An Electronic Perspective on the Reduction of an NN Double Bond at a Conserved Dimolybdenum Core

Density functional theory has been used to assess the role of the bimetallic core in supporting reductive cleavage of the NN double bond in [Cp 2 Mo 2 (μ‐SMe) 3 (μ‐η 1 :η 1 ‐HNNPh)] + . The HOMO of the complex, the Mo–Mo δ orbital, plays a key role as a source of high‐energy electrons, available for transfer into the vacant orbitals of the NN unit. As a result, the metal centres cycle between the Mo III and Mo IV oxidation states. The symmetry of the Mo–Mo δ “buffer” orbital has a profound influence on the reaction pathway, because significant overlap with the redox‐active orbital on the NN unit (π* or σ*) is required for efficient electron transfer. The orthogonality of the Mo–Mo δ and N–N σ* orbitals in the η 1 :η 1 coordination mode ensures that electron transfer into the N–N σ bond is effectively blocked, and a rate‐limiting η 1 :η 1 →η 1 rearrangement is a necessary precursor to cleavage of the bond.