# Mechanism of Dehydrogenation Reaction

In the hydrogenation of alkenes over a metal catalyst, the two hydrogen atoms are added with syn stereochemistry.

In the metal-catalysed dehydrogenation of alkanes, is the removal of hydrogen likewise concerted with syn stereochemistry? And if so, why?

The answer you seek can be found here uwyo.edu/roddick/site/alkane_dehydrogenation.html , the catalytic cycle of dehydrogenation of alkanes by Iridium complexes does not follow a simple syn addition such as in the hydrogenation of alkenes. In the hydrogenation of alkenes, the $\ce {H2}$ dissociates and is added syn to the substrate in a well understood mechanism.