Perethynylated expanded radialenes

Radialenes (49) are a homologous series of all-eA o-methylenecycloalkanes of molecular formula C H (Fig. 13-3) [60], Upon insertion of butadiynyl moieties into the cyclic framework between each pair of vicinal ejto-methylene units, the carbon-rich expanded radialenes 50 (C3 H ) are obtained. Starting from suitable protected tetraethynylethenes, the perethynylated expanded radialenes 51-53 were prepared via 54, as shown in Scheme 13-11 [41], They possess large carbon cores with silyl-protected peripheral valences and can be viewed as C40 + 8 (/Pr)3Si (51), Cjo + 10 (iPr)3Si (52), and C , + 12 (/Pr)3Si (53). The diameters of these large carbon-rich molecules are in the nanometer range with values of = 17 A (for 51), 19 A (for 52), and 22 A (for 53). 

Keywords Acetylene chemistry. Cross-coupling reactions, Cyclo[n]carbons, Expanded radialenes. Molecular scaffolding. Nanostructures, Perethynylated chromophores, Poly(triacetylene), Tetraethynylethene. 

Molecular scaffoldings with tetraethynylethenes (TEEs, 3,4-diethynylhex-3-ene-l,5-diynes) and trans-1,2-diethynylethenes [DEEs, (E)-hex-3-en-l,5-diynes] are at a particularly advanced stage.114,37 38 441 A collection of dose to one hundred partially protected and functionalized derivatives have been prepared in the meantime, providing starting materials for the perethynylated dehydroannulenes and expanded radialenes shown in Figure 6.136 441 TEEs and DEEs, as well as dimeric derivatives substituted at the terminal alkynes with donor (D, p-(dimethyl-... 

This protocol is applied to the synthesis of the starting monomers for acetylenic nanoarchitectures. For example, geminally bis-deprotected teti aethynylethene 97 is prepared by Pd-catalyzed alkynylation followed by deprotection with K2CO3 in MeOH [Eq. (36)] [54c]. Perethynylated ethene 97 is a synthetic precursor of expanded radialenes, which are novel carbon-rich materials. 

Perethynylated Dehydroannulenes and Expanded Radialenes Large Carbon Cores on the Way to All-Carbon Sheets... 

Since tetraethynylethenes represent a repeat unit in more than one two-dimensional carbon network including 45 and 46 (Fig. 13-1) [1] the preparation of a specific network cannot be accomplished by simple oxidative polymerization of 20, but rather requires a more characteristic macrocydic precursor as starting material. Macrocyclic precursors to extended carbon sheets are perethynylated dehydroannulenes [56] and expanded radialenes, novel carbon-rich materials with interesting and unusual structures and functions. 

Interestingly, the perethynylated core of an expanded [6] radialene contains 60 carbon atoms and can therefore be viewed as an isomer of Buckminsterfullerene C60. X-ray crystal structure analysis of 30b (Figure 10) revealed that the cyclic core adopts a non-planar, chairlike conformation, with an average torsional angle of 57.2° [29d]. Each buta-l,3-diynediyl moiety only deviates slightly from linearity. Thus, the corresponding bond angles vary from 174 to 180°. The six individual TEE units are almost planar, with deviations of no more than 0.03 A from the mean plane. 

Fig. 10. X -ray crystal structure of expanded [6]radialene 30b H-atoms have been omitted for clarity. Atomic displacement parameters at 203 K are drawn at the 20 % probability level. The perethynylated C6o-core is highlighted in bold it adopts a chair-like conformation [29d].

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