title: Organometallic calcium and strontium borohydrides as initiators for the polymerization of ε-caprolactone and L-lactide: combined experimental and computational investigations.
abstract: [Ca(BH4)2(THF)2] (1a), a known compound, was easily prepared following a convenient new procedure from [Ca(OMe)2] and BH3·THF in THF. Reaction of 1a with KCp* (Cp* = (η(5)-C5Me5)) and K{(Me3SiNPPh2)2CH} in a 1 : 1 ratio in THF resulted in the corresponding dimeric heteroleptic mono-borohydride derivatives [Cp*Ca(BH4)(THF)n]2 (2a) and [{(Me3SiNPPh2)2CH}Ca(BH4)(THF)2] (3a), respectively. Both compounds were fully characterized and the solid-state structure of 3a was established by single crystal X-ray diffraction. Compounds 1a, 2a, and 3a, together with the earlier reported compounds [Sr(BH4)2(THF)2] (1b), [Cp*Sr(BH4)(THF)2]2 (2b), and [{(Me3SiNPPh2)2CH}Sr(BH4)(THF)2] (3b), were used as initiators for the ROP of polar monomers. The general performances of the complexes in the ROP of ε-caprolactone and l-lactide demonstrate a relatively good control of the polymerization under the operating conditions established. α,ω-Dihydroxytelechelic poly(ε-caprolactone)s (PCLs) and poly(lactide)s (PLAs) were thus synthesized. DFT calculations on the initiation step of the ROP of ε-CL were carried out. Gibbs free energy profiles were determined for the three calcium complexes highlighting slightly more active calcium complexes as compared to strontium analogues, in agreement with experimental findings.
authors.affiliation: Institut für Anorganische Chemie and Helmholtz Research School: Energy-Related Catalysis, Karlsruher Institut für Technologie (KIT), Engesserstr. 15, Geb. 30.45, 76131 Karlsruhe, Germany.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Kuzdrowska
authors.forename: Liana
authors.initials: L
authors.lastname: Annunziata
authors.forename: Sebastian
authors.initials: S
authors.lastname: Marks
authors.forename: Matthias
authors.initials: M
authors.lastname: Schmid
authors.forename: Cedric G
authors.initials: CG
authors.lastname: Jaffredo
authors.forename: Peter W
authors.initials: PW
authors.lastname: Roesky
authors.forename: Sophie M
authors.initials: SM
authors.lastname: Guillaume
authors.forename: Laurent
authors.initials: L
authors.lastname: Maron
mesh_terms: D001894:Borohydrides / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D002208:Caproates / Q000737:chemistry*; D004146:Dioxanes / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D058105:Polymerization; D011789:Quantum Theory; D013324:Strontium / Q000737:chemistry
chemical_list: D001894:Borohydrides; D002208:Caproates; D004146:Dioxanes; D007783:Lactones; D009942:Organometallic Compounds; C121056:caprolactone; C091880:dilactide; D002118:Calcium; D013324:Strontium