No abstract

New trimetallic cobalt, nickel and zinc complexes 1-3 coordinated by amine-bis(benzotriazole phenolate) ligands and ancillary acetate groups have been developed for the use of CO/epoxide coupling. All complexes were structurally characterized by single crystal X-ray crystallography; tri-Co complex 1 is the first solid-state example in which three different geometrical configurations exist in the same benzotriazole phenoxide metal complex. Tri-nuclear complexes 1 and 2 with cobalt and zinc metal centers were demonstrated to be very active catalysts for cycloaddition of cyclohexene oxide with CO in the presence of ammonium salt co-catalysts to give cis-cyclohexene carbonate under the conditions of 80 °C and 300 psi initial CO pressure. Particularly, tri-cobalt complex 1 was found to efficiently couple CO with epoxides showing broad substrate scope, producing the corresponding cyclic organic carbonates with good activities and high selectivities. This is a successful example of catalysis for cyclic carbonate synthesis using one cobalt(ii) complex as a homogeneous catalyst.

The facile synthesis, structural characterization, and catalytic studies for CO2/epoxide coupling of nickel acetates based on carbazolide-bis­(NHC) (NHC = N-heterocyclic carbene) were reported. Treatment of 3,6-di-tert-butyl-1,8-bis­(3-alkylimidazolium-1-yl)­carbazole salt proligands (bis­(R-Im-X)­Cz, R = benzyl (Bn), n-butyl ( n Bu), methyl (Me), X = Br or I) with nickel acetate tetrahydrate in the presence of excess triethylamine generated monomeric four-coordinate nickel complexes [(bis­(R-Im)­Cz)­Ni­(OAc)] (R = Bn (3), R = n Bu (4), and R = Me (5)). Single-crystal X-ray diffraction of Ni complexes 4 and 5 indicates that the bis­(NHC)-carbazolide fragment behaves as a CNC-tridentate pincer ligand to coordinate the metal center, and the ancillary acetate group assumes a terminal acetate bonding mode. Catalysis for coupling of carbon dioxide with cyclohexene oxide (CHO) by these carbazolide-bis­(NHC)-ligated Ni complexes was systematically examined. Experimental results displayed that cycloaddition of CHO and CO2 catalyzed with complex 4 could give cyclohexene carbonate (CHC) with >99% cis-isomer selectivity on using low catalyst concentrations and high reaction temperature, whereas catalyst 3 was able to copolymerize CHO and CO2 to afford a narrowly dispersed and perfectly alternating poly­(cyclohexene carbonate) (PCHC) as the major product at the higher catalyst loadings and lower copolymerization temperature. This is the first time that the air-stable bis­(NHC)-carbazolide nickel­(II) acetate is an effective and versatile catalyst for the formation of either biodegradable PCHCs or cis-CHCs.

In this study, inorganic perovskite (CsPbBr3) quantum dots are wrapped in SiO2 to provide better performance against external erosion. Long-term storage (250 days) is demonstrated with very little changes in the illumination capability of these quantum dots. While in the continuous aging procedure, different package architectures can achieve very different lifetimes. As long as 6000 h of lifetime can be expected from these quantum dots, but the blue shift of emission wavelength still needs more investigation.

Reduction of the organoditantalum allene complex (eta-C5Me4R)2Ta2(mu-X)X3(mu-eta1,eta3-C3H4) (R = Me (Cp*), Et; X = Cl, Br) with sodium amalgam leads to the propynylidene complex (eta-C5Me4R)2Ta2(mu-H)2X2(mu-HCCCH) by a formal double 1,3-C-H activation of the allene ligand. The solid-state molecular structure contains a planar HCCCH ligand bridging, in parallel coordination mode, the two tantalum atoms, with the HCCCH and Ta atoms coplanar. Key structural features are a Ta-Ta distance of 2.8817(7) A, propynylidene C-C-C angle of 153.7(13) degrees , C-C distance of 1.370(8) A, Ta-C(central) distance of 2.194(9) A, and Ta-C(terminal) distance of 1.970(9) A. Molecular orbital calculations on the complex at the RHF/SBK(d) and B3LYP/LanL2dz levels of theory demonstrate that the propynylidene ligand is best viewed formally as an allenediylidene(4-) ligand bonded to two d0 tantalum atoms via two Ta=C(terminal) double bonds and an unusual three-center, two-electron bridge bond involving both tantalum atoms and a lone pair on the planar, tetracoordinate central carbon. There is no net Ta-Ta bonding based on the orbital analysis.