功能有机材料

1、Synthesis and Characterization of Novel Chiral Conjugated Materials新型手性共轭材料的合成与特性学生 刘晓峰学号 2013110870导师 于海涛教授11. Introduction2. Synthetic Approaches to Highly Annelated Chiral - Conjugated Systems 2.1 Helicenes 2.2 Photochemical Syntheses 2.3 Non-photochemical Syntheses 2.4 Double Helicenesand Chiral

2、 Polycyclic Aromatic Hydrocarbons 2.5 Tetraphenylenes and -Conjugated Double Helices 2.6 Barriers for Racemization of Chiral -Conjugated Systems 3. Conclusion2 Chirality is increasingly important in the design of organic -conjugated materials. One of the aspects of the design involves optimization o

3、f achiral properties through the introduction of chirality. In this context, the inherent three-dimensional character of chirality and the control of intermolecular interactions associated with diastereomeric recognition provide a versatile handle for the optimization of supramolecular structures, f

4、ilm morphology and liquid crystalline order of p-conjugated polymers and oligomers in three dimensions .Introduction3the design involves optimization of chiral counterparts of properties in optics(circular polarization of light), electronics (chiral transport of charge carriers), etc.The challenge i

5、n this area is to obtain materials with inherently strong chiral properties at the macromolecular level, rather than derived from an aggregate or a supramolecular structure. Such inherently strong chiral properties, approaching or exceeding in magnitude their achiral counterparts, would facilitate e

6、xploration of chiral properties of single molecule devices and the design of novel chiral materials.4This chapter addresses synthetic aspects of molecules with highly annelated chiral p-conjugated systems, with the focus on helicene-type oligomers . In addition to synthesis, configurational stabilit

7、y (barriers for racemization) and selected chiroptical properties of such molecules will be discussed.52 .Synthetic Approaches to Highly Annelated Chiral -Conjugated Systems2.1 Helicenes nHelicenes possess angularly annelated aromatic rings, forming a helically shaped p-conjugated system, such as si

8、x ortho-annelated benzene rings in 6helicene (1) 62.2 Photochemical SynthesesVollhardts group adopted the cobalt-catalyzed photochemical cyclotrimerization of alkynes for the rapid construction of a novel class of helicenes782.3 Non-photochemical SynthesesFor nonphotochemical syntheses, there are th

9、ree major approaches: annelation of racemic intermediate leading to racemic nhelicene, followed by resolution, annelation of nonracemic intermediate giving nonracemic nhelicene (3) asymmetric synthesis, i.e. annelation of racemic intermediate in the presence of chiral reagent, catalyst or auxiliary9

10、Carreno. et al. described asymmetric syntheses of 5helicenequinone and helicenebisquinone .This approach is illustrated for 7helicenebisquinone 36 . The key step was diannelation based on the DielsAlder reaction between 3,6-divinyl-1,2,7,8-tetrahydrophenanthrene and enantiopure (S,S)-2-(p-tolylsulfi

11、nyl)-1,4-benzoquinone; subsequent elimination and aromatization steps gave 36 with high ee .102.4 Double Helicenesand Chiral Polycyclic Aromatic HydrocarbonsDouble and triple helicenes are -conjugated molecules, which consist of two or three annelated helicene-like subunits. Such st-ructures may als

12、o be considered as examples of chiral polycyclic aromatic hydrocarbons (PAHs).11(1)Recently, double helicene 48, in which two benzene rings are shared by 5- and 7helicene, was prepared via nonphotochemical Pd-catalyzed cyclotrimerization of 3,4-didehydrophenanthrene derived from 47 .三(二亚苄基丙酮)二钯Pd2(d

13、ba)3 TMS 三甲硅烷基 -OTfFig. 15.17 Palladium-catalyzed cyclotrimerizations of didehydrophenanthrene leading to double helicenes12(2)a conjoined double helicene, in which two hydrazine-based 5helicenes are highly annelated in their mid-sections, was reported。13The synthesis of conjoined double helicene 51

14、-D2 from 49 consists of two annelation steps: (1) FriedelCrafts diannelation to provide pentacyclic diamine 50 (2) one-step oxidative coupling forming one CC and two NN bonds , to give dodecacyclic structure 51-D214The FriedelCrafts diannelation in the first step was based on Hellwinkel and Schmidts

15、 methodology for 4helicenes, except for the use of alkenes instead of alcohols as the precursors to the intermediate carbocations.烯烃形成碳正离子，亲核取代15苯甲酸酐，形成C-C键，N-N键，十二环结构1650 to chiral 51-D2 occurs via achiral tetraamine 52, that is, the CC bond homocoupling occurs first. Upon partial oxidation of 50,

16、tetraamine 52 was isolated in 5970 % yield; 52 was then further oxidized to conjoined double helicene 51-D2 in Z75 % yield. Notably, conjoined double helicene 51-D2 could be reduced to tetraamine 52. Thus, chiral 51-D2 and achiral 52 are interconvertible via redox cleavage and formation of the NN bo

17、nds of the hydrazine moieties. The structures of all key compounds 50, 51-D2 and 52 were established nd formation of the NN bonds of the hydrazine moieties. by X-ray crystallography .1718 (3)0Hexabenzotriphenylene 53（六苯并菲）is the best studied example of chiral, overcrowded PAHs with significant steri

