ic8b02923_si_001.pdf (5.02 MB)
Groups 1, 2 and Zn(II) Heterodinuclear Catalysts for Epoxide/CO2 Ring-Opening Copolymerization
journal contribution
posted on 2018-11-30, 14:48 authored by Arron C. Deacy, Christopher B. Durr, Jennifer A. Garden, Andrew J. P. White, Charlotte K. WilliamsA series of heterodinuclear
complexes are reported where both Zn(II) and a metal from Group 1
or 2 are chelated by a macrocyclic diphenolate-tetra-amine ligand.
The complexes are characterized in the solid state, where relevant
by single crystal X-ray crystallography and elemental analysis, and
in solution, using NMR spectroscopy and mass spectrometry. The complex
synthesis is achieved by reaction of the ligand with diethyl zinc
to form the monozinc complex, in situ, followed by
subsequent coordination of the second metal; this method enables heterodinuclear
conversions >90% as determined by NMR spectroscopy. Alternatively,
the same heterodinuclear complexes are accessed by reaction between
the two homodinuclear complexes at elevated temperatures for extended
periods. These findings suggest that most of the heterodinuclear complexes
are the thermodynamic reaction products; the only exception is the
Na(I)/Zn(II) complex which is unstable with respect to the homodinuclear
counterparts. The catalytic activities and selectivity of the stable
heterodinuclear complexes are compared, against each other and the
relevant homodinuclear analogues, for the ring-opening copolymerization
of CO2 and CHO. Nearly all the heterodinuclear complexes
are less active than the dizinc analogues, but the Mg(II)/Zn(II) catalyst
is more active. The co-ligand influences the product selectivity,
with iodide ligands resulting in cyclic carbonate formation and carboxylate
ligands giving a high selectivity for polycarbonate.