N₂ Provides Insight into the Mechanism of H−C(sp³) Bond Cleavage

Exchange of deuterium in d₆-benzene with all C−H sites in (PNP)Ru(OTf), where PNP is N(SiMe₂CH₂P^tBu₂)₂ and OTf is OSO₂CF₃, is rapid at 22 °C. Although intact planar triplet (PNP)Ru(OTf) binds N₂ only very weakly, these reagents are observed to react rapidly to give a diamagnetic 1:1 adduct whose structure has one ^tBu C−H bond cleaved:  the carbon binds to Ru but the hydrogen is on the PNP nitrogen, creating a secondary amine ligand bound to Ru^II. It is suggested that the benzene C−D cleavage and the N₂ product of ^tBu C−H bond heterolysis both derive from a common intermediate, [HN(SiMe₂CH₂P^tBu₂)(SiMe₂CH₂P^tBuCMe₂CH₂)] Ru(OTf); the formation energy and structure of this species are discussed on the basis of DFT results.