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β-Diketiminate Rare Earth Borohydride Complexes: Synthesis, Structure, and Catalytic Activity in the Ring-Opening Polymerization of ε-Caprolactone and Trimethylene Carbonate

Abstract : The synthesis of a series of divalent and trivalent β-diketiminate borohydrides [(dipp)2NacNacLn(BH4)(THF)2] ((dipp)2NacNac = (2,6-C6H3iPr2)NC(Me)CHC(Me)N(2,6-C6H3iPr2); Ln = Sm, Eu, Yb) and [(dipp)2NacNacLn(BH4)2(THF)] (Ln = Sc, Sm, Dy, Yb, Lu) is reported. All compounds were obtained by salt metathesis in THF from [(dipp)2NacNacK] and the corresponding homoleptic divalent and trivalent borohydrides [Ln(BH4)2(THF)2] (Ln = Sm, Eu, Yb), [Sc(BH4)3(THF)2], and [Ln(BH4)3(THF)3] (Ln = Sm, Dy, Yb, Lu), respectively. The complexes were fully characterized, and their solid-state structures were established by single-crystal X-ray diffraction. In both the divalent and trivalent compounds, the BH4– groups coordinate in a κ3(H) mode to the metal. Only in the lutetium complex [(dipp)2NacNacLu(BH4)2(THF)] does one BH4– group coordinate in a κ3(H) mode, whereas the other one coordinates as κ2(H). This kind of mixed κ2/κ3(H) coordination mode is rare. The application of the divalent and trivalent compounds as initiators in the ring-opening polymerization (ROP) of ε-caprolactone (CL) and trimethylene carbonate (TMC) was investigated. All complexes afforded a generally well-controlled ROP of both of these cyclic esters. High molar mass poly(ε-caprolactone) diols (Mn,NMR < 92 700 g mol–1, ĐM = 1.51) and α-hydroxy,ω-formate telechelic poly(trimethylene carbonate)s (Mn,NMR < 16 000 g mol–1, ĐM = 1.59) were thus synthesized under mild operating conditions.
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https://hal-univ-rennes1.archives-ouvertes.fr/hal-01123644
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Submitted on : Thursday, March 5, 2015 - 11:36:32 AM
Last modification on : Friday, July 10, 2020 - 4:24:32 PM

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Matthias Schmid, Sophie M. Guillaume, Peter W. Roesky. β-Diketiminate Rare Earth Borohydride Complexes: Synthesis, Structure, and Catalytic Activity in the Ring-Opening Polymerization of ε-Caprolactone and Trimethylene Carbonate. Organometallics, American Chemical Society, 2014, 33 (19), pp.5392-5401. ⟨10.1021/om500708x⟩. ⟨hal-01123644⟩

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