| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1326009 | Journal of Organometallic Chemistry | 2012 | 7 Pages |
Reaction of LnCl3 with bridged bis(guanidinate) lithium salt LLi2 (1) (L = iPr(Me3Si)NC(NiPr)N(CH2)3NC(NiPr)N(SiMe3)iPr) afforded the monochlorides LLnCl(THF)2 (Ln = Nd (2), Yb (3), Y (4)) and LYbCl(DME) (5) (DME = 1,2-dimethoxyethane). Complexes 2–5 were structurally characterized. Treatment of the chlorides with NaBH4 gave the monoborohydride complexes LLnBH4(DME) (Ln = Nd (6), Yb (7), Y (8)). X-ray crystal structure analyses of 6–8 revealed each complex was monomer with the central metal ligated by one L, one η3-BH4 group and one DME. Complexes 6–8 initiate ring-opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL), l-lactide (l-LA) and rac-lactide (rac-LA) as single-site initiators. The highest activity and the best molecular mass control for all the three monomers were found for the Nd system 6. The ROP of ɛ-CL in toluene with 6 gave the polymers with the M¯nexp in good agreement with the M¯ntheo (M¯n = the number averaged molar mass) at the molar ratio of monomer to 6 up to 600 and moderate molar mass distributions (M¯w/M¯n=1.43-1.52) (M¯w = the weight averaged molar mass). The ROP of l-LA with 6 in THF afforded the polymers with controlled molar mass and relatively narrow M¯w/M¯n. Complexes 6–8 are active in the ROP of rac-LA affording poly(LA) with a slight heterotactic bias (Pr = 0.62–0.72).
Graphical abstractNovel monoborohydride lanthanide complexes LLnBH4(DME) (Ln = Nd, Yb and Y; L = iPr(Me3Si)NC(NiPr)N(CH2)3NC(NiPr)N(SiMe3)iPr) supported by bridged bis(guanidinate) ligand were synthesized in good yields. All borohydride complexes were proven to be highly active single-site initiators for the polymerization of cyclic esters.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Bridged bis(guanidinate) ligand stabilizing lanthanide monochloride complexes. ► The synthesis of monoborohydride complexes supported by bis(guanidiante) ligand. ► Borohydride complexes serve as highly active initiators for ROP of cyclic esters.
