Abstract
Cross-coupling at aryl halide thin films has been well-established as a technique for the surface-initiated Kumada catalyst transfer polymerization (SI-KCTP), used to produce covalently bound conjugated polymer thin films. In this work, we report that the spontaneous grafting of 4-iodobenzenediazonium tetrafluoroborate on gold substrates creates a durable iodoarene layer which is effective as a substrate for cross-coupling reactions including SI-KCTP. Using cyclic voltammetry of a surface-coupled ferrocene terminating agent, we have measured initiator surface coverage produced by oxidative addition of Pd(t-Bu3P)2 and estimated the rate constant of the termination reaction in the SI-KCTP system with 2-chloromagnesio-5-bromothiophene and Pd(t-Bu3P)2. We used this system to prepare uniform polythiophene thin films averaging 90 nm in thickness.
Highlights
Since the development of the first polyacetylenes by Shirakawa and MacDiarmid in the 1970s (Chiang et al, 1977; Chiang et al, 1978), applications of pi-conjugated polymers (CPs) have proliferated along with a number of refined synthetic approaches for forming these polymers
The single greatest refinement in the cross-coupling synthesis of polyarene CPs came in the mid-2000s from the Yokozawa and McCullough groups (Yokoyama & Yokozawa, 2007; Sheina et al, 2004), in which ‘‘AB’’ monomers were prepared by monometallation of an aryl dihalide
We found that 4-iodobenzenediazonium salt spontaneously forms a thin film at a clean gold surface, and that the resulting aryl iodide layer is convenient and effective for cross-coupling (Fig. 2)
Summary
Since the development of the first polyacetylenes by Shirakawa and MacDiarmid in the 1970s (Chiang et al, 1977; Chiang et al, 1978), applications of pi-conjugated polymers (CPs) have proliferated along with a number of refined synthetic approaches for forming these polymers. Oxidative polymerization approaches are common (Kaloni et al, 2017; Niemi et al, 1992). Oxidative polymerization is difficult to control and applicable only to electron-rich arene monomers. Cross-coupling strategies have been developed (Yamamoto, 2002; Heeger, 2001), most commonly coupling of a aryl dihalide with an arene bearing two nucleophilic groups, e.g., an ‘‘AA/BB’’ strategy. The single greatest refinement in the cross-coupling synthesis of polyarene CPs came in the mid-2000s from the Yokozawa and McCullough groups (Yokoyama & Yokozawa, 2007; Sheina et al, 2004), in which ‘‘AB’’ monomers were prepared by monometallation of an aryl dihalide.
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