# How does NMO reform Osmium tetroxide after reaction with an alkene?

After Osmium tetroxide adds to a double bond and is then hydrolysed the following species is formed:

Because Osmium tetroxide is toxic, NMO is used to transform the above back to Osmium tetroxide. NMO is:

What is the mechanism for this?

N-methyl-morpholine-N-oxide (NMO) is used to reoxidize and regenerate osmium tetroxide ($\ce{OsO4}$) in what is known as the "Upjohn Dihydroxylation" procedure.
Mechanistically, the redox occurs when a lone pair of electrons on the reduced $\ce{Os(VI)O3}$ are used to form a bond to the morpholine N-oxygen; the electrons from the former $\ce{N-O}$ bond are, in turn, transferred to the morpholine nitrogen. The $\ce{OsO3}$ gains an oxygen and is oxidized back to osmium (VIII) tetroxide and the NMO is reduced to N-methylmorpholine