From Organotransition-Metal Chemistry toward Molecular Electronics:  Electronic Communication between Ligand-Bridged Metals

Abstract

The molecular sciences of the transition metals have potential applications in a new fascinating field: molecular electronics. 1,2 This hope is based "inter alia" on the fact that the oxidation states of transition metals can be varied to a great extent and thus that many electrontransfer processes can result. 2 By suitable molecular engineering, it should become possible to assemble and tune molecular devices including transition metals and organize their interface with the macroscopic world. The interplay between light, electron transfer, and magnetooptic properties will then provide efficient and precise molecular sensors for the various needs of future technology. [1][2][3][4][5] In this context, we wish to examine the electronic properties of simple bimetallic model systems and the electronic communication between the two metals across a delocalized bridging ligand in these molecules. This is the subject of the present Account, which will address the following questions: (i) Can one design simple ligandbridged bimetallic complexes as good models for molecular conductors? (ii) What factors control the electronic communication between the two metals across a delocalized ligand? (iii) What are the consequences and applications of single-and multiple-electron transfers in such systems? (iv) Can the molecular electronics of hydrocarbon-bridged bimetallic complexes be, in turn, useful for their organometallic chemistry (i.e., synthesis, catalysis, and mechanistic studies)?Electron-transfer processes between two redox centers have been examined with various linkers: simple inorganic atoms or ligands such as, for instance, pyrazine, 4,4′bipyridine, 6 polyenes including -carotene, 7 polyphenyls, 8 polyynes, 9 and polyaromatics. 10 Long-range electron-transfer studies have been especially useful for biological systems 11 including DNA; 11f photoinduced electron-transfer studies have played a key role in providing high driving forces to test Marcus theory. 12,13 The pioneering work in the area of electronic communication between two metals has been reported by Taube with a series of diruthenium complexes following the famous pyrazine-bridged Creutz-Taube ion which allowed the distinction between trapped (class II) and detrapped (class III) mixed-valence compounds. 6 The second example, biferrocene, 14 is already a relatively good example for us to start with, having a single fulvalenyl bridge. Indeed, we will concentrate on * FAX. † Abbreviations: Cp, η 5 -C5H5; Cp*, η 5 -C5Me5; Fv, µ2,η, 5 η 5 -fulvalenyl unless noted otherwise.(1) (a) Balzani, V.; Scandola, F. Supramolecular Chemistry; Ellis Hordwood: New York, 1991. (b) Balzani, V.; Moggi, L.; Scandola, F. In Supramolecular Photochemistry; Balzani, V., Ed.; Reidel: Dordrecht, FIGURE 3. CV of (a) parent series, 5a 2+ (s) and 3a 2+ (---), and (b) permethylated series 5b 2+ (s) and 3b 2+ (---) (3.3 × 10 -5 M DMF solution; 0.1 M [n-Bu 4 N] + [BF 4 ] -; Hg cathode; scan rate 0.4 V‚s -1 ; -35°C). Rearrangement energy [parent series (a)] and ∆E 2 -∆E 1 [permethylated seri...

Trigonal‐Pyramidal Tetra‐Sandwich Complexes as 3D NLOphores

“…These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. 4 ] as supporting electrolyte. An Amel 5000 system was used with a Pt wire as working electrode and a Pt plate (0.6 cm 2 ) as auxiliary electrode.…”

“…in molecular motors, [2] in electron-storage devices, [3] as redox catalysts, [4] and in materials with nonlinear optical properties. [5] In our research regarding new organometallic structural motifs directed towards second harmonic generation (SHG), we quite extensively studied dipolar "1D" NLOphores, containing sandwich-type complexes as electrondonating and -accepting groups.…”

Unique Intramolecular Electronic Communications in Mono-ferrocenylpyrimidine Derivatives: Correlation between Redox Properties and Structural Nature

“…While the redox behavior of multi-center ferrocenyl derivatives was systematically investigated [8][9][10][11][12][13], it is interesting to expand such studies with the investigation of their heterocyclic counterparts. In addition, the recent development of new and efficient coupling methods involving heterocycles such as pyridines and pyrimidines have rendered the access to a new class of ferrocene coupled pyrimidines possible; nonetheless, their electrochemical and spectroscopic properties have not yet been well characterized [14][15][16].…”

Synthesis and Characterization of Nickel Dithiocarbamate Complexes Bearing Ferrocenyl Subunits

“…[6] The redox behavior of linear triferrocenes in which ferrocenyl subunits are in close enough proximity to permit redox coupling has been described by a model in which initial oxidation occurs at both termini. [7] In contrast, reports on molecules that contain three or more ferrocenyl subunits in which the subunits are not linearly linked but appended to a central core are considerably less frequent.…”