10 research outputs found
Bis(phosphinimino)methanide borohydride complexes of the rare-earth elements as initiators for the ring-opening polymerization of trimethylene carbonate: combined experimental and computational investigations
International audienc
Chiral Rare Earth Borohydride Complexes Supported by Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in the Ring-Opening Polymerization of rac-Lactide
International audienceThe monoamidinato bisborohydride rare earth complexes [Ln{(S)-PEBA}(BH4)2(THF)2] (Ln = Sc (1), La (2), Nd (3), Sm (4), Yb (5), Lu (6)) were isolated as crystalline materials upon treatment of potassium N,N′-bis((S)-1-phenylethyl)benzamidinate ((S)-KPEBA) with the homoleptic trisborohydrides [Sc(BH4)3(THF)2] and [Ln(BH4)3(THF)3] (Ln = La, Nd, Sm, Yb, Lu), respectively. Compounds 1-6 are unique examples of enantiopure borohydride complexes of the rare earth metals. Different ionic radii of the metal centers were selected to cover the whole range of these elements with respect to the extent of the coordination sphere. All new complexes were thoroughly characterized by 1H, 13C{1H}, 11B, and 15N NMR and IR spectroscopies, also including single-crystal X-ray diffraction structure determination of each compound. The scandium, lanthanum, samarium, and lutetium complexes 1, 2, 4, and 6 were found active in the ring-opening polymerization of rac-lactide under mild operating conditions, providing atactic α,ω-dihydroxytelechelic poly(lactic acid) (PLA; Mn,SEC up to 18 800 g*mol-1). Most of the polymerizations proceed with a certain degree of control that is directed by molar mass values and relatively narrow dispersities (1.10 < ĐM < 1.34), within a moderate monomer-to-initiator ratio
CCDC 1031814: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
CCDC 1031815: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
CCDC 1031816: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
6‑(Tetrazol-5-yl)-2,2′-bipyridine: A Highly Selective Ligand for the Separation of Lanthanides(III) and Actinides(III)
The
coordination structure in the solid state and solution complexation
behavior of 6-(tetrazol-5-yl)-2,2′-bipyridine (HN<sub>4</sub>bipy) with samarium(III) was investigated as a model system for actinide(III)/lanthanide(III)
separations. Two different solid 1:2 complexes, [Sm(N<sub>4</sub>bipy)<sub>2</sub>(OH)(H<sub>2</sub>O)<sub>2</sub>] (<b>1</b>) and [Sm(N<sub>4</sub>bipy)<sub>2</sub>(HCOO)(H<sub>2</sub>O)<sub>2</sub>] (<b>2</b>), were obtained from the reaction of samarium(III) nitrate
with HN<sub>4</sub>bipy in isopropyl alcohol, resuspension in <i>N</i>,<i>N</i>-dimethylformamide (DMF), and slow crystallization.
The formate anion coordinated to samarium in <b>2</b> is formed
by decomposition of DMF to formic acid and dimethylamine. Time-resolved
laser fluorescence spectroscopy (TRLFS) studies were performed with
curium(III) and europium(III) by using HN<sub>4</sub>bipy as the ligand.
Curium(III) is observed to form 1:2 and 1:3 complexes with increasing
HN<sub>4</sub>bipy concentration; for europium(III), formation of
1:1 and 1:3 complexes is observed. Although the solid-state samarium
complexes were confirmed as 1:2 species the 1:2 europium(III) solution
complex in ethanol was not identified with TRLFS. The determined conditional
stability constant for the 1:3 fully coordinated curium(III) complex
species is more than 2 orders of magnitude higher than that for europium(III)
(log β<sub>3</sub>[Cm(N<sub>4</sub>bipy)<sub>3</sub>] = 13.8
and log β<sub>3</sub>[Eu(N<sub>4</sub>bipy)<sub>3</sub>] = 11.1).
The presence of added 2-bromodecanoic acid as a lipophilic anion source
reduces the stability constant for formation of the 1:2 and 1:3 curium(III)
complexes, but no ternary complexes were observed. The stability constants
for the 1:3 metal ion–N<sub>4</sub>bipy complexes equate to
a theoretical separation factor, SF<sub>Cm<sup>III</sup>/Eu<sup>III</sup></sub> ≈ 500. However, the low solubility of the HN<sub>4</sub>bipy ligand in nonpolar solvents typically used in actinide–lanthanide
liquid–liquid extractions prevents its use as a partitioning
extractant until a more lipophilic HN<sub>4</sub>bipy-type ligand
is developed
Chiral Rare Earth Borohydride Complexes Supported by Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in the Ring-Opening Polymerization of <i>rac</i>-Lactide
The monoamidinato bisborohydride rare earth complexes
[Ln{(<i>S</i>)-PEBA}(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Sc (<b>1</b>), La (<b>2</b>), Nd (<b>3</b>), Sm (<b>4</b>), Yb (<b>5</b>), Lu (<b>6</b>)) were isolated as crystalline materials upon treatment of potassium <i>N</i>,<i>N</i>′-bis((<i>S</i>)-1-phenylethyl)benzamidinate
((<i>S</i>)-KPEBA) with the homoleptic trisborohydrides
[Sc(BH<sub>4</sub>)<sub>3</sub>(THF)<sub>2</sub>] and [Ln(BH<sub>4</sub>)<sub>3</sub>(THF)<sub>3</sub>] (Ln = La, Nd, Sm, Yb, Lu), respectively.
Compounds <b>1</b>–<b>6</b> are unique examples
of enantiopure borohydride complexes of the rare earth metals. Different
ionic radii of the metal centers were selected to cover the whole
range of these elements with respect to the extent of the coordination
sphere. All new complexes were thoroughly characterized by <sup>1</sup>H, <sup>13</sup>C{<sup>1</sup>H}, <sup>11</sup>B, and <sup>15</sup>N NMR and IR spectroscopies, also including single-crystal X-ray
diffraction structure determination of each compound. The scandium,
lanthanum, samarium, and lutetium complexes <b>1</b>, <b>2</b>, <b>4</b>, and <b>6</b> were found active in
the ring-opening polymerization of <i>rac</i>-lactide under
mild operating conditions, providing atactic α,ω-dihydroxytelechelic
poly(lactic acid) (PLA; <i>M</i><sub>n,SEC</sub> up to 18
800 g·mol<sup>–1</sup>). Most of the polymerizations proceed
with a certain degree of control that is directed by molar mass values
and relatively narrow dispersities (1.10 < <i>Đ</i><sub>M</sub> < 1.34), within a moderate monomer-to-initiator ratio