A series of magnesium and zinc complexes, [(L1-3)2M2(μ-OBn)2] (M = Mg (1-3), Zn (4-6)), have been synthesized by the reaction of NNO-tridentate ketiminate ligands (L1-3-H) and a stoichiometric amount of MgnBu2 (or ZnEt2) and BnOH. In addition, the reaction of these ketiminate ligands (L1-4-H) with a half equivalent of MgnBu2 (or ZnEt2) in toluene provides [M(L1-4)2] (M = Mg (7-10), Zn (11-14)) in good yields. All of these complexes have been fully characterized by NMR spectroscopy and elemental analysis, and the molecular structures of [(L1)2Mg2(μ-OBn)2] (1), [(L3)2Mg2(μ-OBn)2] (3), [(L1)2Zn2(μ-OBn)2] (4), [Mg(L1)2] (7), [Zn(L1)2] (11) and [Zn(L4)2] (14) have been further confirmed by X-ray crystallographic studies. X-ray diffraction studies revealed that complexes 1, 3 and 4 were dimeric in the solid state, bridging through the benzyloxy groups, while the solid-state structures of 7, 11 and 14 revealed a mononuclear species, six-coordinated by N, N, and O atoms of two ketiminate ligands, forming a distorted octahedron around the metal centre. Complexes 1-6 acted as efficient initiators for the ring-opening polymerization of lactides, producing PLAs with controlled molecular weights and narrow molecular weight distributions. Complex 6 [(L3)2Zn2(μ-OBn)2] exhibited the highest activity towards the ROP of lactides. And complexes 1-6 initiated rac-lactide polymerization to afford heterotactic enriched polymers (Pr up to 0.82). In addition, complexes 7-14 were also shown to efficiently catalyze the ring-opening polymerization of lactides in the presence of BnOH.
The reactions of pyrrolidine derived salalen-type {ONNO} ligands (S)-L-H with 1 equiv. M(OPr)(HOPr) (M = Zr or Hf) in diethyl ether yielded complexes [LM(OPr)] (L = L, M = Zr (1); L = L, M = Zr (2), Hf (3); L = L, M = Zr (4), Hf (5)). All of these complexes were well characterized by NMR spectroscopy, elemental analyses and single-crystal X-ray analysis in the case of complexes 1 and 3-5. X-ray structural determination revealed that these complexes were analogous mononuclear species and had a similar structure in which the metal centers were six-coordinated to two oxygen atoms and two nitrogen atoms of one ligand and two oxygen atoms of two isopropoxy groups. All of these complexes efficiently initialized the ring-opening polymerization of lactides to afford polymers with controlled molecular weight and narrow polydispersity. Furthermore, the ring-opening polymerization of rac-lactide catalyzed by complexes 1-5 afforded isotactic-enriched polymers in solution (P = 0.74-0.80) and under melt conditions (P = 0.63-0.72).
Biomass conversion to heteroatom-doped carbon materials is considered to be an effective and inexpensive method for energy conversion. Orange peel is rich in the elements carbon, nitrogen and oxygen. Herein, nitrogen and oxygen co-doped carbon is prepared by high-temperature carbonization and activation of orange peels. Two activating agents, KOH and K2FeO4, are adopted in the preparation. The OC-1-K sample derived from orange peel activated by KOH has a large specific surface area of 917.66 cm 2 g -1 . When used as a supecapacitor electrode material, the OC-1-K sample displays a high specific capacitance of 282.3 F g -1 at 1 A g -1 . Even when the current density increases to 20 A g -1 , the discharge capacity is 212 F g -1 , indicating good rate performance. After 4000 chargedischarge cycles in 2 mol L -1 KOH electrolyte, the capacitance is maintained at 209.8 F g -1 at 20 A g -1 , achieving good cycling stability. All these results are superior to those of the OC-1-G sample obtained by K2FeO4 activation. These results indicate that KOH is more effective in activating orange peels. The excellent electrochemical performance of the OC-1-K sample suggests good application prospects in supercapacitors.
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