Redox-Active Molecular Wires Derived from Dinuclear Ferrocenyl/Ruthenium(II) Alkynyl Complexes: Covalent Attachment to Hydrogen-Terminated Silicon Surfaces

Abstract

International audienceAfter their brief characterization, a voltammetric study of the Fe(II)/Ru(II) heterobinuclear organometallic complexes [Fe]C≡C-1,4-(C6H4)C≡C[Ru]C≡C-1,4-(C6H4)C≡CH (2), FcC≡C[Ru]C≡C-1,4-(C6H4)C≡CH (3), and PhC≡C[Ru]C≡C-1,1′-Fc(C≡CH) (4) ([Fe] = Fe(κ2-dppe)(η5-C5Me5), [Ru] = trans-Ru(κ2-dppe)2; Fc = ferrocenyl; dppe =1,2-bis(diphenylphosphino)ethane) is reported in solution. These complexes which possess pendant ethynyl groups have then been grafted onto hydrogenated silicon surfaces using a mild photochemical protocol, to yield redox-active functional interfaces (Si-2/Si-3/Si-4) that were characterized by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. The resulting interfaces Si-2, Si-3, and Si-4 possess surface coverages and electrochemical responses that differ significantly and that depend on the nature of the grafted molecule. While the coverages calculated for the more rigid of these systems (Si-2 and Si-3) are similar (around 10–10 mol cm–2), the significantly lower coverage achieved for Si-4 (4.3 × 10–11 mol cm–2) can be ascribed to the presence of a flexible linker between the redox sites in 4. The two grafted redox centers can be electrochemically addressed in a stepwise fashion, the species exhibiting apparent charge transfer rate constants with the Si surface that are considerably higher than those reported for many related systems (>200 s–1). Comparison between Si-2 and Si-3 reveals that the use of the ferrocenyl group instead of a “Fe(κ2-dppe)(η5-C5Me5)” moiety improves the kinetic stability of the first oxidized state and its apparent charge transfer rate constant, while also increasing the first oxidation potential. However, an enhanced fragility is observed for Si-3 and even more so for Si-4 at higher oxidation potentials; this may be related to the larger spin density present on the ferrocenyl terminus of the grafted dications 32+ and 42+, as evidenced by molecular modeling calculations. Several ways to solve this important issue are discussed in the conclusion

Approach to the Mechanism of Hydrogen Evolution Electrocatalyzed by a Model Co Clathrochelate: A Theoretical Study by Density Functional Theory

“…Therefore, for the present study we selected the B3LYP functional and the basis 1 to run the geometry optimizations and hessian calculations, while chose basis 2 to refine the calculated energy through single point calculations. The choice of B3LYP functional and LANL2DZ basis set as an adequate choice is further supported by several publications describing the behavior of various organometallic compounds including a phthalocyaninoclathrochelate …”

Reactions of alkynes with cis-RuCl2(dppm)2: exploring the interplay of vinylidene, alkynyl and η3-butenynyl complexes

“…The formation, isolation and characterisation of the vinylidene complexes [1]BF4 and mono-alkynyl complexes 2 allowed the sequence of events leading to the formation of trans-bis(alkynyl) complexes 3 vs. the η 3 -butenynyl complexes [4]BF4 to be followed by in situ 31 P{ 1 H} NMR spectroscopy. From a mixture of cis-RuCl2(dppm)2 TlBF4, HC≡CC6H4-4-R and 1,8-bis-dimethylaminonaphthalene in CH2Cl2 solutions, the mono-alkynyl complexes 2 (s, ca.…”

“…For cases when the R substituent is electron withdrawing ( Figure 5), 3 were ultimately formed without any appreciable byproducts. However, when the R substituent is electron donating (Figure 6), before complete conversion of 2 to 3, the η 3 -butenynyl complex [4] + is observed with four new 31 P{ 1 H} NMR resonances in a characteristic ABMX coupling pattern. 35 As the reaction proceeds, the product distribution shifts to give the η 3 -butenynyl species cleanly without any appreciable by-products, implying the intermediacy of 3 in the formation of [4] + .…”

Redox Properties of Graphenes Functionalized with Cyclopentadiene–Transition Metal Complexes: A Potential Redox-Active Material

“…[16][17][18] For instance Grelaud et al recently reported the attachment of a dinuclear ferrocenyl/ruthenium(II) alkynyl redox-active side chain onto hydrogen-terminated silicon. 19 However, most of these synthesis efforts involve multistep synthesis processes of the complex side chains and some high-value (noble metal) materials to improve the resulting conductivity and stability. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4 In contrast to the current experimental approaches for attaching metallocenes onto supports, our previous simulation study identified an extraordinarily strong direct immobilization of cyclopentadienyl-transition metal complexes (CpTM) onto B-doped nanocarbons (including carbon nanotubes (CNTs) and graphene supports).…”