Surface Organolanthanide and ‐Actinide Chemistry

Roux, Erwan Le; Anwander, Reiner

doi:10.1002/9783527627097.ch12

Cited by 13 publications

(8 citation statements)

References 216 publications

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“…The infrared spectrum of 1-Cr@SiO 2 shows bands at 3450 and 3412 cm –1 consistent with N–H stretching vibrations and bands at 2965 and 2906 cm –1 which are blue shifted by 6 and 2 cm –1 compared to the corresponding infrared bands of −SiMe 3 in 1-Cr/SiO 2 (ESI Figure S1). This is consistent with −SiMe 3 groups bound to oxygen instead of nitrogen in 1-Cr@SiO 2 as found for the grafting of other silyl amide metal complexes . The −OSiMe 3 and Cr–N(H)– are formed from −N(SiMe 3 ) 2 via reaction of nearby silanol groups or the opening of siloxane bridges.…”

Section: Resultssupporting

confidence: 87%

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

et al. 2017

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Grafting molecular precursors on partially dehydroxylated silica followed by a thermal treatment yields silica-supported M(III) sites for a broad range of metals. They display unique properties such as high activity in olefin polymerization and alkane dehydrogenation (M = Cr) or efficient luminescence properties (M = Yb and Eu) essential for bioimaging. Here, we interrogate the local structure of the M(III) surface sites obtained from two molecular precursors, amides M(N(SiMe)) vs siloxides (M(OSi(OBu))·L with L = (THF) or HOSi(OBu) for M = Cr, Yb, Eu, and Y, by a combination of advanced spectroscopic techniques (EPR, IR, XAS, UV-vis, NMR, luminescence spectroscopies). For paramagnetic Cr(III), EPR (HYSCORE) spectroscopy shows hyperfine coupling to nitrogen only when the amide precursor is used, consistent with the presence of nitrogen neighbors. This changes their specific reactivity compared to Cr(III) sites in oxygen environments obtained from siloxide precursors: no coordination of CO and oligomer formation during the polymerization of ethylene due to the presence of a N-donor ligand. The presence of the N-ligand also affects the photophysical properties of Yb and Eu by decreasing their lifetime, probably due to nonradiative deactivation of excited states by N-H bonds. Both types of precursors lead to a distribution of surface sites according to reactivity for Cr, luminescence spectroscopy for Yb and Eu, and dynamic nuclear polarization surface-enhanced Y NMR spectroscopy (DNP SENS). In particular, DNP SENS provides molecular-level information about the structure of surface sites by evidencing the presence of tri-, tetra-, and pentacoordinated Y-surface sites. This study provides unprecedented evidence and tools to assess the local structure of metal surface sites in relation to their chemical and physical properties.

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Section: Resultssupporting

confidence: 87%

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

et al. 2017

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“…It could be anticipated that silica, which behaves like a bulky, rigid, and electron-withdrawing ligand, might markedly affect the steric environment and electronic parameters of such half-heterometallocene complexes. Furthermore, AlR 4 /OR ligand exchange by applying protonolysis protocols, that is, the reaction of Ln–AlMe 4 moieties with protic substrates such as alcohols or silica silanol groups, is well-documented. , Herein, we report the reactivity of (η 5 -PC 4 Me 2 R 2 )Ln(AlMe 4 ) 2 ( 1a , b and 2a , b ) toward SBA-15, which is a high-surface-area periodic mesoporous silica (PMS) with hexagonal symmetry ( p 6 mm ). , In order to comprehend the surface reactivity, tris( tert -butoxy)silanol [( t BuO) 3 SiOH] has been employed as a model surface site ,,, and siloxide complex (η 5 -PC 4 Me 4 )Nd[{μ-OSi(O t Bu) 3 }(μ-Me)AlMe 2 ][(μ-Me) 2 AlMe 2 ] has been crystallographically characterized.…”

Section: Introductionmentioning

confidence: 99%

Heterogenization of Lanthanum and Neodymium Monophosphacyclopentadienyl Bis(tetramethylaluminate) Complexes onto Periodic Mesoporous Silica SBA-15

