Unfortunately, there is not a similar increase in the energy of the NH + 3 intermediate, which results in a 9.8 kcal/mol barrier to reduction (compared to 0.1 kcal/mol for the Schrock catalyst). This barrier (10.6 kcal/mol) is also present in a catalyst where the HIPT substituents are replaced by methyl groups. So, in a sense this barrier is a "canonical" barrier presumably due to the decrease in Mo charge upon reduction that results in a weaker Mo NH 3 interaction (the Mo-N distance increases by 0.035 Å).