Osmium dioxo derivative

Osmium(IV) complexes containing terminal 0s=0 units are rather rare, and it is more usual for a bridging mode to be adopted as in [OszOClio]" - One example of a mononuclear species is shown in scheme 23.89, in which the Os(IV) dioxo derivative is obtained by activation of molecular O2 via an Os(VI) intermediate. The square planar geometry of the Os(IV) product is unusual for a configuration. The precursor in scheme 23.89 is prepared by treating OsCls xHzO with P Pr3, and has a distorted 6-coordinate coordination sphere. 

X-ray crystallographic structures of the cw-dioxo osmium(VI) esters derived from dihy-droquinine-4-chlorobcnzoate/Os04/( )-2,2,5,5-tetramethyl-3-hexene and dihydroquinidine 4-chlorobenzoate/Os04/(i )-2,5-dimethyl-3-hexene have also been reported 22. Inspection of these sixteen-electron complexes reveals that, despite the considerable distance between the ligand stereocenters and the reacting site, the 4-chlorobenzoyl moieties effectively shield one of the two possible modes of alkene approach. 

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