TETRAETHYNYLETHENES - FULLY CROSS-CONJUGATED PI-ELECTRON CHROMOPHORESAND MOLECULAR SCAFFOLDS FOR ALL-CARBON NETWORKS AND CARBON-RICH NANOMATERIALS

The preparation of tetraethynylethene (3,4-diethynylhex-3-ene-1,5-diyn e) 1 as well as of a great diversity of differentially mono-, di-, and triprotected derivatives by newly developed synthetic routes is descr ibed. These fully cross-conjugated molecules are versatile building bl ocks and precursors to two-dimensional all-C networks and novel C-rich nanoarchitecture with unusual structural and electronic properties, s uch as perethynylated expanded radialenes, or molecular wires and poly mers with the novel polytriacetylene backbone. A key step in all of th ese routes was the Corey-Fuchs dibromoolefination of aldehydes and ket ones. Dibromoolefination of silyl-protected penta-1,4-diyn-3-ones yiel ded the corresponding dibromomethylidene derivatives which, by twofold Pd-catalyzed alkyne coupling, were transformed into tetraethynylethen e derivatives. In routes to tetraethynylethenes with free cis- or tran s- enediyne moieties, dibromoolefination of aldehyde groups produced g eminal dibromoethenes which, upon elimination/metallation with LDA fol lowed by quenching with H+ or other electrophiles, yielded free or sub stituted ethynyl groups in high yields. Tetra- and triprotected tetrae thynylethenes are rather stable compounds that could be isolated in pu re form, whereas derivatives with two or more free =C-H termini were o nly stable in dilute solution and polymerized rapidly in pure form. A trans- bis-deprotected, trans -bis(triisopropylsilyl)-protected deriva tive represented an exception and could be isolated as stable crystals . X-Ray analysis revealed that the two bulky (i-Pr)(3)Si groups isolat e the reactive chromophores from one another in the crystal and preven t intermolecular reactions. The structures of several tetraethynylethe nes were revealed in high-quality X-ray crystal structures.