The cycloaddition of carbon dioxide to epoxides to produce cyclic carbonates is quite promising and does not result in any side products. A discrete single-walled metal-organic nanotube was synthesized by incorporating a tetraphenyl-ethylene moiety as the four-point connected node. The assembled complex has a large cross-section, with an exterior wall diameter of 3.6 nm and an interior channel diameter of 2.1 nm. It features excellent activity toward the cycloaddition of carbon dioxide, with a turnover number of 17,500 per mole of catalyst and an initial turnover frequency as high as 1000 per mole of catalyst per hour. Only minimal decreases in the catalytic activity were observed after 70 h under identical reaction conditions, and a total turnover number as high as 35,000 was achieved. A simple comparison of relative porous MOFs suggested that the cross-section of the channels is an important factor influencing the transport of the substrates and products through the channel.
The widely studied porous coordination
polymers, possessing large pores to adsorb waste carbon dioxide gas
and further transform it into valuable chemical products, have been
attracting research interest, both industrially and academically.
The active silver(I) ions endow the specific alkynophilicity to activate
CC bonds of alkyne-containing molecules via π activation.
Incorporating catalytic Ag metal sites into the porous frameworks
represents a promising approach to construct heterogeneous catalysts
that cyclize propargylic alcohols with CO2, which is highly
desirable for the environmentally benign conversion of carbon dioxide
to fine chemicals. We report the preparation of porous coordination
polymers (PCPs) with active silver sites and efficient silver–silver
bond formation by carefully modifying the coordination geometries
of the silver sites. The decentralized silver(I) chains in the porous
frameworks enable the efficient conversion of CO2 and derivatives
of acetylene to α-alkylidene cyclic carbonates in a heterogeneous
manner. X-ray structure analysis reveals two kinds of substrate molecules
positioned within the pores of the framework, which correspond to
trapping and activated modes through the multiple interactions with
the functional Ag chains. The example of tandem conversion of simple
alkynes and carbon dioxide to α-alkylidene cyclic carbonates
is also presented. The well-positioned catalytic silver(I) sites and
the crystalline properties of the frameworks facilitated the structural
analyses of the intermediates of each catalytic step, providing knowledge
of the synergistic nature of the σ and π activation of
CC bonds. The successful catalysis of azide–alkyne
cycloaddition and synthesis of propargylic alcohols via terminal alkynes
could also give another indicator for the activation properties of
Ag sites.
By using the reduced Schiff base tricarboxylate ligand H 3 cip, one novel 3D Cd-based coordination polymer (Cd-CP) with the formula [Cd(Hcip)(bpea) 0.5 (H 2 O)] n (H 3 cip = 5-(3-carboxybenzylamino)isophthalic acid, bpea = 1,2-bis(4-pyridyl)ethane) has been solvothermally synthesized. The prepared Cd-CP possesses a 4-connected CdSO 4 net based on dinuclear {Cd 2 } units. Luminescence measurements revealed that the complex exhibited ratiometric turn-on luminescence responses toward Al 3+ and Cr 3+ with a significant color change, which could be easily distinguished by the naked eye under ultraviolet light. Cd-CP can also respond to Fe 3+ through a turn-off mechanism. Interestingly, the luminescence quenched by Fe 3+ @Cd-CP can be recovered and increased significantly by adding some competitive Al 3+ , while Cr 3+ can only marginally increase the luminescence intensity of Fe 3+ @Cd-CP. Moreover, the detection of the three aforementioned metal ions can be realized by using Cd-CP-coated test papers, extending the potential application regions of the reported material to point-of-care tests and environmental field studies.
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