What is the mechanism for the reaction of alkenes with diborane and chloramine?
Organoboranes react with chloramine to give the corresponding amine as reported by Brown et al. [1], so P is n-propylamine (propan‐1‐amine).

The mechanism is similar to the oxidation of boranes using $\ce{H2O2}/\ce{NaOH}$, but instead of migration to an oxygen atom, the alkyl chain migrates to a nitrogen atom. The $\ce{N-B}$ bond is cleaved in the same way.



Reference


Brown, H. C.; Heydkamp, W. R.; Breuer, Eli.; Murphy, W. S. The Reaction of Organoboranes with Chloramine and with Hydroxylamine-O-Sulfonic Acid. A Convenient Synthesis of Amines from Olefins via Hydroboration. J. Am. Chem. Soc. 1964, 86 (17), 3565–3566. DOI: 10.1021/ja01071a036.