2010_12_03_lecture_ch24 - " LQc’furc ’Dec.3...

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Unformatted text preview: " LQc’furc ’Dec .3 LO-s" QM:‘L +QC‘C7 ‘. C‘qs‘} '2", “W 9": LVPV'H- +q (3mg CO“A\PC k“, Yo‘7rb—rr; W‘Qng‘g, ?c\ Cake/‘73? \<‘/ L:- P I.) ’95 L... + 2—134 ,4 Q L K S? V‘ ‘ _ yr 6! Owtv \78/ _ L / \‘5’ SO‘VQ-vl' *- ‘DO‘C: cdvra*\‘¢ Sowvewl’, DY“: 0 o "g h / “- / “‘"p’ ‘\ DMSO w * 12.— s-r I 1/ ‘1 TE L: YA S4 L13’F\ :2. c /“$ 4 v'eAv-okfl \ [P 'Ckflthv-A'o-n [:2‘. /“' LL Ya /" 3\ h LLYC) R \ __./ L / fw‘ at J?" h’u H a 07* 1.. \ 3 * 1: S‘fi'N h‘nn' M Macromolecules, Val. 42, No. 5, 2009 Low—Bandgap Conjugated Polymers 1483 .4: Scheme 1. Synthesis of PTVBT S S Pd(OAc)2,P(o-tol)3 HO N N . N N Br —COOH O \ | r NBS, lOAC Br \ i r B<j> Eth,CH;,CN—THF, reflux 0 CH3CN—H20,rt B, 65 % 2 0H 50% 3 iQ 8V H5 B 0‘; Oath: CaHn \ s '3 5 \ I n Pd2(dba}3,P(o—tyl)3,El4NOH 38Hfir CeHn N toiuene-water, 60 °C PTVBT 81% B B CH 103 Bo: 0' S 9‘; r r1)CaH1gBr,Mg.E120 Ca 1/7 deal-l” DB \ I 3‘0 I \ fr [IatOMelCODb-dflmy s 2) N-(dppnca. Etzo. reflux Heplane. 50°C CeHw 63H" 88 % 4 81 % 5 soluble in most common solvents, except THF, DMF, and DMSO, which makes it difficult to purify through chromatog- raphy. Fortunately, its triethylamine salt was soluble in water. Hence, the purification of compound 2 was readily achieved by forming the tn'ethylamine salt, following by acidification with aqueous HCl. The catalytic Hunsdiecker reaction of compound 2 with N—bromosuccimide in the presence of lithium acetate as catalyst afforded compound 3 in 60—64% yield as light yellow crystals, which appear to be green fluorescent. Low yield or no reaction was noticed when triethylamine or potassium acetate was used instead of lithium acetate. in addition, the choice of solvents played a critical role in this reaction. It turned out that a mixture of acetonitrile and water gave the best results when their volume ratio was around 20—25%, while it was usually around 3% for other catalytic Hunsdieclrer reactions in the literature.25 Compound 5 was obtained in 71% overall yield through two steps. Kumada reaction of 3,4-dibromothiophene with l-bromooctane gave compound 4 in 88% yield, which after ir—catalyzed borylation afforded compound 5 in 81% yield?“5 PTVBT was prepared by a Suzuki polycondensation between compound 3 and 5 in 87% yield after Soxhlet extraction and precipitation.27 The polymer from the chloroform fraction was soluble in THF, toluene, and chlorinated solvents (> 10 mg/ mL in chloroform). GPC analysis revealed that PTVBT had number-average molecular weights ranging 20 000 to 31 000 Da and polydispersity indices from 1.7 to 2.4 on the base of batch to batch. As a model compound, bisTVBT was prepared by a similar synthetic route, which can be found in the Supporting Information. Polymer Characterization. The structure of PT VBT was confirmed by ‘H NW, 13C NMR, IR, and elemental analysis. The 1H NMR of PTVBT is here compared with that of bisTVBT to illustrate the polymer structure (see Supporting Information, Figure St). The model complex bisTVBT shows a very clear splitting pattern. Two doublets are assigned to two tram—vinyl protons, which have a coupling constant of 16.2 Hz. Two singlets (7.50 and 6.84 ppm) are evident from the protons on the benzothiadiazoie and thiophene rings, respectively. The 1H NMR of PTVBT appears broad at room temperature and even N.S.N \ f \ \ s \ I n Caan CsH17 PTVBT Figure 1. Chemical structures of PTVBT and bisTVBT. at 60 °C, a feature common to high molecular weight polymers. In addition, the existence of strong polymer aggregation in solution is also responsible for N MR broadening. When heated to 100 °C in deuterated tetrachloroethane, the 1H NMR of PT VBT clearly exhibits three broad, but distinguishable, signals among 7.2—8.5 ppm, corresponding to 11,, 11,, and H, in the model complex. It is worth mentioning that no 11-1 NMR signals are found in the region of 5.0—6.0 ppm, where the 1H NMR signals of 1,1—diarylenevinylene defects (CL-vinyl coupling defects) usually appear in Heck polymerization.22 The presence of the trans-vinylene functionality is also confirmed by the appearance of FT-IR bands at 955 and 947 cm‘1 for bisTVBT and PTVBT (see Supporting Information, Figure 82), respec. tively. These bands are due to the out—of—plane C—H bending of trans-vinylene linkages.