Lanthanide Borohydride Complexes Supported by Diaminobis(phenoxide) Ligands for the Polymerization of ε-Caprolactone and l- and <i>r</i><i>ac</i>-Lactide

Reaction of Na2O2NN‘ [H2O2NN‘ = (2-C5H4N)CH2N{2-HO-3,5-C6H2tBu2}2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN‘)(μ-BH4)(THF)n]2 [M = YIII, n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN‘)(μ-Cl)(THF)n]2 (2-M; M = LaIII or SmIII, n = 0; M = NdIII, n = 1) and the corresponding pyridine adducts [M(O2NN‘)(μ-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = LaIII, NdIII, or SmIII] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of ε-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (Pr = 87%). Compound 1-Nd catalyzed the block copolymerization of ε-caprolactone and l- and rac-lactide provided that ε-caprolactone was added first. Attempted block polymerization by the addition of l-lactide first, or random copolymerization of a ca. 1:1 mixture of ε-caprolactone and l-lactide, gave only a poly(l-lactide) homopolymer

Lanthanide Borohydride Complexes Supported by Diaminobis(phenoxide) Ligands for the Polymerization of ε-Caprolactone and l- and <i>r</i><i>ac</i>-Lactide

Reaction of Na2O2NN‘ [H2O2NN‘ = (2-C5H4N)CH2N{2-HO-3,5-C6H2tBu2}2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN‘)(μ-BH4)(THF)n]2 [M = YIII, n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN‘)(μ-Cl)(THF)n]2 (2-M; M = LaIII or SmIII, n = 0; M = NdIII, n = 1) and the corresponding pyridine adducts [M(O2NN‘)(μ-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = LaIII, NdIII, or SmIII] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of ε-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (Pr = 87%). Compound 1-Nd catalyzed the block copolymerization of ε-caprolactone and l- and rac-lactide provided that ε-caprolactone was added first. Attempted block polymerization by the addition of l-lactide first, or random copolymerization of a ca. 1:1 mixture of ε-caprolactone and l-lactide, gave only a poly(l-lactide) homopolymer

Mechanistic Insights of the Initiation Process of the Ring-Opening Polymerization of ε-Caprolactone by Divalent Sm(BH₄)₂(THF)₂ with DFT: Concerted or Oxidative Reaction?

Concerted and oxidative mechanisms for the initiation of the ROP of ε-caprolactone by divalent Sm(BH4)2(THF)2 have been computed at the DFT level and compared with experimental data. The concerted polymerization pathway is proposed to occur via divalent [Sm]–(BH4) active species through classical O-acyl cleavage, leading to α,ω-dihydroxy telechelic polycaprolactone, which is fully compatible with chain end groups observed for low-Mn samples prepared with Sm(BH4)2(THF)2. Although it is calculated to be favorable, the oxidative route affording radical species is not in accordance with these experimental results, unless one considers transfer reactions with the solvent

Poly(l‑lactide-<i>co</i>-ε-caprolactone) Matrix Composites Produced in One Step by <i>In Situ</i> Polymerization in TP-RTM

Poly(l-lactide) (PLLA) is a semicrystalline biopolymer of great interest due to its biosourced, biocompatible, and compostable nature. However, its brittleness prevents its use in a wide range of applications. In order to reinforce PLLA, it is often used in polymer blends or in composites. In this contribution, an unprecedented family of PLLA-based/glass fabric composites with poly(l-lactide-co-ε-caprolactone) statistical copolymers as the matrix are reported. These biocomposites were produced in a one-step synthesis by in situ copolymerization of l-lactide and ε-caprolactone in the thermoplastic resin transfer molding (TP-RTM) process. These materials display high matrix/fabric wettability along with strong rubbery character

Mixed Allyl–Borohydride Lanthanide Complexes: Synthesis of Ln(BH₄)₂(C₃H₅)(THF)₃ (Ln = Nd, Sm), Characterization, and Reactivity toward Polymerization

