Discrete cationic zinc and magnesium complexes for dual organic/organometallic-catalyzed ring-opening polymerization of trimethylene carbonate.

摘要: We describe herein an original approach for the efficient immortal ring-opening polymerization (iROP) of trimethylene carbonate (TMC) under mild conditions using dual-catalyst systems combining a discrete cationic metal complex with tertiary amine. A series new zinc and magnesium complexes type [{NNO}M](+) [anion](-) ({NNO}(-) = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate; M Zn, [B(C(6)F(5))(4)](-) (2), [H(2)N-{B(C(6)F(5))(3)}(2)](-) (3), [EtB(C(6)F(5))(3)](-) (4); Mg, [H(2)N{B(C(6)F(5))(3)}(2)](-) (7)) have been prepared from corresponding neutral compounds [{NNO}ZnEt] (1) [{NNO}-Mg(nBu)] (6). Compounds 2-4 7 exist as free ion pairs, revealed by (1)H, (13)C, (19)F, (11) B NMR spectroscopy in THF solution, X-ray crystallographic analysis bis(THF) adduct compound 7, 7⋅(THF)(2). The 1 6, combination one equivalent or excess benzyl alcohol (BnOH), initiate rapid iROP TMC, bulk toluene at 45-60 °C (turnover frequency, TOF, up to 25-30,000 mol(TMC)⋅mol(Zn)⋅h(-1) 220-240,000 mol(TMC)⋅mol(Mg)⋅h(-1) 6), afford H-PTMC-OBn controlled macromolecular features. ROP reactions mediated 2/BnOH 7/BnOH proceeded much more slowly (TOF 500 3000 mol(TMC)⋅mol(Zn Mg)⋅h(-1) 110 °C) than those based on parent 1/BnOH 6/BnOH, respectively. Use dual organic/organometallic catalyst systems, obtained adding 0.2-5 equiv amine such NEt(3) [{NNO}Zn](+) (2-4), promoted high activities 18,300 45 giving good control over M(n) M(w)/M(n) values. Variation nature anion did not significantly affect performance these systems. On other hand, magnesium-based system 7/NEt(3) proved be poorly effective.