Gorczynski Jessica L, Chen Jianbin, Fraser Cassandra L
Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
J Am Chem Soc. 2005 Nov 2;127(43):14956-7. doi: 10.1021/ja0530927.
Poly(lactic acid) (PLA)-supported dibenzoylmethane (dbm) and corresponding metal complexes have potential applications as biomaterials and catalysts. Using hydroxyl-functionalized dbm (i.e., dbmOH) as the initiator and Sn(oct)2 as the catalyst, lactide ring-opening polymerizations were unexpectedly slow (6 h), and PDIs broadened when molecular weights >10 000 were targeted. Because interactions between the dbm ligand and Sn(oct)2 may be responsible for the diminished catalyst activity and molecular weight control, iron(III) was employed as a protecting group to form Fe(dbmOH)3. Shorter reaction times (10 min) were noted with this trifunctional metalloinitiator and Sn(oct)2, and higher molecular weights were achievable. Moreover, it was discovered that Fe(dbmOH)3 serves not only as an initiator but also as a catalyst and activating group for the polymerization. Even without the tin catalyst, iron-centered polymers with low PDIs (<1.1) were obtained within 10 min ( approximately 70% monomer conversion). The resulting Fe(dbmPLA)3 stars were demetalated by acid treatment to generate dbmPLA for subsequent coordination to other metals. To explore the scope of iron beta-diketonate complexes as catalysts, additional studies were performed with dbmOH and benzyl alcohol initiators using either iron tris(dbm) or iron tris(acac) (acac = acetylacetonate) as the catalyst. Here too, PLA products were obtained, and the iron catalysts were readily separated by treatment with aqueous HCl.
聚乳酸（PLA）负载的二苯甲酰甲烷（dbm）及其相应的金属配合物作为生物材料和催化剂具有潜在应用价值。以羟基官能化的dbm（即dbmOH）为引发剂、Sn（oct）2为催化剂时，丙交酯开环聚合反应意外地缓慢（6小时），且当目标分子量>10000时，聚合物分散指数（PDI）变宽。由于dbm配体与Sn（oct）2之间的相互作用可能导致催化剂活性降低和分子量控制不佳，因此使用铁（III）作为保护基团形成Fe（dbmOH）3。使用这种三官能金属引发剂和Sn（oct）2时，反应时间缩短（10分钟），且可实现更高的分子量。此外，还发现Fe（dbmOH）3不仅作为引发剂，还作为聚合反应的催化剂和活化基团。即使不使用锡催化剂，在10分钟内（单体转化率约70%）也能得到低PDI（<1.1）的铁中心聚合物。通过酸处理使所得的Fe（dbmPLA）3星型聚合物脱金属，生成dbmPLA，以便随后与其他金属配位。为了探索铁β-二酮配合物作为催化剂的适用范围，使用dbmOH和苄醇引发剂，以三（dbm）铁或三（乙酰丙酮）铁（acac = 乙酰丙酮）作为催化剂进行了额外的研究。同样在此处得到了PLA产物，并且通过用盐酸水溶液处理可轻松分离铁催化剂。