18、c congestion of the bay hydrogens.Hexabenzotriphenylene 53 may be viewed as a triple helicene, composed of three 5helicene units, sharing the tri-phenylene core.手性，三重螺烯三5螺烯单元共同占有（三亚苯基）核心19类似的三螺烯结构20Another recent example of a triple helicene, with three 5helicene-like units, is an extended derivativ

19、e of symmetrical triindole, a triaza analog of truxene.21 PAH, 9,10,11,20,21,22-hexaphenyltetrabenzo a,c,l,npentacene (55), showed an interesting screw-type helicity (Fig. 15.21) .An end-to-endtwist of 144h was estimated from the X-ray structure of 55. Pentacene 55 was prepared by the reaction of 1,

20、3-diphenylphenanthro9,10-cfuran 54 with the bisaryne equivalent generated from 1,2,4,5-tetrabromo-3,6-diphenylbenzene in the presence of n-butyllithium, followed by deoxygenation of the double adduct with low-valent titanium. 221,3-二苯异苯并呋喃的Diels-Alder（狄尔斯-阿尔德反应）反应，双烯加成。232425Tetra-o-phenylene (tetra

21、phenylene（四邻亚苯）,is an achiral tube-shaped molecule.However, tetraphenylene can be readily desymmetrized(去对称化）, by sub-stitution or annelation, to produce a chiral -conjugated system with an ex-traordinarily high barrier for racemization（外消旋） .In the X-ray structures of tetraphenylenes, the dihedral

22、angles between adjacent phenylenes are in the 6070h range.2.5 Tetraphenylenes and p-Conjugated Double Helices2627（1）Asymmetric synthesis of tetraphenylenes 5860 consists of two key steps, as illustrated by the synthesis of tetraphenylene 58: (1) regioselective arylation at the sterically hindered bi

23、aryl positions, to give 65.(2) annelation based on oxidative homocoupl-ing of 2,2l-dilithiobiaryls in the presence of ()-sparteine, to give nonracemic tetra-phenylene (R)-(+)-58 with60% ee.2829根岸偶联反应（Negishi coupling）有机锌试剂与卤代烃在镍或钯的配合物的催化下发生偶联，生成新的碳碳键.在这个反应中具有催化活性的是零价的金属（M0）。反应整体上经过了卤代烃对金属的氧化加成、金属转移与

24、还原消除这三步,催化剂中的金属M可以是镍或者钯；配体L可以是三苯基膦双(二苯基膦)丁烷30（2）Tetraphenylene may be viewed as a building block of“three-dimensional graphite”, i.e. complete annelation of tetraphenylenes would give a three-dimensional carbon network (Pn3m). Such a relatively low strain structure (e.g. compared with fullerenes) wa

25、s first considered by Riley and coworkers, in their studies of amorphous carbon. However, this structure remains experimentally elusive31The achiral network of tetraphenylenes served as an inspiration for the design of a -conjugated double helix. Double helical polymers, in which two poly-phenylene

26、helices are intertwined or tetraphenylenes are sequentially annelated, were recognized as the chiral building block of the network32（3） Racemic synthesis of double helical octaphenylene 67 was carried out via a convergent route. In the annelation step, the Cu(II)-mediated oxidative homocoupling of d

27、ilithiotetraphenylene(二锂四苯基), derived from the dibromotetraphenylene 66,gave octa-phenylene 67 .33The reaction of 68 under the conditions typical for the conversion of biphenylene to tetraphenylene failed to yield the double helicalpolymer or corresponding oligomer.34（4）Another racemic tetraarylene-

28、based double helical fragment was prepared by Marsella et al. using a divergent synthetic route.炔基负离子，强碱，很强的亲核性，进攻C原子发生亲核取代。35Analogous Pd/Cu-mediated arylalkyne annelation was employed to prepare binaphthyl-based double helical fragments in good yields . Starting from enantiopure dialdehyde 72, bot

29、h enantiomers of 73 and 74 could be obtained362.6 Barriers for Racemization of Chiral -Conjugated SystemsConfigurational stability (or persistence) is one of the important properties of achiral material. The definition of the lower limit for the free energy barrier forracemization may depend on the

30、specific application. the lower limit for the free energy barrier for racemization is of the order of35 kcal mol1. 37 For nhelicenes, the free energy barriers for racemization increase with n and with substitution at the inner helix sites . Thus, the free energy barriers (kcal mol1 at 27 hC) for par

31、ent nhelicenes increase in the following order: 24.1 (n = 5), 36.2 (n = 6), 41.7 (n = 7), 42.4 (n = 8), 43.5 (n = 938Upon introduction of a sterically large substituent at the end of the inner helix, even 4helicenes become con-figurationally stable at room temperature, e.g. 4helicene19.3940 Conjoine

32、d double helicene 51-D2 that barrier for racemization is expected to be significantly greater than the barrier of 24.1 kcal mol1 for 5helicene. The free energy barrier of 35 kcal mol1(half life of 3 h at 180 in naphthalene solution) for isomeri-zation of 51-D2to its meso diastereomer 51-C2h was dete

33、r-mined in the absence of acid.41Barriers for inversion of configuration in chiral, overcrowded PAHs are relatively low.Pentacene, racemized slowly at room temperature (25 23.8 kcal mol1) , that is, the barrier for racemization is similar to that in 5helicene (24.1 kcal mol1). 过度拥挤的多环芳烃的手性构型转化的能垒是比较低的。并五苯55,在室温（2523.8千卡摩尔-1）缓慢地消旋。外消旋能