Heterobimetallic Aryloxides of Titanatranes with

The titanatrane titanium complexes were treated with Aluminum Alkyls to prepare their bimetallic derivatives (1a-4a). The compounds were confirmed by means of NMR and elemental analysis. The complexes were used as catalysts for ring opening polymerization of racemic lactide. The complexes exhibit high activity and selectivity in the polymerization process. Abbreviations: ROP: Ring Opening Polymerization; LA: Rac-lactide ISSN: 2637-4609 DOI: 10.32474/AOICS.2018. 01.000110 Arc Org Inorg Chem Sci Copyrights@ Prabhuodeyara M Gurubasavaraj. Citation: Prabhuodeyara M G. Heterobimetallic Aryloxides of Titanatranes with Aluminum Alkyls for Ring opening polymerization (ROP) of rac-Lactide. Arc Org Inorg Chem Sci 1(2)2018. AOICS.MS.ID.000110. DOI: 10.32474/AOICS.2018. 01.000110. 71 Results and Discussion The titanatranes and their bimetallic derivatives are prepared as reported earlier [8]. The following complexes were confirmed by NMR and elemental analysis. The pure crystalline products were used for the polymerization process (Figure 1). There has been considerable attention on the study of ring-opening polymerization (ROP) of cyclic esters such as rac-lactide (LA) with metal complexes for the past few decades [10a-b]. Various types of metal alkoxides such as tin [11a-e], aluminum, zinc , magnesium, iron [12a-b], lanthanide [13a-c], and lithium [14] organometallic complexes have been found to be active LA polymerization catalysts, and many afford materials with controlled molecular weights and narrow molecular weight distributions. Despite the fact that some excellent initiators have been reported for the polymerization of LA, the search for new catalysts that generate well-defined polylactides remains of keen interest. The roles of the structure of metal alkoxide complexes in determining molecular weights and molecular weight distributions, as well as the polymerization pathway, are significant current research issues. Figure 1: Bulk Polymerization of rac-Lactide (rac-LA). Recently, Verkade et al. [15a-b] reported that several titanium alkoxides showed reasonably good catalytic activity in the bulk homopolymerization of rac-LA at 130 °C. Harada et al. [16] also reported the living polymerization of LA by a Ti chloride complex, whose chloride apparently plays the same role as an alkoxide. We thus believed it would be interesting to test heterobimetallic titanium catalysts and compare the activity and control of the molecular and physical properties of the PLA produced by mononuclear and binuclear complexes with well-defined ligand environments. Here, we describe discrete heterobimetallic titanium alkoxide/aryloxide complexes and their bimetallic derivatives for the study of the ROP of LA under bulk polymerization conditions. We also demonstrate the difference in monometallic and bimetallic catalysts towards the ROP of rac-Lactide. Preliminary results on the use of heterobimetallic catalysts for the bulk polymerization of rac-LA are summarized for 1a-4a, are presented in Table 1. Polymerizations were performed at 130 °C with the [LA]/[Ti] ratio fixed at 300. This table reveals that all the titanium compounds catalyze LA polymerization. Moreover, it appears that chelation aluminium methyl to the tripodal tetradentate ligand significantly decreases the polydispersity index and polymer yield. However, some transesterification probably occurred during the polymerization reaction since the polydispersity indices of both PLA products were somewhat higher than expected for a controlled polymerization. The bimetallic complexes exhibit high activity and produce polylactide with high molecular weight and lower polydispersity compare to their mononuclear precursors [15]. Table 1: Ring opening polymerization (ROP) of rac -Lactide Data for Heterobimetallic complexes. Run Complex g polymer Yield Mw b Mnb M/Mn 1 1a 1.82 91 64 009 49 045 1.31 2 2a 1.68 84 81 725 53 373 1.53 3 3a 1.76 88 48.104 38 115 1.26 4 4a 1.80 90 61 076 44 188 1.38 LA (2.027g) LA/Ti = 300, polymerization temperature = 130 °C, time = 20min. The weight average molecular weight (Mw), the number average molecular weight (Mn), and the polydispersity index (PDI) Mw/Mn) were determined by GPC.