Issue 36, 2013

Ring-opening polymerization of cyclic esters by phenoxy-thioether complexes derived from biocompatible metals

Abstract

A series of novel Mg(II) and Zn(II) complexes of the form LMX or L2M, supported by phenoxy-thioether ligands bearing different substituents at the ortho position of the thiophenol rings [L = 4,6-tBu2-OC6H2-2-CH2S(2-R-C6H4)] [M = Zn, R = H, X = N(SiMe3)2 (1) and X = Et (2); M = Mg, X = n-Bu, R = H (3), R = CH3 (4), R = Br (5); M = Mg, R = H (6)], were synthesized and characterized. Reaction of the proper zinc precursor (Zn[N(SiHMe2)2]2 or ZnEt2) with one equivalent of the phenoxy-thioether proligand produced the corresponding amido (1) and ethyl (2) zinc complexes in high yields. The monoalkylmagnesium complexes (3–5) were all obtained by butane elimination reaction of the dialkylmagnesium reagent, Mg(n-Bu)2, with one equivalent of the proligand in good yields. The homoleptic complex 6 was obtained by reaction of 0.5 equivalent of Mg(n-Bu)2 and the proper proligand. Variable temperature 1H NMR studies performed on 2 and 3 demonstrated that the named complexes are involved in fluxional processes concerning a fast conformational change of the six-membered metallacycle. DOSY (Diffusion Ordered SpectroscopY) 1H experiments and ligand scrambling strongly suggested that complexes 1–6 exist as dimeric species in solution. All complexes were active as catalysts in the ring-opening polymerization of cyclic esters. In particular, magnesium complexes showed superior ε-caprolactone and lactide ROP behavior in terms of activity, control of molecular weights and molecular weight distributions.

Graphical abstract: Ring-opening polymerization of cyclic esters by phenoxy-thioether complexes derived from biocompatible metals

Supplementary files

Article information

Article type
Paper
Submitted
09 May 2013
Accepted
29 Jun 2013
First published
01 Jul 2013

Dalton Trans., 2013,42, 13036-13047

Ring-opening polymerization of cyclic esters by phenoxy-thioether complexes derived from biocompatible metals

A. Pilone, M. Lamberti, M. Mazzeo, S. Milione and C. Pellecchia, Dalton Trans., 2013, 42, 13036 DOI: 10.1039/C3DT51219C

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