF) x. X-ray structure analysis revealed monomeric structures with two terminal BH 4 ligands, one π-allyl ligand, and three THF molecules. In an assessment of isoprene polymerization, 1 afforded trans-1,4-polyisoprene in good yield, as a single component or in combination with Mg cocatalyst. Both 1 and 2 were found to be extremely active toward ε-caprolactone polymerization.
In this work, we describe a new synthetic strategy in organolanthanides chemistry, allowing the o... more In this work, we describe a new synthetic strategy in organolanthanides chemistry, allowing the one-pot preparation of two unprecedented families of heterobimetallic half-lanthanidocenes (Nd, La) and lanthanidocenes of general formula [(CpR)Ln(BH4)3]2[Mg(THF)6] and [(CpR)2Ln(BH4)(m-BH4)]2(Mg(THF)3, respectively (CpR is a cyclopentadienyl ligand). This efficient synthetic approach, that we call the “borohydride/alkyl route”, is based on the employ of the very common trisborohydride derivatives Ln(BH4)3(THF)3, and requires a minimal experimental work-up. We will present the syntheses and X Ray structures of several complexes belonging to this new family, including a very rare example of half-neodymocene bearing just one C5H5 ligand. The isolated complexes afford efficient precatalysts for selective and controlled ethylene, isoprene and styrene polymerization.
We became aware, in the course of our ongoing research, that the number-average molecular weight ... more We became aware, in the course of our ongoing research, that the number-average molecular weight of poly(1,4-trans isoprene) determined by conventional gel permeation chromatography (GPC) in tetrahydrofuran (THF) using polystyrene standards differs from its true value by a factor 2. As far as we know, the Mark-Houwink coefficients of this polymer in a widespread GPC eluent such as THF have never been determined. We provide in this contribution a simple relationship between the number-average molecular weight of poly(1,4-trans isoprene) determined by GPC in THF using polystyrene standards and its true value.
The insertion of single styrene units into polyisoprene is demonstrated using borohydrido rare ea... more The insertion of single styrene units into polyisoprene is demonstrated using borohydrido rare earth/dialkylmagnesium systems. This yields a new family of styrene/diene copolymers (SBR rubbers). The resulting poly[(1,4‐trans‐isoprene)‐co‐styrene] exhibits quite narrow molecular weight distributions, up to 30% inserted styrene, and a 96–98% 1,4‐trans‐microstructure. The presence of a bulky and electron‐rich ligand in the coordination sphere of the metal leads to an increase of the amount of styrene inserted and narrower chemical composition and molecular weight distributions. The presence of significant quantities of styrene in the medium does not alter the selectivity of the reaction, in contrast with cis‐specific polymerizations.magnified image
We present in this study a new and one-step method allowing the preparation of an unprecedented f... more We present in this study a new and one-step method allowing the preparation of an unprecedented family of stable half-lanthanidocenes. X Ray analysis shows that the isolated compounds all display the same ionic Ln-Mg bimetallic structure consisting of
De nouveaux complexes borohydrures de lanthanides ont été synthétisés avec pour objectif de valor... more De nouveaux complexes borohydrures de lanthanides ont été synthétisés avec pour objectif de valoriser en tant que précurseurs les trisborohydrures de lanthanides, composés stables et facilement accessibles. Pour cela, une nouvelle voie de synthèse qui s'apparente à une métathèse de liaison sigma et faisant intervenir l'alkylation in situ du trisborohydrure par un dialkylmagnésien, a été développée. Ces complexes ont été utilisés en combinaison avec un dialkylmagnésien pour la polymérisation 1,4- trans- stéréospécifique de l'isoprène et la copolyrnérisation statistique de l'isoprène avec le styrène. Les aspects mécanistiques de ce type de polyinérisation ont également été abordés.New lanthanide borohydride complexes were synthesized, aiming to increase the value as precursors of the lanthanide trisborohydrides, which are stable and easily accessible compounds. ln this frame, a new method of synthesis was developped, whichis apparented to a sigma bond metathesis and wh...
We became aware, in the course of our ongoing research, that the number-average molecular weight ... more We became aware, in the course of our ongoing research, that the number-average molecular weight of poly(1,4-trans isoprene) determined by conventional gel permeation chromatography (GPC) in tetrahydrofuran (THF) using polystyrene standards differs from its true value by a factor 2. As far as we know, the Mark-Houwink coefficients of this polymer in a widespread GPC eluent such as THF have never been determined. We provide in this contribution a simple relationship between the number-average molecular weight of poly(1,4-trans isoprene) determined by GPC in THF using polystyrene standards and its true value.
