title: Lanthanide borohydride complexes supported by diaminobis(phenoxide) ligands for the polymerization of epsilon-caprolactone and L- and rac-lactide.
abstract: Reaction of Na2O2NN' [H2O2NN' = (2-C5H4N)CH2N[2-HO-3,5-C6H2(t)Bu2]2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN')(mu-BH4)(THF)n]2 [M = Y(III), n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN')(mu-Cl)(THF)n]2 (2-M; M = La(III) or Sm(III), n = 0; M = Nd(III), n = 1) and the corresponding pyridine adducts [M(O2NN')(mu-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = La(III), Nd(III), or Sm(III)] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of epsilon-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (P(r) = 87%). Compound 1-Nd catalyzed the block copolymerization of epsilon-caprolactone and L- and rac-lactide provided that epsilon-caprolactone was added first. Attempted block polymerization by the addition of L-lactide first, or random copolymerization of a ca. 1:1 mixture of epsilon-caprolactone and L-lactide, gave only a poly(L-lactide) homopolymer.
authors.affiliation: Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK.
authors.forename: Fanny
authors.initials: F
authors.lastname: Bonnet
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Cowley
authors.forename: Philip
authors.initials: P
authors.lastname: Mountford
mesh_terms: D001894:Borohydrides / Q000138:chemical synthesis / Q000737:chemistry*; D002208:Caproates / Q000737:chemistry*; D015392:Chemistry, Inorganic / Q000379:methods; D002712:Chlorides / Q000138:chemical synthesis / Q000737:chemistry; D003959:Diamines / Q000737:chemistry; D019344:Lactic Acid / Q000737:chemistry; D007783:Lactones / Q000737:chemistry*; D008024:Ligands; D015394:Molecular Structure; D011108:Polymers / Q000138:chemical synthesis
chemical_list: D001894:Borohydrides; D002208:Caproates; D002712:Chlorides; D003959:Diamines; D007783:Lactones; D008024:Ligands; D011108:Polymers; D019344:Lactic Acid; C121056:caprolactone