MODELLING OF INFLUENCE OF PARAMETERS OF THE BUNKER AND TRANSPORT WINDOWS ON PRODUCTIVITY OF THE BUNKER OF SEEDERS

In the article the influence of parameters of the bunker and transport boxes on the performance of the hopper units are plated. Recommendations on the choice of the main parameters for a given rate of sowing the seed culture

Lanthanide(II) Complexes Supported by N,O-Donor Tripodal Ligands: Synthesis, Structure, and Ligand-Dependent Redox Behavior

The preparation and characterization of a series of complexes of the Yb and Eu cations in the oxidation state II and III with the tetradentate N,O-donor tripodal ligands (tris(2-pyridylmethyl)amine (TPA), BPA(-) (HBPA=bis(2-pyridylmethyl)(2-hydroxybenzyl)amine), BPPA(-) (HBPPA=bis(2-pyridylmethyl)(3.5-di-tert-butyl-2-hydroxybenzyl)amine), and MPA(2-) (H(2)MPA=(2-pyridylmethyl)bis(3.5-di-tert-butyl-2-hydroxybenzyl)amine) is reported. The X-ray crystal structures of the heteroleptic Ln(2+) complexes [Ln(TPA)I-2] (Ln=Eu, Yb) and [Yb(BPA)I(CH3CN)](2), of the Ln(2+) homoleptic [Ln(TPA)(2)]I-2 (Ln=Sm, Eu, Yb) and [Eu(BPA)(2)] complexes, and of the Ln(3+) [Eu(BPPA)(2)]OTf and [Yb(MPA)(2)K(dme)(2)] (dme=dimethoxyethane) complexes have been determined. Cyclic voltammetry studies carried out on the bis-ligand complexes of Eu3+ and Yb3+ show that the metal center reduction occurs at significantly lower potentials for the BPA(-) ligand as compared with the TPA ligand. This suggests that the more electron-rich character of the BPA(-) ligand results in a higher reducing character of the lanthanide complexes of BPA(-) compared with those of TPA. The important differences in the stability and reactivity of the investigated complexes are probably due to the observed difference in redox potential. Preliminary reactivity studies show that whereas the bis-TPA complexes of Eu2+ and Yb2+ do not show any reactivity with heteroallenes, the [Eu(BPA)(2)] complex reduces CS2 to afford the first example of a lanthanide trithiocarbonate complex

Lanthanide chloride complexes of amine-bis(phenolate) ligands and their reactivity in the ring-opening polymerization of ε-caprolactone

Reaction of two equivalents of n-BuLi with sterically demanding amine-bis(phenol) compounds, H2O2NN′R (Me2NCH2CH2N{CH2-3,5-R2-C6H2OH}2; R = t-Bu or t-Pe (tert-pentyl)) yields isolable lithium complexes, Li2(O2NN′R), in good yields. Upon reaction with one equivalent of LnCl3(THF)x, the lithium salts afford rare earth amine-phenolate chloride complexes in good yields, Ln(O2NN′R)Cl(THF); Ln = Y, Yb, Ho, Gd, Sm, Pr. Crystals of Y(O2NN′t-Bu)Cl(THF), 1, and Sm(O2NN′t-Bu)Cl(DME), 2, suitable for single crystal X-ray crystallographic analysis were obtained. In contrast to previously reported [{Gd(O2NN′t-Pe)(THF)(μ-Cl)}2] and related La and Sm complexes, these species are monomeric. 1 contains Y in a distorted octahedral environment bonded to two amine, two phenolate, one THF and one chloride donor. 2 contains Sm in a distorted capped trigonal prismatic environment bonded to two amine, two phenolate, two DME oxygens and one chloride donor. The Ln(O2NN′t-Pe)Cl(THF) complexes were active initators for the controlled ring-opening polymerization of ε-caprolactone with a tendency to form low molecular weight cyclic polyesters (Mn 3000–5000). The conversion rates, although slower than related amido and alkyl species, were different for monomeric and dimeric initiators. The size of the metal centre also affected the conversions and the molecular weights achieved

Rare-Earth Complexes with Multidentate Tethered Phenoxy-Amidinate Ligands: Synthesis, Structure, and Activity in Ring-Opening Polymerization of Lactide

