Publisher: American Chemical Society (ACS)

Issue: 24

License: http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html

Publication date(s): 2015/12/21 (print) 2015/12 (online)

Pages: 11842-11851

Volume: 54 Issue: 24

Journal: Inorganic Chemistry

Link: https://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.5b02038

URL: http://dx.doi.org/10.1021/acs.inorgchem.5b02038

The synthesis of three new dizinc(II) complexes bearing a macrocyclic [2 + 2] Schiff base ligand is reported. The bis(anilido)tetraimine macrocycle reacts with diethylzinc to form a bis(ethyl)dizinc(II) complex, [LEtZn2Et2] (1). The reaction of complex 1 with isopropyl alcohol is reported, forming a bis(isopropyl alkoxide)dizinc complex, [LEtZn2(iPrO)2] (2). Furthermore, complex 1, with 2 equiv of alcohol, is applied as an initiator for racemic lactide ring-opening polymerization. It shows moderately high activity, resulting in a pseudo-first-order rate coefficient of 9.8 × 10–3 min–1, with [LA] = 1 M and [initiator] = 5 mM at 25 °C and in a tetrahydrofuran solvent. Polymerization occurs with good control, as evidenced by the linear fit to a plot of molecular weight versus conversion, the narrow dispersities, and the limited transesterification. The same initiating system is inactive for the ring-opening copolymerization of carbon dioxide (CO2) and cyclohexene oxide at 80 °C and 1 bar of CO2 pressure. However, stoichiometric reactions between complex 2 and CO2, at 1 bar pressure, result in the reversible formation of new dizinc carbonate species, [LEtZn2(iPrO)(iPrOCO2)] (3a) and [LEtZn2(iPrOCO2)2] (3b), and the reaction was studied using density functional theory calculations. All of the new complexes, 1–3b, are fully characterized, including NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.