Ring-Opening Polymerization of rac-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 Na2O 2NL (L = OMe, NMe2, py, or Pr) with Sm(BH 4)3(THF)3 gave the borohydride complexes Sm(O2NL)(BH4)(THF) (L...
| Main Authors: | , , , , , , , |
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| Format: | Journal article |
| Language: | English |
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2010
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| _version_ | 1826277051403862016 |
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| author | Dyer, H Huijser, S Susperregui, N Bonnet, F Schwarz, A Duchateau, R Maron, L Mountford, P |
| author_facet | Dyer, H Huijser, S Susperregui, N Bonnet, F Schwarz, A Duchateau, R Maron, L Mountford, P |
| author_sort | Dyer, H |
| collection | OXFORD |
| description | 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 Na2O 2NL (L = OMe, NMe2, py, or Pr) with Sm(BH 4)3(THF)3 gave the borohydride complexes Sm(O2NL)(BH4)(THF) (L = OMe (2), NMe 2 (3), or py (4)) or Sm(O2NPr)(BH 4)(THF)2 (5). Compounds 4 and 5 lost THF in vacuo, forming phenolate O-bridged dimers 1 and 6, respectively. Reaction of H 2O2NL with Sm{N(SiHMe2) 2}3(THF)2 formed monomeric Sm(O 2NL){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 O 2NPr. Reaction of Sm{N(SiMe3)2} 3 with H2O2NL (L = OMe or NMe 2) led to zwitterionic products Sm(O2NL) (HO2NL). The bulkier amide compounds Sm(O 2NL){N(SiMe3)2}(OEt 2)n (n = 1, L = OMe (12) or py (13); n = 0, L = NMe 2 (14)) were prepared by reaction of Sm(O2N L)(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/M n) 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 < O2NNMe2. The latter ligand also gave the best control of the ROP, as judged by the PDIs and M n values. All gave heterotactically enriched poly(rac-LA) with P r 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′N NMe2)(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, CH 2NMe2, py, or Et for L = OMe, NMe2, py, or Pr, respectively; O2′NNMe2 = Me2NCH 2CH2N(CH2-2-O-C6H4) 2.) © 2010 American Chemical Society. |
| first_indexed | 2024-03-06T23:23:05Z |
| format | Journal article |
| id | oxford-uuid:69709e8f-8217-42d8-a310-42f35cbb4429 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T23:23:05Z |
| publishDate | 2010 |
| record_format | dspace |
| spelling | oxford-uuid:69709e8f-8217-42d8-a310-42f35cbb44292022-03-26T18:51:06ZRing-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT StudyJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:69709e8f-8217-42d8-a310-42f35cbb4429EnglishSymplectic Elements at Oxford2010Dyer, HHuijser, SSusperregui, NBonnet, FSchwarz, ADuchateau, RMaron, LMountford, PThe 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 Na2O 2NL (L = OMe, NMe2, py, or Pr) with Sm(BH 4)3(THF)3 gave the borohydride complexes Sm(O2NL)(BH4)(THF) (L = OMe (2), NMe 2 (3), or py (4)) or Sm(O2NPr)(BH 4)(THF)2 (5). Compounds 4 and 5 lost THF in vacuo, forming phenolate O-bridged dimers 1 and 6, respectively. Reaction of H 2O2NL with Sm{N(SiHMe2) 2}3(THF)2 formed monomeric Sm(O 2NL){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 O 2NPr. Reaction of Sm{N(SiMe3)2} 3 with H2O2NL (L = OMe or NMe 2) led to zwitterionic products Sm(O2NL) (HO2NL). The bulkier amide compounds Sm(O 2NL){N(SiMe3)2}(OEt 2)n (n = 1, L = OMe (12) or py (13); n = 0, L = NMe 2 (14)) were prepared by reaction of Sm(O2N L)(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/M n) 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 < O2NNMe2. The latter ligand also gave the best control of the ROP, as judged by the PDIs and M n values. All gave heterotactically enriched poly(rac-LA) with P r 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′N NMe2)(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, CH 2NMe2, py, or Et for L = OMe, NMe2, py, or Pr, respectively; O2′NNMe2 = Me2NCH 2CH2N(CH2-2-O-C6H4) 2.) © 2010 American Chemical Society. |
| spellingShingle | Dyer, H Huijser, S Susperregui, N Bonnet, F Schwarz, A Duchateau, R Maron, L Mountford, P Ring-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study |
| title | Ring-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study |
| title_full | Ring-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study |
| title_fullStr | Ring-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study |
| title_full_unstemmed | Ring-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study |
| title_short | Ring-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study |
| title_sort | ring opening polymerization of rac lactide by bis phenolate amine supported samarium borohydride complexes an experimental and dft study |
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