et al. 2012

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International audienceThe monophosphacyclopentadienyl bis(tetramethylaluminate) lanthanide complexes (η5-PC4Me4)Ln[(μ-Me)2AlMe2]2 and [η5-PC4Me2(SiMe3)2]Ln[(μ-Me)2AlMe2]2 (Ln = La, Nd) have been immobilized onto mesoporous silica SBA-15, which was dehydroxylated at 500 °C. Major reaction pathways comprise methane elimination, that is, silanolysis of Ln(μ-Me)Al moieties with surface silanol groups, and trimethylaluminum separation resulting from donor-induced tetramethylaluminate cleavage. The formation of bis- and monosiloxy surface species is discussed involving transient [(η5-PC4Me4)Ln[(μ-OSi≡)(μ-Me)AlMe2]x[(μ-Me)2AlMe2]2-x] and [{η5-PC4Me2(SiMe3)2}Ln[(μ-OSi≡)(μ-Me)AlMe2]x[(μ-Me)2AlMe2]2-x] (Ln = La, Nd, x = 1, 2) as well as more stable entities such as [(η5-PC4Me2R2)(≡SiO)Ln[(μ-Me)2AlMe2]] and/or [(η5-PC4Me2R2)[(μ-OSi≡)(μ-Me)AlMe2]Ln(Me)] and [(η5-PC4Me2R2)(≡SiO)Ln[(μ-OSi≡)(μ-Me)AlMe2]] and/or [(≡SiO)2Ln(η5-PC4Me2R2)]. Moreover, surface alumination via released trimethylaluminum and the formation of [(≡SiO)3-yAlMey] (with y = 1, 2) surface sites is observed. The organometallic/inorganic hybrid materials (η5-PC4Me2R2)Ln(AlMe4)2@SBA-15-500 have been characterized by DRIFT and solid-state NMR spectroscopy, elemental analysis, and nitrogen physisorption. The equimolar reaction of complex (η5-PC4Me4)Nd[(μ-Me)2AlMe2]2 with tris(tert-butoxy)silanol (HOSi(OtBu)3) produces the siloxide complex (η5-PC4Me4)Nd[{μ-OSi(OtBu)3}(μ-Me)AlMe2][(μ-Me)2AlMe2], which was crystallographically authenticated as a model of a potential monophosphacyclopentadienyl neodymium surface species. All of the mesoporous hybrid materials are moderately active initiators for isoprene polymerization, producing 1,4-cis polyisoprene PI (>99%), which is in contrast to the case for the borate-activated molecular precursors (η5-PC4Me2R2)Ln(AlMe4)2 giving preferentially 1,4-trans PI. The surface organometallic chemistry as well as the polymerization performance markedly depend on the thermal pretreatment of the SBA-15 silica, as shown for the corresponding hybrid materials obtained from SBA-15-200 and SBA-15-700

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“…5-7), which is often considered a drawback with regard to the fabrication of heterogeneous catalysts. [28] This property might be turned into an advantage for the relaxivity, which profits from incomplete surface reactions, meaning low metal loading. [21] The alkoxide [Gd(OCH 2 CMe 3 ) 3 ] 4 , featuring a tetranuclear arrangement, [29] was considered a promising candidate based on a previous study of the reactivity of the cerium congener towards silica conducted in our group.…”

Section: Choice Of Metal-organic Precursors and Pms Materialsmentioning

confidence: 99%

High ¹H Relaxivity Gadolinium‐Grafted Mesoporous Silica Materials

Skår

Bienfait

Schnitzlbaumer

et al. 2014

Zeitschrift anorg allge chemie

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Abstract. Soft metal-organic grafting of periodic mesoporous silica (PMS) has recently been demonstrated to give gadolinium-loaded nanostructured hybrid materials with interesting 1 H relaxometric properties. Here, the sterically demanding alkoxide and aryloxide complexes, [Ln(OCH 2 CMe 3 ) 3 ] 4 and Ln(OC 6 H 3 tBu 2 -2,6) 3 (Ln = La, Gd), respectively, were grafted onto PMS materials MCM-41, SBA-15, and SBA-1. Support materials with distinct topology and pore diameters were utilized in order to direct the metal precursors towards the PMSs internal or external surfaces. All hybrid materials were examined by N 2 physisorption, Diffuse Reflectance Infrared Fourier Transform (DRIFT) and solid-state NMR spectroscopy, as well as elemental

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Surface Organolanthanide and ‐Actinide Chemistry

Cited by 13 publications

References 216 publications

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

Heterogenization of Lanthanum and Neodymium Monophosphacyclopentadienyl Bis(tetramethylaluminate) Complexes onto Periodic Mesoporous Silica SBA-15

High ¹H Relaxivity Gadolinium‐Grafted Mesoporous Silica Materials

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Surface Organolanthanide and ‐Actinide Chemistry

Cited by 13 publications

References 216 publications

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

Heterogenization of Lanthanum and Neodymium Monophosphacyclopentadienyl Bis(tetramethylaluminate) Complexes onto Periodic Mesoporous Silica SBA-15

High 1H Relaxivity Gadolinium‐Grafted Mesoporous Silica Materials

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High ¹H Relaxivity Gadolinium‐Grafted Mesoporous Silica Materials