Convenient Transfer Semihydrogenation Methodology
for Alkynes Using a Pd<sup>II</sup>-NHC Precatalyst
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Abstract
A convenient
and easy-to-use protocol for the <i>Z</i>-selective transfer
semihydrogenation of alkynes was developed, using
ammonium formate as the hydrogen source and the easily prepared and
commercially available, highly stable complex PdCl(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)(IMes) (<b>1</b>) as the (pre)catalyst.
Combined with triphenyl posphine as an additional ligand, this system
provides a robust catalytic synthetic method that shows little to
no over-reduction or isomerization after full substrate conversion.
The system allows the direct use of solvents and reagents, as received
from the supplier without drying or purification, thus providing a
practical method for semihydrogenation of a broad range of alkynes.
The mechanism behind these high and enhanced selectivities was determined
through a set of kinetic experiments
