1 Synthesis and properties of regioregular poly(3-substituted thiophene) bearing disiloxane moiety in the substituent. Remarkably high solubility in hexane Atsunori Mori, 1 * Kenji Ide, 1 Shunsuke Tamba, 1 Satoru Tsuji, 1 Yuka Toyomori, 1 and Takeshi Yasuda 2 1 Department of Chemical Science and Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501 2 Organic Thin-Film Solar Cells Group, Photovoltaic Materials Unit, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Received <Month> <Date>, <Year>; CL-<No>; E-mail: <insert corresponding e-mail address>) Regioregular poly(3-substituted thiophene) derivative bearing pentamethyldisiloxane moiety at the 3-substituent is prepared by nickel-catalyzed polymerization reactions with dehydrobrominative or debrominative generation of the organometallic monomer. The monomer precursors 2-bromo- 3-(4-pentamethyldisiloxy-butan-1-yl)thiophene (1a) and 2,5- dibromo-3-(4-pentamethyldisiloxy-butan-1-yl)thiophene (1b) are prepared from 3-methylthiophene with 4-5 steps in good overall yields. Treatment of 1a with TMPMgCl·LiCl at room temperature for 3 h forms organometallic monomer and following addition of a nickel catalyst affords the corresponding polythiophene bearing a disiloxane moiety in the side chain. The reaction of 1b with Grignard reagent leads to the similar monomer and addition of a catalytic amount of NiCl2dppe also affords polythiophene in highly regioregular manners. The obtained polythiophene is found to be dissolved in a hydrocarbon such as hexane. Synthesis of regioregular poly(3-substituted thiophene)s attracts much attention due to their wide variety of utilities as materials. 1 It is therefore important to develop a new class of polythiophene derivatives of high performance. In particular, considerable attention has been paid to develop flexible and highly processible materials. Siloxane bearing SiOSi linkage with a longer bond distance and a strong bond energy generating flexible but chemically and thermally stable compounds 2 is a promising structure that may fulfill the above requirements. It is thus intriguing to introduce siloxane moieties into the substituent since it has been well known that the polymeric materials bearing a siloxane group generally improve solubility in organic solvents particularly in hydrocarbons as well as such compounds exhibit excellent thermal stability that induces easy fabrication of functionalized polymeric thin films. 3 However, there has been few example for the preparation of regioregular poly(3- substituted thiophene) bearing a siloxane moiety in the substituent. Only limited reports of non-regioregular polythiophene that is synthesized by oxidative polymerization with Fe III reagents have been shown with a siloxane- containing 3-substituted thiophene as a monomer species. 4 On the other hand, regioregular polythiophenes are shown to be synthesized with 2-halo or 2,5-dihalothiophene derivatives as a monomer precursor, which is in situ transformed into the corresponding organometallic thiophene by deprotonation with a metallic amide 5 or dehalogenative metalation with Grignard metathesis (GRIM) via halogen-metal exchange. 6-8 Nevertheless, few report on the synthesis of halogenated thiophenes bearing a siloxane group has been shown 4 probably due to the synthetic difficulties in halogenation of thiophene ring when a siloxane group exists in the substituent. Herein, we report preparation of regioregular poly(3- substituted thiophene) bearing a pentamethyldisiloxy group by dehydrogenative or GRIM polymerization with a nickel catalyst, whose success is based on an effective synthetic pathway for the monomer precursor. Synthesis of the monomer precursor bromothiophenes 1a and 1b was achieved as represented in Scheme 1. Both compounds are prepared starting from ubiquitous 3- methylthiophene (2) via halogenation of the thiophene ring and following radical bromination to afford 3-bromomethyl halothiophenes 3a and 3b. Treatment of 2 with an equimolar amount of N-bromosuccinimide (NBS) lead to 2-bromo-3- methylthiophene while the reaction with 2 equivalents of NBS furnished 2,5-dibromo-3-methylthiophene. These thiophenes are subjected to radical bromination with NBS in the presence of AIBN in CCl4 lead to 4a and 4b in 62% and 55% yields, respectively. The reaction of 4a with allylmagnesium chloride afforded 2-bromo-3-(3-butenyl)thiophene 5a, whereas the similar reaction of 4b afforded a side product also allylated at the 5-position along with the desired 5b. Transformation into 5b with an improved yield was achieved by the use of the iodomethyl derivative, which was formed by treatment of NaI in acetone, to result in giving 5b. Introduction of pentamethyldisiloxy group into the obtained 5a and 5b was carried out with pentamethyldisiloxane by hydrosilylation with a platinum catalyst leading to 1a and 1b in >99% and 93% yields, respectively. Scheme 1. Preparation of thiophene monomers 1a and 1b bearing a pentamethyldisiloxane moiety The key for successful preparation of brominated thiophene derivatives bearing a pentamethyldisiloxane moiety is the use of 3-halomethylated thiophene, which allowed treatment of S CH 3 S CH 3 Br NBS S CH 3 Br Br NBS (2 eq) S Br i S Br Br THF iii S Br Br Br ii, iii S Br Br S Br X 5a: X=H 5b: X=Br 2 3a 3b 4a 5a 4b 5b Si O Si H Pt cat. S Br X 1a: X=H (>99%) 1b: X=Br (93%) Si O Si i) NBS, AIBN/CCl 4 ii) NaI (2 eq)/(CH 3 ) 2 CO iii) H 2 C=CHCH 2 MgCl/THF i (>99%) (>99%) (62%) (55%) (82%) (34%)