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Związki magnezu z ligandami aryloksanowymi : inicjatory polimeryzacji laktydów

Ejfler J.

Wiadomości Chemiczne

2008

[Z] 62, 9-10

875-899

Magnesium alkoxides and aryloxides are systematically explored in various kinds of chemical processes and among other, their use as reagents in organic transformations [1-5], supports or catalyst components in polyolefin industry [6, 7], chemical precursors for advanced materials [8-10], as well as initiators for the polymerization of cyclic esters [11, 12] are worth mentioning. Over the past few years we have witnessed an increasing research on the use of magnesium aryloxides in the synthesis of new, biodegradable polymers, which have been preferential candidates for applications in medicine, pharmacy and production of eco-friendly bulk packing materials [13-15, 54-56]. Ready availability of monomers from inexpensive, renewable resources and the fact that resulted materials do not degrade the environment are an additional asset. Biodegradable polymers for the biomedical applications are preferably obtained using initiators containing non-toxic metals, and aryloxides of metals such as magnesium are especially interesting in this context. Despite the high utility limited number of magnesium alkoxides and aryloxides reported in the literature have a well-defined structure proved by X-ray analysis, which is required to design "single-site" catalysts. However, it is possible to identify and characterise certain types of frameworks. Homoleptic magnesium bis-aryloxides depending on synthesis procedures and ligand structure can crystallise as monomers [12, 40, 44], dimers [47, 48], trimers [47, 48] and tetramers [47, 48] with the coordination number ranging from three to six. Among them candidates of primary importance for the application in the ring-opening polymerization (ROP) of cyclic esters are monomeric compounds. Up to now, however, only few examples of such species displaying the certain activity in living polymerization have been published [60-63]. Extremely important are homoleptic compounds able to act as initiators for ROP in presence of exterior alcohols which form end-groups in the resulting polymer [12, 50]. This constitutes a chance for the polymer chain modyfication achieved by simple introduction of functional groups and enable to obtain new drug-polymer complex.