“28 'Ihermogravitnetric analysis (TGA) was carried out to evalu- ate the thermal stability of PT VET. A mass loss of 5% is defined as the threshold for thermal decomposition. PTVBT demon— strated good thermal stability with an onset of decomposition at 380 oC. Differential scanning calorimetry (DSC) was performed to characterize the thermal transitions of PTVBT. PTVBT exhibited a glass transition-like feature at 100 °C and a broad endothermic transition at 235 ”C on the forward sweep of the first DSC heating cycle. No thermal transitions were observed after the first cycle in the range of —100 to 300 °C. Optical Properties. The absorption spectrum of PTVBT exhibits a significant change in comparison with that of bisTVBT. BisTVBT has a two-band spectrum with absorption maxima at 359 and 499 nm in THF, while PTVBT shows absorption maxima at 416 and 618 nm, as shown in Figure 2. There is a ~119 nm red shift in the Arm of the low-energy peaks between PT VBT and bisTVBT. In contrast, because of the steric hindrance imparted by the octyl solubilizing groups, only a 60 nm red shift is observed for a directly linked benzotl'iiadiazole—thiophene altematin g polymer and its model cornpoud.29 More strikingly, PTVBT has a more red-shifted absorption maximum than its analogous polymer with a thie- nylene linkage, which has a 11mm at 602 um in chloroform.30 Clearly, the red shift in PTVBT indicates the polymer is highly conjugated through the planarization of the benzothiadiazole and thiophenc units along the polymer backbone. The absorption maximum of PT VBT on ITO (see Supporting Information, Figure S3) exhibits another 15 nm red shift compared to its absorption maximum in THF, due to enhanced ar—ar interactions in the solid state. In the fluorescence measurement, bisTVBT shows a well-resolved emission spectrum with a maximum at m 610 nm (see Supporting Information, Figure S4). The photo- ”Eaunch g wransmmmrm "3 mamram WWW 5W Press Release 5 October 2005 The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Chemistry for 2005 jointly to Yves Chauvin U‘F m a. 3% :1 5 Institut Francais du Pétrole, Rueil—Malmaison, France, / "bum CW‘W") Robert H. Grubbs C California Institute of Technology (Caltech), Pasadena, CA, USA and g e 5 )- ‘Q _‘ g y" Richard R. Schroek Massachusetts Institute of Technology (MIT), Cambridge, MA, USA "for the development of the metathesis method in organic synthesis". Wa-mxpm-Ra ., Metathesijl— a change-your—partners dance This year‘s Nobel Prize Laureates in chemistry have made metathesis into one of organic chemistry‘s most important reactions. Fantastic opportunities have been created for producing many new molecules — pharmaceuticals, for example. Imagination Will soon be the only limit to what molecules can be built! Organic substances contain the element carbon. Carbon atoms can form long chains and rings, bind other elements such as hydrogen and oxygen, form double bonds, etc. All life on Earth is based on these carbon compounds, but they can also be produced artificially through organic synthesis. The word metathesis means 'change-places'. In metathesis reactions, double bonds are broken and made between carbon atoms in ways that cause atom groups to change places. This happens with the assistance of special catalyst molecules. Metathesis can be compared to a dance in which the couples change partners. Animation (Plug in requirement: Flash Player 6! In 1971 Yves Chauvin was able to explain in detail how metatheses reactions function and what types of metal compound act as catalysts in the reactions. Now the "recipe" was known. The next step was, if possible, to develop the actual catalysts. Richard Schrock was the first to produce an efficient metal-compound catalyst for methasesis. This was in 1990. Two years later Robert Grubbs developed an even better catalyst, stable in air, that has found many applications. Metathesis is used daily in the chemical industry, mainly in the development of pharmaceuticals and of advanced plastic materials. Thanks to the Laureates' contributions, synthesis methods have been develOped that are . more efficient (fewer reaction steps, fewer resources required, less wastage), . simpler to use (stable in air, at normal temperatures and pressures) and o environmentally friendlier (non-injurious solvents, less hazardous waste products). This represents a great step forward for "green chemistry", reducing potentially hazardous waste through smarter production. Metathesis is an example of how important basic science has been applied for the benefit of man, society and the environment. Yves Chauvin, born 1930 (74 years), French citizen. Directeur de recherche honoraire a l'Institut francais du pétrole, Rueil—Malmaison, France. Robert H. Grubbs, born 1942 (63 years) in Calvert City, KY, USA (US citizen). PhD in chemistry in 1968 from Columbia University, New York, NY, USA. Victor and Elisabeth Atkins Professor of Chemistry at California Institute of Technology (Caltech), Pasadena, CA, USA. Richard R. Schrock, born 1945 (60 years) in Berne, IN, USA (US citizen). PhD in chemistry in 1971 from Harvard University, Cambridge, MA, USA. Frederick G. Keyes Professor of Chemistry at Massachusetts Institute of Technology (MIT), Cambridge, MA, USA. Prize amount: SEK 10 million, will be shared equally among the Laureates. ...
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