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 (HN₄bipy) with samarium­(III) was investigated as a model system for actinide­(III)/lanthanide­(III) separations. Two different solid 1:2 complexes, [Sm­(N₄bipy)₂(OH)­(H₂O)₂] (<b>1</b>) and [Sm­(N₄bipy)₂(HCOO)­(H₂O)₂] (<b>2</b>), were obtained from the reaction of samarium­(III) nitrate with HN₄bipy 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 HN₄bipy as the ligand. Curium­(III) is observed to form 1:2 and 1:3 complexes with increasing HN₄bipy 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 β₃[Cm­(N₄bipy)₃] = 13.8 and log β₃[Eu­(N₄bipy)₃] = 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–N₄bipy complexes equate to a theoretical separation factor, SF_{Cm^III/Eu^III} ≈ 500. However, the low solubility of the HN₄bipy ligand in nonpolar solvents typically used in actinide–lanthanide liquid–liquid extractions prevents its use as a partitioning extractant until a more lipophilic HN₄bipy-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}­(BH₄)₂(THF)₂] (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(BH₄)₃(THF)₂] and [Ln­(BH₄)₃(THF)₃] (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 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 <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>_n,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 < <i>Đ</i>_M < 1.34), within a moderate monomer-to-initiator ratio