We describe the facile synthesis
of several two-dimensional covalent–organic
frameworks (2D COFs) as films by vapor-assisted conversion at room
temperature. High-quality films of benzodithiophene-containing BDT-COF
and COF-5 with tunable thickness were synthesized under different
conditions on various substrates. BDT-COF films of several micrometer
thickness exhibit mesoporosity as well as textural porosity, whereas
thinner BDT-COF films materialize as a cohesive dense layer. In addition,
we studied the formation of COF-5 films with different solvent mixture
compositions serving as vapor source. Room temperature vapor-assisted
conversion is an excellent method to form COF films of fragile precursors
and on sensitive substrates.
Polyfunctional zinc and magnesium organometallic reagents occupy a central position in organic synthesis. Most organic functional groups are tolerated by zinc organometallic reagents, and Csp(2)-centered magnesium organometallic reagents are compatible with important functional groups, such as the ester, aryl ketone, nitro, cyano, and amide functions. This excellent chemoselectivity gives zinc- and magnesium-organometallic reagents a central position in modern organic synthesis. Efficient and general preparations of these organometallic reagents, as well as their most practical and useful reactions, are presented in this Perspective. As starting materials, a broad range of organic halides (iodides, bromides, and also to some extent chlorides) can be used for the direct insertion of magnesium or zinc powder; the presence of LiCl very efficiently promotes such insertions. Alternatively, aromatic or heterocyclic bromides also undergo a smooth bromine-magnesium exchange when treated with i-PrMgCl·LiCl. Alternative precursors of zinc and magnesium reagents are polyfunctionalized aryl and heteroaryl molecules, which undergo directed metalations with sterically hindered TMP bases (TMP = 2,2,6,6-tetramethylpiperide) of magnesium and zinc. This powerful C-H functionalization method gives access to polyfunctional heterocyclic zinc and magnesium reagents, which undergo efficient reactions with numerous electrophiles. The compatibility of the strong TMP-bases with BF3·OEt2 (formation of frustrated Lewis pairs) dramatically increases the scope of these metalations, giving for example, a practical access to magnesiated pyridines and pyrazines, which can be used as convenient building blocks for the preparation of biologically active molecules.
An in-depth discussion of the properties of perylene is presented. Tuning the properties of perylene by introducing nitrogens is also explored. Finally, we do not discuss the synthesis and properties of oligorylenes functionalized with dicarboxyimide bonds.
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