Ruthenium-Catalyzed Hydroamination of Unactivated Terminal Alkenes with Stoichiometric Amounts of Alkene and an Ammonia Surrogate by Sequential Oxidation and Reduction

Hydroamination
of alkenes catalyzed by transition-metal complexes
is an atom-economical method for the synthesis of amines, but reactions
of unactivated alkenes remain inefficient. Additions of N–H
bonds to such alkenes catalyzed by iridium, gold, and lanthanide catalysts
are known, but they have required a large excess of the alkene. New
mechanisms for such processes involving metals rarely used previously
for hydroamination could enable these reactions to occur with greater
efficiency. We report ruthenium-catalyzed intermolecular hydroaminations
of a variety of unactivated terminal alkenes without the need for
an excess of alkene and with 2-aminopyridine as an ammonia surrogate
to give the Markovnikov addition product. Ruthenium complexes have
rarely been used for hydroaminations and have not previously catalyzed
such reactions with unactivated alkenes. Identification of the catalyst
resting state, kinetic measurements, deuterium labeling studies, and
DFT computations were conducted and, together, strongly suggest that
this process occurs by a new mechanism for hydroamination occurring
by oxidative amination in concert with reduction of the resulting
imine.