The hydroamination reaction is approximately thermochemically neutral.  The reaction however suffers from a high activation barrier, perhaps owing to the repulsion of the electron-rich substrate and the amine nucleophile. The intermolecular reaction also is accompanied by highly negative changing entropy, making it unfavorable at higher temperatures.
   Consequently, catalysts are necessary for this reaction to proceed.  As usual in chemistry, intramolecular processes occur at faster rates than intermolecular versions.