No abstract

A series of Al complexes bearing Schiff base and thio-Schiff base ligands were synthesized, and their application for the ring-opening polymerization of ε-caprolactone (CL) and l-lactide (LA) was studied. It was found that steric effects of the ligands caused higher polymerization rate and most importantly the Al complexes with N,S-Schiff base showed significantly higher polymerization rate than Al complexes with N,O-Schiff base (5-12-fold for CL polymerization and 2-7-fold for LA polymerization). The reaction mechanism of CL polymerization was investigated by density functional theory (DFT). The calculations predicted a lower activation energy for a process involved with an Al complex bearing an N,S-Schiff base ligand (17.6 kcal/mol) than for that of an Al complex bearing an N,O-Schiff base ligand (19.0 kcal/mol), and this magnitude of activation energy reduction is comparable to the magnitude of rate enhancement observed in the experiment. The reduction of activation energy was attributed to the catalyst-substrate destabilization effect. Using a sulfur-containing ligand to decrease the activation energy in the ring-opening polymerization process may be a new strategy to design a new Al complex with high catalytic activity.

Supporting Information Supporting Information Available: Compound characterization data, including NMR spectra, details of the kinetic study, and DFT atom coordinates and absolute energies for all relevant computationally studied species. This material is available free of charge via the Internet.

Research into the synthesis of nanoporous materials developed from zeolites, [1] aluminosilicates, [2] open-framework metal phosphates, [3][4] coordination polymers, [5] and metalorganic frameworks (MOFs) [6][7][8] has progressed faster than ever in the last twenty years. MOFs, the most recently established of these materials, have received most attention because of their high hydrogen storage capacity and therefore their potential for use in high-performance fuel cells. [9][10] While major attention has been focused on pore-size-related absorption properties, we have concurrently discovered extraordinary photoluminescence (PL) properties in openframework metal phosphates. [11][12][13][14][15][16] We discovered two metal phosphates, NTHU-4 [12] and NTHU-6, [13] which have novel nanoporous structures. These metal phosphates, unlike commercialized or developed color-conversion phosphors with emissions that originate from emitting activators doped into condensed host lattices, [17] contained no metal activators or any form of chromophores, but could emit intense yellow light under the excitation of near-ultraviolet (NUV) and blue light. A yellow-light phosphor integrated with a blue light-emitting diode (LED) to produce white light is the current mainstream of display technology, [18] although existing yellow phosphors that can be efficiently excited by NUV or blue light are very limited in number and range. A larger variety of advanced materials to add to the yellow phosphor YAG:Ce (YAG = yttrium aluminum garnet) is therefore in great demand. The intriguing optical properties of NTHU-4 and NTHU-6 has led us to explore a new class of color-conversion phosphors based on nanoporous host structures that have an intrinsic emission mechanism beyond our current understanding. [19] Existing inorganic yellow-light phosphors are all extrinsic illuminants. Before the two nanoporous structures were reported by us, no inorganic phosphate host that could emit yellow light but was not doped with lanthanide ions had been reported. The extraordinary intrinsic yellow emission was proposed to closely correlate with defects that result from the disorder in the large pores of the structure, firstly observed in NTHU-4 and later in NTHU-6. In the latter study, we had also speculated that the molecule 4,4'-trimethylenedipyridine (tmdp), the common template of both structures, acted as a sensitizer. To affirm and enhance the new phosphor system and rationalize an emission mechanism for the activator-free PL, it was imperative to produce further examples of these structures. In the pursuit of advanced and economical synthetic procedures for making new functional materials, we focused on the environmentally friendly deep eutectic solvent (DES). [20][21][22][23] Herein, we report the first nanosized channel structure successfully synthesized in a DES and also the first organically templated gallium oxalatophosphite compound, NTHU-7. It adopts an unprecedented organicinorganic hybrid nanotubular structure (Figure 1), which exhibits an even mor...

A series of lithium and sodium iminophenoxide complexes have been successfully synthesized and characterized by X-ray crystallography and investigated as catalysts for the ring opening polymerization of L-lactide. The nature and steric bulk of the ligands coordinated to the central metal ions greatly influence the catalytic properties. Complexes with bidenate ligands exhibit higher catalytic activity than tridentate counterparts because the third coordination atom contends with L-lactide, which decreases activity. Oxygen is the third atom in the tridentate ligand, providing stronger chelation ability with Li and Na than nitrogen or sulfur and occupies the space with which L-lactide is coordinated.