Surface Functionalization of Metals by Alkyl Chains through a Radical Crossover Reaction

Abstract

Alkyl chains are covalently attached onto metal surfaces by indirect reduction of the bromoalkyl derivative (RBr). This indirect reaction involves the formation (by spontaneous or electrochemical reduction of the 2,6-dimethylbenzenediazonium salt) of a sterically hindered aryl radical that abstracts a Br atom from RBr but does not react with the surface. This crossover reaction furnishes an alkyl radical that reacts with the surface. Starting from 6-bromohexanoic acid, carboxylic functionalized gold surfaces are prepared. "Layer-by-layer" assemblies are built from these surfaces and present some ionic selectivity.

Direct vs Indirect Grafting of Alkyl and Aryl Halides

“…Removal of a halogen atom from an alkyl halide by 2.6-dimethylphenyl radical is not restricted to alkyl iodides but also occurs with alkyl bromides, which are more difficult, even impossible to graft by electrochemical reduction. [3,50] As alkyl bromides are easily available with different terminal functional groups, they can provide a tethered film that can be further modified. For example, the same procedure as above, starting from 6-bromo-1-hexanoic acid, provides a gold electrode modified with hexanoic acid groups.…”

“…The electrografting of alkyl moieties is also possible by diverting the reactivity of aryl radicals derived from other diazonium salts, such as those that are prone to react with surfaces. An example is reported when using 4‐nitrobenzenediazonium and 4‐methylbenzenediazonium salts [49] . Aryl radicals undergo two reactions: i) with the surface, ii) with alkyliodides in solution to generate alkyl radicals by iodine abstraction.…”

Surface modification of materials: Electrografting of organic films

“…The reaction can be performed at much less negative potential (with a gain > 1.7 V) in the presence of 2,6-DMBD following the atom abstraction mechanism of Scheme 2. This reaction leads to different modified surfaces GC-C 6 H 13 or GC-(CH 2 ) 2 C 6 F 13 [22], Au, PMMA, PE-C 5 H 10 -COOH [23,24] (PMMA= polymethylmethacrylate, PE = polyethylene). The activation of C-I bonds is also possible with aryl iodides at the reduction potential of 2,6-DMBD [25].…”

From Langmuir–Blodgett to Grafted Films

“…29,14 Combined reflection and diffraction measurements have been conducted to reveal structural features as the pressure increases in the film. 30 Electrografted films, 31 are obtained by electrochemical oxidation of amines 32 , carboxylates 33 , alcohols 34 or reduction 12,35,36 of diazonium salts, 12 and alkyl or aryl halides 35,36 . They result from the attack of very reactive radicals on the surface.…”

“…Electrografted films are obtained by electrochemical oxidation of amines, carboxylates, and alcohols or by reduction ,, of diazonium salts and alkyl or aryl halides. , They result from the attack of very reactive radicals on the surface. The bond dissociation energies (BDE) of the metal - and Si-aryl or alkyl films (obtained by reduction of diazonium salts or alkyl iodides) have been calculated by density functional theory methods, ,, and they vary from 100 to 293 kJ mol –1 from Au to Si indicating a strong bonding of the organic film .…”