Osmium complexes trinuclear

In addition to those complexes summarized in Tables I—III, X-ray structural analyses of some bi- and trinuclear complexes with a supporting metal-metal bond,1 -115 a trinuclear complex without a metal-metal bond supporting the bridge,3839 116 and two trinuclear osmium complexes with a terminal diphenylthioketone ligand117 have been reported. 

A new class of binuclear nitrido complexes of tetravalent osmium and ruthenium is described in which the metal atoms are symmetrically bridged by a nitride ligand to give a linear M-N—M unit They have the stoichiometries M2NX8(H20)2]3 and [M2N(NH3)8Y2]3+ (M = Os, Ru X = Cl, Br Y = Cl, Br, etc.). Studies are reported on their vibrational spectra, structures, and bonding. Preliminary studies are reported also on trinuclear complexes of osmium and iridium. Finally, the use of vibrational spectroscopy in the study of metal-nitrido and metal-oxo complexes is discussed briefly. 

Figure 4. Ruthenium and osmium hetero-bi- and trinuclear complexes with bis(terpyridine) ligands bridged by one and two phenylene groups (98).

When iron is replaced by ruthenium or osmium the trinuclear anions are photo-chemically inert. For these compounds, once the photoexcited species M -Pt -M° is formed, the rate constant for the formation of products is much smaller than for Fe, and the thermal reaction to regenerate the trinuclear complex is favored by a lower activation barrier. ... 

For trinuclear cluster complexes, open (chain) or closed (cycHc) stmctures are possible. Which cluster depends for the most part on the number of valence electrons, 50 in the former and 48 in the latter. The 48-valence electron complex Os2(CO)22 is observed in the cycHc stmcture (7). The molecule possesses a triangular arrangement of osmium atoms with four terminal CO ligands coordinated in a i j -octahedral array about each osmium atom. The molecule Ru (00) 2 is also cycHc and is isomorphous with the osmium analogue. 

The various modes of bonding that have been observed for alkenes to the trinuclear osmium clusters are shown in Fig. 7 [see (88)]. The simple 77-bonded structure (a) is relatively unstable and readily converts to (c) the vinyl intermediate (b) is obtained by interaction of alkene with H2Os3(CO)10 and also readily converts to (c) on warming. Direct reaction of ethylene with Os3(CO)12 produces (c), which is considered to be formed via the sequence (a) — (b) — (c) and (d). Both isomers (c) and (d) are observed and involve metal-hydrogen and metal-carbon bond formation at the expense of carbon-hydrogen bonds. In the reaction of Os3(CO)12 with C2H4, the complex 112088(00)902112, (c), is formed in preference to (d). Acyclic internal olefins also react with the carbonyl, with isomerization, to yield a structure related to (c). Structure (c) is... 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

Ru3(CO)10(Ph2C2)2, and Ru3(CO)9(C2(Ph)2)3 (128). The dinuclear complex Ru2(CO)6(C2Ph2)2, containing a metallocyclopentadiene ring similar to that observed for both iron and osmium, is a further product in the reaction this does imply very similar structures for the trinuclear adducts to those observed for iron and osmium. The carbonyl reacts with tetracyclone to yield the complex Ru3(CO)i0(C2Ph2)2, which may be related to the osmium compounds discussed later. Phosphine substitution of the carbonyls in some of these compounds has been established. 

A trinuclear nitrido-bridged osmium complex, [Os3(N)2(CN)io(OH2)4]", has been reported. 

Penta- and hexanuclear clusters of the metals osmium and ruthenium coordinate with the same r ri ri - binding mode as the trinuclear clusters to CgQ. Such complexes are known for the clusters OsjC [75,76], RU5C [77-79], RugC [78], PtRu5C [77] and Rhg [80], In this collection of metal clusters rhenium plays a special role, because it forms a new fullerene-metal sandwich complex, where two C50 are bound to one cluster. 

NLO properties, 12, 771 from oxygenated ligands, 6, 842 with palladium, 8, 213 and Rh Cp complexes, 7, 160 trinuclear clusters, overview, 6, 835-871 Osmium complexes... 

Not only N, but also C atoms can take part as donor centers in azacymantrene 760 (E = N, R = H) and azaferrocene 763 (R = H). In this respect, the formation of a trinuclear osmium-carbonyl adduct 768 is representative, which takes place in the reaction of the indicated azacenes with acetonitrile complex of triosmium decarbonyl [482] ... 

No mononuclear osmium(IV) nitrido complexes have been established, but /i-nitrido species containing a linear Os—N—Os unit are known, and there are trinuclear species of osmium(IV) and of mixed oxidation state containing Os—N—Os—N—Os units. The existence of both types is predictable from bonding considerations. They are dealt with on p. 564. 

All three Group 8 metals form trinuclear clusters M3(CO)i2. However, while all carbonyl ligands in ruthenium and osmium dodecacarbonyl complexes coordinate to the metal center as terminal carbonyls, there are two bridged carbonyl groups in iron dodecacarbonyl. This may be due to the smaller van der Waals radius of the iron atom. In this section, Fe(CO)5, Fe2(CO)9and Na2[Fe(CO)4] are reviewed. 

---