We present in this study a new and one-step method allowing the preparation of an unprecedented f... more We present in this study a new and one-step method allowing the preparation of an unprecedented family of stable half-lanthanidocenes. X Ray analysis shows that the isolated compounds all display the same ionic Ln-Mg bimetallic structure consisting of
New mixed allyl−borohydrido lanthanide complexes Ln(BH 4) 2 (C 3 H 5)(THF) 3 (Ln = Nd (1), Sm (2)... more New mixed allyl−borohydrido lanthanide complexes Ln(BH 4) 2 (C 3 H 5)(THF) 3 (Ln = Nd (1), Sm (2)) could be prepared in good yield by reacting Ln(BH 4) 3 (THF) 3 (Ln = Sm, Nd) with 1/2 equiv of Mg(C 3 H 5) 2 (THF) x. X-ray structure analysis revealed monomeric structures with two terminal BH 4 ligands, one π-allyl ligand, and three THF molecules. In an assessment of isoprene polymerization, 1 afforded trans-1,4-polyisoprene in good yield, as a single component or in combination with Mg cocatalyst. Both 1 and 2 were found to be extremely active toward ε-caprolactone polymerization.
In this work, we describe a new synthetic strategy in organolanthanides chemistry, allowing the o... more In this work, we describe a new synthetic strategy in organolanthanides chemistry, allowing the one-pot preparation of two unprecedented families of heterobimetallic half-lanthanidocenes (Nd, La) and lanthanidocenes of general formula [(CpR)Ln(BH4)3]2[Mg(THF)6] and [(CpR)2Ln(BH4)(m-BH4)]2(Mg(THF)3, respectively (CpR is a cyclopentadienyl ligand). This efficient synthetic approach, that we call the “borohydride/alkyl route”, is based on the employ of the very common trisborohydride derivatives Ln(BH4)3(THF)3, and requires a minimal experimental work-up. We will present the syntheses and X Ray structures of several complexes belonging to this new family, including a very rare example of half-neodymocene bearing just one C5H5 ligand. The isolated complexes afford efficient precatalysts for selective and controlled ethylene, isoprene and styrene polymerization.
We became aware, in the course of our ongoing research, that the number-average molecular weight ... more We became aware, in the course of our ongoing research, that the number-average molecular weight of poly(1,4-trans isoprene) determined by conventional gel permeation chromatography (GPC) in tetrahydrofuran (THF) using polystyrene standards differs from its true value by a factor 2. As far as we know, the Mark-Houwink coefficients of this polymer in a widespread GPC eluent such as THF have never been determined. We provide in this contribution a simple relationship between the number-average molecular weight of poly(1,4-trans isoprene) determined by GPC in THF using polystyrene standards and its true value.
The insertion of single styrene units into polyisoprene is demonstrated using borohydrido rare ea... more The insertion of single styrene units into polyisoprene is demonstrated using borohydrido rare earth/dialkylmagnesium systems. This yields a new family of styrene/diene copolymers (SBR rubbers). The resulting poly[(1,4‐trans‐isoprene)‐co‐styrene] exhibits quite narrow molecular weight distributions, up to 30% inserted styrene, and a 96–98% 1,4‐trans‐microstructure. The presence of a bulky and electron‐rich ligand in the coordination sphere of the metal leads to an increase of the amount of styrene inserted and narrower chemical composition and molecular weight distributions. The presence of significant quantities of styrene in the medium does not alter the selectivity of the reaction, in contrast with cis‐specific polymerizations.magnified image
We present in this study a new and one-step method allowing the preparation of an unprecedented f... more We present in this study a new and one-step method allowing the preparation of an unprecedented family of stable half-lanthanidocenes. X Ray analysis shows that the isolated compounds all display the same ionic Ln-Mg bimetallic structure consisting of
De nouveaux complexes borohydrures de lanthanides ont été synthétisés avec pour objectif de valor... more De nouveaux complexes borohydrures de lanthanides ont été synthétisés avec pour objectif de valoriser en tant que précurseurs les trisborohydrures de lanthanides, composés stables et facilement accessibles. Pour cela, une nouvelle voie de synthèse qui s'apparente à une métathèse de liaison sigma et faisant intervenir l'alkylation in situ du trisborohydrure par un dialkylmagnésien, a été développée. Ces complexes ont été utilisés en combinaison avec un dialkylmagnésien pour la polymérisation 1,4- trans- stéréospécifique de l'isoprène et la copolyrnérisation statistique de l'isoprène avec le styrène. Les aspects mécanistiques de ce type de polyinérisation ont également été abordés.New lanthanide borohydride complexes were synthesized, aiming to increase the value as precursors of the lanthanide trisborohydrides, which are stable and easily accessible compounds. ln this frame, a new method of synthesis was developped, whichis apparented to a sigma bond metathesis and wh...
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