McCullough method

McCullough Method of Preparation of Regioregular HT Poly(3-Alkylthiophenes) (Chart 2.162)... 

Poly[(i )-2-bromo-5-(tributylstannyl)-3-l4-(4-ethyl-2-oxazolin-2-yl)-phenyl]thiophene [Polymerization of (i )-2-bromo-5-(tributylstannyl)-3-[4-(4-ethyl-2-oxazolin-2-yl)phenyl]thiophene (EOPT-Br,Sn) with Pd2(dba)3 as a catalyst, the CuO-modified Stille-McCullough method] [74]. 

Similar thermochromic and solvatochromic effects have been observed by Bidan and coworkers71 for the optically active polymer 25 prepared in a regiospecihc fashion (100% HT-HT coupling) by the McCullough method. In contrast, the analogous regiorandom polymer prepared by oxidation with FeCl3 in chloroform has only weak optical activity. However, the disubstituted chiral polythiophene 26, synthesized by... 

Scheme 6 One-pot synthesis of P3HT-MI macroinitiators for NMRP using the McCullough method followed by in situ endcapping with the Grignard derivative of a common alkoxyamine initiator. Starting from these macroinitiators, the acceptor monomer PerAcr is polymerized to give fully functionalized, double-crystalline block copolymers P3HT-/ -PPerAcr...

Soon after the report of the McCullough method, the Rieke method (Scheme 2.2B) was published (Chen and Rieke, 1992). In this method, the stcuting material is changed to 2,5-dibromo-3-alkylthiophenes 34, which reacts with Rieke zinc at low temperature to yield a mixture of two isomeric organozinc intermediates 35 and 36 in a ratio of 90 10 directly. The intermediates are polymerized in the presence of Ni(dppe)Cl2. The yield of P3ATs 33 is increased to 75%, and the polymer parameters (Mn = 24,000-34,000, PDI = 1.4) are maintained in a comparison to McCullough method. 

The first synthesis of HT rr-P3AT (Scheme 9.1), known as the McCullough method was reported in 1992 (Scheme 9.1, Table 9.1, entry 1) [25,26]. The key to this method is the regiospecific generation of 2-bromo-5-bromomagnesio-3-alkylthiophene 3 from 2-bromo-3-alkylthiophene, which is then polymerized by Kumada and coworkers [27-29] cross-coupling methods using catalytic amounts of... 

SCHEME 9.1 The McCullough method for the regioregular synthesis of poly(3-alkylthiophene) (P3AT) with 100% head-to-tail couplings. 

Table 9.1 is a quick reference to the large number of side-chain functionalized PTs that have been synthesized to date. All of these have been covered throughout the chapter. The primary methods of synthesis used have been designated as Method A (McCullough), Method B (Rieke), Method C (GRIM), Method D (Stille), Method E (FeCl3), and Method F (derivatization). Please refer to the previous section for the general schemes of these synthesizes. 

Figure 2.2 Conversion (filled symbols) and logarithm of monomer concentration (open symbols) vs time plots for 2-bromo-3-hexylthiophenepolymerization at different concentration ofNi(dppp)Cl2 initiator (23-25°C) [M]o = 0.075 mol L (M, [M]o [Ni(dppp)Cl2] = 136 1 ( , o) [M]o [Ni(dppp)Cl2] = 57 1 (A, A) [M]o [Ni(dppp)Cl2] = 49 1. The McCullough method was used for polymerization of2-bromo-3-hexylthiophene. Reprinted with permission from E. E. Sheina, J. Liu, M. C. lovu, D. W. Laird and R. D. McCullough. Chain growth mechanism for regioregular nickel-initiated cross-coupling polymerizations. Macromolecules 37(10), 3526-3528 (2004). Copyright 2004 American Chemical Society...

Method A (McCullough), Method B (RIeke), Method C (GRIM), Method D (Stille), Method E (FeCIs), Method F (Suzuki) Method C (post-functionallzation) Method H (Ullmann). 

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