New mixed allyl–borohydrido lanthanide complexes Ln­(BH₄)₂(C₃H₅)­(THF)₃ (Ln = Nd (<b>1</b>), Sm (<b>2</b>)) could be prepared in good yield by reacting Ln­(BH₄)₃(THF)₃ (Ln = Sm, Nd) with 1/2 equiv of Mg­(C₃H₅)₂(THF)_<i>x</i>. X-ray structure analysis revealed monomeric structures with two terminal BH₄ ligands, one π-allyl ligand, and three THF molecules. In an assessment of isoprene polymerization, <b>1</b> afforded <i>trans</i>-1,4-polyisoprene in good yield, as a single component or in combination with Mg cocatalyst. Both <b>1</b> and <b>2</b> were found to be extremely active toward ε-caprolactone polymerization

Ring-Opening Polymerization of <i>rac</i>-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study

The synthesis and ring-opening polymerization (ROP) capability of bis(phenolate)amine-supported samarium borohydride and amide complexes are reported, together with a DFT study. Reaction of Na2O2NL (L = OMe, NMe2, py, or Pr) with Sm(BH4)3(THF)3 gave the borohydride complexes Sm(O2NL)(BH4)(THF) (L = OMe (2), NMe2 (3), or py (4)) or Sm(O2NPr)(BH4)(THF)2 (5). Compounds 4 and 5 lost THF in vacuo, forming phenolate O-bridged dimers 1 and 6, respectively. Reaction of H2O2NL with Sm{N(SiHMe2)2}3(THF)2 formed monomeric Sm(O2NL){N(SiHMe2)2}(THF) (L = OMe (7), NMe2 (8), or py (9)) with tetradentate O2NL ligands, but dimeric Sm2(μ-O2NPr)2(O2NPr)(THF) (10) with tridentate O2NPr. Reaction of Sm{N(SiMe3)2}3 with H2O2NL (L = OMe or NMe2) led to zwitterionic products Sm(O2NL)(HO2NL). The bulkier amide compounds Sm(O2NL){N(SiMe3)2}(OEt2)n (n = 1, L = OMe (12) or py (13); n = 0, L = NMe2 (14)) were prepared by reaction of Sm(O2NL)(BH4)(THF) with KN(SiMe3)2. The X-ray structures of 2, 5, 6, 7, 10, 13, and 14 were determined. The borohydrides 2−5 were very efficient initiators for the ROP of ε-CL, giving linear dihydroxytelechelic poly(ε-CL). Selected amide initiators were also assessed but gave poorer control, as judged by broad PDI (Mw/Mn) values and significant amounts of cyclic poly(ε-CL)s. Of the borohydrides, only 2−4 were active for the ROP of rac-LA, and activity increased in the order O2NL = O2NOMe ≈ O2Npy 2NNMe2. The latter ligand also gave the best control of the ROP, as judged by the PDIs and Mn values. All gave heterotactically enriched poly(rac-LA) with Pr values in the range 0.82−0.84. The ROP of rac-LA with the amides 7, 9, and 12 was faster but much less well controlled. Overall, the borohydride initiators were superior for the ROP of both ε-CL and rac-LA when compared to otherwise identical amide initiators. MALDI-ToF MS analysis of the poly(rac-LA) formed with 3 showed both −CH(Me)CHO and −CH(Me)CH2OH end groups originating from the insertion of the first LA monomer into the Sm−BH4 moiety of 3. In contrast, 2 and 4 formed only α,ω-dihydroxy-terminated polyesters with −CH(Me)CH2OH and −CH(Me)OH end groups. DFT calculations on Eu(O2′NNMe2)(BH4) found two mechanisms for the initial ring-opening step of LA by the borohydride group, giving pathways leading to either aldehyde- or alcohol-terminated poly(lactide)s. Of these two pathways, the one giving α,ω-dihydroxy-terminated polymers was the most favored, in agreement with experiment. (Ligand abbreviations: O2NL = RCH2N(CH2-2-O-3,5-C6H2tBu2)2 where R = CH2OMe, CH2NMe2, py, or Et for L = OMe, NMe2, py, or Pr, respectively; O2′NNMe2 = Me2NCH2CH2N(CH2-2-O-C6H4)2.

