Ruthenium bonding models

Two types of NO coordination to ruthenium are known linear Ru-N—O 180° and bent, Ru-N-O 120°. Since NO+ is isoelectronic with CO, linear Ru-N-O bonding is generally treated as coordination of NO+, with bent coordination corresponding to NO- thus, in the former an electron has initially been donated from NO to Ru, as well as the donation of the lone pair, whereas in the latter an electron is donated from the ruthenium to NO (making it NO-) followed by donation of the lone pair from N. Though an oversimplification, this view allows a rationale of metal-nitrogen bond lengths, as with the Ru—NO+ model 7r-donation is important and a shorter Ru—NO bond is predicted - and, in fact, observed. 

Plutonium-noble metal compounds have both technological and theoretical importance. Modeling of nuclear fuel interactions with refractory containers and extension of alloy bonding theories to include actinides require accurate thermodynamic properties of these materials. Plutonium was shown to react with noble metals such as platinum, rhodium, iridium, ruthenium, and osmium to form highly stable intermetallics. 

Fig. 6.3 Cluster model structure for Ru99Se54 showing the selenium bonding onto the ruthenium clusters (a) with a statistical distribution (b) with an ordered positioning. (Adapted with permission from [24]. Copyright 2009, American Chemical Society)...

Fig. 8. Energies calculated with a polarizable continuum model, differences of the sums of all metal-oxygen bond lengths, AS(M-O), and energy profiles for water exchange on rhodium(III) and ruthenium(II) hexaaqua ions.

The electrochemistry of dinitrogen bridging two porphyrin ligated ruthenium centers has been studied as a possible route to fixed nitrogen [45 -47]. Diazene stabilized by bonding to two iron centers in a FeS system has been advanced as a structural model of a plausible intermediate in biological nitrogen fixation [48-50]. 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

Most of the recent synthetic applications of M-RCM involve one of the above catalysts, particularly G1 or G2, chosen as a function of its own reactivity profile, generally after preliminary reaction assays on the genuine substrate or specific model compounds. The sensitivity of the RCM reaction to steric hindrance is well established. These ruthenium catalysts exhibit high affinity for carbon-carbon double bonds and are compatible with the presence of many functional groups, even the presence of free polar hydroxyl or amino groups. Their use does not require special conditions such as glove boxes, which are required when using Schrock s molybdenum catalyst. 

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