Osmium complexes bonding

Comparison with data (mainly obtained from EXAFS measurements) on osmium diarsine complexes (Table 1.14) shows that as the oxidation state increases, osmium—halogen bonds shorten whereas Os-P and Os—As bonds lengthen. Bond shortening is predicted for bonds with ionic character,... 

B. Ruthenium and Osmium o-Bonded Alkyl and Aryl Complexes. 266... 

B. Ruthenium and Osmium a -Bonded Aikyi and Aryi Complexes... 

Diols are applied on a multimilhon ton scale as antifreezing agents and polyester monomers (ethylene and propylene glycol) [58]. In addition, they are starting materials for various fine chemicals. Intimately coimected with the epoxidation-hydrolysis process, dihydroxylation of C=C double bonds constitutes a shorter and more atom-efficient route to 1,2-diols. Although considerable advancements in the field of biomimetic nonheme complexes have been achieved in recent years, still osmium complexes remain the most efficient and reliable catalysts for dihydroxylation of olefins (reviews [59]). 

The reactions of a neutral 10 as well as a cationic dihydrido(acetato)osmium complex 12 with acetylenic compounds were examined (Scheme 6-17) [11-13]. A vinyU-dene 99, an osmacyclopropene 100, or a carbyne complex 101 were obtained, depending on the starting hydrido(acetato) complexes or the kind of acetylene used. In any case, the reaction proceeded by insertion of a C C triple bond into one of the two Os-H bonds, but the acetato ligands do not take part in the reaction and act as stabilizing ligands. 

Compound 72 has been crystallographically characterized. The most striking feature of this structure is how little structural reorganization accompanies this adduct formation. The osmium-carbon bond length at 1.90(2) A is not detectably altered from that of the parent complex 47 and the C—Os—C angle is increased by only 8°. 

The X-ray structure determination of 107 reveals that the osmium-carbon bond length is increased by 0.07 A on going from the parent carbyne complex 79 to the silver adduct 107. This may be contrasted with the weaker interaction between the metal-carbon bond and the Aul fragment in Os(CH2AuI)Cl(NO)(PPh3)2 (see Section IV,C,1). 

In our laboratory we have examined the reactivity pattern of [0s3(y-H)2(C0)10], an unsaturated cluster which can be represented as possessing an osmium-osmium double bond in its classical valence bond representation. We find (2,3) that this compound undergoes a number of reactions with metal carbonyls which in some cases can be formulated as proceeding through intermediates analogous to metal olefin complexes ... 

A similar range of reactions has also been reported for the ruthenium carbonyl-triphenylphosphine systems (148). In these systems, a high percentage of the products were dinuclear, reflecting the weaker bonding in the ruthenium system, and as for some of the osmium complexes discussed above, some contain orthometallated phenylphos-phine groups (see Fig. 29, structures I, IV, X). 

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. 

In contrast, the plane of the CF2 ligand in the osmium complex 6 lies perpendicular to the equatorial plane of the trigonal bipyramid, the conformation expected in order to maximize back bonding, and the rate of rotation of the CF2 ligand is slow on the NMR time scale, due to more extensive back bonding from the Os(O) center (70). 

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