Stepwise Formation of Ruthenium(II) Complexes by Direct Reaction on Organized Assemblies of Thiol‐Terpyridine Species on Gold

Abstract

Surface-confined polypyridinebased metal complexes are of importance in several applications such as solar energy conversion, luminescent sensors and molecular electronics [1] . Anchoring of complexes on metal surfaces can be obtained, among others, via an intermediate step involving the preparation of a self-assembled monolayer (SAM) with suitable functional tail groups. The SAM can then be used for binding the metal complex, by a stepwise procedure involving coordination chemistry reactions, directly at the surface. However, the known synthetic routes for bulk preparation of metal complexes, such as polypyridine complexes of ruthenium, osmium and iridium (among the most interesting polypyridine metal complexes, because of their outstanding photophysical and redox properties) [2] are based on reaction conditions that could be incompatible with the properties (e.g. thermal stability) of the monolayer that acts as one of the reactants. Indeed, whereas for example, surface-confined iron or cobalt polypyridine complexes have been prepared by a stepwise procedure based on suitably-derivatized surfaces, [3] analogous ruthenium systems have been elusive up to now, in spite of the large interest of these latter species.Here we report the "proof of concept" that stepwise synthesis of polypyridine-ruthenium complexes by direct coordination reaction at surface is feasible. This is made by means of the reaction between a terpyridine functionalized thiol-based SAM on gold with a suitable precursor of the complex (see Scheme 1). This method allows the preparation of2 + (1; tpy = 2,2':6',2"-terpyridine; MPTP = 4'(4-mercaptophenyl)-2,2':6',2"-terpyridine) directly at the surface of a mixed component SAM of MPTP and mercaptobenzene (MB) (3-surface in Scheme 1). The SAM employed as platform for the reaction is reproducibly obtained with 1:1 MPTP/MB ratio.[4] To the best of our knowledge, this is the first time that preparation of a surface-confined Ru II polypyridine compound by direct coordination of a Ru II precursor to a polypyridine-derivatized gold surface is reported.The surface-anchored ruthenium complex (hereafter called 1-surface) obtained in this way has been studied by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Such investigations involve the comparison of these systems with analogous ones prepared via surface anchoring of the pre-synthesized ruthenium complex 1, whose synthesis is sketched in Scheme 2 and described in the Experimental Section.The stepwise synthesis of 1-surface according to method A (Scheme 1) implies that the terpyridine-based (MB/MPTP) SAM used as reactant should not be damaged under the conditions used for reaction. The usual protocol employed for the synthesis of heteroleptic Ru II terpyridine-type complexes requires relatively severe conditions, since it involves several hours of reaction in refluxing solvent.[5] However, probably due to the relatively weak link of thiolate on gold, the MB/MPTP SAM does not stand long refluxing conditio...

Synthesis, Characterization, and Metal Ion Coordination of a Multichromophoric Highly Luminescent Polysulfurated Pyrene

“…A classical synthetic path to provide similar molecules was reported in the literature 16. We used an optimized protocol17 to afford 1 in acceptable yields. Two equivalents of 2‐acetylpyridine undergo condensation with 4‐(methylthio)benzaldehyde in a basic media for building the terpyridyl skeleton.…”

Terpyridine‐Functionalized Surfaces: Redox‐Active, Switchable, and Electroactive Nanoarchitecturesgland

“…[ 23 ] The coordination of these surface-bound terpyridine moieties to Ru II ions was later shown. [ 24 ] Almost quantitative loading of the terpyridine sites by reaction with Ru(tpy)Cl 3 was confi rmed by XPS.…”

Organothiol‐Based Hybrid‐Layer Strategy for High‐Performance Copper Adhesion and Stress‐Migration via Simultaneous Oxide Reduction

“…Unlike aluminum oxide (Al 2 O 3 ) which is dense and tenacious, the native Cu‐oxide is voluminous and weak, and acts as a weak interlayer preventing sufficient adhesion . Multiprocess and multilayer solutions do exist to promote adhesion such as the use of electroless‐plating in conjunction with heat treatment to control the formation/structure of the Cu oxide, the use of hot alkaline solutions as an oxide forming agent, and the combined use of a chemical reducing pretreatment followed by an organic‐solvent‐based self‐assembly of organothiol monolayer . These processes are, however, generally expensive and not compatible with low‐vcost manufacturing.…”