Diruthenium paddlewheel

The first diruthenium paddlewheel complex, RUjfii-OjCMej Cl, was prepared in 1966 by Stephenson and Wilkinson [3]. The paddlewheel geometry was validated in 1969 when Cotton and coworkers reported the X-ray crystal structure of an analogous complex, Ru2(p-OjC"Pr) Cl [4j. In the crystal, RUjlii-OjC Prl Cl assembles in an infinite zig-zag chain, where each chloride atom bridges two diruthenium units. More significantly, a short Ru-Ru bond distance of 2.281(4) A was revealed. The FSR of this bond is 0.92, which is consistent with a multiple bond order. 

Ru/ Most diruthenium paddlewheels contain Ru " cores, which are formally mixed-valent, Ru(II)Ru(III). These cores are delocalized with Ru(2.5)Ru(2.5) oxidation states [44]. Two other redox states of the diruthenium core, Ru and RUj, have also been isolated, though only for a subset of the ligands listed above for Ru. Generally, RUj paddlewheels have weaker donors, for example, carboxylates and amidates, while Ru paddlewheels have more electron-rich donors, for example, amidinates and aminopyridinates. 

Toward Electronic and Magnetic Materials and Devices One potential application of diruthenium paddlewheels is their use as building blocks in molecular electronic devices and magnetic materials. 

Another direction has been to develop heterogeneous applications of diruthenium paddlewheels [97]. By using multitopic carboxylate ligands, for example, 1,4-benzenedicarboxyate, RUj tetracar-boxylates are assembled into microporous networks. Interesting applications such as the catalytic hydrogenation of alkenes, the oxidation of primary aliphatic alcohols, and photocatalytic hydrogen production from water have been reported [98-101]. 

Mixed-valence Ru"-Ru" paddlewheel carboxylate complexes also have potential for oxidation reactions after incorporation in a microporous lattice with porphyrinic ligands. This MOF can be used for oxidation of alcohols and for hydrogenation of ethylene. Both the porosity of the lattice and the abihty of the diruthenium centers to chemisorb dioxygen are essential for the performance of the catalyst [62, 64]. 

Stoichiometric Aryl C-H Bond Amination Toward the goal of developing catalysts that can activate strong C-H bonds. Berry and coworkers have investigated diruthenium terminal nitrides supported by formamidinate ligands in a paddlewheel arrangement. Unlike mononuclear Ru nitrides, the RUj " "... 

Of the Group 8 metals, OSj complexes are the least well developed. In this section, we summarize the small family of Osj complexes, most of which have been reviewed previously [39,137]. A majority of Osj complexes are paddlewheels or have tetragonal geometries, akin to their Ruj counterparts. They also occur in similar oxidation states, namely OSj +, OSj +, and Os ". However, a key difference is that the Osj " core is the most prevalent (stability of Osj " > OS2 " ), whereas the lower oxidation state of RUj is more common (stability of RUj + < RUj +). Finally, an OSj complex has been isolated in the unusually high oxidation state of +7, which remains unknown for Ruj and Fej cores, with the exception of the (Ruj +N ") core in the diruthenium nitride complex (vide supra) [113,115]. 

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