Heck Coupling of Olefins to Mixed Methyl/Thienyl Monolayers on Si(111) Surfaces

Abstract

The Heck reaction has been used to couple olefins to a Si(111) surface that was functionalized with a mixed monolayer comprised of methyl and thienyl groups. The coupling method maintained a conjugated linkage between the surface and the olefinic surface functionality, to allow for facile charge transfer from the silicon surface. While a Si(111) surface terminated only with thienyl groups displayed a surface recombination velocity, S, of 670 ± 190 cm s(-1), the mixed CH3/SC4H3-Si(111) surfaces with a coverage of θSC4H3 = 0.15 ± 0.02 displayed a substantially lower value of S = 27 ± 9 cm s(-1). Accordingly, CH3/SC4H3-Si(111) surfaces were brominated with N-bromosuccinimide, to produce mixed CH3/SC4H2Br-Si(111) surfaces with coverages of θBr-Si < 0.05. The resulting aryl halide surfaces were activated using [Pd(PPh3)4] as a catalyst. After activation, Pd(II) was selectively coordinated by oxidative addition to the surface-bound aryl halide. The olefinic substrates 4-fluorostyrene, vinylferrocene, and protoporphyrin IX dimethyl ester were then coupled (in dimethylformamide at 100 °C) to the Pd-containing functionalized Si surfaces. The porphyrin-modified surface was then metalated with Co, Cu, or Zn. The vinylferrocene-modified Si(111) surface showed a linear dependence of the peak current on scan rate in cyclic voltammetry, indicating that facile electron transfer had been maintained and providing evidence of a robust linkage between the Si surface and the tethered ferrocene. The final Heck-coupled surface exhibited S = 70 cm s(-1), indicating that high-quality surfaces could be produced by this multistep synthetic approach for tethering small molecules to silicon photoelectrodes.

Covalent Surface Modification of Gallium Arsenide Photocathodes for Water Splitting in Highly Acidic Electrolyte

“…Surface chlorination followed by salt‐metathesis chemistry on semiconductor surfaces has successfully provided organic functionalization of both Si(1 1 1) and III–V(1 1 1) surfaces . Unlike these (1 1 1) surfaces that feature one type of surface atom (in the case of III–V surfaces, either the group III or V element, depending on the A or B side of the crystal), (1 0 0) surfaces contain both group III and V elements (here, Ga and As, respectively).…”

Energetic Tug‐of‐War between Pt and Leaky TiO2: Positive and Negative Effects on the Function of Molecularly‐Modified p‐Si(111)|TiO2|Pt Photocathodes

“…As Pt is a well‐known proton reduction catalyst, Pt nanoparticles were also deposited to study catalyst effects on interfacial energetics. The Si‐diOMePh mixed‐monolayer surface with and without TiO 2 ALD layers has been characterized in detail in other publications including Pt nanoparticles deposited via ALD under similar conditions …”

A post-functionalization toolbox for diazonium (electro)-grafted surfaces: review of the coupling methods

“…242 These features also make convenient the use of Pd-catalyzed coupling methods for interfacial reactions with immobilized organic films. 243,244 Pd-Catalyzed coupling reactions are commonly carried out at moderate temperatures (50-100 1C) to achieve high conversion yields. Thus, one of the fundamental prerequisites to perform this kind of catalyzed process on an anchored organic film is the thermal stability of the bond linking the organic layer to the underlying substrate.…”