Versatile Design Principles for Facile Access to Unstrained Conjugated Organoborane Macrocycles

Abstract

Af acile and versatile approach was developed to access ambipolar boron-containing macrocycles.T wo examples of new conjugated cyclic motifs are presented with carbazole moieties as donors and borane moieties as acceptors embedded into the ring system. They were first predicted using computational methods.P ossible targets with appropriately shaped p-conjugated bridges that minimizet he overall ring strain were identified and their geometry was optimized by DFT methods.T he synthetic demonstration was then accomplished using organometallic condensation reactions under high dilution conditions.T he resulting monodisperse macrocycles providei mportant insights into the design principles necessary for the preparation of new unstrained macrocycles with interesting optical and electronic characteristics.T he current researcha lso offers am ore general approacht o conjugated ambipolar B/N macrocycles as ap romising new family of (opto)electronic materials.Conjugated materials continue to attract immense research interest, motivated by potential applications in molecular electronics,energy,chemical sensors,and biomedical fields.[1]Arecent focus on conjugated macrocycles has been triggered by the expectation that favorable (and different) properties and functions can be achieved owing to their unique structural features.[2] Thus,t he synthesis,e lectronic features,s upramolecular assembly,a nd host-guest interactions of shapepersistent conjugated macrocycles have been investigated extensively.[3] An attractive current direction is the incorporation of heteroatoms into p-conjugated carbon-based cycles that provide added functionality and may enable new applications.[4] In 2010, Ito,T anaka, and co-workers reported an interesting example of ah exaaza[1 6 ]paracyclophane,a n electron-rich macrocycle with an unusual electronic structure and intriguing redox properties. [5,6] Our group recently developed a" charge-reverse" [7] electron-deficient hexaboracyclophane, MC-B6, [8] and an ambipolar macrocycle, MC-B3N3, [9] in which electron-rich arylamines alternate with electron-deficient arylboranes (Scheme 1a). These macrocycles are unique representatives of the larger class of conjugated organoboranes,which have attracted tremendous interest in recent years for applications in non-linear optics, organic light emitting devices,asphotochromic smart materials,int he detection of anions,and many other fields. [10] Thes ynthetic access to fully conjugated macrocycles can pose significant challenges,w hich is especially true when the intrinsic ring strain energy of the products disfavors the cyclization process. [11] Realizing that the trigonal coordination geometry in organoboranes should favor sixfold symmetry, we previously targeted hexameric macrocycles with BorNat the six corners and linear aromatic moieties as p-conjugated linkers. [8,9,12] Them acrocycle MC-B6 was obtained in high yield, but the cyclic tetramer MC-B4 as as maller analogue could not be generated selectively and, although detected by MALDI-MS,i ts isol...

Synthesis and Structure‐Property Relationships in Regioisomeric Alternating Borane‐Terthiophene Polymers

“…In our case, cyclic tetramers and pentamers are obtained preferentially, possibly also aided by the bent shape of the dithienylborane building blocks (Figure 4b). These macrocycles resemble previously reported hexameric boracyclophanes with phenylene or fluorenylene bridges [14a,d] and related hybrid macrocycles containing boron in combination with other heteroatoms [14c,e,g,20] that were assembled in stepwise processes. They are also related to tetrameric thienylboranes, introduced by Siebert et al.…”