Osmium complexes oxygen donors

In summary, the reaction of osmium tetroxide with alkenes is a reliable and selective transformation. Chiral diamines and cinchona alkakoid are most frequently used as chiral auxiliaries. Complexes derived from osmium tetroxide with diamines do not undergo catalytic turnover, whereas dihydroquinidine and dihydroquinine derivatives have been found to be very effective catalysts for the oxidation of a variety of alkenes. OsC>4 can be used catalytically in the presence of a secondary oxygen donor (e.g., H202, TBHP, A -methylmorpholine-/V-oxide, sodium periodate, 02, sodium hypochlorite, potassium ferricyanide). Furthermore, a remarkable rate enhancement occurs with the addition of a nucleophilic ligand such as pyridine or a tertiary amine. Table 4-11 lists the preferred chiral ligands for the dihydroxylation of a variety of olefins.61 Table 4-12 lists the recommended ligands for each class of olefins. 

Two significant surveys are published in the sane edition of Coordination Chemistry Reviews. Oxygen donor-ligand derivatives of tri-osmium dodecacarbonyl are covered by Frauenhoff and the reactions of transition metal dihydrogen complexes (of which many are carbonyl-containing) are outlined by Jessop and Morris. The crucial role of matrix Isolation studies is well covered in this article. A shorter review of interest here has been published on the role of the phosphorus d-orbitals in M-P bonding. ... 

Because these ligands coordinate through oxygen atoms, they stabilize high as well as low oxidation states. Two representative Mo(II) and W(II) dinuclear complexes are given in equation (2.65). The 18e osmium complexes may serve as 2e ligands, which may coordinate to other metals, such as (Me3P)(OC)4 OsW(CO)s. There is a donor-acceptor Os —W bond in this compound. In the solid state... 

Osmium(IV), d, halides are the most important osmium salts, with K2[OsCl6] as the most prominent example. The most common complexes of osmium(IV) involve oxygen donor ligands. 

Nitrogen is, after oxygen, the most frequently encountered donor atom in the coordination chemistry of osmium. There is a large and growing body of work on the ammine, pyridine, ethylenediamine and porphyrin complexes, but the most popular and rapidly growing field of study at the present time is that of the polypyridyls , the 2,2 -bipyridyl, 1,10-phenanthroline and 2,2,2,6 - terpyridyl complexes of the metal. 

The Corey mechanistic proposal is founded on the ability of the alkene substrate to bind between the two quinohne ring walls which are spaced parallel with a separation of 7.2 A. When the substrate binds in this elongated cleft, the alkene complexes to the osmium center in the W-complexated osmium tetroxide through a donor-acceptor (d-Jt) interaction (Scheme 10). The interaction between the alkene and osmium tetroxide is also complemented with favorable van der Waals interactions between the alkene and the binding cleft. These interactions are implied by the Michaelis-Menten kinetics [72] observed in the process. The observation of Michaelis-Menten kinetics in the AD process has however been questioned as an experimental artifact by the Sharpless group [73]. The (3+2) addition takes place between the axial and one of the equatorial oxygen atoms in osmium tetroxide which are in close proximity with the alkene. This represents the minimum motion pathway in the formation of the pentacoordinate os-mium(VI) glycolate ester. In the Corey model the rate acceleration observed in... 

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