Ring-Opening Polymerization of <i>rac</i>-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study

The synthesis and ring-opening polymerization (ROP) capability of bis(phenolate)amine-supported samarium borohydride and amide complexes are reported, together with a DFT study. Reaction of Na2O2NL (L = OMe, NMe2, py, or Pr) with Sm(BH4)3(THF)3 gave the borohydride complexes Sm(O2NL)(BH4)(THF) (L = OMe (2), NMe2 (3), or py (4)) or Sm(O2NPr)(BH4)(THF)2 (5). Compounds 4 and 5 lost THF in vacuo, forming phenolate O-bridged dimers 1 and 6, respectively. Reaction of H2O2NL with Sm{N(SiHMe2)2}3(THF)2 formed monomeric Sm(O2NL){N(SiHMe2)2}(THF) (L = OMe (7), NMe2 (8), or py (9)) with tetradentate O2NL ligands, but dimeric Sm2(μ-O2NPr)2(O2NPr)(THF) (10) with tridentate O2NPr. Reaction of Sm{N(SiMe3)2}3 with H2O2NL (L = OMe or NMe2) led to zwitterionic products Sm(O2NL)(HO2NL). The bulkier amide compounds Sm(O2NL){N(SiMe3)2}(OEt2)n (n = 1, L = OMe (12) or py (13); n = 0, L = NMe2 (14)) were prepared by reaction of Sm(O2NL)(BH4)(THF) with KN(SiMe3)2. The X-ray structures of 2, 5, 6, 7, 10, 13, and 14 were determined. The borohydrides 2−5 were very efficient initiators for the ROP of ε-CL, giving linear dihydroxytelechelic poly(ε-CL). Selected amide initiators were also assessed but gave poorer control, as judged by broad PDI (Mw/Mn) values and significant amounts of cyclic poly(ε-CL)s. Of the borohydrides, only 2−4 were active for the ROP of rac-LA, and activity increased in the order O2NL = O2NOMe ≈ O2Npy 2NNMe2. The latter ligand also gave the best control of the ROP, as judged by the PDIs and Mn values. All gave heterotactically enriched poly(rac-LA) with Pr values in the range 0.82−0.84. The ROP of rac-LA with the amides 7, 9, and 12 was faster but much less well controlled. Overall, the borohydride initiators were superior for the ROP of both ε-CL and rac-LA when compared to otherwise identical amide initiators. MALDI-ToF MS analysis of the poly(rac-LA) formed with 3 showed both −CH(Me)CHO and −CH(Me)CH2OH end groups originating from the insertion of the first LA monomer into the Sm−BH4 moiety of 3. In contrast, 2 and 4 formed only α,ω-dihydroxy-terminated polyesters with −CH(Me)CH2OH and −CH(Me)OH end groups. DFT calculations on Eu(O2′NNMe2)(BH4) found two mechanisms for the initial ring-opening step of LA by the borohydride group, giving pathways leading to either aldehyde- or alcohol-terminated poly(lactide)s. Of these two pathways, the one giving α,ω-dihydroxy-terminated polymers was the most favored, in agreement with experiment. (Ligand abbreviations: O2NL = RCH2N(CH2-2-O-3,5-C6H2tBu2)2 where R = CH2OMe, CH2NMe2, py, or Et for L = OMe, NMe2, py, or Pr, respectively; O2′NNMe2 = Me2NCH2CH2N(CH2-2-O-C6H4)2.

Lactide Lactone Chain Shuttling Copolymerization Mediated by an Aminobisphenolate Supported Aluminum Complex and Al(O<i>i</i>Pr)₃: Access to New Polylactide Based Block Copolymers

The chain shuttling ring-opening copolymerization of l-lactide with ε-caprolactone has been achieved using two aluminum catalysts presenting different selectivities and benzyl alcohol as chain transfer agent. A newly synthesized aminobisphenolate supported aluminum complex affords the synthesis of lactone rich poly­(l-lactide-co-lactone) statistical copolymeric blocks, while Al­(OiPr)3 produces semicrystalline poly­(l-lactide) rich blocks. Transalkoxylation is shown to operate efficiently. The crystalline ratios and glass transition temperatures of these new classes of polylactide based block copolymers can be tuned by adjusting the catalysts and the comonomers ratio