Controlling dinitrogen functionalization at rhenium through alkali metal ion pairing

The rhenium(i) salt Na[Re(eta(5)-Cp)(BDI)] can be cooled in solution under a dinitrogen atmosphere to selectively access complexes containing rhenium(iii) centers bound to direduced, doubly-bonded N-2 (i.e. diazenide) fragments. We demonstrate this reactivity is critically dependent on ion pairing involving the Na+ ion in the starting material, as N-2 binding by Na[Re(eta(5)-Cp)(BDI)] proved to be much less favorable when the Na+ was sequestered by benzo-12-crown-4. The analogous chemistry of Na[Re(eta(5)-Cp)(BDI)] with carbon monoxide (CO) and 2,6-xylylisocyanide (XylNC) was also investigated, which provided structural and spectroscopic bases for determining the impact of ion pairing on pi-acid activation in this system.