Phenylene-ethynylene macrocycles

This review will focus on systems that are able to adopt supramolecular order in both intra- and intermolecular fashion. Because of this,para-phenylene ethynylenes (pPE)s will not be covered in this review. However, there are several excellent reviews of pPE synthesis, structure, and function in the recent literature that discuss the intermolecular order of those systems [7-15]. Similarly, phenylene ethynylene macrocycles, which form a wide range of supramolecular aggregates with interesting stacking behavior, will not be covered but have been extensively reviewed [16-22]. 

High-yield Synthesis of Shape-persistent Phenylene-Ethynylene Macrocycles ... 

Scheme 6.22 High-yield synthesis of Schiff base-containing phenylene-ethynylene macrocycles.

ADIMAC has been utilized in the formation of many other types of novel macrocycHc scaffolds. VoUhardt reported the preparation of o-phenylene ethynylene macrocycles 21 with the Schrock catalyst (Me3CO)3W=CCMe3 in moderate yield (Scheme 6.11) [67]. Notable here was the unreactivity of monomers containing substituents ortho to the alkynes. The Mortreux catalyst system was utilized in the preparation of macrocycles from monomer 22 containing a disiloxane hinge (see Scheme 6.12). A mixture of macrocycles 23 and 24 was isolated in moderate yield [68]. One particularly impressive example of the use of ADIMAC to prepare large, extended r-systems (Scheme 6.13) was reported by Haley this was based... 

In 1999, Youngs reported the formation of a dibenzopentalene derivative 267 from an o-iodoethynylbenzene 268 under Sonogashira coupling conditions (Scheme 6.68) [157]. Unfortunately, this reaction seems to be an exceptional case because the Sonogashira reaction of o-iodoethynylbenzenes generally affords phenylene-ethynylene macrocycles [158]. 

Further insights into the interactions between conjugated segments may also be gained from the spectroscopic analysis of chromophores that are held in well-defined architectures by new stacked scaffolds (e.g., Smith s m-terphenyl oxacyclo-phanes [167,168] and Swager s benzene-sandwiched phenylene ethynylenes [ 169]) or by their incorporation into larger macrocycles (e.g., shape-persistent conjugated macrocycles [170,171]). 

In an effort to overcome steric interactions due to -substituents in cyclotetra(2,3-thienylene)s 4.6 (see above), Marsella et al. synthesized expanded thiophene-fused didehydro [12]annulene 4.32, which incorporated two additional ethynylene groups between the -positions of the cycUc stmcture (Scheme 1.44) [408]. Regiospeciflc halogenation of a 2,2 -bithiophene and Sonogashira-type cross-coupling with the ethynylated counter part were key elements of the synthetic strategy, which was also used to prepare a further extended macrocycle 4.33 (Chart 1.54), profiting from quadrupolar interactions of the central phenylene units [409]. 

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