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The complexes {(Me3Si)2NC(NPri)2}2LnOBut (Ln = Y (1), Lu (2)) initiate the bulk polymerization of racemic lactide (LA) at 130 °C. At the monomer: initiator molar ratio ([LA]: 1) equal to 1000: 1, the quantitative conversion of the monomer is achieved within 6 h. The resulting polymers are characterized by a rather narrow monomodal molecular weight distribution (M w/M n = 1.46–1.82) and molecular weights up to 33400 g mol−1. The molecular weights of the resulting polylactides measured by gel permeation chromatography are 3–11 times lower than the values calculated from the monomer: initiator ratio on the assumption of one growing polymer chain per catalytic center. The reaction of the in-situ prepared complex [(Me3Si)2NC(NPri)2]NdCl2 with 2 equiv. of PriOLi produced the 11-nuclear cluster [{(Me3Si)2NC(NPri)2}Nd]4(μ3-OPri)8Li7(μ2-Cl)3(μ3-Cl)2(μ4-Cl)2 (3), which was isolated in 62% yield. The structure of compound 3 was established by X-ray diffraction. Complex 3 initiates both the bulk and solution polymerization of rac-lactide. In the bulk polymerization at the molar ratio [LA]: [Nd] = 500: 1, the 89% conversion of the monomer was achieved within one hour. The polylactide thus synthesized has the molecular weight M n = 19720 g mol−1 and a rather narrow polydispersity M w/M n = 1.54.

International audience; New heterobimetallic borohydrido neodymium complexes {[OONN]1Nd(BH4)(μ-BH4)Li(THF)}2 (1) and [OONN]3Nd(BH4)(μ-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 β-butyrolactone under mild conditions (20 °C), 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.

International audience; New 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).

Reaction of two equivalents of n-BuLi with sterically demanding amine-bis(phenol) compounds, H(2)O(2)NN'(R) (Me(2)NCH(2)CH(2)N{CH(2)-3,5-R(2)-C(6)H(2)OH}(2); R = t-Bu or t-Pe (tert-pentyl)) yields isolable lithium complexes, Li(2)(O(2)NN'(R)), in good yields. Upon reaction with one equivalent of LnCl(3)(THF)(x), the lithium salts afford rare earth amine-phenolate chloride complexes in good yields, Ln(O(2)NN'(R))Cl(THF); Ln = Y, Yb, Ho, Gd, Sm, Pr. Crystals of Y(O(2)NN'(t-Bu))Cl(THF), 1, and Sm(O(2)NN'(t-Bu))Cl(DME), 2, suitable for single crystal X-ray crystallographic analysis were obtained. In contrast to previously reported [{Gd(O(2)NN'(t-Pe))(THF)(micro-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(O(2)NN'(t-Pe))Cl(THF) complexes were active initators for the controlled ring-opening polymerization of epsilon-caprolactone with a tendency to form low molecular weight cyclic polyesters (M(n) 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.

A series of new bis(guanidinate) alkoxide Group 3 metal complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) has been synthesized. X-ray structural determinations revealed that bis(guanidinate) tert-butoxides are monomeric complexes. The isopropoxide complex [Y((Me3Si)2NC(NiPr)2)2(OiPr)] undergoes slow decomposition in solution, to afford the unusual dimeric amido complex [(Y((Me3Si)2NC(NiPr)2)2(mu-N(iPr)C triple chemical bond N))2]. Complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) are active catalysts/initiators for the ROP of rac-lactide and rac-beta-butyrolactone under mild conditions. Most of those polymerizations proceed with a significant degree of control. Bis(guanidinate) alkoxides appear to be well suited for achieving immortal polymerization of lactide, through the introduction of large amounts of isopropanol as a chain-transfer agent. The synthesized complexes are able to promote the stereoselective ROP of rac-beta-butyrolactone to afford syndiotactic poly(hydrobutyrate) through a chain-end control mechanism, while they are surprisingly non-stereoselective for the ROP of lactide under strictly similar conditions.