International audienceNew multidentate tethered amidine-phenol proligands {4,6-tBu2C6H2O-(2-C(N-R)dN-R}H2 ({LONR}H2, R = iPr, cyclohexyl (Cy), 2,6-iPr2C6H3 (Ar)) were synthesized from the corresponding carbodiimines and 2-bromo-2,4-(ditert-butyl)phenol. Pro-ligands {LONiPr}H2 and {LONAr}H2 were metalated by 2 equiv of nBuLi to provide the corresponding dilithiumsalts {LONiPr}Li2 (1) and {LONAr}Li2 (2), which were authenticated by elemental analysis, X-ray crystallography, and NMR spectroscopy. Three different approaches were explored to coordinate these (pro)ligands onto rare earths: salt metathesis, and amine and methane elimination reactions. The salt metathesis reaction between 1 and YCl3 afforded the chloro complex [{LONiPr}YCl]n (3), which was, in turn, converted into the corresponding amide {LONiPr}YN(SiMe3)2 (6) by reaction withMN(SiMe3)2 (M = Li, Na). Similar reactions between 2 and YCl3, followed by recrystallization from DME, led systematically to the isolation of the monoprotonated product, that is, phenoxy-amidino complex {LOHNAr}YCl2(DME) (5). Amine elimination reactions between {LONiPr}H2 or {LONCy}H2 and Ln[N(SiMe3)2]3 afforded the corresponding phenoxy-amidinate amides {LONR}LnN(SiMe3)2 (Ln = Y, R = iPr, 6; R = Cy, 8; Ln = Nd, R = Cy, 9), whereas the same reaction between{LONAr}H2 and Y[N(SiMe3)2]3, under various conditions, always yielded the homoleptic tris(phenoxy-amidinate) complex {LOHNAr}3Y (11). Bimetallic "ate"-complexes {LONR}2Ln2Me4Li2(TMEDA)2 of yttrium (12 and 13), neodymium (14), samarium (15), and {LONiPr}2Yb2Me2(OH)2Li2(TMEDA)2 (16) were prepared by alkane elimination of the corresponding pro-ligand and [Li(TMEDA)][LnMe4] complex. Both amido and methyl "ate"- complexes were shown by X-ray diffraction studies to be dimeric in the solid state. The multidentate nature of the ligands in these dimeric species generates a cis/trans isomerism related to the nitrogen atoms in the nonsymmetrically coordinated amidinate fragments. Amido complexes 6, 8, and 9 are effective initiators for the ring-opening polymerization (ROP) of racemic lactide (rac-LA), giving atactic or heterotactic-enriched (Pr up to 76%) polymers with high molecular weights (Mn up to 158 800 g 3 mol#1), but broad molecular weight distributions (Mw/Mn = 1.5#2.8). An effective immortal ROP of rac-LA was feasible by combining complex 6 with 5#50 equiv of isopropanol or benzyl alcohol, affording PLAs with well-controlled molecular weights and narrow polydispersities (Mw/Mn = 1.11#1.38)

Bis(Guanidinate) Alkoxide Complexes of Lanthanides: Synthesis, Structures and Use in Immortal and Stereoselective Ring-Opening Polymerization of Cyclic Esters

International audienc

Neodymium borohydride complexes supported by diamino-bis(phenoxide) ligands: diversity of synthetic and structural chemistry, and catalytic activity in ring-opening polymerization of cyclic esters

New heterobimetallic borohydrido neodymium complexes {[OONN]1Nd(BH4)(m-BH4)Li(THF)}2 (1) and [OONN]3Nd(BH4)(m-BH4)Li(THF)2 (3) supported by diamino-bis(phenoxide) ligands ([OONN]1 = {CH2N(Me)CH2-3,5-Me,t-Bu-C6H2O}2; [OONN]3 = C5H4NCH2N-{CH2-3,5-Me,t-Bu-C6H2O}2) were synthesized by the reactions of Nd(BH4)3(THF)2 with equimolar amounts of dilithium derivatives of diamino-bis(phenol)s Li2[OONN]n and isolated in high yields. In the case of Li2[OONN]2 ([OONN]2=Me2NCH2CH2N{CH2-3,5-t-Bu-C6H2O}2), the same synthetic procedure afforded the heterobimetallic bis(phenoxide) complex Li{Nd[OONN2]2} (2). The structures of complexes 1–3 were established by X-ray diffraction studies. Compounds 1–3 act as single-site initiators for the ring-opening polymerization (ROP) of racemic lactide and racemic b-butyrolactone under mild conditions (20 1C), providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (Mw/Mn = 1.07–1.82). While 1 and 3 initiate polymerization via their borohydride groups, ROP with 2 proceeds via insertion into the Nd–O(ligand) bond