Complex sentence: In combination with sodium periodate, OsO 4 is used for the oxidative cleavage of alkenes (Lemieux-Johnson oxidation) when the periodate serves both to cleave the diol formed by dihydroxylation, and to reoxidize the OsO 3 back to OsO 4.
Split into simpler sentences: In combination with sodium periodate, OsO 4 is used for the oxidative cleavage of alkenes (the Lemieux-Johnson oxidation). Here the periodate serves both to cleave the diol formed by dihydroxylation, and to reoxidize the OsO 3 back to OsO 4.