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The utility and scope of Cu-catalyzed halogen atom transfer chemistry have been exploited in the fields of atom transfer radical polymerization and atom transfer radical addition, where the metal plays a key role in radical formation and minimizing unwanted side reactions. We have shown that electrochemistry can be employed to modulate the reactivity of the Cu catalyst between its active (CuI) and dormant (CuII) states in a variety of ligand systems. In this work, a macrocyclic pyridinophane ligand (L1) was utilized, which can break the C–Br bond of BrCH2CN to release •CH2CN radicals when in complex with CuI. Moreover, the [CuI(L1)]+complex can capture the •CH2CN radical to form a new species [CuII(L1)(CH2CN)]+in situthat, on reduction, exhibits halogen atom transfer reactivity 3 orders of magnitude greater than its parent complex [CuI(L1)]+. This unprecedented rate acceleration has been identified by electrochemistry, successfully reproduced by simulation, and exploited in a Cu-catalyzed bulk electrosynthesis where [CuII(L1)(CH2CN)]+participates as a radical donor in the atom transfer radical addition of BrCH2CN to a selection of styrenes. The formation of these turbocharged catalysts in situduring electrosynthesis offers a new approach to the Cu-catalyzed organic reaction methodology.

Copper-catalyzed electrochemical atom transfer radical addition (eATRA) is a new method for the creation of new C–C bonds under mild conditions. In this work, we have explored the reactivity of an analogous series of N4macrocyclic CuIIcomplexes as eATRA precatalysts, which are primed by reduction to their monovalent oxidation state. These complexes were fully characterized structurally, spectroscopically, and electrochemically. A spectrum of radical activation reactivity was found across the series [CuI(Me4cyclen)(NCMe)]+(Me4cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane), [CuI(Me4cyclam)(NCMe)]+(Me4cyclam = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), and [CuI(Me2py2clen)(NCMe)]+(Me2py2clen = 3,7-dimethyl-3,7-diaza-1,5(2,6)-dipyridinacyclo-octaphane). The rate of radical production by [Cu(Me2py2clen)(NCMe)]+was modest, but rapid radical capture to form the organocopper complex [CuI(Me2py2clen)(CH2CN)] led to a dramatic acceleration in catalysis, greater than seen in any comparable Cu complex, but this led to rapid radical self-termination instead of radical addition.

The most probable single-molecule conductance of each member of a series of 12 conjugated molecular wires, 6 of which contain either a ruthenium or platinum center centrally placed within the backbone, has been determined. The measurement of a small, positive Seebeck coefficient has established that transmission through these molecules takes place by tunneling through the tail of the HOMO resonance near the middle of the HOMO–LUMO gap in each case. Despite the general similarities in the molecular lengths and frontier-orbital compositions, experimental and computationally determined trends in molecular conductance values across this series cannot be satisfactorily explained in terms of commonly discussed “single-parameter” models of junction conductance. Rather, the trends in molecular conductance are better rationalized from consideration of the complete molecular junction, with conductance values well described by transport calculations carried out at the DFT level of theory, on the basis of the Landauer–Büttiker model.

The syntheses and crystallographically determined structures of metal complexes trans-[M(C≡CR)2Ln] (MLn= Ru(dppe)2, Ru{P(OEt)3}4, Pt(PEt3)2) featuring acetylide ligands further functionalized by aryl thioether groups are reported, together with those of analogous organic buta-1,3-diyne (RC≡CC≡CR) and 1,4-diethynylbenzene (RC≡CC6H4C≡CR) compounds for comparative purposes. The terminal thioether functional groups have an affinity for binding to the surface of gold electrodes and are considered as “anchor” groups in the design of molecules for study within metal|molecule|metal molecular junctions. The influence of the Lewis acidic and π-basic thioether moiety on a number of physical properties important to the electrical behavior of molecules within molecular junctions has been explored using spectroscopic, electrochemical, and quantum chemical methods. The thioether functional group serves as a moderately strong π-electron-donating substituent, similar in electronic character to the OMe group, resulting in relatively high lying HOMOs that are delocalized over the length of the molecule and well-suited to promote coherent tunneling within the junction. In addition, the facile oxidation processes and the relatively small reorganization energies associated with the one-electron oxidation of these compounds indicate the potential for effective hopping mechanisms of charge transport through longer structures based on these organometallic motifs.