Hydroamination as a route to nitrogen -containing oligomers

Hydroamination of H2NC6H4-p-CCPh (1) with 10 mol% Ti(NR2)4 (R = Me and Et) at 70 °C for 3.5 days affords oligomers (2) ((2a) R = Me and (2b) R = Et), characterized by NMR, IR, and UV/Vis spectroscopy, and by matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry and gel permeation chromatography (GPC). These data indicate 10 to 15 repeat units in the chain. Model reactions, performed using phenylacetylene or diphenylacetylene and aniline or 2,6-diisopropylaniline, generated a variety of enamines and imines (compounds (3)–(11)), three of which were characterized by X-ray crystallography. Evidence suggests the hydroamination oligomerization follows the widely accepted [2 + 2] cycloaddition mechanism, although chain capping with NR2 (R = Me and Et) appears to occur via alkyne insertion in a Ti–N σ-bond.