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Author: search.filters.author.Balasanthiran, VagulejanSubject: search.filters.subject.Ring-opening polymerization

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    TMPZnN(SiMe3)2, [TMPZn(μ-OiPr)]2 and TMPZn[OCMe2C(O)OEt]. Their role in the ring-opening of rac-lactide and ϵ-caprolactone where TMP = 1,5,9-trimesityldipyrromethene
    (2016-06-15)
    Balasanthiran, Vagulejan
    ;
    Chisholm, Malcolm H.
    ;
    Choojun, Kittisak
    ;
    Durr, Christopher B.
    ;
    Wambua, Pasco M.
    From the reaction between Zn[N(SiMe<inf>3</inf>)<inf>2</inf>]<inf>2</inf> and TMP-H (1 equiv.) in toluene at room temperature TMPZn[N(SiMe<inf>3</inf>)<inf>2</inf>] was prepared and subsequently reacted with Pr<sup>i</sup>OH (1 equiv.) and HOCMe<inf>2</inf>C(O)OEt (1 equiv.) to give [TMPZn(μ-OPr<sup>i</sup>)]<inf>2</inf> and TMPZn[OCMe<inf>2</inf>C(O)OEt], respectively. The three compounds were each crystallized and characterized by single crystal X-ray diffraction. The compound TMPZn[N(SiMe<inf>3</inf>)<inf>2</inf>] was a three coordinated N<inf>3</inf>Zn compound with an anagostic N(SiMe<inf>3</inf>)<inf>2</inf> ligand where one SiMe<inf>3</inf> was annexed to the Zn<sup>2+</sup> ion. The compound [TMPZn(μ-OPr<sup>i</sup>)]<inf>2</inf> has a molecular C<inf>2</inf> axis and is dimeric in toluene-d<inf>8</inf> solution having a N<inf>2</inf>ZnO<inf>2</inf> core for each Zn<sup>2+</sup> ion. In TMPZn[OCMe<inf>2</inf>C(O)OEt] compound the Zn<inf>2</inf> + ion is four-coordinated. This too is present in solution (IR) and also present in toluene-d<inf>8</inf> and THF where there is evidence of fluxionality with T<inf>c</inf> ∼15 °C and -85 °C, respectively. The compound [TMPZn(μ-OPr<sup>i</sup>)]<inf>2</inf> polymerizes both ϵ-caprolactone (ϵ-CL) and rac-lactide (rac-LA) to give polycaprolactone (PCL) and polylactic acid (PLA), respectively. The rate of the reactions are ϵ-CL > LA and are influenced by the nature of solvent, THF > CD<inf>2</inf>Cl<inf>2</inf>/CH<inf>2</inf>Cl<inf>2</inf>. The nature of PLA derived from rac-LA is heterotactic: P<inf>r</inf> = 0.96 in THF and P<inf>r</inf> = 0.75 in CD<inf>2</inf>Cl<inf>2</inf>/CH<inf>2</inf>Cl<inf>2</inf>. In the copolymerization of rac-LA: ϵ-CL by both [TMPZn(μ-OPr<sup>i</sup>)]<inf>2</inf> and TMPZn[OCMe<inf>2</inf>C(O)OEt] only PLA is produced, PCL is not formed.