A novel series of well-defined dicarboxylate
dinuclear nickel complexes
containing benzotriazole based 1,3-diamine-bisphenolate (1,3-DiBTP)
ligands were readily synthesized through a one-pot procedure, which
were highly active single-component catalysts for copolymerization
of CO2 and epoxides. X-ray structural determination of
dinickel complexes 1–11 indicates
that the DiBTP ligand acted as a N,O,N,N,O,N-hexadentate framework to chelate two nickel atoms, and
two carboxylates are nonequivalently coordinated. The best benzoate-bonded
dinickel catalyst 6 displayed the effective activity
for both high-pressure and 1 atm CO2-copolymerization of
cyclohexene oxide (CHO) in a controllable manner. Noteworthily, a
high turnover frequency up to 9600 h–1 could be
reached at 140 °C and a CO2 pressure of 20.7 bar utilizing
a low catalyst loading of 0.01 mol %, and the same copolymerization
conditions were capable of producing narrowly dispersed poly(cyclohexene
carbonate) (PCHC) having >99% polycarbonate selectivity. In addition
to CO2/CHO copolymerization, 4-vinyl-1,2-cyclohexene oxide
or cyclopentene oxide was also applied to efficiently copolymerize
CO2 under conditions of 80 °C and 20.7 bar initial
CO2 pressure. Kinetic studies of CO2/CHO copolymerization
catalyzed by 6 were investigated. Such polymerization
revealed first-order dependence for both catalyst 6 and
CHO concentrations, and the activation energy for PCHC generation
by 6 is 57.69 kJ mol–1. A possible
polymerization mechanism for CO2-copolymerization of CHO
was proposed based on kinetics and structural studies of the obtained
polycarbonates.
Four new 2D indium metal-organic frameworks (MOFs) (Me2NH2)[In(SBA)2] (1), (Me2NH2)[In(SBA)(BDC)] (2), (Me2NH2)[In(SBA)(BDC-NH2)] (3), and (NH4)3[In3Cl2(BPDC)5] (4), (H2SBA = 4,4'-sulfonyldibenzoic acid; H2BDC = 1,4-benzenedicarboxylic acid; H2BDC-NH2 = 2-amino-1,4-benzenedicarboxylic acid; H2BPDC = 4,4'-biphenyldicarboxylic acid) have been synthesized under solvothermal reaction conditions for compounds 1 to 3 and the DES (deep eutectic solvent) reaction has been attempted for compound 4. The structure of these MOFs has been determined by using single crystal X-ray diffraction study and all of theses four 2D monolayer framework with porous properties. The N2 gas sorption measurements indicated that Brunauer-Emmer-Teller (BET) and Langmuir surface areas of compound 1 are 207 and 301 m2 g-1, respectively, which is probably the first one having substantial gas uptake properties in the entire 2D In-MOF family to date. Furthermore, these new indium MOFs on the addition of n-Bu4NBr were active for the cycloaddition of CO2 and propylene oxide, generating propylene carbonates in high conversions under mild conditions. Particularly, the most active MOF 4 was found to efficiently couple CO2 with a series of terminal epoxides to give the corresponding cyclic organic carbonates with high selectivities.
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