Hydroamination
Catalytic rates correlated inversely with the ionic radius of the metal, perhaps as a consequence of steric interference from the ligands.
Amines that have been investigated span a wide scope including primary, secondary, cyclic, acyclic, and anilines with diverse steric and electronic substituents.
Also, direct catalytic hydroamination strategies have in principle significant benefits over more classical methods to prepare amine containing compounds, including the reduction in the number of synthetic steps required.
Late transition metal hydroamination catalysts have multiple models based on the regioselective determining step.
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.
In general, most hydroamination catalysts require elevated temperatures to function efficiently, and as such, only the thermodynamic product is observed.
The isolation and characterization of the rarer and more synthetically valuable kinetic allyl amine product was reported when allenes was used at the unsaturated substrate.
[25] The other reported system utilized a palladium catalyst at room temperature with a wide range of primary and secondary cyclic and acyclic amines.
[26] Both systems produced the desired allyl amines in high yield, which contain an alkene that can be further functionalized through traditional organic reactions.
Titanocene amido and sulfonamido complexes catalyze the intra-molecular hydroamination of aminoalkenes via a [2+2] cycloaddition that forms the corresponding azametallacyclobutane, as illustrated in the figure below.
Experimental and theoretical evidence support the proposed imido intermediate and mechanism with neutral group IV catalysts.
Although the advantages of atom economy and/or ready available of the nitrogen source are diminished as a result, the greater thermodynamic driving force, as well as ability to tune the aminating reagent are potentially useful.
